SETI Institute has Homepage
NASA Origins Program
Astronomy images from various sources, including HST, VLA; Astronomical Society of the Pacific Slide sets about COBE, Compton Gamma Ray Observatory, Galaxies, Infrared, Life on Mars, M31, Multiwave Sky, Past Astronomers, Quasars, Rosat,Seti, and Search for Extrasolar Planets; plus artwork by William Hartmann
NASA's main astrobiology site
See astrobiology sites at astrobiology.arc.nasa.gov, astrobiology.com, and, for NASA's Astrobiology Institute, nai.arc.nasa.gov.
Interview with Stanley Miller
GAIA mission: mapping 1 billion stars
Life on Venus (!)?
Extrasolar Planets Encyclopedia
Geoff Marcy's Web page on new planets
Michel Mayor's Web page on new planets
Eddington mission: transits of extrasolar planets
Carl Sagan Sites:
p. 313 line -5 "star" should be "planet"; at the top of the next page, a marginal note could be: "Only this type of motion toward or away from us can be measured by the method used; side-to-side motions do not have Doppler shifts, which are what are being observed."
California astronomers are broadening the search for extraterrestrial intelligence (SETI) with a new experiment to look for powerful light pulses beamed our way from other star systems. Scientists from the University of California's Lick Observatory, the SETI Institute (Mountain View, California), UC Santa Cruz, and UC Berkeley are coupling the Lick Observatory's 40-inch Nickel Telescope with a new pulse-detection system capable of finding laser beacons from civilizations many light-years distant. Unlike other optical SETI searches, this new experiment is largely immune to false alarms that slow the reconnaissance of target stars.
"This is perhaps the most sensitive optical SETI search yet undertaken," said Frank Drake, Chairman of the Board of the SETI Institute and a co-investigator on the new experiment. Drake, who in 1960 conducted the first modern hunt for evidence of extraterrestrial intelligence, is usually associated with radio SETI, an approach in which large antennas are connected to specialized, multi-million channel receivers. "This is different," noted Drake. "We are looking for very brief but powerful pulses of laser light from other planetary systems, rather than the steady whine of a radio transmitter."
While optical SETI has been undertaken before, it is only recently that major experiments, scrutinizing hundreds or even thousands of star systems, have been initiated. This is largely the consequence of a study conducted by the SETI Institute during the years 1997 - 1999 which showed that new technology has made optical SETI an appealing approach for finding technologically sophisticated civilizations. However, unlike its radio counterpart, optical SETI requires that any extraterrestrial civilization be deliberately signaling precisely in our direction.
The new experiment is unique in exploiting three light detectors (photomultipliers) to search for bright pulses that arrive in a short period of time (less than a billionth of a second). Of course, light from the central star will trigger the detectors as well, but seldom will all three photomultipliers be hit by photons within a billionth of a second time frame. The expected number of false alarms for the stars being looked at is about one per year.
Other optical SETI experiments use only one or two detectors and have been plagued by false alarms occurring on a daily basis. Starlight, cosmic rays, muon showers, and radioactive decays in the glass of photomultiplier tubes can all contribute confusing "events" to optical SETI searches. Dan Werthimer and Richard Treffers of UC Berkeley designed the hardware and software for the new, three-tube system. It was built by Shelley Wright, an undergraduate physics student at UC Santa Cruz, under the direction of principal investigator Remington Stone, a research astronomer at Lick Observatory. The astronomers expect that the new approach will produce a clean experiment that can be run automatically, and for which the results will be far less ambiguous.
So far, the experiment at Lick Observatory has examined about 300 individual star systems, as well as a few star clusters. The intention is to continue the search at least on a weekly basis for the coming year. The project is being sponsored by the SETI Institute. "One great advantage of optical SETI is that there's no terrestrial interference," comments Drake. "It's an exciting new field."
Eight New Very Low-Mass Companions to Solar-Type Stars Discovered at La Silla
The intensive and exciting hunt for planets around other stars ("exoplanets") is continuing with great success in both hemispheres.
Today, a team of astronomers of the Geneva Observatory  are announcing the discovery of no less than eight new, very-low mass companions to solar-type stars. The masses of these objects range from less than that of planet Saturn to about 15 times that of Jupiter.
The new results were obtained by means of high-precision radial-velocity measurements with the CORALIE spectrometer at the Swiss 1.2-m Leonhard Euler telescope at the ESO La Silla Observatory. An earlier account of this research programme is available as ESO Press Release 18/98. Recent views of this telescope and its dome are available below as PR Photos 13a-c/00.
This observational method is based on the detection of changes in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. The evaluation of the measured velocity variations allows to deduce the planet's orbit, in particular the period and the distance from the star, as well as a minimum mass .
The characteristics of the new objects are quite diverse. While six of them are most likely bona-fide exoplanets, two are apparently very low-mass brown-dwarfs (objects of sub-stellar mass without a nuclear energy source in their interior).
From the first discovery of an exoplanet around the star 51 Pegasi in 1995 (by Michel Mayor and Didier Queloz of the present team), the exoplanet count is now already above 40.
"The present discoveries complete and enlarge our still preliminary knowledge of extra-solar planetary systems, as well as the transition between planets and "brown dwarfs", say Mayor and Queloz, on behalf of the Swiss team.
Whereas all giant planets in our own solar system (Jupiter, Saturn, Neptune, Uranus) have nearly circular orbits, most of the extra-solar planets that have been discovered with periods of months to years are elongated. The origin of the elongated shape of those planetary orbits is still under debate.
While about 40 giant exoplanet-candidates have so far been detected with masses in the range from 0.22 to 8.13 times that of Jupiter, only one companion object (in orbit around the star HD 114762) was known until now with a minimum mass between 10 and 15 times that of Jupiter. Such objects, referred to as "brown dwarfs", are easier to detect than giant planets with similar periods because their greater mass induces larger velocity changes of the central star; they must therefore be very rare. This strongly points towards different formation/evolution processes for giant planets and stellar companions in the brown-dwarf domain.
