Chapter 8

Pluto, Comets, and Space Debris

RedShift Listings

Misconceptions

WWW Icons

Pluto

Pluto Links

SEDS (Students for the Exploration and Development of Space) Homepage
Lots of Pluto Web Sites
Pluto Express
Pluto has several homepages
Gemini infrared views of Pluto and Charon

Articles and News Updates

Planet-Like or Oort-Cloud Object Found 3 Times Farther than Pluto

NASA-funded researchers have discovered the most distant object orbiting Earth's sun. The object is a mysterious planet-like body three times farther from Earth than Pluto.

"The sun appears so small from that distance that you could completely block it out with the head of a pin," said Dr. Mike Brown, California Institute of Technology (Caltech), Pasadena, Calif., associate professor of planetary astronomy and leader of the research team. The object, called Sedna for the Inuit goddess of the ocean, is 13 billion kilometers (8 billion miles) away, in the farthest reaches of the solar system.

This is likely the first detection of the long-hypothesized "Oort cloud," a faraway repository of small icy bodies that supplies the comets that streak by Earth. Other notable features of Sedna include its size and reddish color. After Mars, it is the second reddest object in the solar system. It is estimated Sedna is approximately three- fourths the size of Pluto. Sedna is likely the largest object found in the solar system since Pluto was discovered in 1930.

Brown, along with Drs. Chad Trujillo of the Gemini Observatory, Hawaii and David Rabinowitz of Yale University, New Haven, Conn., found the planet-like object, or planetoid, on Nov. 14, 2003. The researchers used the 48-inch Samuel Oschin Telescope at Caltech's Palomar Observatory near San Diego. Within days, telescopes in Chile, Spain, Arizona and Hawaii observed the object. NASA's new Spitzer Space Telescope also looked for it.

Sedna is extremely far from the sun, in the coldest know region of our solar system, where temperatures never rise above minus 240 degrees Celsius (minus 400 degrees Fahrenheit). The planetoid is usually even colder, because it approaches the sun only briefly during its 10,500- year solar orbit. At its most distant, Sedna is 130 billion kilometers (84 billion miles) from the sun, which is 900 times Earth's solar distance.

Scientists used the fact that even the Spitzer telescope was unable to detect the heat of the extremely distant, cold object to determine it must be less than 1,700 kilometers (about 1,000 miles) in diameter, which is smaller than Pluto. By combining available data, Brown estimated Sedna's size at about halfway between Pluto and Quaoar, the planetoid discovered by the same team in 2002.

The elliptical orbit of Sedna is unlike anything previously seen by astronomers. However, it resembles that of objects predicted to lie in the hypothetical Oort cloud. The cloud is thought to explain the existence of certain comets. It is believed to surround the sun and extend outward halfway to the star closest to the sun. But Sedna is 10 times closer than the predicted distance of the Oort cloud. Brown said this "inner Oort cloud" may have been formed by gravity from a rogue star near the sun in the solar system's early days.

"The star would have been close enough to be brighter than the full moon, and it would have been visible in the daytime sky for 20,000 years," Brown explained. Worse, it would have dislodged comets farther out in the Oort cloud, leading to an intense comet shower that could have wiped out some or all forms of life that existed on Earth at the time.

Rabinowitz said there is indirect evidence that Sedna may have a moon. The researchers hope to check this possibility with NASA's Hubble Space Telescope. Trujillo has begun to examine the object's surface with one of the world's largest optical/infrared telescopes, the 8-meter (26- foot) Frederick C. Gillett Gemini Telescope on Mauna Kea, Hawaii. "We still don't understand what is on the surface of this body. It is nothing like what we would have predicted or what we can explain," he said.

Sedna will become closer and brighter over the next 72 years, before it begins its 10,500-year trip to the far reaches of the solar system. "The last time Sedna was this close to the sun, Earth was just coming out of the last ice age. The next time it comes back, the world might again be a completely different place," Brown said.

Competition for Pluto

The planetoid, currently known only as 2004 DW, could be even larger than Quaoar--the current record holder in the area known as the Kuiper Belt--and is some 4.4 billion miles from Earth.

According to the discoverers, Caltech associate professor of planetary astronomy Mike Brown and his colleagues Chad Trujillo (now at the Gemini North observatory in Hawaii), and David Rabinowitz of Yale University, the planetoid was found as part of the same search program that discovered Quaoar in late 2002. The astronomers use the 48-inch Samuel Oschin Telescope at Palomar Observatory and the recently installed QUEST CCD camera built by a consortium including Yale and the University of Indiana, to systematically study different regions of the sky each night.

Unlike Quaoar, the new planetoid hasn't yet been pinpointed on old photographic plates or other images. Because its orbit is therefore not well understood yet, it cannot be given an official name.

"So far we only have a one-day orbit," said Brown, explaining that the data covers only a tiny fraction of the orbit the object follows in its more than 300-year trip around the sun. "From that we know only how far away it is and how its orbit is tilted relative to the planets."

The tilt that Brown has measured is an astonishingly large 20 degrees, larger even than that of Pluto, which has an orbital inclination of 17 degrees and is an anomaly among the otherwise planar planets.

The size of 2004 DW is not yet certain; Brown estimates a size of about 1,400 kilometers, based on a comparison of the planetoid's luminosity with that of Quaoar. Because the distance of the object can already be calculated, its luminosity should be a good indicator of its size relative to Quaoar, provided the two objects have the same albedo, or reflectivity.

Quaoar is known to have an albedo of about 10 percent, which is slightly higher than the reflectivity of our own moon. Thus, if the new object is similar, the 1,400-kilometer estimate should hold. If its albedo is lower, then it could actually be somewhat larger; or if higher, smaller.

According to Brown, scientists know little about the albedos of objects this large this far away, so the true size is quite uncertain. Researchers could best make size measurements with the Hubble Space Telescope or the newer Spitzer Space Telescope.

The continued discovery of massive planetoids on the outer fringe of the solar system is further evidence that objects even farther and even larger are lurking out there. "It's now only a matter of time before something is going to be discovered out there that will change our entire view of the outer solar system," Brown says.

Rosetta Ready to Explore a Comet's Realm

New Destination for ESA's Rosetta Spacecraft

Comet-chasing mission Rosetta will now set its sights on Comet Churyumov-Gerasimenko. During its meeting on 13-14th May 2003, ESA's Science Programme Committee decided Rosetta's new mission baseline. The spacecraft will be launched in February 2004 from Kourou, French Guiana, using an Ariane-5 G+ launcher. The rendezvous with the new target comet is expected in November 2014.

http://sci.esa.int/content/news/index.cfm?aid=13&cid=36&oid=32381

MUSES-C Mission Launched to an Asteroid

New Images of Pluto

Pluto 1	Author's First Image WITH Pluto!!!	Pluto entering...

Stardust Images Asteroid Annefrank

JPL press releases, November 2, 2002, and November 4, 2002

NASA's Stardust spacecraft successfully completed a close flyby of asteroid Annefrank early today, Nov 2, as an opportunity for a full dress rehearsal of procedures the spacecraft will use during its Jan. 2, 2004, encounter with it primary science target, comet Wild 2.

Annefrank is about 4 kilometers (2.5 miles) across. Stardust passed within about 3,300 kilometers (2,050 miles) of the asteroid at 04:50 today, Universal Time (8:50 p.m. Nov. 1, Pacific Standard Time). Radio signals confirming the basic health of the spacecraft after the flyby were received about 30 minutes later via an antenna at the Canberra, Australia, complex of NASA's Deep Space Network, said Thomas Duxbury, project manager for Stardust at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Stardust visually tracked the asteroid for 30 minutes as it flew by at a relative speed of about 7 kilometers (4 miles) per second, a major goal of this test opportunity. Although no dust was anticipated near the asteroid, the spacecraft's dust instruments were in use as they will be at Wild 2: the dust collector was open and the dust counter from the University of Chicago and dust mass spectrometer from Germany were turned on.

Images and information from the flyby period are being transmitted from the spacecraft today and through the coming week. Stardust's scientists and engineers are analyzing the data to maximize the probability of success during the 2004 encounter with comet Wild 2.

November 4, 2002

Late Friday evening Pacific time on November 2, 2002 at the Jet Propulsion Laboratory (JPL) in Pasadena, California, and at Lockheed Martin Space Systems - Astronautics (LMA) near Denver, Colorado, the NASA STARDUST flight team pulled off a tremendously successful close flyby of the main belt asteroid Annefrank. This flyby was used as an engineering test of the ground and spacecraft operations that will be implemented at the primary scientific target, Comet Wild 2 (pronounced "Vilt" 2) just over one year from now.

STARDUST is a low-cost Discovery Mission that continues to perform as expected after more than three and a half years into a planned seven-year mission to rendezvous with Comet Wild 2 in January 2004. STARDUST will collect cometary dust samples, flowing from the nucleus just hours before spacecraft flyby, and return the samples to Earth in a Sample Return Capsule in January 2006. The close flyby of Annefrank offered a unique opportunity to thoroughly test all planned operations on the spacecraft and ground support operations which will be used during the rendezvous with Comet Wild 2.

"We performed a full dress rehearsal with the cometary dust collector deployed as we flew STARDUST within 3,300 kilometers of Annefrank," said Professor Donald Brownlee, the project's Principal Investigator from the University of Washington. "The spacecraft was poised in its flyby attitude with all the science instruments on. The flyby has exceeded all of our expectations and provided us with unexpected data about the asteroid," said Brownlee.

The approach geometry to Annefrank was much more difficult than will be the case for Comet Wild 2. The spacecraft was pointed over 60 degrees off of the normal Sun and Earth pointing attitude and was running on its battery in order to attempt to detect and capture images of Annefrank.

"The spacecraft performed every command perfectly and did everything asked of it," said Allan Cheuvront, Spacecraft Engineer at Lockheed Martin Space Systems near Denver. "We are thrilled with how well the entire operation went. We couldn't have asked for better performance from STARDUST and the images it captured of the asteroid exceeded everyone's expectations. The spacecraft's pointing, attitude and flight operations were excellent. This really adds to our level of confidence about how well the spacecraft will perform when we reach Wild 2," added Cheuvront. Cheuvront and a team of engineers at Lockheed Martin's spacecraft control center, known as the Mission Support Area, control the spacecraft in conjunction with JPL and the Deep Space Network.

The Navigation Camera was straining to see Annefrank during approach. "This camera was operating at its limit of performance and seeing very dim stars down to about 11th visual magnitude", said Ray Newburn, the Lead Scientist for the camera at JPL.

However, the brightness predicted by Drs. Stephen Synnott and Donald Yeomans of JPL was dimmer than 11th visual magnitude. "We tried everything we could think of including taking multiple long exposures and adding these on the ground", said Dr. T. S. Mike Wang, Optical Navigation Specialist at JPL, "but Annefrank was not cooperating. It was just too dim."

Because of the high probability of not seeing Annefrank during the approach, the flyby was designed to be successful without having to see it up to 20 minutes from encounter. "A flyby distance of 3,000 km (1,864 miles) was chosen so that there was no risk of the spacecraft flying near any possible dust environment or small satellites of Annefrank", said Ed Hirst, JPL Mission Design Manager. "We also wanted to ensure that Annefrank would be in the camera view at the start of the encounter sequence," added Hirst.

Since Annefrank was not seen in the approach images, the flight team felt that the asteroid was at least as dim as predicted and possibly even dimmer. The team decided to send up a new encounter configuration file and set the initial flyby exposures longer. "We had a planned uplink six hours before encounter for this very purpose," said Robert Ryan, Mission Manager at JPL. "We had some communications problems the day before that gave us some difficulty, but NASA's Deep Space Network gave us highest priority, and excellent communications on Friday, allowing us to play back earlier images we missed as well as sending our final encounter commands," added Ryan.

At 8:00 pm (PST) Friday evening, communications were established with the spacecraft to watch its pre-loaded sequence command turn the spacecraft away from the Sun and Earth into its flyby attitude. "We have built up over three years of flight experience and a tremendous amount of confidence and respect for our spacecraft to perform such operations routinely," said Joe Vellinga, STARDUST Program Manager at Lockheed Martin who led the development and manufacture of the spacecraft. "The spacecraft did not miss a beat during its flyby and it maintained all critical thermal, power, attitude, memory and reserves at or above design levels," added Vellinga.

The main function to be tested during flyby was a sophisticated flight computer program that would take over control of the spacecraft to keep the camera view locked on Annefrank during a 25-minute period around its closest encounter. "This software was a derivative of the nucleus tracking software successfully flown on the Deep Space 1 (DS1) flyby of Borrelly," said Dr. Shyam Bhaskaran, developer of the algorithms at JPL. "Based upon my previous experience on DS1, it performed up to my expectations with this encounter at Annefrank with over 60 successful images having Annefrank right in the middle of each image," added Bhaskaran. David Gingerich, Flight Software specialist at LMA who implemented and tested the nucleus tracking software said, "its performance was executed just like the coach drew it on the blackboard."

Over 70 encounter images were obtained that show a typical small solar system body, highly irregularly shaped and cratered. Annefrank is about twice as large as predicted, at least 6 kilometers in diameter, but darker than expected and therefore more difficult to detect in the early images. Not only did the camera perform well but the University of Chicago Dust Flux Measurement Instrument (DFMI) and the German Cometary and Interstellar Dust Analyzer (CIDA) performed as expected.

Professor Tom Economou, DFMI scientist from University of Chicago, stated "we ran for 28 minutes as we will at Wild 2 with DFMI performing all expected functions". Dr. Jochen Kissel, Lead Scientist for CIDA from Max Planck Institute in Garching, Germany, said "I will be able to put CIDA into an even better configuration at Wild 2 based upon the Annefrank experience." Both dust instrument teams are combing through their data to see if by chance they may have seen a dust particle.

"Performing such flight testing before the primary encounter is a critical part of reducing risks and significantly increasing the probability of success when we reach Wild 2", said JPL Project Manager, Thomas Duxbury. "We have performed exhaustive testing and training with LMA at their spacecraft test laboratory and through flight simulations, but these cannot totally replace actual flight operations testing. We learned a lot that will improve our operations at Wild 2 based upon the lessons learned at Annefrank. The bottom line is that if Annefrank had been Wild 2, we would have succeeded in every respect," added Duxbury.

"I applaud the entire flight team," said Don Brownlee. "We could not have asked for more, except possibly for Annefrank to be a little brighter. However, for everything that we could control with the spacecraft, we were nearly perfect.

Even though this was an engineering test, the flyby with Annefrank provided new information previously unknown about the asteroid about its size, shape, spin state and brightness as a function of viewing angle.

"It was an exciting Friday evening for those of us involved in this mission," Brownlee said. "We captured images of a primitive asteroid with a highly significant name and one whose size turned out to be similar to the asteroid that likely killed the dinosaurs 65 million years ago. We have now validated STARDUST's systems and operations and we are eagerly awaiting our encounter with Comet Wild 2, just over one year from now".

Asteroid Annefrank images are available here:

http://stardust.jpl.nasa.gov/photo/annefrank.html
http://photojournal.jpl.nasa.gov/catalog/PIA02885
http://photojournal.jpl.nasa.gov/catalog/PIA02886

Working Group On Near Earth Objects

Triennnial Report for the International Astronomical Union, November 4, 2002

The past three years have seen a tremendous growth in the study of NEOs. This period includes the one-year orbital study of 433 Eros by the NASA spacecraft NEAR-Shoemaker, followed by a landing on the asteroid surface http://near.jhuapl.edu. This mission has effectively resolved in the affirmative the long-standing issue of the association between S-type asteroids and the primitive ordinary chondrite meteorites. New radar studies have provided images of NEAs and include the discovery of several binary objects, which permit the calculation of densities http://echo.jpl.nasa.gov. Automated orbital calculation and risk estimates are now continuously available on-line through the NEO Dynamics system at Pisa http://newton.dm.unipi.it/cgi-bin/neodys/neoibo and the Sentry system at JPL http://neo.jpl.nasa.gov/risk/. The Spaceguard Survey discovery programs, led by the LINEAR MIT system http://www.ll.mit.edu/LINEAR/, have found more than 600 of the estimated 1100 +/- 100 NEAs brighter than absolute magnitude H=18 (diameter approximately 1 km). The primary Spaceguard search programs are supported by the United States government (NASA and the U.S. Air Force), with an international team for astrometric follow-up. The goal of the Spaceguard Survey is to find 90% of the NEAs larger than 1 km diameter by the end of 2008.

Communication with the international scientific community and with the interested public represents an important part of the WG efforts. One tool for public communication is the Torino Impact Scale, which has been adopted by the WG and other NEO scientists for this purpose. The Torino Scale is a "Richter Scale" for categorizing the Earth impact hazard associated with newly discovered asteroids and comets. The scale is described at http://impact.arc.nasa.gov. Other websites, although not formally endorsed by the IAU, also provide a valuable communication functions. These include the NASA NEO Program Office http://neo.jpl.nasa.gov, the NASA impact hazard website http://impact.arc.nasa.gov, the UK NEO Information Centre http://www.nearearthobjects.co.uk, and the Spaceguard Foundation and its on-line magazine Tumbling Stone http://spaceguard.ias.rm.cnr.it/SGF/.

David Morrison, November 4, 2002

Causes of Chicxulub and Sudbury Craters

University of Illinois at Urbana-Champaign press release, October 25, 2002

Champaign, Illinois. -- Two of the three largest impact craters on Earth have nearly the same size and structure, researchers say, but one was caused by a comet while the other was caused by an asteroid. These surprising results could have implications for where scientists might look for evidence of primitive life on Mars.

Susan Kieffer of the University of Illinois at Urbana-Champaign, Kevin Pope of Geo Eco Arc Research and Doreen Ames of Natural Resources Canada analyzed the structure and stratigraphy of the 65 million-year-old Chicxulub crater in Mexico and the 1.8 billion-year-old Sudbury crater in Canada.

Chicxulub is well preserved, but buried, and can be studied only by geophysical means, remote sensing and at a few distant sites on land where some ejecta is preserved. In contrast, Sudbury has experienced up to 4-6 kilometers of erosion, and is well exposed and highly studied by mining exploration companies because of its rich mineral resources.

By working back and forth with data from the two craters, the researchers were able to re-create the structures and then estimate the amount of melt in each structure. The amount of melt is critical for determining if long-lived hot-water circulation systems that might host life formscould have been formed after the impacts.

In their field studies, the researchers found that both craters were about 200 kilometers in diameter. In addition, they identified five ring-shaped structures with similar character and dimensions. A sixth ring -- the peak ring in the central basin -- was present at Chicxulub, but had been eroded away at Sudbury.

"While the size and structure of the two craters were similar, they differed greatly in the amount of impact melt that was produced," said Kieffer, who presented the team's findings at the annual meeting of the Geological Society of America, held Oct. 27-30 in Denver.

"Through field studies, we determined that Chicxulub has about 18,000 cubic kilometers of impact melt, approximately four times the volume of water in Lake Michigan," Pope said. "Sudbury has about 31,000 cubic kilometers of impact melt, approximately six times the volume of lakes Huron and Ontario combined, and nearly 70 percent more than the melt at Chicxulub. These differences in volume have significant implications about the amount of heat available to drive hot-water circulation systems."

The researchers then used an analytical cratering model to examine possible causes for the huge difference in melt. According to the simulation results, the difference in melt volume could be readily explained if Chicxulub -- the impact crater that doomed the dinosaurs - -- was formed by an asteroid and Sudbury was formed by a comet.

