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Though there has been a fair amount of evidence that the Earth's
atmosphere is undergoing global warming, the process is slow enough that
there are plenty of skeptics, including some very influential people who
argue that it may not be happening at all.
Global climate change does occur, however, and sometimes so quickly
that you can watch it happening. Just look at our neighbor, Mars: within the
last month, the global atmospheric temperature of Mars has increased by
approximately 50 degrees Fahrenheit, according to data being received by the
Thermal Emission Spectrometer (TES) on NASA's Mars Global Surveyor
spacecraft.
The cause of this sudden shift is a giant dust storm that has
snowballed and now has enveloped almost the entire planet, absorbing a lot
of the Sun's energy in the upper atmosphere.
"It started out as a large dust storm in the southern latitudes in
late June," said Arizona State University's Korrick Professor of Geology
Philip Christensen, the principal investigator for TES. "The dust trapped
sunlight and heated the atmosphere locally. As this warm air flowed to
regions where the air was still cool it generated winds which raised more
dust into the atmosphere.
"By the end of the first week in July, most of the planet was enveloped and
our readings of atmospheric temperature had increased by about 30 degrees
Centigrade."
TES is an instrument designed to take detailed readings of energy emissions
in the infrared range (heat energy) to aid in studying Mars' geology and
atmosphere. A movie showing the instrument's readings over the last month,
tracking the expanding dust storm and the accompanying increase in
atmospheric temperature, is available on the web at:
http://tes.la.asu.edu.
Curiously, just as Earth's global warming may theoretically cause the
opposite thermal effect on some parts of the planet, so Mars' current heat
wave is likely to bring on a big chill further on down the road.
"In the end, the cloaking of the entire planet with dust is probably going
to cool down the surface of Mars significantly and ultimately shut this
entire weather system down again," said Christensen. "It's kind of like what
we imagine would happen with a nuclear winter on Earth."
In fact, Christensen points out, it was another global dust storm observed
on Mars in the early 1970's that gave astronomer Carl Sagan and others the
idea of the kind of catastrophic climate change that might be caused by a
global nuclear war.
"But Mars' atmosphere is a much simpler system than Earth's," Christensen
cautions, "since it is much thinner and lacks most of the water that we have
in ours, trapping energy and moderating changes.
"Still, it provides us with an interesting model for how global climate
changes can occur, albeit much more quickly than on our planet. Nonetheless,
some large scale changes here could be abrupt as well."
A NASA/JPL press release on the current martian dust storm is available at:
http://www.jpl.nasa.gov/releases/2001/duststorm_010709.html .
NASA's Mars Odyssey spacecraft pointed its camera homeward last week and took its first picture -- a shot of a faint crescent Earth -- as the spacecraft heads off toward its destination, the planet Mars.
The image was taken as part of the calibration process for the Thermal Emission Imaging System (THEMIS), the camera system that is one of three science instrument packages on the spacecraft. The imaging system will study the Martian surface in both the visible and the infrared and will help determine what minerals are present. It also will map landscapes on Mars at resolutions comparable to that of NASA's Landsat Earth observing satellite.
"The spacecraft team did a fantastic job to image the Earth. These images are spectacular, especially given how far away we were. They have given us the first-ever thermal-infrared view of Earth and the moon from interplanetary space," said Dr. Philip Christensen, principal investigator for the THEMIS imaging system at Arizona State University, Tempe.
The visible image shows the night side of the crescent Earth looking toward the South Pole. Taken at the same time, the infrared image measures temperature, showing its "night- vision" capability to observe Earth even in the dark.
"The instrument measured a low surface temperature of minus 50 degrees Celsius (minus 58 degrees Fahrenheit) for Antarctica in winter, and a high of 9 degrees Celsius (48.2 degrees Fahrenheit) at night in Australia. These temperatures agree remarkably well with observed temperatures of minus 63 degrees Celsius at Vostok Station in Antarctica, and 10 degrees Celsius in Australia. Thus we demonstrated that the instrument can accurately measure temperatures, even from a distance of more than 3 million kilometers (2 million miles)," Christensen said.