The search for exoplanets: current status
Most of the stars around which giant planets have been found so far show a significant excess of heavy elements in their atmosphere when compared to the majority of stars of the solar vicinity. This is also the case for most of the central stars of the eight new objects described here. This additional indication of an abnormal chemical composition of stars with giant gaseous planets provides a promising line for a better understanding of the mechanism(s) that ultimately lead to the formation of planetary systems.
The high-precision radial-velocity survey with CORALIE in the southern hemisphere has the ambitious goal to make a complete inventory of giant exoplanets orbiting about 1600 stars in our galactic neighbourhood, all of which are relatively similar to our Sun. To date, 11 such exoplanets have been detected by CORALIE within this programme.
Up to now, a total of 43 low-mass companions to solar-type stars have been detected by different research teams with minimum masses less than 15 Jupiter masses. Of these, 34 have minimum masses smaller than 5 Jupiter masses, 6 are between 5 and 10 Jupiter masses, and 3 are between 10 and 15 Jupiter masses.
This repartition of observed planetary masses (and low-mass brown dwarfs) strongly suggests that the maximum mass for giant exoplanets is less than 10 Jupiter masses.
Continuation of the programme
Significant progress within the current programme is expected soon, when the Very Large Telescope Interferometer (VLTI), now being constructed at Paranal, will become available. This new instrument will have the observational capability of very high-accuracy astrometry and thus to detect even very small wobbles of stellar positions that are due to orbiting planets. This will provide a crucial contribution to the determination of the true repartition of exoplanetary masses, a hotly debated question.
Important advancement in our understanding of the formation of planetary systems is also expected with the advent of HARPS. This new high-resolution spectrograph, capable of reaching a radial-velocity precision of 1 m/sec, will be installed on the ESO 3.6-m telescope at La Silla. HARPS will extend the domain of planets accessible with the radial-velocity technique towards significantly lower masses - down to about ten Earth masses on short-period orbits. It will also greatly improve our capability of detecting planets with longer periods and multi-planet systems.
More information about this project
Further detailed information about these new planet candidates, as well as
the corresponding radial-velocity curves, are available on the dedicated web
page at the Geneva Observatory web site:
 The team consists of Michel Mayor, Dominique Naef, Francesco Pepe, Didier Queloz, Nuno Santos, Stephane Udry and Michel Burnet (Geneva Observatory, Sauverny, Switzerland).
 A fundamental limitation of the radial-velocity method, currently used by all planet-hunting research teams, is that because of the uncertainty of the inclination of the planetary orbit, it only allows to determine a lower mass limit for the planet. However, statistical considerations indicate that in most cases, the true mass will not be much higher than this value. The mass units for the exoplanets used in this text are 1 Jupiter mass = 3.35 Saturn masses = 318 Earth masses; 1 Saturn mass = 95 Earth masses.
 The exoplanet in orbit around HD 52265 was independently announced last week by another group, cf. http://www.physics.sfsu.edu/~gmarcy/planetsearch/planetsearch.html)
See the Web site of the Astrochemistry Division of NASA's Ames
SANTA CRUZ, CA--The world's most prolific team of planet hunters has found six new planets orbiting nearby stars, bringing the total number of planets astronomers have detected outside the solar system to 28. The researchers also found evidence suggesting that two previously discovered planets have additional companions, said Steven Vogt, professor of astronomy and astrophysics at the University of California, Santa Cruz.
Vogt and his colleagues, Geoffrey Marcy of UC Berkeley, Paul Butler of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington in Washington, D.C., and Kevin Apps of the University of Sussex, England, made the discoveries using the High Resolution Echelle Spectrograph (HIRES, designed and built by Vogt) on the Keck I Telescope in Hawaii. Their findings will be published in the Astrophysical Journal.
The researchers have been using the facilities at the W. M. Keck Observatory for the past three years to conduct a survey of 500 nearby sunlike stars in search of planets. The project is supported by the NASA Origins Program, which has provided both funding and telescope time, and by the National Science Foundation.
The six new planets increase by about 25 percent the number of known "extrasolar" planets, giving astronomers a substantial amount of additional information about planetary systems, Vogt said. One of the planets, HD 192263, was also recently detected by Nuno Santos and collaborators in Geneva, Switzerland, who reported it while Vogt and his colleagues were preparing their paper.
The new planets orbit stars that are similar in size, age, and brightness to the Sun and are at distances ranging from 65 to 192 light-years from Earth. The planets themselves range in mass from slightly smaller to several times larger than the planet Jupiter (0.8 to 6.5 times the mass of Jupiter). They are probably also similar to Jupiter in their compositions--basically giant balls of hydrogen and helium gas, Vogt said.
The presence of a planet around a star is indicated by a telltale wobble in the motion of the star as a result of the gravitational force exerted by the orbiting planet. Vogt and his coworkers recently achieved independent confirmation of this method for detecting planets when they were able to predict and measure the dimming of a star as a planet passed in front of it.
The orbits of the new planets, like those of most of the extrasolar planets discovered so far, tend to be quite eccentric, tracing paths that are oval rather than circular. One of the planets, around a star called HD 222582, has the most wildly eccentric orbit yet known, carrying it from as close as 0.39 astronomical units (AU: the distance from Earth to the Sun) to as far as 2.31 AU from its parent star in the course of its 576-day orbit.
"It is beginning to look like neatly stacked, circular orbits such as we see in our own solar system are relatively rare," Vogt said.
Interestingly, five of the six planets are located within the so-called "habitable zones" of their stars. This is the region where temperatures would allow water to exist in liquid form. Most of the extrasolar planets the researchers have studied have turned out to be outside the habitable zone, either too close to their star or too far away, and therefore too hot or too cold, Vogt said.