"Our calculation of 18,000 cubic kilometers of impact melt at Chicxulub agreed well with model estimates for an asteroid striking at a 45 degree angle," said Kieffer, the Walgreen Professor of Geology at Illinois. "None of the comet impact examples came close to agreeing."

In contrast, the Sudbury impact melt volume of 31,000 cubic kilometers fell between model estimates for a comet striking at an angle of 30-45 degrees, Kieffer said. "Similarly, none of the asteroid impact examples came close to agreeing with the Sudbury melt volume."

Another clue to the craters' origins lies in the impact melts themselves. The majority of the excess melt at Sudbury is in the form of a melt-rich breccia -- called suevite -- inside the crater. This material tends to form in impacts where the crustal target rock contains a lot of water. Sudbury has much more suevite in the preserved crater than Chicxulub.

"The mystery was that there probably wasn't a lot of water in the original rocks at Sudbury to account for the excess suevite," Kieffer said. "But in a comet impact of this size, somewhere around 1,400-2,000 cubic kilometers of water from the comet gets mixed into the impact melt, and that could play a major role in disrupting the melt and creating the excess suevite."

There is other independent evidence for an asteroid impact at Chicxulub, the team said, including the purported find of an asteroid fragment in an oceanic drill core, the amount of iridium spread around the world at the time of impact, and a telltale chromium 53 isotopic signature.

By studying the origin and structure of large impact craters on Earth, scientists might narrow the search for life on Mars. At Sudbury, for example, "there is evidence of a huge hydrothermal system that was driven by the heat of the impact melt," Ames said. "As a result, there was widespread hot spring activity on the crater floor possibly capable of supporting life."

The researchers are interested in "extrapolating these conclusions about comet and asteroid impacts to Martian conditions and asking where we might go to look for similar hydrothermal systems that could have hosted primitive life forms on Mars," Kieffer said. "Our next step is to model these hot-water circulation systems that were set up by the impact melts with fluid flow controlled by structures (fractures) inside the crater, and then extrapolate the results to Martian conditions."

The National Aeronautics and Space Administration and the Natural History Museum of Los Angeles County funded this work.

A geological map and RADARSAT-1 image of the Sudbury impact crater is available at

http://www.ccrs.nrcan.gc.ca/ccrs/rd/apps/geo/sudbury/sudbury_e.html

A Kuiper-Belt Object Half the Size of Pluto

STScI Press Release N.: STScI-PR02-17, October 9, 2002

Michael Brown and Chadwick Trujillo of Caltech are reported the findings at the 34th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Birmingham, Ala.

Earlier this year, Trujillo and Brown used the Palomar Oschin Schmidt telescope to discover Quaoar as an 18.5-magnitude object creeping across the summer constellation Ophiuchus (it's less than 1/10,000th the brightness of the faintest star seen by the human eye). Brown had to do follow-up observations using Hubble's new Advanced Camera for Surveys on July 5 and August 1, 2002, to measure the object's true angular size of 40 milliarcseconds, corresponding to a diameter of about 800 miles (1300 kilometers). Only Hubble has the sharpness needed to actually resolve the disk of the distant world, leading to the first-ever direct measurement of the true size of a Kuiper belt object (KBO).

See http://oposite.stsci.edu/pubinfo/pr/2002/17

Pluto is Undergoing Global Warming, Researchers Find

MIT and Williams College Press Release, October 9, 2002

CAMBRIDGE, Mass., and WILLIAMSTOWN, Mass.--Pluto is undergoing global warming, as evidenced by a three-fold increase in the planet's atmospheric pressure during the past 14 years--a team of astronomers from Massachusetts Institute of Technology (MIT), Williams College, the University of Hawaii, Lowell Observatory, and Cornell University announced in a press conference at today's meeting of the Division of Planetary Sciences of the American Astronomical Society in Birmingham, AL.

The team, led by James Elliot, professor of planetary astronomy and director of MIT's Wallace Observatory, made this finding by watching the dimming of a star when Pluto passed in front of it last August 20. The team carried out observations using eight telescopes at Mauna Kea Observatory and Haleakala in Hawaii, Lick Observatory and Palomar Observatory in California, and Lowell Observatory in Arizona. Data were successfully recorded at all sites. An earlier attempt to observe an occultation of Pluto on July 20 in Chile with observations only from two sites with small telescopes, as the giant telescopes involved lost out to bad weather or from being in the wrong location.

The Williams College team included Jay Pasachoff, Bryce Babcock, Steven Souza, and undergraduate David Ticehurst. For the August event, they used a Williams College electronic camera mounted to a University of Hawaii telescope on Mauna Kea to make studies of the occultation in visible light. They found a dimming lasting 7 minutes, about one-third of their 2400 data frames, with fine detail that remains under study and reanalysis. Their visible-light data are being compared with infrared data obtained by the team at other telescopes.

Elliot said the new results have surprised the observers, who as recently as July thought that Pluto's atmosphere may be cooling. "From the July data we know that Pluto's atmosphere had changed since 1988, but the August data allowed us to probe much more deeply into Pluto's atmosphere and have given us a more accurate picture of the changes that have occurred," he said.

Pasachoff, an astronomy professor at Williams College, said that Pluto's global warming was "likely not connected with that of the Earth. The major way they could be connected is if the warming was caused by a large increase in sunlight. But the solar constant--the amount received of sunlight each second--is carefully monitored by spacecraft, and we know the Sun's output is much too steady to be changing the temperature of Pluto."

Pluto's elliptical orbit is much more out of round than that of the other planets, and its rotational pole is tipped by a large angle relative to its orbit. Both factors could contribute to drastic seasonal changes. .Pluto's atmospheric temperature varies between around minus 235 and minus 170 degrees Centigrade, depending on the altitude above the surface. The main gas in Pluto's atmosphere is nitrogen, and Pluto has nitrogen ice on its surface that can evaporate into the atmosphere when it gets warmer, causing an increase in surface pressure. If the observed increase in the atmosphere also applies to the surface pressure--which is likely the case--this means that the average surface temperature of the nitrogen ice on Pluto has increased slightly less than 2 degrees Centigrade over the past 14 years.

Marc Buie, an astronomer at Lowell Observatory, has been measuring the amount of sunlight reflected by Pluto and says that "the pressure increase can be explained if the average amount of sunlight reflected by the surface has decreased, which means that more heat is absorbed from the sun. This could be the reason that the pressure has been pumped up."

David Tholen, an astronomer at the University of Hawaii who measured the size of Pluto in the late 1980s using a series of occultations and eclipses involving Pluto's satellite, noted that even though Pluto was closest to the Sun in 1989, a warming trend 13 years later shouldn't be unexpected. "It takes time for materials to warm up and cool off, which is why the hottest part of the day on Earth is usually around 2 or 3 p.m. rather than local noon, when sunlight is the most intense," Tholen said. Because Pluto's year is equal to about 250 Earth years, 13 years after Pluto's closest approach to the Sun is like 1:15 p.m. on Earth. "This warming trend on Pluto could easily last for another 13 years," Tholen estimated.

Researchers study faraway objects through occultationsQeclipse-like events in which a body passes in front of a star (Pluto in this case), blocking the star's light from view. By recording the dimming of the starlight over time, astronomers can calculate the density, pressure and temperature of Pluto's atmosphere. Observing two or more occultations at different times provides researchers with information about changes in the planet's atmosphere. The structure and temperature of Pluto's atmosphere was first determined during an occultation in 1988.

Pluto's brief pass in front of a different star on July 19 led researchers to believe that a drastic atmospheric change was under way, but it was unclear whether the atmosphere was warming up or cooling down.

In August 2002, a team from Williams College, the University of Hawaii, and MIT, in an expedition arranged by Elliot, Tholen, and Pasachoff to the University of Hawaii's telescope in Mauna Kea, successfully observed the occultation of a faint star by Pluto.

The data resulting from this occultation, when Pluto passed in front of a star known as "P131.1," led to the current results. "This is the first time that an occultation has allowed us to probe so deeply into the atmosphere with a large telescope, which gives a high spatial resolution of a few kilometers," Elliot said.

A 1997 occultation of a star by Triton (Neptune's largest moon) revealed that its surface had warmed since the Voyager spacecraft first explored it in 1989. Pasachoff and Babcock, along with then Williams student Tim McConnochie, participated in those observations. On Triton, "Voyager saw dark material rising up as much as 12 km above the surface, indicating some kind of eruptive activity," Elliot said. "There could be more massive activity on Pluto, since the changes observed in Pluto's atmosphere are much more severe. The change observed on Triton was subtle. Pluto's changes are not subtle."

Pluto and Triton are presently about the same distance from the sun, and each has a predominantly nitrogen atmosphere (with a surface pressure 100,000 times less than that on Earth), so one might expect similar processes to be occurring on these two bodies.

NASA is still deciding whether to send a spacecraft to Pluto, the only planet not yet observed at close range. The Pluto-Kuiper Belt mission in the New Horizons Program, if approved, would be launched in 2006 and would reach Pluto 10 years later, seeks to answer questions about the surfaces, atmospheres, interiors and space environments of the solar system's outermost objects, including Pluto and its moon, Charon.

Researchers are looking forward to observing additional Pluto occultations in the years before the Pluto-Kuiper mission flies by Pluto. Of particular interest is the prospect of using SOFIA, a 2.5-meter airborne telescope being built by NASA in collaboration with German astronomers, for Pluto-occultation events when it begins operating in 2004. Edward Dunham, who leads the occultation effort at Lowell Observatory, is also leading a team that is building HIPO, a SOFIA instrument designed specifically to observe occultations. The combination of HIPO and SOFIA will provide very high quality data on a much more frequent basis than is possible using ground-based telescopes alone.

"This is a very complex process, and we just don't know what is causing these effects" on Pluto's surface, Elliot said. "That's why you need to send a mission."

This work is funded by Research Corporation, the National Science Foundation, and NASA's Planetary Astronomy Program.

A press release from Lowell Observatory last summer (based on results of the July occultation) is at the website: http://www.lowell.edu/Press/20020815.html
A map of Pluto's shadow crossing the Earth for the August occultation: http://occult.mit.edu/research/occultations/Candidates/Predictions/P131.1.html
Images and further discussion of the observations for the August occultation are on the Williams College site: http://www.williams.edu/Astronomy/mkpluto.html

TEAM PARTICIPANTS IN THE PLANNING, PREDICTION, AND OBSERVATION, AND STUDY OF THE 2002 AUGUST PLUTO OCCULTATION

AEOS Telescope, Haleakala: Lewis Roberts, John Africano, Doyle Hall, Paul Kerwin, Mark Skinner

Cornell University: Stephen Eikenberry, Dae-Sik Moon, Philip Nicholson

Joint Astronomy Centre: Sandy K. Leggett

Lowell Observatory: Edward Dunham, Amanda Bosh (also Boston University), Marc Buie, Catherine Olkin, Brian Taylor

MIT: James Elliot, Katie Carbonari, Kelly Clancy, Erica McEvoy, Alison Klesman, Susan Kern, David Osip, Michael Person, Shen Qu

University of Hawaii: David Tholen and John Rayner

US Naval Observatory (Flagstaff): Stephen Levine and Ronald Stone

Williams College: Jay M. Pasachoff, Steven P. Souza, Bruce A. Babcock, David R. Ticehurst

Pluto Reveals Its Atmosphere by Occulting a Star

Jay M. Pasachoff 7/30/2002

Pluto, 6 billion kilometers away, is so small that it occults (hides) a star very rarely. In fact, the only previous time it had been known to do so was 1988, when a team led by MIT professor James Elliot had detected its atmosphere. Note that if Pluto or another body had no atmosphere, the star would wink out abruptly (aside, technically, from optical effects), but that an atmosphere can bend and distort the starlight so that it fades gradually. In that way, the 1988 occultation gave a lot of information about Pluto's atmosphere. The light curve (the graph of brightness versus time) showed an abrupt change at a certain height above Pluto's surface, and two competing models have been invoked to explain it: a temperature inversion or the presence of dust.

Elliot and his colleagues have worked since then to find another Pluto occultation to observe. Pluto is only 0.1 arcsec across, about 1/10 the smallest size normally seen by the best telescopes and 1/5 the smallest size resolvable by Hubble. Stars are so far away that their light is parallel, and they project Pluto's shadow full size on the Earth. Thus the shadow of Pluto on the Earth from a star is about 2300 km across. Even the best astrometry (position measuring) gives an uncertainty of 1000 km or so a few days in advance of the occultation, though the Elliot group monitors the positions of Pluto and the star as time progresses, continually improving their predictions.

They predicted that on July 19/20, a Pluto occultation would be observable from Chile. They assembled a team of scientists to observe it and got observing time on some of the world's largest and newest telescopes, including 8-m Gemini South and the two 6.5-m Magellan telescopes in Chile. Three teams with portable 35-cm telescopes but with fast-readout CCD's, capable of observing twice a second to give time resolution unlike ordinary CCD's, were also participating: one team from MIT, one team from Lowell Observatory, and my own team from Williams College. We were to be deployed to the sides of the large telescopes, perhaps 200 km north or south, to increase the chance that somebody would see the event. A similar consortium, headed by Bruno Sicardy of the Observatory of Paris at Meudon, had the 8-m Very Large Telescope and other fixed and mobile telescopes.

As the time approached, the prediction shifted considerably north, making it look that sites from mid-Peru north through Central America would see the occultation, and some of our teams prepared to shift north. My own team was going to Aruba, given some connections with a customs agent there from the 1998 solar eclipse expedition and the weather that was predicted to be better than that in Central America. Customs and shipping problems prevented us finally from getting there, though we tried. But by that time, we were in contact with scientists at four large telescopes at the major observatories in the Canary Islands, which were in the same part of the track as Aruba, and helped arrange the use of two of them, including Pablo Perez at the 4.2 m William Herschel telescope on La Palma and a Belgian group of astronomers (Katrien Uytterhoeven, Roeland Van Malderen, Geert Davignon) at the 1.2 m telescope on La Palma. Mark Kidger was already using the 1.5 and 0.8 m telescopes on Tenerife for both optical and infrared observations.

In the event, the track shifted back south. The Canary Island telescopes got good data, but showed a steady light curve, with no occultation. One member of the French team saw the occultation from near Arica at Chile's northern boundary, though he used the drift technique across the CCD to give time resolution, making it relatively difficult to get accurate photometry. The Elliot-related team of Marc Buie of the Lowell Observatory and Oscar Saa of the Cerro Tololo Inter-American Observatory had complete success in observing the occultation from a site near Iquique, Chile, a couple of hundred kilometers south of the Peruvian border. They saw an occultation lasting about 104 s, with a dimming of about a factor of 2 at maximum. It will take some time for the results to be studied and to percolate into new models of Pluto's atmosphere.

Pluto is moving into a part of the sky with more stars, and a couple of occultations may be visible each year. The next one is scheduled for August 20, 2002, and as of this writing is to go over the major telescopes at Mauna Kea, Hawaii, several of which are to be devoted to the occultation. My own team from Williams College is taking our CCD to the 2.2-m telescope of the University of Hawaii there.

New Horizons Team Plots a Faster Path to Pluto

Johns Hopkins University Applied Physics Laboratory press release February 22, 2002

New Horizons mission planners have developed a new strategy that could trim nearly a year off their original schedule to send a spacecraft to the solar system's outermost planet.

Now in preliminary development for NASA, New Horizons would be the first mission to explore Pluto and its moon, Charon, as well as the ancient Kuiper Belt of rocky, icy objects beyond the planets. If approved and funded later this year, New Horizons would launch in January 2006, swing around Jupiter for scientific studies and a gravity boost in 2007, and reach Pluto as early as 2015.

"As we continued to study the mission, and optimized our launch window, we realized that we could get the spacecraft to Pluto sooner," says New Horizons Mission Director Robert W. Farquhar, of The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which manages the mission and will build and operate the spacecraft. "In our best estimates we can cover the 3 billion miles from Earth to Pluto faster than we once thought, while keeping all the mission's goals intact."

New Horizons project leaders say a faster trip benefits the mission in many ways.

"This a great opportunity to improve our scientific return while reducing mission risks and costs," says New Horizons Principal Investigator S. Alan Stern, of the Southwest Research Institute in Boulder, Colo. "We'll get a better look at Pluto itself, since more of the surface will be sunlit and the atmosphere will be another year away from freezing onto the planet's surface. We'll have more fuel for the journey into the Kuiper Belt after exploring Pluto-Charon, and the shorter cruise time reduces some of the costs associated with flight operations."

New Horizons will characterize the global geology and geomorphology of Pluto and Charon, map their surface compositions and temperatures, and study Pluto's complex atmosphere in detail. The spacecraft will then visit up to three Kuiper Belt objects beyond Pluto.

See http://pluto.jhuapl.edu/

Pluto Mission Cancelled Again; NASA Space Budget Released

The Administration released its proposed FY2003 budget for NASA today. This is the first budget developed by the Bush Administration and the new NASA Administrator, Mr. Sean O'Keefe. The Division for Planetary Sciences (DPS) of the American Astronomical Society commends the support this budget provides for planetary exploration, which includes a new initiative for nuclear power and propulsion, and a second new initiative for a New Frontier line of competitively procured planetary space flight missions. Funding has been increased in real dollars for Research and Analysis programs, which provide a fundamental knowledge base allowing for the design of focused, efficient missions.

The Administration gave high ratings to the Discovery program of low-cost planetary missions and as a result has introduced a new line of moderately priced missions modeled on the Discovery program. The New Frontier missions would be about twice the cost of Discovery missions. The budget proposal would provide for about one Frontier mission every three years, bringing a new level of flight opportunity to the science community with competitively procured missions of higher capability.

The DPS is concerned about the cancellation of the outer planets program, which included the New Horizons mission to Pluto and the Europa Orbiter. The cost-capped New Horizons mission was recently selected after an open competition in which scientists and their industry partners spent millions of dollars and months of time in good faith response to a NASA call for proposals. This precedent discourages community participation in NASA's efforts to produce cost-effective missions through competition. It should not be repeated. Whether New Horizons may be resurrected in the New Frontier program will depend on its ultimate prioritization in the Planetary Decadal Survey.

The surprise in this budget is the proposal to revive development of nuclear technology for in-space propulsion and power. Development of this technology was terminated in the 1970s and planetary exploration has been limited ever since to long, complex flight missions using conventional propulsion and to spacecraft barely capable of powering a single light bulb. Nuclear propulsion will increase accessibility of Solar System objects and decrease the flight time for some missions. On-board nuclear power will provide a power-rich environment for science investigations at the planets and increase the lifetime of these systems to years instead of a few weeks or months.

The planetary Research and Analysis program was given a 3% increase above inflation, and a new program was funded at $10M to develop planetary instruments for biological investigations on other planets. Mars exploration will continue as planned through this decade, but the large rover planned for 2007 is delayed until 2009 in order to substitute nuclear for solar power and increase its lifetime from months to years. A fully competed Discovery-class Mars Scout mission will be flown in 2007.

The DPS calls upon Congress to support the President's proposed FY03 NASA budget. It builds on the strengths and successes of our planetary program. New nuclear technology for both power and propulsion will extend our reach and capabilities to the outermost regions of our Solar System while increasing our capabilities in the inner Solar System. The New Frontier program offers exciting opportunities, including restoration of missions to the outer solar system.

The DPS is the world's largest professional organization dedicated to the exploration of the Solar System.

Stardust En Route to Comet Wild 2 in 2004

PASADENA, Calif., Jan. 24, 2002 (AScribe Newswire) -- NASA's comet-bound spacecraft, Stardust, successfully completed a critical deep space maneuver, positioning itself on a course to encounter comet Wild 2 in January 2004 and collect dust from the comet.