These observations of Antarctica provide an excellent test for how the imaging system will perform at Mars, where afternoon temperatures are comparable to those in the winter night at Earth's South Pole. The Antarctic continent, which was uncharted less than 100 years ago, was the last landmass observed by Odyssey as it left Earth on its way to Mars.
The images were taken on April 19, 2001, and are available on the Internet at:
http://mars.jpl.nasa.gov/odyssey
and
http://themis.asu.edu
More information about the Mars Exploration Program can be found at:
[NASA Press Release, December 4, 2000]
In what ultimately may be their most significant discovery yet, Mars scientists say high-resolution pictures showing layers of sedimentary rock paint a portrait of an ancient Mars that long ago may have featured numerous lakes and shallow seas.
"We see distinct, thick layers of rock within craters and other depressions for which a number of lines of evidence indicate that they may have formed in lakes or shallow seas. We have never before had this type of irrefutable evidence that sedimentary rocks are widespread on Mars," said Dr. Michael Malin, principal investigator for the Mars Orbiter Camera on NASA's Mars Global Surveyor spacecraft at Malin Space Science Systems (MSSS), San Diego, CA. "These images tell us that early Mars was very dynamic and may have been a lot more like Earth than many of us had been thinking."
Such layered rock structures where there were once lakes are common on Earth. The pancake-like layers of sediment compressed and cemented to form a rock record of the planet's history.
The regions of sedimentary layers on Mars are spread out and scattered around the planet. They are most common within impact craters of Western Arabia Terra, the inter-crater plains of northern Terra Meridiani, the chasms of the Valles Marineris, and parts of the northeastern Hellas Basin rim. The scientists compare the rock layers on Mars to features seen in the American Southwest, such as the Grand Canyon and the Painted Desert of Arizona.
"We caution that the Mars images tell us that the story is actually quite complicated and yet the implications are tremendous. Mars has preserved for us, in its sedimentary rocks, a record of events unlike any that occur on the planet today," said Dr. Ken Edgett, staff scientist at MSSS. "This is changing the way we think about the early history of Mars -- a time perhaps more than 3.5 billion years ago."
"On Earth, sedimentary rocks preserve the surface history of our planet, and within that history, the fossil record of life. It is reasonable to look for evidence of past life on Mars in these remarkably similar sedimentary layers," said Malin. "What is new in our work is that Mars has shown us that there are many more places in which to look, and that these materials may date back to the earliest times of Martian history."
Malin added, "I have not previously been a vocal advocate of the theory that Mars was wet and warm in its early history. But my earlier view of Mars was really shaken when I saw our first high- resolution pictures of Candor Chasma. The nearly identically thick layers would be almost impossible to create without water."
As an alternative to lakes, Malin and Edgett suggest that a denser atmosphere on early Mars could have allowed greater amounts of windborne dust to settle out on the surface in ways that would have created the sedimentary rock.
"We have only solved one little piece of a tremendous puzzle," Malin said. "There is no illustration on the box to show us what it is supposed to look like when it is completed and we are sure most of the pieces are missing."
"These latest findings from the Mars Global Surveyor tell us that more study both from orbit and at the surface is needed to decipher the tantalizing history of water on Mars," said Dr. Jim Garvin, Mars Exploration Program Scientist at NASA Headquarters. "Our scientific strategy of following the water by seeking, conducting in situ studies, and ultimately sampling will follow up on these latest discoveries about Mars, and adapt to the new understanding."
"Mars seems to continually amaze us with unexpected discoveries," said Dr. Edward Weiler, Associate Administrator for Space Science at NASA Headquarters. "This finding just might be the key to solving some of the biggest mysteries on Mars, and it also tells us that our new Mars exploration program needs the flexibility to follow up in a carefully thought-out manner."
"The finding of layered sedimentary deposits is something that biologists have been hoping for," said Dr. Ken Nealson, director of the Center for Life Detection at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "Perhaps the favorite sites for biologists to search for fossils or evidence of past life on Earth are layered lake or oceanic sediments such as in these sites Malin and Edgett describe."