"These planets are at just the right distance, with temperatures in one case around 108 degrees Fahrenheit--like a hot day in Sacramento," he said.
Planetary systems with Jupiter-sized planets in oval-shaped orbits are not expected to harbor Earthlike planets, Vogt added. In fact, if an Earthlike planet were put into such a system, it would be quickly ejected by the gravitational influence of the Jupiter-mass planet. Vogt noted, however, that if these Jupiter-sized planets are similar to those in our own solar system, they probably have numerous moons associated with them.
"For a planet in the habitable zone of its star, such moons offer the possibility of liquid water and the eventual emergence of life," he said.
In addition to the discovery of six new planets, the researchers gathered new data on four previously known planets. Two of them, around the stars HD 217107 and HD 187123, showed long-term trends in their orbits indicating the presence of an additional companion. These companions, which may be planets or larger objects (e.g., brown dwarfs), appear to be orbiting their host stars in a long period, taking at least two to three years to complete an orbit, Vogt said. These findings are significant because previously only one other system of multiple planets, around the star Upsilon Andromedae, had been identified.
"It will take years of additional observations to work out the masses and orbits of these companions, but the evidence suggests there are a fair number of multiple planet systems out there," Vogt said.
Specific details about the new planets and their host stars are given below:
HD 10697 is a G5IV star, slightly cooler and a bit larger than the Sun. It lies 106 light-years away in the constellation Pisces. Its planet has a minimum mass of 6.35 Jupiter masses and a 1,072-day orbit. The radius of this orbit is about 2.13 AU, but the orbit is somewhat eccentric, so the planet's distance from its star ranges from 1.87 AU to 2.39 AU. At its average orbital distance, it lies just at the outside edge of the habitable zone of its star, and is expected to have an equilibrium temperature (due to energy received from its parent star) of about 15 degrees F.
HD 37124 is a G4V star, slightly cooler than the Sun. It lies 108 light-years away in the constellation Taurus. Its planet has a minimum mass of 1.04 Jupiter masses and a 155.7-day orbit. This orbit is also quite eccentric. At its average orbital distance of 0.55 AU, it sits just within the inner edge of the habitable zone of its star, and is expected to have an equilibrium temperature of about 130 degrees F. This is the lowest metallicity star known to have a planet.
HD 134987 is a G5V star, 83 light-years away in the constellation Libra. Its planet orbits in a 260-day eccentric orbit. This planet has a minimum mass of 1.58 Jupiter masses. At its average orbital distance of 0.81 AU, its expected equilibrium temperature is a balmy 108 degrees F. It lies well within the habitable zone of its star.
HD 177830 is a K2IV star, about 1,000 degrees Kelvin cooler than the Sun, lying about 192 light-years away in the constellation Vulpecula. It harbors a 1.22 Jupiter mass planet in a 392-day, highly eccentric orbit. This orbit carries the planet from as close as 0.63 AU from its star to as far as 1.57 AU. At its mean orbital distance of 1.10 AU its expected temperature is about 192 degrees F. The planet is probably within the habitable zone of its star.
HD 192263 is a K2V star lying 65 light-years away in the constellation Aquila. A planet around this star was first reported by Nuno Santos, a Portuguese graduate student at the University of Geneva. Vogt's team has obtained essentially the same results as Santos: a 0.78 Jupiter mass planet orbiting in a 24.36-day orbit. This orbit has a radius of only 0.15 AU, with little or no eccentricity. It orbits well outside the habitable zone of its star.
HD 222582, a G3V star, is a near solar twin, 137 light-years away in the constellation Aquarius. Its planet orbits in a widly eccentric 576-day orbit, which carries the planet from 0.39 AU to 2.31 AU from the parent star in the course of its oval orbit. This is the most eccentric extrasolar planet orbit yet known. The planet's expected temperature is about -38 degrees F. Its mean orbital distance places it squarely in the habitable zone of its star.
Further information about the planet search is available on the Web at
Information about the NASA Origins Program can be found at
http://origins.jpl.nasa.gov/ and about NSF's astronomy program at
(Cornell Press Release)
ITHACA, N.Y. -- Twenty-five years ago next week, humanity sent its first and only deliberate radio message to extraterrestrials. Nobody has called back yet, but that's OK -- we weren't really expecting an answer.
The message was sent during the dedication of a major upgrade to the Arecibo radio telescope in Puerto Rico on the afternoon of Nov. 16, 1974, and contained some very basic information about the human race. It included representations of the fundamental chemicals of life, the formula for DNA, a crude diagram of our solar system and simple pictures of a human being and the Arecibo telescope.
"It was strictly a symbolic event, to show that we could do it," explains Donald Campbell, Cornell University professor of astronomy, who was a research associate at the Arecibo Observatory at the time. Arecibo Observatory is operated by the National Astronomy and Ionosphere Center, managed by Cornell University for the National Science Foundation.
The real purpose of the message was to call attention to the tremendous power of the radar transmitter newly installed at Arecibo and the ability of the telescope's 1,000-foot diameter dish antenna to project a powerful signal into space. But many of those present took the event seriously, according to Harold Craft, Cornell's vice president for services and facilities, who was then director of the Arecibo Observatory. "We translated the radio-frequency message into a warbling audio tone that was broadcast over speakers at the ceremony. When it started, much of the audience spontaneously got up and walked out of the tent and gazed up at the telescope."
While the audience that had gathered beside the huge Arecibo dish was impressed by the idea of sending messages to space, others were critical. Some actually suggested that sending such a message was dangerous, because it might attract the attention of hostile aliens.
They probably needn't have worried. The chance that the message might actually be detected by some extraterrestrial intelligence is extremely small. It was sent only once, over a period of about three minutes, on a narrow beam directed toward a group of about 300,000 stars called the Great Cluster in Hercules, Messier 13. The globular cluster is 25,000 light-years away in our galaxy, the Milky Way. So far, moving at the speed of light, the message has traveled only one thousandth of the distance, or about 147 trillion miles. There are stars closer to our solar system than that, but none of them is in the path of the message.