At 21:56 Universal Time (1:56 p.m. Pacific Time), January 18, 2002, Stardust fired its thrusters for nearly 111 seconds, increasing the speed of the spacecraft by 2.65 meters per second (about 6 miles per hour).

"This is the maneuver that sets us up for the bigger maneuver. It's a combination of increasing the speed of the spacecraft and at the same time putting it on the path to reach Wild 2," said Robert Ryan, Stardust's mission manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's like the setup pass in a basketball game. Now we're ready to shoot the basket."

The spacecraft responded exactly as planned, said Ryan, although communication was tricky. Stardust is currently the farthest solar-powered object from the Sun, over 395 million kilometers (245 million miles) away. The spacecraft's signal confirming it had completed the maneuver took almost 30 minutes to reach Earth.

In January 2004, Stardust will fly through the halo of dust that surrounds the nucleus of comet Wild 2. The spacecraft will return to Earth in January 2006 to make a soft landing at the U.S. Air Force Utah Test and Training Range. Its sample return capsule, holding microscopic particles of comet and interstellar dust, will be taken to the planetary material curatorial facility at NASA's Johnson Space Center, Houston, Texas, where the samples will be carefully stored and examined.

Stardust's cometary and interstellar dust samples will help provide answers to fundamental questions about the origins of the solar system. More information on the Stardust mission is available at http://stardust.jpl.nasa.gov.

Stardust, a part of NASA's Discovery Program of low-cost, highly focused science missions, was built by Lockheed Martin Astronautics and Operations, Denver, Colo., and is managed by the Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. The principal investigator is astronomy professor Donald E. Brownlee of the University of Washington in Seattle.

Pluto in 2014-18

San Antonio -- November 30, 2001 -- After a two-month evaluation, NASA has selected the "New Horizons" proposal, led by Southwest Research Institute (SwRI), to proceed with preliminary design studies for a mission to the Pluto-Kuiper Belt (PKB) system. The mission, including science payload, spacecraft, and launch vehicle, will examine the last unexplored planet in the solar system and move beyond Pluto to explore multiple objects in the Kuiper Belt. The mission will also make the next planned exploration of Jupiter and its moons.

Led by Principal Investigator Dr. S. Alan Stern, director of the SwRI Department of Space Studies, the winning proposal involves constructing and flying a complete mission, including development of the spacecraft, trajectory, science instruments, and an education and public outreach plan.

"We'll be exploring frontier worlds near the edge of the planetary system," says Stern, who is based in the SwRI Boulder, Colo., office. "This mission is likely to rewrite textbooks regarding the origin of the planets, the nature of the outer solar system, and even the origin of primitive materials that may have played a role in the development of life."

SwRI leads the New Horizons team, which also includes major partners at the Johns Hopkins University Applied Physics Laboratory of Laurel, Md.; Stanford University of Palo Alto, Calif.; Ball Aerospace Corp. of Boulder, Colo.; the NASA Goddard Space Flight Center of Greenbelt, Md.; and the Jet Propulsion Laboratory of Pasadena, Calif.

During the New Horizons feasibility study that occurred this summer, the team designed a spacecraft equipped with sensitive, miniaturized cameras, a radio science instrument, ultraviolet and infrared spectrometers, and space plasma experiments. The team believes this combination of science instruments is ideal to characterize the global geology and geomorphology of Pluto and its moon Charon, to map their surface compositions, and to characterize Pluto's atmosphere and its atmospheric escape rate. The feasibility study also showed the mission could save money using technologies for deep space exploration that are essentially off the shelf.

Congress has approved $30 million of fiscal year 2002 funds to conduct final design work of the spacecraft and science instruments and to contract the launch vehicle. For the mission to continue beyond 2002, the program must meet two conditions set by NASA. First, the team must pass a NASA-led "confirmation review" of its work. Second, Congress must approve additional funding.

"We couldn't be more pleased to be leading this pioneering space mission," says Dr. James L. Burch, vice president of the SwRI Space Science and Engineering Division. "We are happy to have such quality institutions participating on this mission and are confident of its success."

Pluto is the most distant planet known and the largest member of the Kuiper Belt. Kuiper Belt Objects -- a class of objects composed of material believed to have been left over after the formation of the other planets -- have never been exposed to the higher temperatures and solar radiation levels of the inner solar system. Pluto has large quantities of ices of nitrogen and simple molecules containing combinations of carbon, hydrogen, and oxygen that are the necessary precursors of life. The gases comprising these ices would be largely lost to space if Pluto had come close to the sun. Instead they remain on Pluto as a sample of the primordial material that set the stage for the evolution of the solar system as it exists today - -- including life.

With additional funding, the launch of New Horizons is expected to occur in January 2006, with the spacecraft arriving at Pluto between 2014 and 2018, depending on the selection of the launch vehicle. Along the way to Pluto, New Horizons will capitalize on a gravitational boost from Jupiter.

Plans for the Pluto mission

NASA has selected a team led by The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD, and Southwest Research Institute (SwRI) in San Antonio, TX, to develop the first mission to explore Pluto and the Kuiper Belt region beyond the distant planet.

Headed by Principal Investigator Dr. S. Alan Stern of SwRI, the New Horizons: Shedding Light on Frontier Worlds mission team also includes Ball Aerospace, Boulder, CO; Stanford University, Palo Alto, CA; NASA Goddard Space Flight Center, Greenbelt, MD; and a variety of other universities and research institutions. Thomas Coughlin is the project manager at APL, which will manage the mission for NASA and design, build and operate the New Horizons spacecraft. SwRI will lead the science team and guide development of the spacecraft's scientific instruments. Ball Aerospace and NASA Goddard will help develop the payload.

Aiming for a 2006 launch and arrival at Pluto before 2020, NASA officials say the mission must pass a confirmation review that will address significant risks such as schedule and technical milestones and regulatory approval for launch of the mission's nuclear power source. Funding must also be available; Congress provided $30 million in fiscal 2002 for the mission to procure a launch vehicle and start developing the spacecraft and science instruments, but no funding for subsequent years is included in the administration's budget plan.

Pluto is the most remote planet in the solar system; its elliptical orbit has an average distance of 3.66 billion miles (5.91 billion kilometers) from the sun - nearly 40 times the distance between Earth and the sun. The Kuiper Belt is a source of comets and believed to be the source of much of Earth's water and the simple chemical precursors of life.

"We'll explore frontier worlds near the edge of the planetary system," says Stern, who is also the director of SwRI's Department of Space Studies, Boulder. "This mission is likely to rewrite textbooks regarding the origins of the planets, the nature of the outer solar system, and even the origin of primitive materials that may have played a role in the development of life. We are very excited to be a part of this wonderful NASA mission."

NASA will work with Stern to further define mission costs and to finalize the design of the spacecraft and its accommodation of the instrument sets. New Horizons is planned for launch in January 2006 and, depending on the launch vehicle selected, would reach Pluto and its moon, Charon, in July of 2016 or 2018. On the way, the small, lightweight craft would pass Jupiter, using the giant planet's gravity as a slingshot toward Pluto and exploring the Jovian system.

The spacecraft team plans to use several proven subsystems already designed for other APL planetary missions, saving money while reducing risk and shortening the project's development schedule. New Horizons' remote-sensing instruments will characterize the global geology and geomorphology of Pluto and Charon, map their surface compositions and temperatures, and examine Pluto's atmosphere in detail. Encounters with Kuiper Belt Objects will occur after the Pluto-Charon flyby.

"The Kuiper Belt is an archeological dig into the early history of our solar system," says Dr. Andrew Cheng, New Horizons project scientist at APL. "It's full of small, icy, dirty and rocky objects that started to build into planets but, for some mysterious reason, stopped in mid-stride. It's a fascinating region."

Following the successful management model of NASA's Discovery Program, New Horizons is a principal investigator-led team representing academia, industry, NASA centers and other communities. In addition to Stern, Coughlin and Cheng, the management team includes Mission Director Dr. Robert Farquhar of APL and Science Payload Manager William Gibson of SwRI. NASA's Jet Propulsion Laboratory, Pasadena, CA, will provide navigation support, and tracking and communication services through NASA's Deep Space Network.

"Leading the first mission to Pluto is an exciting opportunity for the Applied Physics Laboratory," says APL Director Dr. Richard Roca. "We promise a rewarding mission for NASA and for avid space science supporters, such as Sen. Barbara Mikulski and the Maryland delegation, who have done so much to advance science and technology in the state."

New Horizons is the latest of several NASA projects on APL's roster. The Lab manages the Comet Nucleus Tour (CONTOUR), which launches in July 2002 to study at least two diverse comets, and Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER), set to become the first spacecraft to orbit Mercury after launching in March 2004. APL also managed the Near Earth Asteroid Rendezvous (NEAR) mission - which included the first spacecraft to orbit and land on an asteroid - and recently secured a 12-year, $600 million contract for missions in NASA's Sun-Earth Connection program.

Pluto Express Is On (Sort-of)

In November 2001, Congress inserted $30,000,000 into NASA's budget for a mission to Pluto in 2006. However, the funding at the moment is only for one year. Also, NASA's two existing radioisotope electrical generators are spoken for (for the Europa mission), and a Pluto mission needs one. So the battle isn't over.

Pluto/Kuiper-Belt Mission in 2004?

Boulder, Colorado- September 27, 2001 -- A team led by the Southwest Research Institute (SwRI) and the Johns Hopkins University Applied Physics Laboratory (JHU APL) has just completed a NASA-funded, "Phase A" design study for a Pluto-Kuiper Belt mission. This team, called "New Horizons," was one of two selected by NASA's Office of Space Science early this summer and funded at a level of $450,000 to conduct Pluto-Kuiper Belt mission studies. The principal investigator of the New Horizons Pluto-Kuiper belt mission study is Dr. Alan Stern of SwRI. The New Horizons study team consists of over 20 scientific experts in Pluto and Kuiper Belt studies, along with almost 100 engineers and other personnel at SwRI, JHU APL, Stanford University, Ball Aerospace, and NASA's Goddard Space Flight Center.

Pluto is the most distant planet known and the largest member of the Kuiper Belt. Kuiper Belt Objects -- a class of objects composed of material left over after the formation of the other planets -- have never been exposed to the higher temperatures and solar radiation levels of the inner solar system. Pluto has large quantities of ices of nitrogen and simple molecules containing combinations of carbon, hydrogen, and oxygen that are the necessary precursors of life. These ices would be largely lost to space if Pluto had come close to the sun. Instead they remain on Pluto as a sample of the primordial material that set the stage for the evolution of the solar system as it exists today, including life.

"NASA asked us to perform a detailed feasibility study for flying a mission to explore Pluto and its giant satellite Charon, and to then go on to the Kuiper Belt." Says Principal Investigator Stern, "We found the mission to be feasible with technologies that are essentially off the shelf for deep space exploration. We also found that a launch as soon as December 2004 can be accomplished."

The New Horizons team studied flying a spacecraft equipped with sensitive, miniaturized cameras, a radio science instrument, ultraviolet and infrared spectrometers, and space plasma experiments. The study team found that this combination of instruments is essentially ideal to characterize the global geology and geomorphology of Pluto and its moon Charon, to map their surface compositions, and to characterize Pluto's atmosphere and its atmospheric escape rate. "These are the very objectives NASA set forth as goals for the Pluto-Kuiper Belt mission," says New Horizons Payload Manager Mr. William Gibson, also of SwRI. "We also found that all of this can be accomplished with a significantly smaller, lighter, and far less power hungry spacecraft than the famous Voyager outer planet reconnaissance missions. It's a real step forward for outer planet exploration."

The New Horizons team designed a complete mission, including spacecraft, trajectory, instruments, and even education/public outreach plans for NASA during the Phase A study. Its mission flies to Pluto using a gravitational boost from Jupiter. "This reduces the necessary flight time and saves money," notes Stern. "The savings comes from the fact that by using Jupiter's powerful gravity as a slingshot, NASA can afford to launch the mission on a smaller launch vehicle. Our plan also saves money by using many subsystems already designed for other recent JHU APL planetary missions; this way, NASA gets the maximum leverage on past investments. Beyond saving dollars, this re-use of existing subsystem designs also reduces risk and speeds the project development schedule."

Should NASA select a Pluto-Kuiper Belt mission for development, it would follow the management philosophy of NASA's highly successful Discovery Program, with a principal investigator-led team representing academia, industry, NASA centers, and other communities. Launch would occur in either December 2004 or January 2006, with the spacecraft arriving at Pluto sometime between 2014 and 2018, depending on the type of launch vehicle and the year of launch. Along the way to Pluto, New Horizons will fly through the Jupiter system. Kuiper Belt object flybys would occur in the years following the Pluto-Charon flyby.

NEAR Shoemaker, tremendous success, ends its mission to Eros

On March 1, NASA's Deep Space Network antennas pulled down their last Near Earth Asteroid Rendezvous (NEAR) mission data, bringing to a close the first mission to extensively study an asteroid. NEAR, which was the first mission in NASA's Discovery Program of low-cost, scientifically focused space missions, and the first to land on an asteroid, has delighted astronomy neophytes and scientists alike.

"NEAR has raised the bar," says Dr. Stamatios Krimigis, Space Department head at The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which built the spacecraft and managed the NEAR mission. "The Laboratory is very proud to have managed such a successful mission and other universities. The team had no weak links and the result was an historic mission that surpassed everyone's expectations."

"This mission has been successful far beyond what was in the original mission plan," says NEAR Mission Director Dr. Robert Farquhar of APL. "We got the first images of a C-class asteroid when we added a flyby of asteroid Mathilde in 1997; we added two low altitude series of passes over the ends of Eros this past October and January that gave us spectacular images from 2.7 kilometers above the surface; and we achieved the first landing of a spacecraft on an asteroid on Feb. 12. All this at no extra cost. When you talk about ' faster, cheaper, better,' this is what 'better' means."

On Feb. 12 at 3:01:52 p.m. (EST), NEAR Shoemaker made a gentle, picture-perfect 3-point landing on the tips of two solar panels and the bottom edge of the spacecraft body. But the mission wasn't finished yet. Much to the amazement of the mission team and millions of observers around the world who were following the descent, the touchdown was so elegant that the craft was still operating and sending a signal back to Earth even after landing.

Jumping at the chance to get "bonus science" from the spacecraft, which had already collected 10 times more data than originally planned, the mission team asked for and got a 10-day extension and then four more days of DSN antenna time, enabling NEAR Shoemaker to send back data through Feb. 28. The extension was granted to allow the gamma-ray spectrometer to collect data from an ideal vantage point about four inches from the surface. The spectrometer team quickly redesigned software and uploaded it to the spacecraft so they could begin collecting elemental composition readings.

The results were spectacular. "This is the first gamma-ray experiment that has ever been done on the surface of a body other than Earth," says Dr. Jacob Trombka, of NASA's Goddard Space Flight Center, in Greenbelt, Md., who heads the gamma-ray spectrometer team. "In fact, we can say it's the first feasibility study of how to design an instrument to be used on a rover that could select samples from the surface, look for the presence of water, or map the surface for the purpose of future mining."

The gamma-ray spectrometer team was able to retrieve data for a period of seven days after the spacecraft landed. "Right now we know we have good data with strong signatures," Trombka says. "But it will take months to scrutinize what we've collected. What we're looking for is information that will help us more precisely classify Eros and determine the relationship between the asteroid and meteorites that have fallen to Earth."

NEAR Shoemaker now rests silently just to the south of the saddle-shaped feature Himeros as the asteroid twists more and more away from the sun with each rotation, moving the southern hemisphere into its winter season and temperatures as low as minus 238 degrees Fahrenheit (minus 150 centigrade).

Project Scientist Dr. Andrew Cheng of APL, says the glamorous part of the mission is over but now scientists can get down to studying the data, including the more than 160,000 detailed images taken by the spacecraft. "We solved mysteries, we unveiled more mysteries. Now we're sharing the amazing amount of data that we collected with scientists all over the world, to sort through and debate and hopefully to help us discover facts about Eros and our solar system that no one knows today."

NEAR Shoemaker Makes Historic Touchdown on Asteroid Eros

"This was a bonus," says NEAR (Near Earth Asteroid Rendezvous) Mission Director Dr. Robert Farquhar of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., which built the NEAR Shoemaker spacecraft and manages the mission for NASA.

"The NEAR mission and the spacecraft were not designed to touch down on the asteroid, and such a maneuver has never been attempted before," Farquhar says. "But the risk was worth taking. During our yearlong study of Eros we collected 10 times more data than originally planned. And now, at the end of the mission, we had a chance to gather close-up images of Eros' surface - capturing features as small as 4 inches (10 centimeters) across - by executing a controlled descent to the surface of Eros. So we took it."

A successful engine burn at 10:31 a.m. (EST), nudged NEAR Shoemaker toward Eros from about 16 miles (26 kilometers) away. Then four breaking maneuvers brought the spacecraft to rest on asteroid's surface in an area just outside a saddle-shaped depression, Himeros, at approximately 3:05 p.m. (EST).

Edge to Kuiper Belt Found

Our solar system may have an outer "edge" just outside the orbit of Pluto, astronomers announced. Their results suggest that early in the history of the solar system, some event stripped away most of the planet-building material beyond 50 times Earth's distance from the sun.

Lynne Allen and Gary Bernstein, of the University of Michigan, and Renu Malhotra of the University of Arizona Lunar and Planetary Laboratory presented the evidence at a meeting of the Division of Planetary Sciences of the American Astronomical Society, October 2000.

It has long been thought that some comets must originate from a collection of small icy bodies orbiting beyond Neptune. These so-called "Kuiper Belt Objects" would be left over from the formation of the large planets 5 billion years ago. The Kuiper Belt Objects were purely hypothetical until 1992, when David Jewitt and Jane Luu of the University of Hawaii discovered the first one. Since that time, over 300 Kuiper Belt Objects have been discovered - but none of them are more than about 55 times as far from the sun as Earth, or 55 AU.

Does the solar system really end beyond Pluto's orbit? Or are the more distant objects just too faint to have been found so far? To address this question, Allen, Bernstein, and Malhotra searched 6 patches of sky, each about the size of the full moon, using a state-of-the-art electronic camera at the Cerro Tololo Inter-American Observatory in the Chilean Andes.

Astronomers have discovered more than 300 Kuiper Belt Objects, but none of them are more than 55 times as far from the sun as Earth. Does the solar system really end beyond Pluto's orbit?

These observations, in 1998 and 1999, were sensitive enough to see a 160-kilometer (100-mile) Kuiper Belt Object to at least 65 AU. They discovered 24 new Kuiper Belt Objects, 9 of which are 160 kilometers or bigger, but again the most distant is near the outer limit of Pluto's orbit. This is the strongest evidence yet that more distant objects are missing.

Some of the known Kuiper Belt Objects as well as many comets are on trajectories that will carry them well beyond the orbit of Pluto. But these are all believed to have formed inside Pluto's orbit and then been pushed outward by an encounter with Neptune or another planet. There are still no known objects which appear to have been created outside Pluto's orbit.

So astronomers are left to wonder what explains this apparent edge: was the primordial solar system originally "small"? Or were there once more distant objects that were pulled away by the gravity of a passing star? Astronomers at telescopes around the world are currently conducting further surveys in an effort to learn more about the history of our solar system.

This Kuiper Belt survey was funded by grants from NASA and the National Science Foundation.

Images and text available at http://www.astro.lsa.umich/users/garyb/WWWKBO.