Images for this release are available at:
http://www.msss.com/mars_images/moc/dec00_seds/
Information on the Mars Global Surveyor is available at:
NASA Press Release, 7/27/00
In 2003, NASA plans to launch a relative of the now-famous 1997 Mars Pathfinder rover. Using drop, bounce, and roll technology, this larger cousin is expected to reach the surface of the Red Planet in January, 2004 and begin the longest journey of scientific exploration ever undertaken across the surface of that alien world.
Dr. Edward Weiler, Associate Administrator, Office of Space Science, NASA Headquarters, Washington, DC., announced today that the Mars Rover was his choice from two mission options which had been under study since March.
"Today I am announcing that we have selected the Mars Exploration Program Rover rather than the orbiter option, which was an extremely difficult decision to make," said Weiler. "At the same time, we want to look into what could be an amazing opportunity, as well as a challenge, by sending two such rovers to two very different locations on Mars in 2003 rather than just one."
"We are evaluating the implications of a two-rover option, Weiler added. "I intend to make a decision in the next few weeks so that, if the decision is to proceed with two rovers, we can meet the development schedule for a 2003 launch."
With far greater mobility and scientific capability than the 1997 Mars Pathfinder Sojourner rover, this new robotic explorer will be able to trek up to 110 yards (100 meters) across the surface each Martian day, which is 24 hrs. 37 min. The Mars rover will carry a sophisticated set of instruments that will allow it to search for evidence of liquid water that may have been present in the planet's past, as well as study the geologic building blocks on the surface.
"This mission will give us the first ever robot field geologist on Mars. It not only has the potential for breakthrough scientific discoveries, but also gives us necessary experience in full-scale surface science operations which will benefit all future missions," said Scott Hubbard, Mars Program Director at NASA Headquarters. "A landed mission in 2003 also allows us to take advantage of a very favorable alignment between Earth and Mars."
After launch on top a Delta II rocket, and a cruise of seven and a half months, the spacecraft should enter the Martian atmosphere January 20, 2004. In a landing similar to that of the Pathfinder spacecraft, a parachute will deploy to slow the spacecraft down, and airbags will inflate to cushion the landing. Upon reaching the surface the spacecraft will bounce about a dozen times and could roll as far as a half-mile (about one kilometer). When it comes to a stop, the airbags will deflate and retract, and the petals will open, bringing the lander to an upright position and revealing the rover.
Where the Pathfinder mission consisted of a lander, with science instruments and camera, as well as the small Sojourner rover, the Mars 2003 mission features a design that is dramatically different. This new spacecraft will consist entirely of the large, long-range rover, which comes to the surface inside a Pathfinder landing system, making it essentially a mobile scientific lander.
Immediately after touchdown, the rover is expected to give us a virtual tour of the landing site by sending back a high resolution 360-degree, panoramic, color and infrared image. It will then leave the petal structure behind, driving off as scientists command the vehicle to go to rock and soil targets of interest.
This rover will be able to travel almost as far in one Martian day as the Sojourner rover did over its entire lifetime. Rocks and soils will be analyzed with a set of five instruments. A special tool called the "RAT," or Rock Abrasion Tool, will also be used to expose fresh rock surfaces for study.
The rover will weigh about 300 pounds (nearly 150 kilograms) and has a range of up to about 110 yards (100 meters) per sol, or Martian day. Surface operations will last for at least 90 sols, extending to late April 2004, but could continue longer, depending on the health of the rover.
"By studying a diverse array of martian materials, including the interiors of rocks, the instruments aboard the Rover will reveal the secrets of past martian environments, possibly providing new perspectives on where to focus the quest for signs of past life," said Dr. Jim Garvin, NASA Mars Program Scientist at NASA Headquarters. "Furthermore, the Rover offers never-before-possible opportunities for discoveries about the martian surface at scales ranging from microscopic to that of gigantic boulders. This is a key stepping stone to the future of our Mars exploration program."