Ironically, the globular cluster at which the signal was aimed won't be there when the message arrives. It will have moved well out of the way in the normal rotation of the galaxy. But "anyone" in the target area when the signal arrives, they could detect it with a radio telescope of similar size, and it would appear at 10 million times the intensity of the normal radio signals from our sun. From there, the message will continue on its course through outer space, ultimately, millions of years hence, reaching distant galaxies.
Since the transmitter was installed in 1974, Arecibo radar has been used for extensive explorations of the solar system, including detailed mapping of the surfaces of the moon and Venus. The radar was upgraded to even higher power in 1997. No other formal messages have been sent, but many of the radar signals have continued on out of our solar system and if detected would clearly be seen as created by intelligent beings, Campbell says. In addition, a message, engraved on copper plate, accompanied the Pioneer 10 spacecraft launched in March 1972 and now is about 7 billion miles from Earth.
Meanwhile, researchers constantly use the huge dish antenna to listen for signals from alien intelligence. One project, known as Phoenix, aims the telescope at specific stars; another, called Serendip, collects data on certain likely frequencies during all the telescope's other operations, and distributes the data to thousands of volunteers to process on personal computers. Project Phoenix is directed by the non-profit SETI Institute, based in Mountain View, Calif. Serendip is a project of the University of California at Berkeley.
The 1974 message was transmitted on a frequency of 2380 MHz and consisted of 1,679 binary bits representing ones and zeros, sent by shifting the frequency of the signal up and down over a range of about 10 Hz, a method similar to that used by computer modems to send binary code over a telephone line. If the ones are translated into graphics characters and the zeros into spaces, the message forms a symbolic picture 23 characters wide by 73 long.
The content of the message was developed by Frank Drake, then professor of astronomy at Cornell and now a professor in the Division of Natural Sciences at the University of California at Santa Cruz and president of the SETI Institute; Richard Isaacman, then a Cornell graduate student and now working at Research and Data Systems Corp. in Greenbelt, Mass.; Linda May, another graduate student now professor of physical sciences at Wheelock College in Massachussetts, and James C.G. Walker, then a member of the Arecibo staff and now professor of physical sciences at the University of Michigan at Ann Arbor. Others, especially the late Carl Sagan, who eventually became the David Duncan Professor of Astronomy and Space Sciences at Cornell, contributed to the project.
Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.
--The Arecibo web site: http://www.naic.edu/
- -- Cornell News Service coverage of the most recent Arecibo upgrade:
- -- The SETI Institute:
-- Profile of Jill Tarter, director of Project Phoenix:
The web version of this release, with accompanying graphic, may be found at
Nashville, Tenn., and Berkeley, Calif. - Astronomers have witnessed for the first time a distant planet passing in front of its star, providing direct and independent confirmation of the existence of extrasolar planets that to date have been inferred only from the wobble of their star.
"This is the first independent confirmation of a planet discovered through changes in a star's radial velocity and demonstrates that our indirect evidence for planets really is due to planets," said Geoffrey Marcy, a professor of astronomy at the University of California, Berkeley.
Marcy and his colleagues, Paul Butler of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington in Washington, D.C., and Steve Vogt of UC Santa Cruz and Lick Observatory, first detected a wobble in the star called HD 209458 on Nov. 5. Ascribing the wobble to a nearby planet, they were able to estimate its orbit and approximate mass.
As with all new planets they detect, the team immediately brought it to the attention of collaborator Greg Henry, an astronomer at the Tennessee State University Center of Excellence in Information Systems in Nashville. He conducts research with several automatic telescopes at Fairborn Observatory, a non-profit research foundation located in the Patagonia Mountains of southern Arizona.
Henry turned one of his automated telescope on the star at the time Marcy and Butler predicted the planet would cross the face of the star if the planet's orbital plane were lucky enough to carry it between Earth and the star. Until now, none of the 18 other extrasolar planets Marcy and Butler have discovered has had its orbital plane oriented edge-on to Earth so that the planet could be seen to transit the star, nor have any of the other planets discovered by other researchers.
However, on Nov. 7, Henry observed a 1.7 percent dip in the star's brightness. Because the planet orbits its star once every 3.523 days, he plans to repeat his observations on Sunday, Nov. 14.
"This planetary transit occurred at exactly the time predicted from Marcy's observations, confirming absolutely the presence of a companion," Henry said. "The amount of dimming of the star's light during the transit also gives us the first-ever measure of the size and density of an extrasolar planet. We've essentially seen the shadow of the planet and used it to measure the planet's size."
The star HD 209458 is 47 parsecs (153 light years or 1.4 million billion kilometers or 859,000 billion miles) away in the constellation of Pegasus, and is about the same age, color and size as our own Sun. It is very near the star, 51 Pegasi, around which the first extrasolar planet was discovered in 1995. With the orbital plane of the planet known, the astronomers for the first time could determine precisely the mass of the planet and, from the size of the planet measured during transit, its density.
Interestingly, while the planet's mass is only 63 percent of Jupiter's mass, its radius is 60 percent bigger than that of Jupiter. This fits with theories that predict a bloated planet when, as here, the planet is very close to the star.
The density, about 0.2 grams per cubic centimeter, means it is a gas giant like Jupiter. However, such gas giants could not have formed at the distance this planet is from its star.
"This supports the theory that extrasolar planets very near their star did not form where they are, but formed farther out and migrated inward," Henry said.
Various groups around the world have been searching for planets by looking for dimming of stars, or as Marcy says, "staring at the sky and seeing if any star blinks." To date, none of these searches has turned up a new planet. "With this one, everything hangs together," Marcy said. "This is what we've been waiting for."
The research was supported by the National Aeronautics and Space Administration, the National Science Foundation, Sun Microsystems and the Richard Lounsbery Foundation.