Pluto Express Work Stopped

Astronomers have expressed their major concerns over the NASA-directed work stoppage for the Pluto-Kuiper Express Mission (PKE). The American Astronomical Society's Division for Planetary Sciences (DPS) committee has urged that NASA and the US Congress to find a way to fund this important mission, but not at the expense of other equally important planetary missions or its basic research and analysis programs.

A stop-work order was issued in mid-September, 2000, by NASA Associate Administrator for Space Science Dr. Edward Weiler. The stated reason was ballooning costs for the entire Outer Planets set of missions at JPL (which also includes the Europa Orbiter and Solar Probe), due largely to increased costs for the launch vehicle and radioactive thermal generators (RGTs).

The DPS committee noted that if work on PKE is not resumed before the end of calendar year 2000, it is likely that the 2004 launch opportunity will be lost, and the earliest arrival date would slip by at least 7 years (from 2012 to 2019 or beyond). Pluto is the only planet not yet explored by spacecraft and is therefore of great interest and importance to the planetary science community. It is also moving rapidly outward from the Sun from its perihelion passage in the early 1990s, and if this mission is delayed beyond the 2004 launch, the opportunity to study the tenuous Pluto atmosphere may be lost for centuries.

Statement of an IAU Bureau on Pluto, and Call for Opinions

M.P.E.C. 1999-C03
Issued 1999 Feb. 4, 16:04 UT

The Minor Planet Electronic Circulars contain information on unusual minor planets and routine data on comets. They are published on behalf of Commission 20 of the International Astronomical Union by the Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.

BMARSDEN@CFA.HARVARD.EDU or GWILLIAMS@CFA.HARVARD.EDU URL http://cfa-www.harvard.edu/iau/mpc.html

EDITORIAL NOTICE

On 1801 Jan. 1 Guiseppe Piazzi discovered the object between Mars and Jupiter that he called Ceres Ferdinandea, "the eighth planet". Following the discovery a year later of a similar object, and in subsequent years further objects in what might be termed the "Cisjovian Belt", Piazzi's discovery eventually became known under either the name Ceres or the symbol (1), where the numeral, originally placed inside a complete circle, indicated that this was the first object found in that region of the solar system. By 1849 the sequence of discoveries in the region had reached (10), and 1868 saw the discovery of (100). By 1923, when (1000) was announced, the set of objects, while still mainly members of that Cisjovian Belt (also known simply as the "Asteroid Belt", or "Main Belt" of "minor planets"), also included objects that approached within 0.1 AU of the earth or extended out to the orbit of Saturn.

Next month, we shall pass (10000) in what is a collection of small objects that are not obviously cometary (although three members do also have well-documented dual status in the Catalogue of Cometary Orbits) and travel around the sun in independent orbits (i.e., satellites are excluded) that are well determined (i.e., with one exception that will surely be eventually remedied, the positions of the objects are very precisely predictable). Again, although the vast majority of the objects are in the Cisjovian Belt, there are members that are at perihelion significantly closer to the sun than Mercury or are at aphelion beyond the orbit of Neptune. It has been traditional to have a special celebration with each thousandth numbering. For example, (1000) was named in honor of the discoverer of Ceres, (2000) in honor of the discoverer of Uranus, (5000) in honor of the International Astronomical Union and (6000) in honor of the United Nations. Obviously, it would be appropriate to have some very special celebration to acknowledge (10000).

Most readers of these Circulars will be aware of recent discussions in the press concerning a proposal that the number (10000) should be given to Pluto. The principal reasoning for this is the recognition during the past few years that Pluto was the first discovered and largest known member of the "Transneptunian Belt" (sometimes called the "Kuiper Belt" or "Edgeworth-Kuiper Belt") of small objects beyond Neptune that possess some similarity, at least dynamically, to bodies in the Cisjovian Belt. Although as many as 95 members (or possible members) of the Transneptunian Belt are now listed, most of the orbital solutions are very weak, and none of the bodies has so far been included in the collection of those with "guaranteed" orbit determinations. A few of the discoveries from 1992-1994 are now approaching this state, which will also allow them to receive permanent names.

Although it is not unlikely that further Transneptunian Objects as large as Pluto will be discovered in the future, Pluto obviously holds a very special place in our appreciation of this new population, and by assigning to it the number (10000), we should guarantee that Pluto will be at the head of the Transneptunian list. It is also very important to affirm that there is absolutely no implied "demotion" or "reclassification" of Pluto from its position in the list of the "planets" (or "major planets" or "principal planets"). Unfortunately, many of the articles that have appeared in the press have accidentally (or deliberately) misinterpreted this issue. As with (2060) = 95P/Chiron, (4015) = 107P/Wilson-Harrington and (7968) = 133P/Elst-Pizarro, where the choice of "minor planet" or "comet" designation depends on the context, we are proposing that Pluto would have dual status as a "major" and a "minor" body. Readers of these Circulars, in particular, will appreciate that Pluto is sufficiently fainter than the other major planets that it can be confused with many other minor planets. We have in fact identified observations of Pluto several times during the past couple of years in data reported by the survey programs for Near-Earth Objects, and some astrometric observers specifically report to us observations of Pluto. There is currently no outlet for publishing these observations. It should be emphasized that the number (10000) would be used only in the context of publishing such observations or in matters directly related to Pluto's place in the Transneptunian Belt.

Much has been made in the press that the IAU is "voting" on Pluto's status, and at least one astronomical organization issued a press release on the subject. Members of the public seem completely baffled by this kind of attention. The question of relevance to the readers of these Circulars concerns the numbering and naming of (10000). Indeed, the IAU Small Bodies Names Committee has already been working on this particular matter for the past month or so. Progress is slow and uncertain, however, and there are some who think that democracy would be better served by seeking opinions from a larger, but informed community. The astronomers, amateur and professional, who contribute material to these Circulars--astrometric observations, identifications, orbit determinations--are such an informed community.

Accordingly, any reader with an opinion on the subject is invited to e-mail it to us at the Minor Planet Center, preferably using the address mpc@cfa.harvard.edu. Such a message could consist of a brief statement such as "I approve (10000) Pluto" or "I do not approve (10000) Pluto", although the value of the latter choice would be augmented if an appropriate alternative suggestion were made for (10000). Brief comments on the subject (preferably constructive) would also be welcome, and writers are encouraged to identify themselves. Modern bureaucracy rarely pays much attention to comments from even an informed public, but since this issue is of concern principally to our readers (more so, in fact, than to many professional astronomers with little or no interest in solar-system astronomy who just happen to be serving on a committee), we feel that it is appropriate for us to solicit advice in this way. Your early response is desirable. It is not necessary that you actually subscribe to these Circulars in order to respond. Appropriate responses will be examined and considered in connection with the responses will be examined and considered in connection with the deliberations by the Small Bodies Names Committee by their deadline of Feb. 26.

-- The above is the Editorial Notice that appears on MPC 33615-33616, dated 1999 Feb. 2

Brian G. Marsden
(C) Copyright 1999 MPC

The International Astronomical Union Isn't Demoting Pluto

[An IAU Statement, 2/3/1999]

Recent news reports have given much attention to what was believed to be an initiative by the International Astronomical Union (IAU) to change the status of Pluto as the ninth planet in the solar system. Unfortunately, some of these reports have been based on incomplete or misleading information regarding the subject of the discussion and the decision making procedures of the Union.

The IAU regrets that inaccurate reports appear to have caused widespread public concern, and issues the following corrections and clarifications:

1: No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Accordingly, no such initiative has been considered by the Officers or Executive Committee, who set the policy of the IAU itself.

2: Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet.

A Working Group under the IAU Division of Planetary Systems Sciences is conducting a technical debate on a possible numbering system for TNOs. Ways to classify planets by physical characteristics are also under consideration. These discussions are continuing and will take some time. The Small Bodies Names Committee of the Division has, however, decided against assigning any Minor Planet number to Pluto.

3: From time to time, the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by national or international law, but are accepted because they are rational and effective when applied in practice. It is therefore the policy of the IAU that its recommendations should rest on well-established scientific facts and be backed by a broad consensus in the community concerned. A decision on the status of Pluto that did not conform to this policy would have been ineffective and therefore meaningless. Suggestions that this was about to happen are based on incomplete understanding of the above.

The mission of the IAU is to promote scientific progress in astronomy. An important part of this mission is to provide a forum for debate of scientific issues with an international dimension. This should not be interpreted to imply that the outcome of such discussions may become official IAU policy without due verification that the above criteria are met: The policy and decisions of the IAU are formulated by its responsible bodies after full deliberation in the international scientific community.

Johannes Andersen
General Secretary, IAU

For more information, contact the IAU Secretariat (URL: http://www.iau.org and address below), or the Division President, Prof. Michael A'Hearn, University of Maryland, USA (Tel: (301) 405 6076; Fax: (301) 314 9067; E-mail: ma@astro.umd.edu).

PLUTO AS A PLANET

[from the Division of Planetary Sciences of the American Astronomical Society]

Colleagues,

No doubt, you are aware of the recent media attention implying that Pluto has been "officially" downgraded from planetary status. This was stimulated in large part by a suggestion by the Minor Planet Center to assign the minor planet number 10000 to Pluto in conjunction with the numbering of some Trans-Neptunian Objects. The Small Bodies Names Committee (SBNC) of IAU Commission 20 has been discussing this issue for several months, as has the Executive Committee of IAU Division III (Planetary Systems Sciences). It should be emphasized that, in spite of media perceptions, no action or decision has yet been taken. The number 10000 will likely be reached for the numbered asteroids within a few weeks. Mike A'Hearn, as President of IAU Division III, has established a web page with background information which also solicits input from the astronomical community:

http://www.ss.astro.umd.edu/IAU/div3/pluto.shtml

The DPS committee believes that this situation is harmful to our profession and will become more so if not put quickly to rest. The public is confused, acrimonious rifts are being created within our community and many of our colleagues are being diverted from productive work to counter what they perceive to be an alarming and unnecessary crisis. We have therefore adopted the following brief position statement, which will be forwarded to the appropriate IAU committees:

"The Committee of the Division for Planetary Sciences of the American Astronomical Society is opposed to assigning a minor planet number to Pluto. This action would undoubtedly be viewed by the broader scientific community and the general public as a "reclassification" of Pluto from a major planet to a minor planet. We feel that there is little scientific or historical justification for such an action."

We urge DPS members to visit the above web page and express your opinions. Michael A'Hearn (ma@astro.umd.edu) is President of IAU Div. III and Chair of the Small Bodies Nomenclature Committee, and can relay messages to appropriate others in the IAU.

Don Yeomans, Division of Planetary Sciences/Am Astron Soc Chairman and the other members of the DPS Committee

[Postscript from another message from Don Yeomans: Many of us have been asked when the Planet Pluto will once again have the largest heliocentric distance of any of the nine planets. JPL's Myles Standish notes that on 1999 Feb. 11 at 10:09 ET, Pluto's distance will exceed that of Neptune's. This result is based upon JPL's Planetary ephemeris DE405 and the time refers to Pluto and Neptune themselves rather than their respective barycenters (the latter time would be 09:40).]

Note the additional objection from Deborah Pasachoff:
We can now note the nine planets from the initial letters of "My Very Educated Mother Just Sent Us Nine Pizzas." If we demote Pluto, the mnemonic would become "My Very Educated Mother Just Sent Us Nothing," which is obviously undesirable.

Comets

Comet Links

Gary Kronk's site for comet and meteor showers
Gary Kronk's site for comets
Mini-Comets Hitting Earth All the Time?
Some Comet WWW Links
Hale-Bopp Webpages
The Why Files - Information on Comets
Comet Hyakutake Near the Sun
Stardust mission to comet planned
Caroline Herschel, discover of many comets Comet Borrelly

Articles and News Updates

Rosetta to Be Launched to a Comet

In a week's time the European Space Agency's pioneering Rosetta mission will begin its 12-year expedition to orbit and land on Comet 67P/Churyumov-Gerasimenko. This is one of the most ambitious and complex robotic space projects ever undertaken and the UK has made a significant contribution to the scientific instruments on the orbiter and lander.

Following the launch on an Ariane 5 rocket from Kourou in French Guiana on 26th February (0736 GMT) the spacecraft will make 3 flybys of Earth and one of Mars before reaching the comet in 2014. For much of its journey the spacecraft will be placed in hibernation mode to limit power and fuel consumption. There will be some science observations taking place on the journey and crucially on approach to the comet the onboard camera will provide images which will help improve calculations of the comet's position, orbit, size and shape.

Once in the comet's vicinity around May 2014 the spacecraft will edge closer to the nucleus, as the comet moves towards the sun, before deploying the Philae lander in November 2014. Once on the surface of the comet a whole range of scientific experiments will be conducted in situ with the 10 instruments on board.

As the oldest and most primitive bodies in the solar system comets provide the key to unlocking the secrets of the Universe. Comets have remained unchanged in comparison to other bodies within our solar system and provide the earliest record of materials in a pristine form. In addition comets brought "volatile" light elements to the planets and played an important role in forming oceans and atmospheres. They are also space "carriers" of complex organic molecules that may have been involved in the origin of life on Earth.

The Particle Physics and Astronomy Research Council [PPARC] have funded the development and construction of two key instruments: the Ptolemy experiment on the Rosetta lander [Open University and CCLRC-Rutherford Appleton Laboratory] and the Plasma Interface Unit [PIU, Imperial College, London] built for the Rosetta Plasma Consortium instrument package on the orbiter.

Commenting on the mission and the UK scientific involvement Prof. Ian Halliday, PPARC Chief Executive, said," This mission will turn science fiction into science fact. Every aspect of comet Churyumov-Gerasimenko will be analysed, resulting in the most comprehensive set of scientific measurements ever obtained of a comet - and the UK can be justly proud of the significant part it has played".

He adds, "This ground-breaking mission benefits from considerable involvement by talented scientists from several UK universities. Their contribution endorses the UK's world-leading expertise in the development of technologies needed for planetary landers and miniaturised instrumentation for space missions".

Dr Ian Wright from the Open University is Principal Investigator on PTOLEMY instrument. The size of a shoe box PTOLEMY will analyse samples from the surface of the comet.

He explains "Ptolemy will analyse the nature and distribution of the most important cometary surface materials. From samples of ices extracted by drilling and coring, Ptolemy will use a variety of chemical processing techniques to reduce the samples to their constituent parts, making key measurements of molecules such as water, carbon, monoxide, carbon dioxide and organic compounds."

He adds, "The overall experiment is based around a coupled gas chromatograph and mass spectrometer - together these will determine the abundance and stable isotopic compositions of elements such as hydrogen, carbon, nitrogen and oxygen. The study of these biologically important elements is strongly implicated in humankind's quest to understand the origin of life on Earth".

Dr. Chris Carr from Imperial College is Principal Investigator for the Rosetta Plasma Consortium. "We are extremely pleased to be playing a major role in the Plasma Consortium on Rosetta. The consortium is an international team involving instrumentation from the US, France, Germany, Sweden and the UK, and the whole team has worked really well together to get the instruments ready for launch. Understanding how the comet interacts with the solar wind is a very important part of the Rosetta science objectives, and an area in which the UK is particularly strong. We're really looking forward to some great new results from this mission."

Images

Mission objectives

* Global characterisation of the nucleus, determination of dynamic properties, surface morphology and composition;
* Determination of the chemical, mineralogical and isotopic compositions of volatiles and refractories in a cometary nucleus;
* Determination of the physical properties and interrelation of volatiles and refractories in a cometary nucleus;
* Study of the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma (dust/gas interaction);
* Global characterisation of asteroids, including determination of dynamic properties, surface morphology and composition.

Mission Firsts

Launch and Flight

UK Science Involvement
In total there are 21 instruments/experiments on Rosetta (11 on orbiter and 10 on the lander Philae). UK scientists are involved in 10 of these (7 on orbiter and 4 on Philae).

The institutes involved are:
Armagh Observatory, Cardiff University (Cardiff Centre for Astrobiology), CCLRC, Imperial College, Mullard Space Science Laboratory, UCL, Open University, Oxford University, Queen Mary University of London, University of Sheffield. Imperial College of Science, Technology and Medicine

As part of the Rosetta Plasma Consortium (RPC), the Space and Atmospheric Physics Group at Imperial College has provided the data processing and plasma interface unit (PIU) for the RPC sensors.

The role of the PIU is to act as an interface between the five plasma instruments and the spacecraft by providing a single path for the transmission of scientific data to the ground and commands sent from the ground. The PIU also provides a safely managed power supply to the instruments. It incorporates a number of novel technical solutions to ensure that the scientific output of the RPC instruments is maximised. These solutions also ensure that the risks of malfunction during the mission are minimised by a failure tolerant design. This ensures the required robustness to survive on a long mission and in the cometary environment.

Dr. Chris Carr is the Principal Investigator for RPC/PIU at ICL and is the current spokesman for the Consortium. Dr Chris Lee is the technical manager for the RPC-PIU and will be the operations manager for the Consortium during the mission.

Professor Andre Balogh is a Co-Investigator on the Fluxgate Magnetometer, one of five sensors in the Rosetta Plasma Consortium experiment on the Rosetta Orbiter. The experiment aims to measure the magnetic field in the region where the charged particles of the solar wind plasma interact with the comet. It is also designed to study a possible remnant magnetic field of the nucleus by taking measurements in close co-operation with the Lander magnetometer experiment ROMAP.

Ptolemy is the first example of a new concept in space instrumentation, which has been devised at PSSRI to tackle the analytical challenge of making in situ isotopic measurements of Solar System bodies. The scientific goal of Ptolemy is to understand the geochemistry of light elements, such as hydrogen, carbon, nitrogen and oxygen, by determining their nature, distribution and stable isotopic compositions. The size of a shoebox and weighing just 4.5 kg, Ptolemy will use gas chromatography / mass spectrometry techniques to investigate the comet surface and subsurface.

Samples of material supplied by the Lander's Drilling and Distribution system (SD2) will be placed in a small oven and heated in stages up to 800C. Gases released from the ices will then be analysed to determine their composition.

Ptolemy is the brainchild of Dr. Ian Wright and Prof. Colin Pillinger of the Planetary and Space Sciences Research Institute (PSSRI) based at the Open University in Milton Keynes. The instrument represents the culmination of many years' work by members of the PSSRI along with the Space Sciences Department at the Rutherford Appleton Laboratory. Some of the technological aspects of the experiment have been developed in partnerships with commercial companies (mostly in the UK).

PSSRI has also been involved in the development of the MUPUS experiment on the Rosetta Lander. Dr. Andrew Ball, who is a Co-Investigator for MUPUS, worked with Austrian colleagues on development of the accelerometry experiment built into the harpoon that will anchor the Lander to the comet's nucleus. Dr. Ball helped to develop data analysis tools - by studying the way the harpoon penetrates the surface - the science team will be able to draw conclusions about the strength, texture and layering of the sub-surface material. Dr. John Zarnecki is also a Co-Investigator for both MUPUS and SESAME, another Lander experiment that will investigate the nature of the comet's surface. Professor Tony McDonnell is a Co-Investigator for the GIADA dust analyser instrument on the Orbiter.

Oxford University (Department of Physics, Sub-department of Atmospheric, Oceanic and Planetary Physics). Professor F.W Taylor and Dr P.G Irwin are part of the science team for the VIRTIS imaging spectrometer on the Rosetta Orbiter.

University of Sheffield

The Space Systems Group at the University of Sheffield has helped to develop the Atomic Force Microscope of the MIDAS dust analysis experiment on the Rosetta Orbiter. Dr. Hugo Alleyne of the Space Systems Group is a Co-Investigator for MIDAS.