Geoff Marcy can be reached at email@example.com or (510) 642-1952; Greg Henry is at firstname.lastname@example.org or (615) 963-7017; Paul Butler is at email@example.com or (202) 686-4370 x4401; and Steve Vogt is at firstname.lastname@example.org
Press release, January 1999
A new message will be broadcast in the direction of nearby stars in order to search for extra-terrestrial intelligence. This project was being presented by Dr. Yvan Dutil and Stephane Dumas from the Defence Research Establishment Valcartier, near Quebec City (Canada), to the American Astronomical Society meeting in Austin, TX. This is the first time in a quarter of a century that such a cosmic call will be attempted. This experiment is promoted by the Encounter 2001 project, an international spaceflight project which is planned for launch into interstellar space in the year 2001.
The complete message is about 400,000 bits long and will be transmitted three times over a 3-hour period in the direction of the four selected stars. Then, it will be followed by a series of greetings from people around the world. The first transmission was made on May 24, 1999, and the next will be on February 14, 2000, and February 14, 2001. This message is much larger in size, duration and scope than the one sent by Frank Drake on November 16th, 1974, from the Arecibo observatory which consisted of only 1,679 bits sent over a 3 minute duration.
Finding a transmitter for this task was not easy; the project will use a 70 m (230 ft) Ukrainian antenna equipped with a 150 kW transmitter broadcasting at 5 GHz (6 cm). Using this antenna, any civilization within 100 light-years which has access to a radio-telescope with an area of one squared-kilometer will be able to read the message. The artificial nature of the message should be able to be detected by similar instruments at distances up to 10,000 light-years. A radio-telescope of this size will be built on Earth in the near future.
Astronomers announced today they have found evidence of the first known planet orbiting a pair of stars. Previously, planets have been found circling only single stars.
The Microlensing Planet Search (MPS) project, led by David Bennett and Sun Hong Rhie of the University of Notre Dame, used a technique called gravitational microlensing that may have revealed a planet about three times the mass of Jupiter orbiting a binary star system. The researchers, who are supported by the National Science Foundation (NSF), NASA and the Research Corporation, report their result in the November 4, 1999, issue of Nature.
"Between half and two-thirds of the stars in our solar neighborhood are known to be members of binary or multiple star systems," said Morris Aizenman of NSF's Astronomical Sciences Division. "To find evidence of a planet orbiting a pair of stars means there could be more planetary systems than we previously thought." Astronomers have detected only about 20 planets outside our solar system, all orbiting single stars, although some of those stars are in binary systems.
Gravitational lensing is based on a property first noted by Albert Einstein in the 1930's. When an object such as a star or planet moves in front of a more distant star, the gravity of this star or planet serves as a "lens," magnifying the light from the distant star and making it appear brighter. The MPS astronomers analyzed data from such an event that occurred in 1997, involving a lens estimated to be about 20,000 light years from Earth. During this event -- referred to as MACHO-97-BLG-41, the 41st microlensing event discovered by the Massive Compact Halo Objects (MACHO) collaboration that year -- the pattern of brightness appeared too complex to be produced by a single-star lens.
While Bennett and his colleagues believe the best model for explaining this microlensing event is a planet orbiting a binary star system, other astronomers have proposed alternative models they believe could also fit the data. One possibility is that the orbital motion of the binary star system itself could have caused the change in the observed brightness of the distant star. Another possibility is that the distant star may itself be part of a binary system. These scenarios will be tested in future observations.
The MACHO project, which is supported by NSF as part of the National Science and Technology Center for Particle Astrophysics at the University of California at Berkeley, routinely makes data on microlensing events available to other astronomers. MACHO is using microlensing to explore tens of millions of stars in a search for the "dark matter" that dominates the mass of our galaxy. Dark matter is believed to exist because the combined gravity of the known matter in the universe is not enough to account for the observed gravitational effects.
The MPS astronomers are using the technique to search for planets orbiting other stars besides our Sun. For this analysis, they used observations from telescopes at the Mount Stromlo Observatory in Australia and the Wise Observatory in Israel as well as data from the NSF's Cerro-Tololo Inter-American Observatory in Chile. Astronomers at the Wise Observatory co-authored the Nature report.
Berkeley - Beginning Monday, May 17, anyone in the world with a desktop computer will be able to join the University of California, Berkeley's search for extraterrestrial intelligence.
The campus's SETI@home project already has a list of nearly 400,000 people from 96 countries anxiously awaiting the final version of software that will let them crunch data in search of intelligent radio signals from advanced civilizations. To date, some 12,000 people have been involved in testing the software and have racked up about 200 years' worth of computing time.
"I'm amazed at the extreme eagerness of people to use this," said computer scientist David Anderson, SETI@home project director. "Every day I get email in all languages saying, 'Give me the software NOW!'"
Many others have volunteered their time to do programming, help build a website and even translate instructions into other languages, added Dan Werthimer, the project scientist and a research physicist at the Space Sciences Laboratory at UC Berkeley.
Come Monday, computer geeks and students, science fiction fans and retirees, all can jump to the SETI@home website, http://setiathome.ssl.berkeley.edu/, and download versions of the software for Windows machines, Macintosh computers and 30 varieties of the Unix operating system.
On Windows and Macintosh machines, the software acts like a screensaver - whenever the computer is idle, the SETI@home software takes over and begins analyzing data in search of strong spikes or repetitive patterns in radio signals from space. The data come from the large radio telescope at Arecibo in Puerto Rico and are broken into small chunks that are sent to individual computers for analysis.
As the computer works away at the data, the screen displays a three-dimensional graph charting the signal analysis. Participants also can view maps showing where the SETI@home project is searching and who is taking part in the project.
After the computer is finished with the analysis, it sends the results back to UC Berkeley through the internet and grabs another chunk of data.