Professor David Hughes of the University's Department of Physics is a Co-Investigator for the Ptolemy instrument on the Rosetta Lander, which will analyse the composition of the comet's nucleus.

Dr. Hugo Alleyne
Space Systems Group
Department of Automatic Control & Systems Engineering
Rutherford Appleton Laboratory

RAL was also responsible for the design and manufacture of the thermal insulation for the whole Rosetta Lander, as well as the insulation for the GIADA and VIRTIS instruments.

American Participation in Rosetta

The European Space Agency's Rosetta spacecraft is scheduled to lift off on Feb. 26, 2004, at 2:16 am EST, from the Kourou spaceport in French Guiana, on the northeastern coast of South America. The launch will be the beginning of a ten-and-a-half year odyssey to comet Churyumov-Gerasimenko that includes flybys of Mars (2007) and the Earth (2005, 2007 and 2009).

Among the instruments aboard the Rosetta spacecraft are three instruments funded by NASA and a key component of a fourth. The NASA instruments will examine Churyumov-Gerasimenko from the orbiter.

"This comet has only about three-hundred-thousandths the gravity of Earth," said Dr. Claudia Alexander, project scientist for the U.S. role in the mission, from NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "The Rosetta spacecraft will be able to make observations from as close as 2 kilometers (1.2 miles). The data from our state-of-the-art instruments will be amazing," she added.

Rosetta will reach Churyumov-Gerasimenko, a four-kilometer (2.5-mile) diameter comet, in May 2014. When this rendezvous occurs, Churyumov-Gerasimenko will be about three times as far from the sun as the Earth is. Over the next 18 months Rosetta will study how the comet changes as it moves closer to the sun. In November 2014, Rosetta will drop its experiment-laden, harpoon-firing lander on Churyumov-Gerasimenko's icy nucleus.

"What you have to understand is that comets are primordial remnants of the early solar system," explained Dr. Paul Weissman of JPL. "They are the keys to understanding the way the whole solar system, the Earth, and how even we came into being. And with Rosetta we will be able to observe, study and analyze this primordial material up close for more than a year," he said.

JPL supplied the Microwave Instrument for Rosetta Orbiter, the first of its type on any interplanetary mission. This instrument can reveal the abundances of selected gases, their temperatures, the speed at which they are coming off the nucleus, and the temperature of the nucleus. Scientists will use it to monitor changes in how vapors are released from the nucleus as the coma and tail grow. They will be studying water, carbon monoxide, ammonia and methanol, four of the most abundant gases from comets. Dr. Samuel Gulkis of JPL's Earth and Space Sciences Division is principal investigator.

The Southwest Research Institute, based in San Antonio, supplied two NASA instruments for Rosetta. One is an imaging telescope/spectrometer capable of analyzing the composition both of gases released by the comet and of the comet's surface. A goal of scientists using the instrument is to learn about the temperatures at which comets form and evolve, by determining the relative abundance of noble gases, such as helium, neon and argon. Principal investigator for the ultraviolet instrument is Dr. Alan Stern of the institute's Space Studies Department in Boulder, Colo.

Dr. James Burch, of the Institute's Instrumentation and Space Research Division, San Antonio, is principal investigator for Rosetta's Ion and Electron Spectrometer. This device will measure the environment of charged particles surrounding comet Churyumov-Gerasimenko. It will also study the interaction between that environment and the solar wind of charged particles speeding outward from the sun.

Key electronics for a fourth instrument, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, have been supplied by Lockheed Martin Advanced Technology Center, Palo Alto, Calif. This instrument will examine gases surrounding the comet.

JPL, a division of the California Institute of Technology in Pasadena, manages the microwave instrument for NASA's Office of Space Science, Washington, D.C.

Stardust Mission Encounters a Comet

On January 2nd 2004 the NASA space mission, STARDUST, will fly through comet Wild 2, capturing interstellar particles and dust and returning them to Earth in 2006. Space scientists from the Open University and University of Kent have developed one of the instruments which will help tell us more about comets and the evolution of our own solar system and, critical for STARDUST, its survival in the close fly-by of the comet.

Launched in February 1999, STARDUST is the first mission designed to bring samples back from a known comet. The study of comets provides a window into the past as they are the best preserved raw materials in the Solar System. The cometary and interstellar dust samples collected will help provide answers to fundamental questions about the origins of the solar system.

Scientists from the Open University and University of Kent have developed one set of sensors for the Dust Flux Monitor Instrument (DFMI) built by the University of Chicago, and the software to analyse the data. The DFMI, part funded by the Particle Physics and Astronomy Research Council (PPARC) will record the distribution and sizes of particles on its journey through the centre, or coma, of the comet.

Professor Tony McDonnell and Dr Simon Green from the Open University's Planetary and Space Science Research Institute (PSSRI), will be at the mission command centre, the Jet Propulsion Laboratory in California, when the encounter with Wild 2 begins.

Dr Green explains "By combining the information about each of the tiny grains of dust captured by STARDUST we will discover more about the formation of stars, planets and our solar system."

Professor Tony McDonnell said "The information derived from the signals will tell us on the night if the dust shield has been critically punctured."

Cometary particles will be captured on a tennis racket like grid which contains a substance called aerogel - the lightest solid in the Universe! This is a porous material that allows the particles to become embedded with minimum damage. This means that on their return to Earth they will be as near as possible to their original state.

Once the samples are captured a clam-like shell closes around them. The capsule then returns to Earth in January 2006 where it will land at the US Air Force Utah Test and Training Range. Once collected, the samples will be taken to the planetary material curatorial facility at NASA's Johnson Space Centre, Houston, where they will be carefully stored and examined.

The Open University team hope to be involved in analysing the samples that return to Earth in January 2006.

UK scientists, including a team from the Open University, are also involved with the European Space Agency's Rosetta Mission which will follow and land on Comet Churyumov-Gerasimenko. This mission is due to be launched on 26th February 2004.

Background information

Wild-2 is pronounced Vilt-2. The comet is named after the Swiss discoverer.

New Explanation of the Kuiper Belt's Mass

Boulder, Colorado -- November 26, 2003 -- A new study by researchers at Southwest Research Institute (SwRI) and the Observatoire de la Cote d'Azur provides an explanation for one of the more mysterious aspects of the population of objects beyond Neptune. In doing so, it provides a unique glimpse into the proto-planetary disk from which the Solar System's planets formed. Results will be published in the November 27 issue of Nature.

The Kuiper belt is a region of the Solar System that extends outward from Neptune's orbit, containing billions of icy objects from kilometers to thousands of kilometers across. It was discovered in 1992 and, since that time nearly 1,000 objects have been cataloged. Some of these objects are very large -- the largest having a diameter of more than 1,000 kilometers.

As astronomers have studied this structure, a mystery has unfolded. Like most of the planets in the Solar System, the large Kuiper belt objects are believed to have been formed from smaller objects that stuck together when they collided. For this process to have worked in the distant regions beyond Neptune, the Kuiper belt would have to contain more than 10 times the amount of material than is in the Earth. However, telescopic surveys of this region show that it currently contains roughly one-tenth the mass of the Earth, or less.

To solve the puzzle, researchers have been searching for several years for a way to remove more than 99 percent of the Kuiper belt's material. However, Dr. Harold Levison (SwRI) and Dr. Alessandro Morbidelli (Observatoire de la Cote d'Azur of Nice, France) describe in their article, "Forming the Kuiper Belt by the Outerward Transport of Objects During Neptune's Migration," that the Kuiper belt may not have lost much mass at all.

"The mass depletion problem has been sticking in our throat for some time," says Levison, a staff scientist in the SwRI Space Studies Department. "It looks like we may finally have a possible answer."

Levison and Morbidelli argue that the proto-planetary disk from which the planets, asteroids and comets all formed had a heretofore unanticipated edge at the current location of Neptune, which is at 30 astronomical units (AU, the average distance between the Sun and Earth), and that the region now occupied by the Kuiper belt was empty. All the Kuiper belt objects we see beyond Neptune formed much closer to the Sun and were transported outward during the final stages of planet formation.

Researchers have known for 20 years that the orbits of the giant planets moved around as they formed. In particular, Uranus and Neptune formed closer to the Sun and migrated outward. Levison and Morbidelli show that Neptune could have pushed all the observed Kuiper belt objects outward as it migrated. "We really didn't solve the mass depletion problem, we circumvented it," says Levison. "According to our work, the void beyond Neptune was probably devoid of objects."

However, in this model, the region interior to 30 AU contained enough material for the Kuiper belt objects to form. The mechanisms employed by Neptune to push out the Kuiper belt only affected a small fraction of the objects. These became the objects seen by astronomers; the rest were scattered out of the Solar System by Neptune. This new theory explains many of the observable features of the outer Solar System, including the characteristics of the orbits of the Kuiper belt objects and the location of Neptune.

"One of the puzzling aspects of Neptune's migration is why it stopped where it did," says Morbidelli. "Our new model explains this as well. Neptune migrated until it hit the edge of the proto-planetary disk, at which point it abruptly stopped."

Hubble Observations of Rosetta's Target; February 2004 Launch

Results from NASA's Hubble Space Telescope played a major role in preparing ESA's ambitious Rosetta mission for its new target, comet 67P/Churyumov-Gerasimenko (67P/C-G). For the first time in history, Rosetta will land a probe on a comet and study its origin. Hubble precisely measured the size, shape, and rotational period of comet 67P/C-G.

Hubble's observations revealed that comet 67P/C-G is approximately a three-by-two mile, football-shaped object on which it is possible to land. Mission scientists were concerned that the solid nucleus could be nearly 3.6 miles (6 km) across. The higher gravity on a comet that size might make a soft landing more difficult. "Although 67P/C-G is roughly three times larger than the original Rosetta target, its elongated shape should make landing on its nucleus feasible, now that measures are in place to adapt the lander package to the new configuration before next year's launch," says Dr. Philippe Lamy of the Laboratoire d'Astronomie Spatiale in France. Lamy is presenting the Hubble results on comet 67P/C-G on Sept. 5, 2003 at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society in Monterey, Calif.

Mission scientists began considering the new target when the Rosetta mission's launch date was postponed. The delay made the original target comet, 46P/Wirtanen, no longer easily reachable. But scientists did not have enough information on the new target, comet 67P/C-G, and sought data from the largest telescopes. Using a technique developed over the past decade by Lamy, Imre Toth (Konkoly Observatory, Hungary), and Harold Weaver (Johns Hopkins University Applied Physics Laboratory, Laurel, Md.), the team snapped 61 Hubble images of comet 67P/C-G over an interval of 21 hours between March 11 and 12, 2003. Hubble's Wide Field Planetary Camera 2 isolated the comet's nucleus from the coma, the diffuse cloud of dust and gas surrounding the nucleus, and quickly provided the missing figures. The telescope showed that the nucleus has an ellipsoidal shape. Hubble also measured its rotation rate of approximately 12 hours. Rosetta's launch is currently planned for February 2004, with a rendezvous with the comet about 10 years later.

The Hubble observing team members are P.L. Lamy and L. Jorda (Laboratoire d'Astronomie Spatiale, France), I. Toth (Konkoly Observatory, Hungary), and H.A. Weaver (Johns Hopkins University Applied Physics Laboratory). The movie simulation of the Hubble results is provided by Mikko Kaasalainen (University of Helsinki, Finland) and Pedro Gutierrez (Laboratoire d'Astronomie Spatiale, France). The observations were made possible through a special program approved by the Director of the Space Telescope Science Institute, S. Beckwith.

Halley's Comet Photographed Right Now

See:
http://www.eso.org/outreach/press-rel/pr-2003/phot-27-03.html

CONTOUR spacecraft failed, perhaps exploded

8/20/02

The CONTOUR spacecraft was launched into Earth orbit on July 1 to begin its Comet Tour. But on July 15, when its rocket engine was fired to take it on its orbit to Comet Encke, it apparently broke apart. It did not establish radio contact, and telescopes in Arizona, Hawaii, and elsewhere have been able to follow 3 pieces of something moving rapidly in the orbit that the spacecraft would have followed. Apparently, the rocket-engine burn was about 4% short and then something exploded. Some faint hope remains that the extra pieces are merely unimportant parts that broke off and that the spacecraft will resume radio contact following some automatic sequences, including one with relatively favorable antenna contact scheduled for December 2002, but that seems unlikely. It is a sad ending for a promising mission.

I am writing this note from Mauna Kea Observatory, where our Pluto occultation group of David Ticehurst, Bryce Babcock, and me has been helping David Tholen of the University of Hawaii obtain images using the 2.2-m telescope. Tholen has worked out sun-centered orbits for the three components he has imaged.

Jay M. Pasachoff

http://www.contour2002.org,

Spectacular Split Comet (57P/DU Toit-Neujmin-Delporte)

Institute of Astronomy, U. Hawaii, Press Release, 24 July 2002

SUMMARY
New observations from Mauna Kea with the University of Hawaii's 2.2-meter telescope by Institute for Astronomy astronomers Yanga R. Fernandez, Scott S. Sheppard and David C. Jewitt have revealed a zoo of tiny mini-comets strung out in a line trailing behind the comet 57P/du Toit-Neujmin-Delporte. This comet has apparently suffered a significant catastrophe, violent enough to break off many pieces of its nucleus. The event was probably triggered by thermal stresses within the nucleus due to it being warmed by sunlight. While it is not uncommon for one or two companions to be seen near a comet that has fragmented, our observations reveal at least 19 companions, a rare finding. Monitoring of these fragments over the coming weeks and months should reveal much about the constitution and fragility of cometary material.

DETAILS
Motivated by an earlier report of a previously-unknown companion associated with Comet 57P/du Toit-Neujmin-Delporte, we obtained deep imaging to search for any population of fragments that might exist near the comet. We used the University of Hawaii 2.2-m telescope on Mauna Kea and a charge-coupled device (CCD) to make a digital map of the sky around the comet. The observations were performed on the nights of July 17/18 and July 18/19, 2002 (Hawaii Standard Time).

We found a zoo of fragments strung out in a line extending almost 30 minutes of arc away from the comet itself (for comparison, the diameter of the full Moon also covers 30 minutes of arc). So far we have confirmed the existence of 19 fragments, and the discovery has been announced by the Central Bureau for Astronomical Telegrams, the internationally- recognized official clearinghouse for reporting cometary discoveries. We identified the fragments by taking successive images of a field and detecting their motion against the background stars. A mosaic of the relevant mapped region is shown at

http://www.ifa.hawaii.edu/~yan/57p.html,

with the location of the fragments circled. At the distance of the comet, the mosaic spreads over about 1,000,000 kilometers (about 620,000 miles).

We cannot be sure of the sizes of the fragments but the brightest ones are probably less than a few hundred meters (few hundred yards) across. The smallest fragments are probably no more than a few tens of meters across, roughly the size of a house. A gallery of our 18 new objects is shown on the above WWW site.

FREQUENTLY ASKED QUESTIONS

* What are comets?
Comets are conglomerates of water ice and rocky material formed in the early days of the solar system. When a comet is within roughly 400,000,000 kilometers (250,000,000 miles) of the Sun, the sunlight is strong enough to start evaporating the ice in large quantities. (For comparison, Earth is 150,000,000 km (93,000,000 miles) from the Sun.) Since the ice and rock are intimately mixed, the warming and evaporating ice produces great thermal and physical stresses on the body of the nucleus. Under normal circumstances, only vapor and tiny dust grains are all that fly off the surface of the nucleus -- and here on Earth we see a comet with a long tail, for example as widely seen in the late 1990s with comets Hyakutake and Hale-Bopp.

* Why do comets split?
Occasionally thermal stresses become great enough that entire chunks of the nucleus are ejected. Now while the basic idea is thought to be understood, the details are still uncertain, basically because we do not know many fundamental structural properties of cometary nuclei. In the case of this comet we cannot yet determine even when the fragmentation took place; further observations are necessary. With sufficient data fragmenting comets can provide a laboratory for us to witness major evolutionary events and can help us understand a comet's basic constitution.

* What will happen to the fragments?
We expect that most will fade to the point of invisibility, but we don't know how long that will take. A few might last for years.

* Why that name?
Comet 57P/du Toit-Neujmin-Delporte is named for the 3 people who discovered it in 1941.

* Why 57P?
The "57P" means it is the 57th comet in the list of comets that have been seen on two of their passages around the Sun. (The first comet in this list, "1P", is the famous Halley's Comet.)

* Why didn't somebody see the 19 companions before?
Nobody looked hard enough.

* Can I see this comet by eye?
No, it is 15th magnitude and much too faint to see, even with binoculars.

CONTOUR Spacecraft Launched

CONTOUR Spacecraft Is Launched for Its Comet Tour

JHU APL Press Release, July 3, 2002

NASA's Comet Nucleus Tour (CONTOUR) spacecraft -- set to provide the closest look yet at the "heart" of a comet -- was successfully launched on July 3 aboard a Boeing Delta II rocket from Cape Canaveral Air Force Station, Fla.

Designed and built by The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., the 2,138-pound (970-kilogram) spacecraft was placed into an elliptical Earth orbit 63 minutes after launch. About 19 minutes later the mission operations team at APL acquired a signal from the spacecraft through the Deep Space Network antenna station in Goldstone, Calif., and by 5:45 a.m. EDT Mission Director Dr. Robert W. Farquhar of the Applied Physics Lab confirmed the craft was operating normally and ready to carry out its early orbit maneuvers.

"CONTOUR's launch was a spectacular start to an important project," says Dr. Stamatios M. Krimigis, head of the APL Space Department. "CONTOUR is next in the growing lineup of missions to explore small planetary bodies -- such as comets and asteroids -- and we expect it will add much to what little we know about these ancient samples of the solar system's original materials."

CONTOUR will orbit Earth until Aug. 15, when it's scheduled to fire its main engine and enter a comet-chasing orbit around the sun. The mission's flexible four-year plan includes encounters with comets Encke (Nov. 12, 2003) and Schwassmann-Wachmann 3 (June 19, 2006), though it can add an encounter with a "new" and scientifically valuable comet from the outer solar system, should one be discovered in time for CONTOUR to fly past it. CONTOUR's four scientific instruments will take detailed pictures and measure the chemical makeup of each comet's nucleus -- a chunk of ice and rock -- while analyzing the surrounding gas and dust.

The 8-sided solar-powered craft will fly as close as 62 miles (100 kilometers) from each nucleus, protected by a 10-inch-thick, layered dust shield of heavy Nextel and Kevlar fabric. Scientists expect the data to reveal the differences between comet nuclei and answer questions about the role comets had in shaping the Earth and other planets. "We're looking forward to a fantastic mission," says APL's Edward L. Reynolds, who at launch assumed the role of CONTOUR project manager from Mary C. Chiu, who is retiring from the Applied Physics Laboratory. "From mission design and operations at APL, to the navigation group at NASA's Jet Propulsion Laboratory, to the science effort headed by Cornell University, this team includes the talent and expertise needed to capture and deliver the best data yet on a comet's nucleus."

The $159 million CONTOUR is the sixth mission in NASA's Discovery Program of lower cost, scientifically focused exploration projects. APL manages the mission, built the spacecraft and its two cameras, and will operate CONTOUR during flight. NASA's Goddard Space Flight Center, Greenbelt, Md., provided CONTOUR's neutral gas/ion mass spectrometer and von Hoerner & Sulger, GmbH, Schwetzingen, Germany, built the dust analyzer. NASA's Jet Propulsion Laboratory, Pasadena, Calif., will provide navigation and Deep Space Network (DSN) support. Dr. Joseph Veverka, CONTOUR's principal investigator from Cornell University, Ithaca, N.Y., leads a science team of co-investigators from universities, industry and government agencies in the U.S. and Europe.