"This project lets us do SETI a lot, lot faster, with 10 times more sensitivity and exploring more thoroughly the spectrum of radio frequencies we scan," Werthimer said. "Plus, it's a fun and educational project, a global science project."
"Never before has there been an opportunity for anyone, anywhere in the world to join the scientific search for intelligent beings elsewhere in our universe," said Louis Friedman, executive director of the Planetary Society, which provided early seed money and is a principal sponsor for the project. "This is a grand experiment - in science, in technology and in society - a global cooperative effort at the frontiers of knowledge."
The project also is an experiment in "distributed computing" - a way of breaking down a problem requiring lots of computation into small chunks that can be done by many small computers distributed anywhere in the world. The SETI@home project is the first distributed computing project to offer the general public the opportunity to participate in important research.
"This will be the largest distributed computing project ever," Anderson predicted.
The project was launched three years ago with the Planetary Society (http://planetary.org), in cooperation with Paramount Pictures, providing $100,000 for development of the publicly available software. Sun Microsystems also donated computing equipment and the University of California provided matching funds of $180,000 from its Digital Media Innovation Program (http://www.dimi.ucsb.edu/ ).
The idea of linking computers in a global network to analyze radio data from space originated with David Gedye, a UC Berkeley computer science graduate and a former student of Anderson.
"SETI@home is a way of harnessing all the idle computers to increase our computing capacity and our chance of finding extraterrestrials," Werthimer said.
Werthimer and other UC Berkeley physicists operate several ongoing SETI projects, including a 20-year-old project, the Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations (SERENDIP), whose newest instrument, SERENDIP IV, piggybacks on the Arecibo telescope. But the computer capacity available to SERENDIP is sufficient to look for only the most obvious signals from extraterrestrial civilizations, Werthimer said.
SETI@home will let SERENDIP physicists analyze more thoroughly the data they receive daily from their ongoing survey of the sky using the large radio dish at Arecibo.
The radio data is broken down into small chunks - a 10 kilohertz range of wavelengths in a strip of sky visible from Puerto Rico - through which the screen saver program can search for patterns that may indicate a deliberate broadcast from a distant civilization. The data downloaded to each desktop computer takes up only about 250 kilobytes of computer memory, though the computer must have 32 megabytes of RAM (random access memory) to run the screensaver software.
"You can download enough data through the internet in five minutes to keep the computer analyzing for several days," Anderson said. "The computer then sends back a summary of the interesting stuff it found and gets another chunk of data."
Whatever interesting signals may turn up from SETI@home must be checked by project staff to make sure they are not due to radio interference from Earth or orbiting satellites.
"We're not asking people to call the press when they see a spike on the screen," Werthimer said. "We get strong signals all the time and have to sift through them."
San Francisco State University Press Release
The discovery of the first planetary system around a nearby, Sun-like star, which was already known to have one planetary companion.
SAN FRANCISCO, April 15, 1999 Astronomers from four research institutions have discovered strong evidence for a trio of extrasolar planets that orbit the star Upsilon Andromedae. This is the first multiple planet system ever found around a normal star, other than the nine planets in our Solar System. The closest planet in the Upsilon Andromedae system was detected in 1996 by San Francisco State University (SFSU) astronomers Geoffrey Marcy and R. Paul Butler. Now, after 11 years of telescope observations at Lick Observatory near San Jose, CA, the signals of two additional planets have emerged from the data. Therefore, Upsilon Andromedae harbors the first planetary system that is reminiscent of our own Solar System. In parallel, astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, MA and the High Altitude Observatory (HAO) in Boulder, CO have independently found the two outer planets around Upsilon Andromedae. This tea'as been studying the star for more than four years at the Smithsonian=92s Whipple Observatory near Tucson, AZ.
This first planetary system, found from a survey of 107 stars, offers the first suggestion that planetary systems like our own are abundant in our Milky Way Galaxy, which contains 200 billion stars. SFSU researcher Debra Fischer said, "It implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems." The innermost (and previously known) of the three planets contains at least three-quarters of the mass of Jupiter and orbits only 0.06 AU from the star. (One "AU" equals the distance from the Earth to the Sun). It traverses a circular orbit every 4.6 days. The middle planet contains at least twice the mass of Jupiter and takes 242 days to orbit the star once. It resides approximately 0.83 AU from the star, similar to the orbital distance of Venus. The outermost planet has a mass of at least four Jupiters and completes one orbit every 3.5 to 4 years, placing it 2.5 AU from the star. The two outer planets are both new discoveries and have elliptical (oval) orbits, a characteristic of the nine other extrasolar planets in distant orbits around their stars.
No current theory predicted that so many giant worlds would form around a star. "I am mystified at how such a system of Jupiter-like planets might have been created," said Marcy, SFSU's Distinguished Professor of Science. "This will shake up the theory of planet formation." Robert Noyes, a professor of astronomy at Harvard-Smithsonian CfA and a member of the CfA-HAO team, said, "A nagging question was whether the massive bodies orbiting in apparent isolation around stars really are planets, but now that we see three around the same star, it is hard to imagine anything else."
Currently a staff astronomer at the Anglo-Australian Observatory, Butler, an American, is the lead author of the paper, submitted to the Astrophysical Journal, announcing the triple planet system. Along with Marcy, Fischer, and Noyes, the authors include Sylvain Korzennik, Peter Nisenson, and Adam Contos of the Harvard-Smithsonian CfA, and Timothy Brown of the HAO. "Both of our groups found essentially the same size and shape for the orbits of the companions," said Korzennik. The chances of this happening by accident are infinitesimal." Added Fischer, "This is an extraordinary finding and it demands extraordinary evidence. Having two completely independent sets of observations gives us confidence in this detection."