For more information about the CONTOUR mission or to view images of the spacecraft, visit www.contour2002.org.

Comet Borelly's Surface Is Dry

Press Release, April 5, 2002

PASADENA, Calif., April 5 (AScribe Newswire) -- Comets are sometimes described as "dirty snowballs," but a close flyby of one by NASA's Deep Space 1 spacecraft last fall detected no frozen water on its surface.

Comet Borrelly has plenty of ice beneath its tar-black surface, but any exposed to sunlight has vaporized away, say scientists analyzing data from Deep Space 1, managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

"The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice," said Dr. Laurence Soderblom of the U.S. Geological Survey's Flagstaff, Ariz., station, lead author of a report on the Borrelly flyby results appearing in the online edition of the journal Science.

"We know the ice is there," he said. "It's just well- hidden. Either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice."

The Deep Space 1 science team released pictures and other initial findings days after the spacecraft flew within 2,171 kilometers (1,349 miles) of the comet's solid nucleus on September 22, 2001. This week's report provides additional details about the nucleus and the surrounding coma of gases and dust coming off of the comet as measured by one of Deep Space 1's scientific instruments.

"Comet Borrelly is in the inner solar system right now, and it's hot, between 26 and 71 degrees Celsius (80 and 161 degrees Fahrenheit), so any water ice on the surface would change quickly to a gas, " said Dr. Bonnie Buratti, JPL planetary scientist and co-author of the paper. "As the components evaporate, they leave behind a crust, like the crust left behind by dirty snow."

Borrelly is unusually dark for an object in the inner solar system. The comet's surface is about as dark as a blot of photocopy toner, possibly the darkest surface in the solar system. It is more like objects in the outer solar system such as the dark side of Saturn's moon Iapetus and the rings of Uranus.

"It seems to be covered in this dark material, which has been loosely connected with biological material." Buratti said. "This suggests that comets might be a transport mechanism for bringing the building blocks of life to Earth." Comets may have played an important role in supplying organic materials that are required for life to originate.

Soderblom points out that Borrelly's old, mottled terrain with dark and very dark spots -- different shades of black - -- are apparently inactive. Ground-based observations estimated that 90 percent of Borrelly's surface might be inactive, and the observations taken by Deep Space 1 show that this is indeed true.

> "It's remarkable how much information Deep Space 1 was able to gather at the comet, particularly given that this was a bonus assignment for the probe," said Dr. Marc Rayman, project manager of the mission. Deep Space 1 completed its original goal to test 12 new space technologies and then earned extra credit by achieving additional goals, such as the risky Borrelly flyby. "It's quite exciting now as scientists working with this rich scientific harvest turn data into knowledge."

Images of comet Borrelly from Deep Space 1 are available at http://www.jpl.nasa.gov/images/ds1/ds1_borrelly.html .

More information on the Deep Space 1 mission is available at http://nmp.jpl.nasa.gov/ds1/ .

Deep Space 1 was launched in October 1998 as part of NASA's New Millennium Program, which is managed by JPL for NASA's Office of Space Science, Washington, D.C. The California Institute of Technology, Pasadena, manages JPL for NASA.

Contour mission

NASA has approved the Comet Nucleus Tour, "Contour," for launch in July 2002. it will go first to Comet Encke, a periodic comet with a short period. It will then go on to Comet Schwassmann-Wachmann-3, which split into three parts in 1995. Then it will proceed to Comet d'Arrest, where it will arrive in 2008.

Comet Mission to Hit P/Tempel 1

NASA Press Release

A radical mission to excavate the interior of a comet has been selected as one of the next two flights in NASA's Discovery Program.

The comet mission, called Deep Impact, will be managed by Jet Propulsion Laboratory, led by Dr. Michael A'Hearn from the University of Maryland in College Park, and built by Ball Aerospace in Boulder, Colo. The mission will send a 500-kilogram (1,100-pound) copper projectile into comet P/Tempel 1, creating a crater as big as a football field and as deep as a seven-story building. A camera and infrared spectrometer on the spacecraft, along with ground-based observatories, will study the resulting icy debris blasted off the comet, as well as the pristine interior material exposed by the impact.

"Comets are leftovers from the birth of the Sun and the planets, and Deep Impact will punch through the dark crust of P/Tempel 1 to give us our first look at what's inside," said JPL director Dr. Edward Stone.

Deep Impact will be launched in January 2004 toward an explosive July 4, 2005 encounter with P/Tempel 1. Those impacts will occur at an approximate speed of 10 kilometers per second (22,300 mph). The total cost of Deep Impact to NASA is $240 million.

The comet mission is a complement to the other two comet missions already in the Discovery Program. Those missions, both managed by JPL, are Stardust, launched in February 1999 on a journey to gather samples of comet dust and return them to Earth, and the Comet Nucleus Tour (CONTOUR) that will launch in June 2002 and fly closely by three comets.

Comets you can now observe

Gary Kronk's site
http://comets.amsmeteors.org

Charles Morris's site
http://encke.jpl.nasa.gov/whats_visible.html

Best Halley's Comet Image

The processed Giotto images are on the Max Planck Institut for Aeronomie, Germany.

Hale-Bopp

Comet Hale-Bopp: the European Space Agency has a Web page with various scientific updates and Web links.

Meteorites and Asteroids

Meteorite and Asteroid Links

Articles and News Updates

Loneos Discovers Asteroid with the Smallest Orbit

Flagstaff, AZ The ongoing search for near-Earth asteroids at Lowell Observatory has yielded another interesting object. Designated 2004 JG6, this asteroid was found in the course of LONEOS (the Lowell Observatory Near-Earth Object Search) on the evening of May 10 by observer Brian Skiff.

"I immediately noticed the unusual motion," said Skiff, "so it was certain that it was of more than ordinary interest." He quickly reported it to the Minor Planet Center (MPC) in Cambridge MA, which acts as an international clearinghouse for asteroid and comet discoveries. The MPC then posted it on a Web page for verification by astronomers worldwide. It happened that all the initial follow up observations, however, were obtained by amateur and professional observers in the Southwest US. The additional sky positions measured in the ensuing few days allowed an orbit to be calculated.

The official discovery announcement and preliminary orbit were published by the MPC on May 13. This showed that the object was located between Earth and Venus (presently the very bright "evening star" in the western sky). In addition, 2004 JG6 goes around the Sun in just six months, making it the asteroid with the shortest known orbital period. Ordinary asteroids are located between the orbits of Mars and Jupiter, roughly two to four times farther from the Sun than Earth, taking several years to go around the Sun.

Instead, 2004 JG6 orbits entirely within Earth's orbit, only the second object so far found to do so. "What makes this asteroid unique is that, on average, it is the second closest solar system object orbiting the Sun," said Edward Bowell, LONEOS Director. Only planet Mercury orbits closer to the Sun.

As shown in the included diagram (http://www.lowell.edu/press_room/2004JG6.pdf), JG6 crosses the orbits of Venus and Mercury, passing less than 30 million miles from the Sun every six months. The approximate average orbital speed of this asteroid is more than 30 km/sec, or 67,000 miles per hour. Depending on their locations, the asteroid may pass as close as 3.5 million miles from Earth and about 2 million miles from planet Mercury. In the coming weeks 2004 JG6 will pass between Earth and the Sun, just inside Earth's orbit. It will move through the constellations Cancer and Canis Minor low in the western sky at dusk. Because of the near-exact six-month period, the asteroid should be observable again in nearly the same spot in the sky next May, having gone around the Sun twice while Earth will have made only one circuit.

From present estimates, 2004 JG6 is probably between 500 meters and 1 km in diameter. Despite its proximity, the object poses no danger of colliding with Earth.

Asteroids with orbits entirely within the Earth's orbit have been informally called "Apoheles," from the Hawaiian word for orbit. Apohele also has Greek roots: "apo" for outside, and "heli" for Sun. Objects orbiting entirely within Earths orbit are thought by dynamicist William F. Bottke of Southwest Research Institute and colleagues to comprise just two percent of the total near-Earth object population, making them rare as well as difficult to discover. This is because they stay in the daylight sky almost all of the time. There may exist about 50 Apoheles of comparable size to or larger than 2004 JG6, but many of them are certain to be unobservable from the ground.

The first asteroid found entirely inside Earth's orbit was 2003 CP20, found just over a year ago by the NASA-funded Lincoln Laboratory Near-Earth Asteroid Research project, which observes near Socorro, New Mexico. Although larger than 2004 JG6, 2003 CP20 is a little more distant from the Sun.

LONEOS is one of five programs funded by NASA to search for asteroids and comets that may approach our planet closely. The NASA program's current goal is to discover 90 percent of near-Earth asteroids larger than 1 km in diameter by 2008. There are thought to be about 1,100 such asteroids.

JPL orbit diagram/animations:
http://neo.jpl.nasa.gov/cgi-bin/db_shm?sstr=2004+JG6

Static view of 2004 JG6 by Tom Polakis:
http://www.psiaz.com/polakis/misc/2004JG6.jpg

Diagram of 2004JG6 by Larry Wasserman, Astronomer, Lowell Observatory (a pdf)
http://www.lowell.edu/press_room/2004JG6.pdf

Meteorite Crater from 250-million-year-old Extinction Found

An impact crater believed to be associated with the "Great Dying," the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia.

NASA and the National Science Foundation (NSF) funded the major research project headed by Luann Becker, a scientist at the University of California, Santa Barbara (UCSB). Science Express, the electronic publication of the journal Science, published a paper describing the crater on May 13, 2004.

Most scientists agree a meteor impact, called Chicxulub, in Mexico's Yucatan Peninsula, accompanied the extinction of the dinosaurs 65 million years ago. But until now, the time of the Great Dying 250 million years ago, when 90 percent of marine and 80 percent of land life perished, lacked evidence and a location for a similar impact event.

Becker and her team found extensive evidence of a 125-mile- wide crater, called Bedout, off the northwestern coast of Australia. They found clues matched up with the Great Dying, the period known as the end-Permian. This was the time period when the Earth was configured as one primary land mass called Pangea and a super ocean called Panthalassa.

During recent research in Antarctica, Becker and her team found meteoric fragments in a thin claystone "breccia" layer, pointing to an end-Permian event. The breccia contains the impact debris that resettled in a layer of sediment at end- Permian time.

They also found "shocked quartz" in this area and in Australia. "Few Earthly circumstances have the power to disfigure quartz, even high temperatures and pressures deep inside the Earth's crust," Becker said.

Quartz can be fractured by extreme volcanic activity, but only in one direction. Shocked quartz is fractured in several directions and is therefore believed to be a good tracer for the impact of a meteor.

Becker discovered oil companies in the early 70's and 80's had drilled two cores into the Bedout structure in search of hydrocarbons. The cores sat untouched for decades. Becker and co-author Robert Poreda went to Australia to examine the cores held by the Geological Survey for Australia in Canberra. "The moment we saw the cores, we thought it looked like an impact breccia," Becker said. Becker's team found evidence of a melt layer formed by an impact in the cores.

In the paper, Becker documented how the Chicxulub cores were very similar to the Bedout cores. When the Australian cores were drilled, scientists did not know exactly what to look for in terms of evidence of impact craters.

Co-author Mark Harrison, from the Australian National University in Canberra, determined a date on material obtained from one of the cores, which indicated an age close to the end-Permian era. While in Australia on a field trip and workshop about Bedout, funded by the NSF, co-author Kevin Pope found large shocked quartz grains in end-Permian sediments, which he thinks formed as a result of the Bedout impact. Seismic and gravity data on Bedout are also consistent with an impact crater.

The Bedout impact crater is also associated in time with extreme volcanism and the break-up of Pangea. "We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Becker said. "This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don't think we can call such catastrophes occurring together a coincidence anymore," she added.

The Meteoroid that Broke Up Over Chicago

The meteorites that punched through roofs in Park Forest, Ill., on the evening of March 26, 2003, came from a larger mass that weighed no less than 1,980 pounds before it hit the atmosphere, according to scientific analyses led by the University of Chicago's Steven Simon, who himself also happens to live in Park Forest.

Simon, a Senior Research Associate in Geophysical Sciences at the University of Chicago, and seven co-authors will publish these and other findings in the April issue of the journal Meteoritics and Planetary Science. Simon holds a unique distinction among scientists: his home sits in the middle of the strewnfield, the area from which the meteorites were recovered.

"I don't know of any other time when a meteoriticist was in the middle of a strewnfield," said Lawrence Grossman, Professor in Geophysical Sciences at the University of Chicago and one of Simon's co-authors.

In fact, Simon actually saw the flash the meteorite created. He had the drapes closed when the rock entered the sky over Illinois, but "the whole sky lit up," he said.

Grossman, who lives in Flossmoor, not far from Park Forest, also experienced the meteorite's arrival firsthand. He was awakened by the sound of the meteorite entering the atmosphere that night. "I heard a detonation," Grossman said. "It was sharp enough to wake me up."

The team calculated the projectile's size range based on measurements of the galactic cosmic rays that it absorbed. Measurements of a radioactive form of cobalt provided the projectile's minimum size. "If the object is too small the cosmic rays will just pass through and not make 60cobalt," Simon explained.

Simon and Grossman classify the meteorite as an L5 chondrite, a type of stony meteorite, one low in iron that was heated for a long period of time inside its parent body, probably an asteroid. "It's a fairly common type of meteorite," Simon said.

The Park Forest meteorite also showed signs that it had been highly shocked, probably when it was part of a rock that was broken from a much larger asteroid following a collision. The evidence for shock includes shocked feldspar. Apollo astronauts recovered shocked specimens of the mineral from the moon, as well, Simon said. Impact shock was common in the early history of the solar system because of the large quantity of interplanetary debris then in existence.

Witnesses in Michigan, Illinois, Indiana and Missouri reported seeing the fireball that the meteorite produced as it broke up in the atmosphere, Simon and his colleagues report. Local residents collected hundreds of meteorite fragments totaling approximately 65 pounds from an area extending from Crete in the south to the southern end of Olympia Fields in the north. Located in Chicago's south suburbs, "This is the most densely populated region to be hit by a meteorite shower in modern times," the authors write.

One meteorite narrowly missed striking a sleeping Park Forest resident after it burst through the ceiling of a bedroom. The meteorite sliced through some window blinds, cratered the windowsill, then bounced across the room and broke a mirror before coming to rest.

The meteorites were recovered from a track that trends southeast to northwest. Satellite data analyzed by Peter Brown of the University of Western Ontario indicates that the meteorite traveled from southwest to northeast, however.

"The meteorite broke up in the atmosphere, and the fragments encountered strong westerly winds as they fell," the authors write. "The smallest pieces were deflected the furthest eastward from the trajectory, and the largest pieces, carrying more momentum, were deflected the least."

Contributing to the paper in addition to Simon and Grossman were the University of Chicago's Robert Clayton and the late Toshiko Mayeda, Jim Schwade of the Planetary Studies Foundation in Crystal Lake, Ill.; Paul Sipiera of Harper College in Palatine, Ill.; John Wacker of Pacific Northwest National Laboratory in Richland, Wash.; and Meenakshi Wadhwa of the Field Museum of Natural History in Chicago.

Web-Based Program Calculates Effects of an Earth Impact

Related Web site

Next time an asteroid or comet is on a collision course with Earth you can go to a web site to find out if you have time to finish lunch or need to jump in the car and DRIVE.

University of Arizona scientists are launching an easy-to-use, web-based program that tells you how the collision will affect your spot on the globe by calculating several environmental consequences of its impact.

Starting today, the program is online at:
http://www.lpl.arizona.edu/impacteffects

You type in your distance from the predicted impact site, the size and type of projectile (e.g. ice, rock, or iron) and other information. Then the Earth Impact Effects Program calculates impact energies and crater size. It next summarizes thermal radiation, seismic shaking, ejecta deposition (where all that flying stuff will land), and air-blast effects in language that non-scientists understand.

For those who want to know how all these calculations are made, the web page will include "a description of our algorithm, with citations to the scientific sources used," said Robert Marcus, a UA undergraduate in the UA/NASA Space Grant Program. He discussed the project recently at the 35th Lunar and Planetary Science Conference meeting in Houston, Texas.

Marcus developed the web site in collaboration with planetary sciences Regents' Professor H. Jay Melosh and research associate Gareth Collins of UA's Lunar and Planetary Laboratory.

Melosh is a leading expert on impact cratering and one of the first scientists reporters call when rumors of big, Earth-smashing objects begin to circulate.

Reporters and scientists both want to know the same thing: how much damage a particular collision would wrack on communities near the impact site.

The web site is valuable for scientists because they don't have to spend time digging up the equations and data needed to calculate the effects, Melosh said. Similarly, it makes the information available to reporters and other non-scientists who don't know how to make the calculations.

"It seemed to us that this is something we could automate, if we could find some very capable person to help us construct the website," Melosh said.

That person turned out to be Marcus, who is majoring in computer engineering and physics. He applied to work on the project as a paid intern through the UA/NASA Space Grant Program.

Marcus built the web-based program around four environmental effects. In order of their occurrence, they are:

1) Thermal radiation. An expanding fireball of searing vapor occurs at impact. The program calculates how this fireball will expand, when maximum radiation will occur, and how much of the fireball will be seen above the horizon.

The researchers based their radiation calculations on information found in "The Effect of Nuclear Weapons." This 1977 book, by the U.S. Defense Department and U.S. Department of Energy, details "considerable research into what different degrees of thermal radiation from blasts will do," Melosh noted.

"We determine at a given distance what type of damage the radiation causes," Marcus said. "We have descriptions like when grass will ignite, when plywood or newspaper will ignite, when humans will suffer 2nd or 3rd degree burns."

2) Seismic shaking. The impact generates seismic waves that travel far from the impact site. The program uses California earthquake data and computes a Richter scale magnitude for the impact. Accompanying text describes shaking intensity at the specified distance from the impact site using a modified Mercalli scale This is a set of 12 descriptions ranging from "general destruction" to "only mildly felt."

Now suppose the dinosaurs had this program 65 million years ago. They could have used it to determine the environmental consequences of the 15-kilometer-diameter asteroid that smashed into Earth, forming the Chicxulub Crater.

The program would have told them to expect seismic shaking of magnitude 10.2 on the Richter scale. They also would have found (supposing that the continents were lined up as they are now) that the ground would be shaking so violently 1,000 kilometers (600 miles) away in Houston that dinosaurs living there would have trouble walking, or even standing up.

If the Chicxulub Crater-impact occurred today, glass in Houston would break. Masonry and plaster would crack. Trees and bushes would shake, ponds would form waves and become turbid with mud, sand and gravel banks would cave in, and bells in Houston schools and churches would ring from ground shaking.

3) Ejecta deposition. The team used a complicated ballistics travel-time equation to calculate when and where debris blown out of the impact crater would rain back down on Earth. Then they used data gathered from experimental explosions and measurements of craters on the moon to calculate how deep the ejecta blanket would be at and beyond the impact- crater rim.

They also determined how big the ejecta particles would be at different distances from impact, based on observations that Melosh and UA's Christian J. Schaller published earlier when they analyzed ejecta on Venus.

OK, back to the dinosaurs. Houston would have been covered by an 80.8-centimeter- (32-inch-) thick blanket of debris, with particles averaging 2.8 mm (about 1/8th inch) in size. They would have arrived 8 minutes and 15 seconds after impact (meaning they got there at more than 4,000 mph).

4) Air blast. Impacts also produce a shock wave in the atmosphere that, by definition, moves faster than the speed of sound. The shock wave creates intense air pressure and severe winds, but decays to the speed of sound while it's still close to the fireball, Melosh noted. "We translate that decreasing pressure in terms of decibels --from ear-and-lung-rupturing sound, to being as loud as heavy traffic, to being only as loud as a whisper."

The program calculates maximum pressures and wind velocities based on test results from pre-1960s nuclear blasts. Researchers at those blasts erected brick structures at the Nevada Test Site to study blast wave effects on buildings. The UA team used that information to describe damage in terms of buildings and bridges collapsing, cars bowled over by wind, or forests being blown down.

Hermes Is Found

"This re-sighting of Hermes is the Holy Grail of near-Earth asteroid discovery," said Edward Bowell, LONEOS Director. "Its orbit has been better calculated and observers have confirmed its re-appearance and also shown its binary nature... well, an asteroid's return just does not become more profound than this."

The binary object was some 19 million miles out at the time of re-discovery last Wednesday, nearly 66 years after it was first seen. Hermes, which poses no threat to Earth, will make its closest approach on November 4th. By then it will be 4 million miles away and bright enough for amateurs to see using backyard telescopes.

The same day Skiff captured the first images of Hermes, Discovery Communications, Inc. and Lowell Observatory announced a partnership to build the new Discovery Channel Telescope near Flagstaff, Arizona. (http://www.lowell.edu/press_room/releases/recent_releases/dct_rls.html) One research objective for this new $30-million, 4.3-meter telescope will be to significantly accelerate the search for near-Earth objects, including those smaller than Hermes.

First images of the kilometer-size asteroid were captured by a CCD camera during early morning observation through the LONEOS 24-inch Schmidt telescope. More than six decades ago, Hermes was discovered by Karl Reinmuth at Heidelberg, Germany on October 25, 1937. Fast forward to a few days ago when Andrea Boattini of Instituto di Astrofisica Spaziale, Rome, Italy, and Timothy Spahr of the Minor Planet Center in Cambridge, Massachusetts analyzed the new positions of Hermes and determined what it was: the long- lost asteroid.

"Since we find new near-Earth asteroids fairly regularly (I found, for instance, two near-Earth asteroids the same night), my only reaction upon finding it was that it was unusually bright," Skiff told BBC News Online on Friday.

Asteroid Images with Adaptive Optics

"Asteroid Davida was discovered 100 years ago, but this is the first time anyone has been able to see this level of detail on this object," said Dr. Al Conrad, scientist at the W.M. Keck Observatory. "With adaptive optics, we're finally able to transform asteroids like Davida from a single, faint point-source into an object of true geological study."

Ground-based observations of large, main-belt asteroids are made possible only through a powerful astronomical technique called adaptive optics, which removes the blurring caused by Earth's atmosphere. Without adaptive optics, critical surface information and details about the asteroid's shape are lost. The techniques used at the W.M. Keck Observatory allow astronomers to measure the distortion of light caused by the atmosphere and rapidly make corrections, restoring the light to near-perfect quality. Such corrections are most easily made to infrared light. In many cases, infrared observations made with Keck adaptive optics are better than those obtained with space-based telescopes.

The observations of asteroid (511) Davida were made with the 10-meter (400-inch) Keck II telescope on December 26, 2002. Images were taken over a full rotation period of about 5.1 hours, just a few days before its closest approach to Earth. At that time, Davida's angular diameter was less than one-ten-thousandth of a degree, about the size of a quarter as seen from a distance of 18 kilometers (11 miles). The high angular resolution allowed astronomers to see surface details as small as 46 kilometers (30 miles), about the size of the San Francisco Bay area. The next time Davida comes this close to Earth will be in the year 2030.

At the time of the observations, Davida's north pole faced Earth. While scientists could see the asteroid spinning, only the northern hemisphere was visible. Yet the profile of the asteroid is far from circular: At least two flat facets can be seen on its surface. Although scientists knew previously from light variations that Davida must have an oblong shape, details of that shape were not available until now. Initial evaluation of the images reveal some dark features, and scientists are still working to understand to what extent these are surface markings, topographical features, or artifacts of the image processing.

"Adaptive optics on large telescopes is allowing us to make detailed studies from the ground that were previously impossible or prohibitively expensive," said Dr. William Merline, principal scientist with the Southwest Research Institute, and a participant in this research. "We can now make observations that once required either the scarce resources of space telescopes or spacecraft missions to asteroids. While these space telescopes and space missions are still needed for complete study of the asteroids, ground-based observations such as these will help tremendously in planning the mission observations and focusing the resources where they will be most effective."

Asteroids are the collection of rocky objects orbiting between Mars and Jupiter. They were likely prevented from forming into a planet, partly due to Jupiter's massive gravitational influence.

"Although the asteroids began their lives colliding gently, in a way that would lead them eventually to form a planet, Jupiter's gravity eventually stirred up their orbits, and they began to collide at higher speeds," added participant Dr. Christophe Dumas, planetary astronomer with the Jet Propulsion Laboratory.

"These collisions tended to cause them to break up rather than gently stick together. The resulting fragments, numbering in the hundreds of thousands, are the asteroids we see today. They collide with each other and have impacted the Earth, Moon, and planets over time. One need only look at the scarred surface of our Moon to see the cumulative result. Study of the asteroid's shape, size, and surface features helps us understand how these collisions operate and thus how our planet was, and still is, being affected by these impacts."

Observations of the shapes of asteroids, such as those released today, can tell us about the types and severity of impacts that occurred, and possibly also give clues into the overall structure of an asteroid --- for example, whether it may be solid rock, or a jumble of smaller rocks. Surface features can reveal a history of large impacts or variations in the composition that should, in turn, further help us understand the asteroid's history.

Asteroid (511) Davida was discovered by R. S. Dugan in 1903 in Heidelberg, Germany. The (511) in Davida's name means it was the 511th asteroid to be discovered and included in the list of asteroids maintained by the International Astronomical Union.

Team members responsible for the observations are Al Conrad, David Le Mignant, Randy Campbell, Fred Chaffee, Robert Goodrich, Shui Kwok of the W.M. Keck Observatory; Christophe Dumas, Jet Propulsion Laboratory; William Merline, Southwest Research Institute; Heidi Hammel, Space Science Institute; and Thierry Fusco, Onera, France.

Muses-C is Hayabusa

MUSES-C Mission is Launched to an Asteroid

The Japanese MUSES-C mission was launched in May 2003 to asteroid 1998SF36. It is to bring a gram of dust back to Earth in 2007, after raising the dust by throwing steel projectiles at the asteroid.

Meteorite Hits Girl in Foot

J.M. Pasachoff

http://icnewcastle.icnetwork.co.uk/0100news/0100local/page.cfm?objectid=12151422&method=full&siteid=50081
However, most such "meteorite" finds have more Earthly explanations. See:
http://epswww.unm.edu/iom/Howto.htm

Twice as many asteroids as previously believed

ESA Press Release, April 5, 2002

Asteroids in our Solar System may be more numerous than previously thought, according to the first systematic search for these objects performed in the infrared, with ESA's Infrared Space Observatory, ISO. The ISO Deep Asteroid Search indicates that there are between 1.1 million and 1.9 million 'space rocks' larger than 1 kilometre in diameter in the so-called 'main asteroid belt', about twice as many as previously believed. However, astronomers think it is premature to revise current assessments of the risk of the Earth being hit by an asteroid.

Despite being in our own Solar System, asteroids can be more difficult to study than very distant galaxies. With sizes of up to one thousand kilometres in diameter, the brightness of these rocky objects may vary considerably in just a few minutes. They move very quickly with respect to the stars - they have been dubbed 'vermin of the sky' because they often appear as trails on long exposure images. This elusiveness explains why their actual number and size distribution remains uncertain. Most of the almost 40,000 asteroids catalogued so far (1) orbit the Sun forming the 'main asteroid belt', between Mars and Jupiter, too far to pose any threat to Earth. However, space-watchers do keep a closer eye on another category of asteroids, the 'Near Earth Asteroids' or 'NEAs', which are those whose orbits cross, or are likely to cross, that of our planet.

The ISO Deep Asteroid Search (IDAS), the first systematic search for these objects performed in infrared light, focused on main belt asteroids. Because it is impossible to simply point the telescope at the whole main belt and count, astronomers choose selected regions of the belt and then use a theoretical model to extrapolate the data to the whole belt.

Edward Tedesco (TerraSystems, Inc., New Hampshire, United States) and Francois-Xavier Desert (Observatoire de Grenoble, France) observed their main belt selected areas in 1996 and 1997 with ESA's ISO. They found that in the middle region of the belt the density of asteroids was 160 asteroids larger than 1 kilometre per square degree - an area of the sky corresponding to that covered by four full moons as seen from Earth. Then, a model developed by Tedesco and the astronomers Alberto Cellino and Vincenzo Zappala (Osservatorio Astronomico di Torino, Italy), allowed them to estimate the whole asteroid population in the main belt: between 1.1 million and 1.9 million asteroids with a diameter larger than 1 kilometre.

"If you consider the average value of 1.5 million asteroids, the ISO result is about twice as high as estimated by two other recent studies in visible light," Tedesco says.

The study by Durda et al., published in 1998, gave an estimate of about 860 000 asteroids larger than 1 kilometre in the main belt. In 2001, Ivezic et al. obtained an even lower figure of 740 000 asteroids based on preliminary data from the Sloan Digital Sky Survey.

Why the discrepancy?

The fact that visually dark objects - such as asteroids - are better detected in the infrared might explain the discrepancy between visible and infrared results. For an optical telescope, the brightness of an asteroid depends on the visible light it reflects from the Sun. Observations with infrared telescopes, on the other hand, detect the 'heat' of the asteroid, which does not depend that much on the reflected sunlight, but on the absorbed sunlight.

As an example, let's consider two spheres of the same size, and located close to each other in the asteroid belt, one of which reflects ten times as much of the visible light striking it as the other. As seen by an optical telescope, the sphere which reflects more appears ten times brighter than the other sphere which might be even invisible. However, for ISO both spheres would be visible. Actually, the 'dark' sphere would appear brighter in the infrared because it would have a higher temperature (as it has absorbed more sunlight).

Expert's 'best estimate'

Tedesco assumes that both visible and infrared searches might have their own biases, which is the reason why the given results have an error margin. Considering both the visible and infrared results, the 'best estimate' would be "1.2 million asteroids larger than 1 kilometre in the main belt, give or take 500,000," Tedesco says.

The best strategy for finding the asteroid size distribution, according to this expert, is to combine near-simultaneous observations at infrared and visible light. "They provide different kinds of information and therefore play a complementary role in the search for the asteroid population's size distribution," he says.

The 'impact hazard'

A better knowledge of the number and size distribution of asteroids in the main belt is essential to understand the population of Near Earth Asteroids (NEAs), since most NEA are believed to be former main belt asteroids. In the main belt there are four 'special' regions where Jupiter's gravitational influence is especially disruptive; originally, most asteroids currently known as NEA suffered collisions which resulted in them ending up in one of those four key regions, and because of Jupiter's gravitational influence their orbits quickly evolved into Earth-crossing orbits. Therefore, by studying the asteroids near these so-called 'source regions' in the main belt astronomers can learn about NEA. About 500 NEAs have been found so far, and none of them pose any threat to Earth in this century.

The generally accepted impact rate by objects larger than 1 kilometre in diameter is one every 100,000 to 300,000 years. The new 'best estimate' of about 1.2 million asteroids of 1 kilometre or larger in the main belt will not change the current estimates of impact hazard, the IDAS astronomers say; at least not yet.

"IDAS has contributed to our knowledge of main belt asteroids. And, although we did not observe any NEAs, the ISO data will be used to improve our knowledge regarding asteroids currently near the NEA source regions. This, in turn, will allow us to better understand the population characteristics of the NEAs and so ultimately enable us to refine our estimates of the NEA impact frequency and the magnitude of the impact hazard," Tedesco says.

Note to editors
The European Space Agency's infrared space telescope, ISO, operated from November 1995 until May 1998. As an unprecedented observatory for infrared astronomy ISO made nearly 30 000 scientific observations.

This note is based on the paper "The Infrared Space Observatory Deep Asteroid Search" by Edward F. Tedesco and Francois-Xavier Desert, published in the April 2002 issue of The Astronomical Journal.

(1) 39,462 main belt asteroids were catalogued as of 28 March 2002. This number increases by about 2,000 per month at present.

Eros as Evaluated from Near Shoemaker Observations

Enough time has passed since Near Shoemaker's orbiting of and landing on Eros for scientists to evaluate the results.

A 8-km-wide crater, with the suggested name of Shoemaker, may be the source of many of the over 30,000 boulders that have been catalogued. 44% of the boulders are within the crater itself, and most of the boulders along Eros's equator may also come from the blast that created Shoemaker. But boulders have not been found from the two other large craters on Eros: Himeros and Psyche. It has been suggested (in an article by Peter Thomas and others in the September 27 issue of NATURE) that the boulders may never have been thrown out or had been buried or eroded.

SCIENCE Magazine's planetary-science expert, Richard A. Kerr, summarized (14 December 2001 issue) the attempts to link Eros with types of meteorites found on Earth. He summarized papers from the December 2001 issue of METEORITICS & PLANETARY SCIENCE. Eros is very uniform across its surface, indicating that it was undoubtedly never separated into rock and metal. Its ground-based spectrum resembled that of an ordinary chondrite, which is thought to be primordial material. But the reddish tint shared by a group of asteroids seemed to indicate that it might be differentiated, which would mean that Eros isn't an ordinary chondrite after all. Perhaps, though, the color is only a thin surface layer.

Kerr describes how the remote-sensing apparatus, especially the x-ray/gamma-ray spectrometer, on Near Shoemaker was supposed to resolve the problem. A thiin coating of red material wouldn't be expected to alter the composition that would be detected by examining x-rays and gamma-rays emitted. But the results are inconclusive. Neither chondrites nor achondrites match the iron content or other results. The voting is on the side of chondrites, but the conclusion is not robust.

One limitation, caused by the low-level of funding for missions within NASA's Discovery program, is that the gamma-ray spectrometer was mounted within the spacecraft's body instead of at the end of a long boom. Thus the background noise from cosmic rays hitting the spacecraft was too high. Perhaps the sample return hoped for in 2007 from the Japanese MUSES-C mission will give us sufficiently accurate data to categorize asteroids of Eros's type.

NASA "Dawn" Mission Slated for Asteroid Tour

NASA announced that "Dawn" will be one of the two new Discovery missions slated for launch in 2006. The ion-propulsion powered mission will make a nine-year journey to orbit Vesta and Ceres, the two most massive asteroids known. The asteroids, located in the main asteroid belt between Mars and Jupiter, have recorded what the early solar system was like when the terrestrial planets formed.

"This is terrific," said University of Arizona astronomer Mark V. Sykes, a scientist on the Dawn mission. "We've been proposing advanced propulsion technology missions for many years now, and it's great to have an opportunity to actually fly one."

The Dawn mission is led by Christopher T. Russell of the University of California - Los Angeles. The project is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Orbital Sciences Corp., Dulles, Va., will develop the spacecraft.

"Dawn will study the conditions and processes of planet formation during the earliest epoch of our solar system by orbiting and studying Ceres and Vesta," Sykes said. Dawn builds on decades of asteroid and meteorite studies, he added.

"Ceres is more than a quarter the diameter of the moon, is water-rich, and has retained its primitive composition and condition. Vesta, on the other hand, was dry, heated to the point of melting, and preserves a record of its subsequent differentiation.

"Almost all asteroids that we observe today are the fragments of larger asteroids like Vesta and Ceres that were destroyed by ancient catastrophic collisions. By studying Vesta and Ceres, we gain a much greater understanding of how these modern fragments were once put together," Sykes said.

Actually, scientists already have pieces of one of the asteroids within reach - as meteorites that landed on Earth.

"Cratering collisions have knocked off pieces of Vesta, which have been recovered as meteorites. They provide us with detailed information on geochemical processes that have occurred within specific sites on Vesta from the time of its formation at the beginning of the solar system," Sykes said.

"Going to Vesta will give us the big picture within which these hand-sized pieces fit. It will be like going from studying bits of hair, nail, and bone to seeing and studying the entire animal up close for the first time," he added.

Sykes, an associate astronomer at Steward Observatory, specializes in the study of asteroids, comets and interplanetary dust. He is the Chair of the Division for Planetary Sciences of the American Astronomical Society.

Dawn will carry a framing camera and mapping spectrometer provided by the German Aerospace Center, DLR, Institute of Sensor Technology and Planetary Exploration in Berlin; a laser altimeter experiment provided by the NASA Goddard Space Flight Center in conjunction with the Massachusetts Institute of Technology; a gamma ray/neutron spectrometer from the Department of Energy's Los Alamos National Laboratory; and a magnetometer provided by UCLA.

Ion engines will power the spacecraft to the asteroid belt, where it first orbits Vesta in an ever-tightening circle and then spirals outward and heads to its rendezvous with Ceres. The spacecraft will orbit as high as 800 kilometers (500 miles) to as low as 100 kilometers (about 62 miles) above the surface of the asteroids. Flybys of more than a dozen other asteroids along the way are planned.

NASA also selected the Kepler mission for 2006 launch. Kepler, a spaceborne telescope, will search for Earth-like planets around stars beyond the solar system.

"Kepler and Dawn are exactly the kind of missions NASA should be launching, missions that tackle some of the most important questions in science yet do it for a very modest cost," said Edward Weiler, associate administrator for space science at NASA Headquarters in Washington. "It's an indicator of how far we've come in our capability to explore space when missions with such ambitious goals are proposed for the Discovery Program of lower-cost missions rather than as major projects costing ten times as much."

Information about Dawn and images are available on the Internet at
http://www-ssc.igpp.ucla.edu/dawn/

Sloan Digital Sky Survey lowers estimate of asteroid impact risk

Princeton, N.J. -- The odds of earth suffering a catastrophic collision with an asteroid over the next century are about one in 5,000, which is less likely than previously believed, according to research published this month.

Astronomers using data from the Sloan Digital Sky Survey found that the solar system contains about 700,000 asteroids big enough to destroy civilization. That figure is about one-third the size of earlier estimates, which had put the number at around two million and the odds of collision at roughly one in 1,500 over a one hundred-year period.

"Our estimate for the chance of a big impact contains some of the same uncertainties as previous estimates, but it is clear that we should feel somewhat safer than we did before we had the Sloan survey data," said lead researcher Zeljko Ivezic of Princeton University.

The results were published in the November issue of the Astronomical Journal.

The new estimate draws on observations of many more asteroids, particularly small faint ones, than were available in previous impact risk estimates, said Ivezic. The ability to detect faint objects in large numbers is a hallmark of the Sloan survey, a multi-institutional collaboration that is mapping one-quarter of the sky. While its main purpose is to look at objects outside our galaxy, the survey also records images of closer objects that cross the view of its telescope, which is located at the Apache Point Observatory in New Mexico.

The survey data also allowed the astronomers to gauge the size of asteroids with improved accuracy, which required categorizing the objects by their composition. Asteroids with a surface of carbon -- looking like giant lumps of coal -- are darker than those made of rock. A small rocky asteroid therefore looks just as bright as a much larger one made of carbon.

"You don't know precisely the size of an object you are looking at unless you know what type it is," Ivezic said, noting that the Sloan survey provides information about the color of objects, which allows astronomers to distinguish between carbon and rock.