Marcy and Butler had suspected that there was something strange about Upsilon Andromedae. The velocity variations that revealed the closest planet to the star in 1996 had an unusual amount of scatter. Not until early this year had enough observations been made of the star to confirm the presence of an additional planet, which explained some of the confusing pattern in the data. But another object still seemed to be tugging on the star. "We looked at the two planet solution that we had been expecting and there was still too much extra noise," said Fischer. "We arrived at the conclusion that the extra observed wobble could only be explained by the presence of a third planet." Both teams of astronomers considered astrophysical effects that could mimic the velocity signature from these planets, but no such effects are viable. A computer simulation by Greg Laughlin of U.C. Berkeley suggests that these three giant planets could co-exist in stable orbits.
One big question left to answer is how such a solar system arose. "The usual picture is that gas giant planets can only form at least four AU away from a star, where temperatures are low enough for ice to condense and begin the process of planet formation," said Brown. "But all three giant planets around Upsilon Andromedae now reside inside this theoretical ice boundary." The planets may have formed close to the host star, or, like balls on a billiard table, the planets may have scattered off of each other, migrating into their current orbits from a more distant place of origin.
The discovery of this multiple planet system suggests a new paradigm for planet formation where many small seed planets known as planetesimals might develop in the disk of matter surrounding a star. Those planets that grow fastest would engage in a gravitational tug of war that weeds out some of the smaller worlds and determines which planets ultimately remain in orbit. "The Upsilon Andromedae system suggests that gravitational interactions between Jupiter-mass planets can play a powerful role in sculpting solar systems," said Butler.
If these Jupiter-mass planets are like our own Jupiter, they would not be expected to have solid Earth-like surfaces. But, Nisenson noted, "Our observations can't rule out Earth-sized planets as well in this planetary system, because their gravity would be too weak for them to be detectable with present instruments."
A bright star visible to the naked eye starting this June, Upsilon Andromedae is 44 light-years away from Earth, and it is roughly 3 billion years old, two-thirds the age of the Sun. This star should make an ideal target for NASA's upcoming Space Interferometry Mission (SIM). Expected to be launched in 2005, SIM will spend five years probing nearby stars for Earth-sized planets and will test technology slated for future planet-searching telescopes. The ongoing ground-based planet search will enable SIM to home in on those stars most likely to harbor small planets.
[from a press release, 2/8/1999]
Berkeley/Mountain View, Calif. - The University of California, Berkeley, and the SETI Institute have teamed up to design and build an array of 500 to 1,000 radio telescopes whose primary task will be to seek out signals from civilizations elsewhere in our galaxy.
Rather than construct one large and expensive radio telescope like the famous dish at Arecibo, Puerto Rico, or even an array of many large, custom-built telescopes like the Very Large Array in New Mexico, the UC Berkeley/SETI Institute team will explore the use of many inexpensive antennas similar to those used for backyard TV reception. By electronically coupling many dishes together, a large "radio ear" can be constructed at a fraction of the cost of more conventional approaches. The project is estimated to cost less than $25 million, and could be completed by 2004.
"This represents a paradigm shift in the design and construction of radio telescopes," said Jill Tarter, science team leader for the Institute's current SETI program. "We hope to demonstrate that a premium instrument need not have a premium price."
UC Berkeley researchers emphasize, though, that the novel array will be spectacular for radio astronomy, too. Because of its unique construction, the telescope could be used simultaneously for SETI and other radio astronomy observations.
"The instrument we want to build will have unique capabilities for observing objects from the solar system to the edge of the Universe," said Leo Blitz, director of the UC Berkeley Radio Astronomy Lab and professor of astronomy. "Our goal is nothing short of standing the way radio astronomy has been done up to now on its head."
The array will eventually comprise a total collecting area of 10,000 square meters, or one hectare (2.47 acres), hence the project's current name, the One Hectare Telescope, or 1hT. When completed, the 1hT will be among the world's largest radio telescopes. By comparison, the Arecibo telescope, which is the world's largest, is 1,000 feet in diameter and has a collecting area of about 73,000 square meters (about 18 acres).
Once completed, the 1hT will be the world's largest observing facility devoted substantially to SETI. SETI observations require not only a large collecting area-to find the weak signals expected from a transmitter many light years away-but also highly sophisticated digital receivers to scrutinize millions of radio channels.
For SETI observations, dedicated time on large radio telescopes is scarce and expensive. The result for SETI is less than optimal; at best, SETI scientists are able to scan only a few hundred star systems per year. The 1hT would allow this number to expand at least tenfold. In the Milky Way Galaxy alone, there are an estimated 400 billion stars.
"UC Berkeley has one of the world's premier radio astronomy programs, along with first-rate programs in engineering and computer science, " said Tarter. "Together, we can design and build an instrument for that will have no peer for this type of work."
The first goal will be to build a prototype composed of perhaps a dozen small radio dishes at UC Berkeley's Hat Creek Observatory, located near Mt. Lassen in northern California. The Hat Creek Observatory is the site of the ten-telescope array now operated by UC Berkeley, called BIMA (Berkeley-Illinois-Maryland Array). Once the 1hT concept has been proven and the electronics are working, the team would embark on the construction of an array of up to 1,000 telescopes, probably also at Hat Creek. The number of telescopes will depend on the ultimate size of the individual dishes, which could be 12 feet or 18 feet in diameter, whichever provides the most cost-effective solution.
The design concept of the 1hT should significantly reduce the cost of construction, according to UC Berkeley and SETI Institute researchers. A comparably sized instrument, the 300-foot Green Bank Telescope now under construction at the National Radio Astronomy Observatory in West Virginia, will cost at least $75 million. The 1hT, whose sensitivity at the frequencies of interest to SETI will be similar to the Green Bank Telescope, is predicted to cost less than one-third as much as that instrument. The smaller telescopes of the 1hT would also be much less expensive to maintain.
Unlike conventional radio telescopes, the 1hT is also scalable. By adding new dishes to the array, the 1hT could be made larger at relatively low cost. And while damage to the collecting surface of a traditional radio telescope is expensive and time-consuming to repair, the individual dishes of the 1hT can be replaced quickly and cheaply.