Based on observations of 10,000 asteroids, the researchers estimated that the asteroid belt contains about 700,000 that are bigger than one kilometer (six-tenths of a mile) in diameter, which is the minimum size thought to pose a catastrophic risk to humans and other species. The asteroid belt is the source for a smaller group of asteroids called "near- earth objects," which have broken from the belt and have the potential to collide with earth. Although they did not specifically observe near earth objects, the researchers believe that their census of main belt asteroids reveals the likelihood of collisions with similarly sized near-earth asteroids.

Ivezic noted that the new impact risk estimate, like most previous ones, relies on assumptions about a single event 65 million years ago when a 10-kilometer asteroid collided with earth and killed the dinosaurs. The researchers assumed that such impacts occur on roughly 100 million-year intervals and used that statistic to calculate the impact odds for the more common asteroids of smaller sizes. This calculation required knowing how much more common one-kilometer asteroids are than 10-kilometer ones, which was hard to measure before the Sloan data was available.

"There is a lot of uncertainty when you have a sample of only one event," Ivezic said, referring to the dinosaur-killing impact. "But this is the best information we have."

Previous studies could detect only asteroids five kilometers or larger, so astronomers had to extrapolate to estimate the number of smaller ones, said Ivezic. The Sloan researchers found that this approach produced high estimates. When they could actually observe them, the small asteroids were not as plentiful as had been expected from observations of large ones.

The reason for this reduced number of smaller asteroids is an open question, which, if answered, may offer important clues about the history of the solar system and the factors that shaped the asteroid belts, said team member Serge Tabachnik of Princeton.

Another valuable piece of information for scientists is the observation that the rock and carbon asteroids are separated into two bands, said co-author Tom Quinn of the University of Washington. The heart of the rocky asteroid belt is 260 million miles from the sun, while the other is 300 million miles from the sun. The sun and earth, by comparison, are 93 million miles apart.

The astronomers attribute much of the success of the study to software that automatically identifies asteroids from among the millions of images observed by the Sloan survey. Independent tests by Mario Juric from the University of Zagreb, Croatia, have shown that the Sloan software finds at least nine of every ten asteroids.

"We have only five minutes to follow the motion of an asteroid as it passes in front of the telescope," said Robert Lupton, a Princeton researcher who developed the software for automatic detection of asteroids. "But we have found that we detect them very efficiently and reliably." Lupton said the team benefited greatly from software for finding the positions and relative movements of objects, developed by Jeff Pier, Jeff Munn, Robert Hindsley and Greg Hennessy of the U.S. Naval Observatory.

"The Sloan study is a major advance in our understanding of the gross asteroid belt structure," said Robert Jedicke, an asteroid expert at the University of Arizona. "Their determination of the Earth impact rate for killer asteroids agrees with soon-to-be-published results based on data from the Spacewatch Project at the University of Arizona." The Arizona team based its risk estimate on a study of near-earth objects, rather than main belt asteroids.

The Sloan Digital Sky Survey (www.sdss.org) is a joint project of the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, the Johns Hopkins University, the Max-Planck-Institute for Astronomy, the Max-Planck-Institute for Astrophysics, New Mexico State University, Princeton University, the United States Naval Observatory and the University of Washington.

Funding for the survey has been provided by the Alfred E. Sloan Foundation, the participating institutions, the National Aeronautics and Space Administration, The National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho and the Max Planck Society.

Observations reveal curiosities on the surface of asteroid Ceres

Boulder, Colorado -- October 19, 2001 -- An international team led by scientists at the Southwest Research Institute (SwRI) has discovered some curious properties of the largest asteroid, Ceres. The astronomers observed Ceres with the Hubble Space Telescope (HST) at ultraviolet wavelengths using a resolution higher than previously attained. The resulting images are the first to resolve detail on the surface of Ceres and show features as small as 50 kilometers across.

Led by Principal Investigator Dr. Alan Stern of SwRI, the team detected a dark spot on the surface of Ceres, which it nicknamed "Piazzi" in honor of the discoverer of Ceres. "Although we can't determine the nature of the spot with these data, whether it is an area of different coloration or possibly a crater from an impact by another asteroid, it is pretty big," says Dr. Joel Parker, also of SwRI, who led the team in the analysis of the images. "The Piazzi feature has a diameter of about 250 kilometers, which is more than a quarter the size of Ceres. If it resulted from an impact, the object that hit Ceres would have been about 25 kilometers across. It must have really shaken things up."

The high-resolution images allowed the team to refine measurements of Ceres. Although Ceres is the largest known asteroid -- estimated to contain more than one-third of the total mass of all other asteroids combined -- researchers still dispute its size, even after 200 years of observations. The new HST measurements indicate that the asteroid is slightly flattened, with a diameter ranging from 930 to 970 kilometers. Spinning objects can have a flattened or "squashed" shape depending on how big they are, how fast they spin, and what kind of material they are made of. However, the amount of flattening seen on Ceres is more than expected and may indicate that the inner structure is not as homogeneous as previously assumed.

"These results are very tantalizing," says Stern. "What we need to be definitive are observations with better resolution and frequent enough to follow Ceres through a nine-hour rotation period to track surface features. This 'movie' would allow us to finally map the surface of Ceres and figure out what the Piazzi feature is." The team has already proposed such an experiment with a new instrument to be installed on HST next year.

The analysis of the Ceres images will be published in the January 2002 issue of The Astronomical Journal. Authors include researchers from SwRI, the Massachusetts Institute of Technology, Cornell University, the University of Arizona, and the Observatoire Midi-Pyrenees in France.

In addition to being the largest asteroid, Ceres was also the first asteroid to be discovered. In the latter part of the 18th century, astronomers noted a regular spacing in the planets of the solar system, but with a gap between Mars and Jupiter where they expected to find a planet. On January 1, 1801, the Sicilian astronomer Giuseppe Piazzi at the Palermo Observatory discovered a moving object in the region. Researchers at the time assumed that this object, Ceres, was the missing planet. However, early observations indicated that Ceres was too small to be a planet, and as more such objects were discovered in the region, they became known as "asteroids" or "minor planets." Ceres orbits the sun once every 4.6 years at a distance of 41 million kilometers, and it spins on its axis once every nine hours.

EDITORS: The Ceres images are available for viewing and download at www.swri.org/press/ceres.htm.

The Source of Rocks on Eros

ITHACA, N.Y. -- The first detailed global mapping of an asteroid has found that most of the larger rocks strewn across the body were ejected from a single crater in a meteorite collision perhaps a billion years ago.

"One big impact spread all this debris," says Peter Thomas, senior researcher in Cornell University's Department of Astronomy. "This observation is helping us start answering questions about how things work on the surface of an asteroid."

Thomas' report on the crater -- which has the proposed name of Shoemaker -- as a major source of ejected rocks on asteroid 433 Eros appears in the latest issue (Sept. 27) of the journal Nature. Thomas' fellow authors are Joseph Veverka, professor of astronomy at Cornell; Mark Robinson of Northwestern University and Scott Murchie of Johns Hopkins University. The paper is one of three detailing the first findings from the controlled landing of the spacecraft NEAR-Shoemaker on the surface of Eros on Feb. 12, 2001.

Before the landing, the spacecraft had orbited Eros for a year, taking thousands of high-resolution images of the 21-mile-long asteroid. From the global map of the surface that was assembled, Thomas and his colleagues were able to count 6,760 rocks larger than about 16 yards across (15 meters) strewn over the asteroid's 434 square miles (1,125 square kilometers). They found that nearly half (44 percent) of these rocks were inside the Shoemaker crater, positioned near one end of the potato-shaped asteroid. And most of the rocks of this size along the asteroid's equator appear to have been ejected from Shoemaker, Thomas says.

"We know they came from Shoemaker because the mapping of the geography of the pattern [of the rocks] on the surface closely matches the predicted paths from the one impact event that made Shoemaker," he says. Eros is estimated to be about 4 billion years old, probably the remnant of a larger asteroid broken up by a collision with another asteroid. Perhaps a billion years ago, Eros itself was struck by an object -- a meteorite or small comet -- creating a crater nearly 5 miles (7.6 kilometers) wide and shattering into rocks of all sizes. Some of these rocks "went straight up and straight down," says Thomas. Most of the remainder traveled as far as two-thirds of the way around the rotating asteroid in either direction (the asteroid rotates once every 5 1/4 hours), finally coming to rest on the surface. The mystery posed by the Eros maps for the researchers is why the same thing didn't happen with two other large craters on Eros: Himeros, on the body's convex side, and Psyche, on the concave side. Either the rocks have been buried, have been eroded or weren't made in the first place, says Thomas.

One of the big surprises from the maps, Robinson reports in his Nature paper, is that Eros' surface appears to have a global cover of "loose fragmental debris." The surface appears to be blanketed with a fine material, some of which has created flat deposits, particularly in depressions, such as craters. These fine deposits, Robinson's paper reports, appear to have been "sorted" from the upper portion of the asteroid's regolith, or soil.

These so-called "ponded" deposits were visible in the final images transmitted by the spacecraft before it hit the asteroid's surface. Indeed, in his paper Veverka reports, "A strong argument is that the last image shows that the spacecraft landed on or within a few meters of a pond, a landform known to occur predominantly on the floors of craters."

How has this sorting occurred? Robinson's paper postulates an electrostatic effect, similar to that indicated on the moon's surface by the Surveyor spacecraft. Particles can build up photoelectric charges with long exposure to the sun, and this charge might separate out finer particles, says Thomas. But he concedes, "This requires a lot of assumptions, and does not explain all the mechanisms."

The big question for researchers is: Do these observations of the surface mechanics of Eros indicate that similar processes are under way on other astronomical bodies? In his paper, Veverka notes it is difficult to make comparisons because no other such distant body has been so closely mapped. There are high-resolution views of the asteroids Gaspra and Ida and of Phobos, a satellite of Mars. Phobos, he writes, does show groupings of rocks in the vicinity of the crater Stickney that are comparable to those on Eros. "Nothing comparable to the flat 'pond' deposits has been noted on Gaspra, Ida or Phobos, even though Phobos coverage is certainly adequate to show such features if they were present," he writes. In making his assessment of rock distribution on Eros, Thomas counted about 30,000 rocks. He was able to do this by using software created by Cornell analyst Jonathan Joseph. The software allows a researcher to mark a rock in an image, then calculate from a shape model where the rock is and its size and then to record this information in a data file.

Thomas's report in Nature is titled "Shoemaker Crater: A major source of ejecta on asteroid 433 Eros." Veverka's report, which has several co-authors, is titled "The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros." (Veverka was the principal investigator on the multispectral imager, or camera, and the NEAR infrared spectrometer, two of the five instruments on board the spacecraft.) Robinson's report, co-authored by Thomas, Veverka, Murchie and Brian Carcich of Cornell, is titled "Morphology, Distribution and Origin of Ponded Deposits on Eros." The research was supported by NASA.

The web version of this release, with accompanying photos, may be found at
http://www.news.cornell.edu/releases/Sept01/Eros.Nature.deb.html

NEAR Shoemaker spacecraft to land on Eros on Feb 12

Cornell University Press Release

ITHACA, N.Y. -- As NASA's Near Earth Asteroid Rendezvous spacecraft, known as NEAR Shoemaker, closes in on asteroid 433 Eros, Cornell University astronomers hope that surface details as small as a hand-size rock will be captured by the camera before the spacecraft bumps down on the boulder-strewn surface Feb. 12. 2001.

Since last October, the NEAR imaging team has been puzzling over strange surface features of Eros seen in new, high-resolution images. There is the hope that the close-up images taken in the final few minutes before the spacecraft drops onto the surface will help to answer their questions about the geology of the 22-mile-long asteroid more than 196 million miles (316 million kilometers) from Earth.

"Since last October we have seen details of Eros at 1 meter resolution that we haven't seen anywhere else before and don't understand," says Cornell astronomer Joseph Veverka, who heads the imaging team. "That's why we are so excited about getting close to the surface."

The landing -- what NASA is calling a "controlled descent" -- is a highly risky maneuver, involving four thruster firings over four hours intended to slow the rate of descent to 7 mph from 20 mph. In the final 45 minutes, when the spacecraft is about 3.5 to 4.5 miles (about 6 to 7.5 kilometers) from its landing site at the edge of the crater Himeros, the camera will begin taking a new image about every 30 seconds.

The final picture will be captured at just 550 yards (500 meters) from the surface, enough to capture details as small as perhaps 4 inches (10 centimeters) across. Mission leaders at the Applied Physics Laboratory at Johns Hopkins University, which built the spacecraft and manages the NEAR mission, do not expect images to be transmitted from the surface because Eros's spin and topography will almost certainly prevent communication between Earth and the craft.

Why does Veverka's team want to get such a close look at Eros' surface details? Because, says Veverka, who is professor of astronomy at Cornell, his team is frankly puzzled by what it has seen on Eros over the past few weeks. Last October, with much of NEAR's mission accomplished, the spacecraft was sent into orbit just 4 miles (about 6 kilometers) or so from the asteroid's surface. For the first time the imaging team was seeing details as small as a yard (0.9 meter) across, compared with the approximately 5.5 yards (5 meters) resolution that had been captured by the camera since the spacecraft went into orbit around Eros on Feb. 14, 2000.

"Suddenly, we started seeing things we didn't expect and hadn't seen on other surfaces in the solar system," says Veverka. "It's like another door has opened."

The biggest surprise, says Cornell researcher Peter Thomas, who has been interpreting the geology of the asteroid's surface, "is that some small craters and other small depressions have flat, smooth floors, unlike most craters you see on Eros and other objects. It looks as if fine-grain material has slid down the craters' sides and ponded in the bottoms." Apparently, he says, there is some mechanism "we hadn't anticipated" that moves fine-grain material around on the surface. Although gravity on Eros is only one one-thousandth of that on Earth -- an average person would weigh only an ounce or two -- it is still "very effective in gathering materials in very flat floors on the bottom of depressions."

Another surprise, says Veverka, is the discovery that some small boulders are surrounded by material that appears to have disintegrated from the boulders' surfaces. "There is some process that is very gentle that somehow disintegrates rock. We haven't seen this on the moon, and we haven't seen this before on Eros," he says. "But it seems to be very common."

It is just possible, says Veverka, that the final image will be taken almost at the surface itself. He explains that the camera will remain in focus until about 220 yards (200 meters) from the landing site. If the spacecraft is still on course, it is possible that the camera will take one final image and have time to send a partial image on its way to Earth before the spacecraft touches down. It takes 10 milliseconds for the exposure, 1 second to read the image into the spacecraft recorder and 30 seconds for the data to emerge from the recorder. The data then take 17 to 18 minutes to reach Earth tracking stations.

The imaging team now is getting even higher-resolution images of these features. On Jan. 24 the spacecraft entered a close flyby sequence, including a four-day orbit that produced images from as close as 2 miles (3.2 kilometers) above the surface. These new images are enabling the Cornell imaging team to accumulate data at a resolution of about 1.1 yards (1 meter). "The hope is that during the descent we can improve this resolution by perhaps a factor of 10 so that we can find out more about what is going on there," says Veverka.

See also:
o Near Earth Asteroid Rendezvous Mission: < http://near.jhuapl.edu>

The web version of this release, with accompanying photos, may be found at http://www.news.cornell.edu/releases/Feb01/NEAR.landing.deb.html

NEAR Mission Discoveries Highlighted in Latest Issue of Science

Findings from NASA's Near Earth Asteroid Rendezvous (NEAR) mission - appearing in a special section of the Sept. 22 issue of the journal Science - confirm that asteroid 433 Eros is a consolidated, primitive sample from the solar system's beginnings.

"We can now say that Eros is an undifferentiated asteroid with homogeneous structure, that never separated into a distinct crust, mantle and core," says NEAR Project Scientist Dr. Andrew F. Cheng of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which manages the NEAR mission. "We have definitive mass and density measurements plus spectacular images and movies showing ridges, pits, troughs and grooves that provide fascinating clues about its history."

NEAR is the first in-depth study of an asteroid. Now more than halfway through a yearlong orbit mission that began Feb. 14, 2000, the NEAR Shoemaker spacecraft has taken more than 103,300 images and extensive measurements of Eros' composition, structure and landforms, at distances ranging from 22 to 220 miles (35 to 350 kilometers).

NEAR Shoemaker's multispectral imager and now-silent infrared spectrometer have returned a flood of observations revealing heavily cratered expanses abutting relatively smooth areas. The asteroid's largest crater measures 3.4 miles (5.5 kilometers) wide and sits opposite from an even larger 6.2-mile (10-kilometer), saddle-shaped depression. Ejecta blocks - rocks and boulders created by impacts - are abundant and measure up to 330 feet (100 meters) across, although they are not distributed evenly on the asteroid.

Some areas are heavily saturated with craters wider than 660 feet (200 meters). Images taken from lower orbits also reveal "younger" sections where craters have been filled or covered by loose material.

More than 8 million measurements taken by the laser rangefinder to definitively establish Eros' shape have determined the asteroid is a consolidated body rather than an agglomerate of loosely bound, much smaller components. Such a "rubble pile" structure has been inferred for many asteroids, but does not apply to Eros. Its irregular, peanut shape - which a body as large as Earth could not maintain - houses a homogeneous internal structure. Although Eros is consolidated, the ubiquitous fabric of ridges and grooves suggests an extensively fractured interior.

NEAR Shoemaker's X-ray spectrometer has detected low levels of aluminum relative to magnesium and silicon, indicating an undifferentiated composition. Eros, or the parent body it could have broken from, has not experienced the extensive melting process that planets like Earth undergo in their development. This finding leads researchers to believe that Eros may be related to the primitive ordinary chondrites, the most common type of meteorite. NEAR Shoemaker's imager and infrared spectrometer have also found spectral properties consistent with a primitive, chondritic composition.

Using ground-based Doppler and range measurements - and by tracking surface landmarks - scientists have determined the asteroid's mass is 6.687 x 1015 kilograms and density is 2,700 kg/m3, which is about the average density of Earth's crust. The density is relatively uniform throughout the asteroid.

Eros has a stable rotation and an escape velocity that ranges from 3.1 to 17.2 meters per second, which would allow a baseball thrown from its surface to leave forever. The acceleration of gravity on the surface of Eros varies from 2.3 to 5.5 millimeters per second squared, thousands of times smaller than on Earth. A person who weighs 150 pounds on Earth would weigh from 0.56 to 1.3 ounces on Eros - about as much as one or two bags of airline peanuts.

The research detailed in the four Science articles covers the first six months of orbit around Eros. NEAR Shoemaker moves in for a low- altitude flyover of Eros on Oct. 25, 2000, coming within 3.7 miles (6 kilometers), and will end the mission in February 2001 with a slow, controlled descent to the asteroid's surface. The spacecraft is currently 109 million miles (176 million kilometers) from Earth, circling Eros at just under 5 miles per hour.

Visit the NEAR Web site ( near.jhuapl.edu) for the latest images, movies and mission news.

Crash your own asteroid

In this Web site from Douglas Hamilton at the University of Maryland, you can choose the size, velocity, and type of asteroid that will crash into an object of your choice, and then see a typical picture of of a similar crash.
Other innovative astronomy labs are linked to the site.

http://janus.astro.umd.edu/astro/impact.html.

Also, see impact sites around the Earth at
http://gdcinfo.agg.emr.ca/toc.html?/crater/world_craters.html

Eros Reports and Images

See images at http://near.jhuapl.edu/iod/archive.html
See discussions at http://near.jhuapl.edu/

Back to top