UC Berkeley's lead astronomer on the 1hT project, Professor of Astronomy William "Jack" Welch, plans to support a targeted SETI search in addition to conducting observations of star-forming regions. The newly-appointed Watson and Marilyn Alberts Chair for SETI at UC Berkeley, Welch said that the 1hT team will begin the search with 1,000 nearby sun-like stars and gradually moving outward to encompass 100,000 then one million candidate stars in our galaxy. The team will search for strong signals at a single frequency - like radar or radio broadcasts from Earth - as well as pulsed signals that repeat. The 1hT computer system will conduct an analysis, to be performed eventually by a receiver on a mass-produced integrated circuit chip, designed to alert researchers immediately to signals of interest.
Funds for the 1hT will be raised from private sources under the direction of the SETI Institute. The Institute's Project Phoenix is currently the world's largest privately supported radio astronomy enterprise, with an annual budget of more than $3 million.
Blitz and Tarter note that the 1hT would also prove the feasibility of an even larger array of telescopes-perhaps as many as 100,000-with a total collecting area of a square kilometer, or one million square meters. This so-called Square Kilometer Array (SKA) is being developed as a major international collaboration for radio astronomers in the next century. If built, the SKA would surpass Arecibo as the world's largest radio telescope.
Observations with the NICMOS infrared camera on the Hubble Space Telescope have revealed what appears to be rings around other stars, and these rings are thought to indicate the presence of planets. A bright ring at 70 AU around the A0 star HR4796 ( http://nicmos.as.arizona.edu:8000/AASJ98/AAS98.html) would have to be shepherded by at least one and probably two planets, though the planets themselves are too faint to see. A dark ring in the middle of a bright disk around another A0 star, HD 141569, at 270 AU is suggestive of a planet orbiting to cause that drop in brightness. A0 stars have masses about twice that of the sun.
Dust structures have been imaged around Vega and Fomalhaut, two of the brightest
stars in the sky. See NATURE for April 23, 1998, for the article about this
research from the James Clerk Maxwell Telescope. The press release summarizes
An article entitled "The Rise of Life on Earth" appeared in National Geographic, March 1998, pp. 54-81.
December 4 Nature article offers point-counterpoint approach to controversy
The famous Martian meteorite, ALH84001, contains no biological life forms, according to a Case Western Reserve University researcher and colleagues.
The team issues this report in the December 4 issue of Nature, duplicating the methods of a team of scientists from the Johnson Space Center and Stanford University. In rare counterpoint writings in the "Scientific Correspondence" section, Nature allowed the Johnson team to respond to the group's findings. The Johnson paper also appears in the December 4 issue.
CWRU's Ralph Harvey, senior research associate in the Department of Geological Sciences, was on the research team. The lead researcher on the paper was John Bradley from MVA Inc. and the School of Material Science and Engineering at Georgia Institute of Technology. The third researcher is Hap McSween from the University of Tennessee.
The trio reports that most of the purported nanofossils or "worm-like images" are nothing more than lamellae, or fractured surfaces of pyroxene and carbonate crystals.
Last year, the Johnson-Stanford team announced it found evidence of nanofossils in the meteorite. Reports of life on Mars spurred the July 4 mission to Mars to look for further evidence of life.
Allan Hills 84001 -- a meteorite the size of a potato -- remains in the center of a spirited controversy about the possibility of life on Mars. The meteorite was found in the 1980s in Antarctica by the National Science Foundation's Antarctic Search for Meteorite Program (ANSMET), headed by Harvey with headquarters at CWRU.
Harvey, who is currently on his annual expedition to Antarctica to collect meteorites, commented before leaving November 21 that the Johnson-Stanford team has always argued that they had used different techniques to study the meteorite.
Bradley, Harvey, and McSween published a paper last year in Geochimica et Cosmochimica Acta (GCA), announcing that what the other researchers observed was formed geologically, not biologically. The Johnson-Stanford group also announced that these nanofossils were laying on the surface of the meteorite.
In the first GCA study, which used transmission electron microscope imagining (TEM), the researchers found non-biological magnetite whiskers on or near the surfaces of the carbonates. Superficially the whiskers look like worms, but in fact they have nothing to do with biological processes, according to Harvey and colleagues.
The latest study took place over the past six months as the researchers re-examined the meteorite using the new techniques. This time they found yet another population of worm-like forms that are actually mineral lamellae formed by non-biological, geological processes. The lamellae look like worms or nanofossils, but when the specimen is tilted and viewed from another angle, it clearly shows that the lamellae are attached and part of the mineral surfaces.
"The surface topography is highly irregular on a nanometre scale, with emergent lamellae following the major cleavage direction of the substrate," Bradley writes in the paper. The researchers have published pictures of the TEM images to support their findings.
"Peculiar surface structures or segmentation on the worm-like forms are artifacts from conductive metal coatings applied to the samples for imaging in the electron microscope. This is not the first time metal coating artifacts have lead to misidentification of nanofossils in rocks," Bradley said.
"We have now found two different types of mineral forms in ALH84001 that look just like nanofossils, but they are strictly non-biological origins. Sometimes even nature has a perverse sense of humor," he added.
Harvey stressed that during this latest study, the team was careful to use exactly the same methods as the Johnson-Stanford group to lay to rest any arguments that the research methods had affected the findings.
The worm-like mineral lamellae are commonly found at the fractured surfaces of planar crystals. Harvey noted that lunar rocks -- in which there has been no evidence of life found -- contain these same formations.
Does this put an end to the life on Mars debate? "We haven't driven the final nail in the coffin yet about organisms in this Martian rock, but our latest article offers a lot of insight that shows these fractures zones in the rock are incredibly complex," Harvey said, "and that it is very dangerous to try to draw any hypothesis from a few pictures from here or there."