One aspect of the Mars Rover's mission is to determine history of climate and water at a site or sites on Mars where conditions may once have been warmer and wetter and thus potentially favorable to life as we know it here on Earth.
The exact landing site has not yet been chosen, but is likely to be a location such as a former lakebed or channel deposit - a place where scientists believe there was once water. A site will be selected on the basis of intensive study of orbital data collected by the Mars Global Surveyor spacecraft, as well as the Mars 2001 orbiter, and other missions.
The alternative mission, which had been under consideration for the 2003 opportunity, was a Mars scientific orbiter, which featured a camera capable of imaging objects as small as about two feet (60 cm) across, an imaging spectrometer designed to search for mineralogical evidence of the role of ancient water in martian history, and other science objectives.
In what could turn out to be a landmark discovery in the history of Mars exploration, imaging scientists using data from NASA's Mars Global Surveyor spacecraft have recently observed features that suggest there may be current sources of liquid water at or near the surface of the red planet.
The new images show the smallest features ever observed from martian orbit -- the size of an SUV. NASA scientists compare the features to those left by flash floods on Earth.
"We see features that look like gullies formed by flowing water and the deposits of soil and rocks transported by these flows. The features appear to be so young that they might be forming today. We think we are seeing evidence of a ground water supply, similar to an aquifer," said Dr. Michael Malin, principal investigator for the Mars Orbiter Camera on the Mars Global Surveyor spacecraft at Malin Space Science Systems (MSSS), San Diego, CA. "These are new landforms that have never been seen before on Mars."
The findings were published in the June 30, 2000, issue of Science magazine.
"Twenty-eight years ago the Mariner 9 spacecraft found evidence -- in the form of channels and valleys -- that billions of years ago the planet had water flowing across its surface," said Dr. Ken Edgett, staff scientist at MSSS and co-author of the paper in Science. "Ever since that time, Mars science has focused on the question, 'Where did the water go?' The new pictures from Global Surveyor tell us part of the answer -- some of that water went under ground, and quite possibly it's still there."
"For two decades scientists have debated whether liquid water might have existed on the surface of Mars just a few billion years ago," said Dr. Ed Weiler, Associate Administrator for Space Science, NASA Headquarters. "With today's discovery, we're no longer talking about a distant time. The debate has moved to present-day Mars. The presence of liquid water on Mars has profound implications for the question of life not only in the past, but perhaps even today. If life ever did develop there, and if it survives to the present time, then these landforms would be great places to look."
The gullies observed in the images are on cliffs -- usually in crater or valley walls -- and are made up of a deep channel with a collapsed region at its upper end (an "alcove") and at the other end an area of accumulated debris (an "apron") that appears to have been transported down the slope. Relative to the rest of the martian surface, the gullies appear to be extremely young, meaning they may have formed in the recent past.
"They could be a few million years old, but we cannot rule out that some of them are so recent as to have formed yesterday," Malin said.
Because the atmospheric pressure at the surface of Mars is about 100 times less than it is at sea level on Earth, liquid water would immediately begin to boil when exposed at the martian surface. Investigators believe that this boiling would be violent and explosive. So how can these gullies form? Malin explained that the process must involve repeated outbursts of water and debris, similar to flash floods on Earth.
"We've come up with a model to explain these features and why the water would flow down the gullies instead of just boiling off the surface. When water evaporates it cools the ground -- that would cause the water behind the initial seepage site to freeze. This would result in pressure building up behind an 'ice dam.' Ultimately, the dam would break and send a flood down the gully," said Edgett.
The occurrence of gullies is quite rare: only a few hundred locations have been seen in the many tens of thousands of places surveyed by the orbiter camera. Most are in the martian southern hemisphere, but a few are in the north.
"What is odd about these gullies is that they occur where you might not expect them -- in some of the coldest places on the planet," Malin indicated. "Nearly all occur between latitudes 30 degrees and 70 degrees, and usually on slopes that get the least amount of sunlight during each martian day."
If these gullies were on Earth they would be at latitudes roughly between New Orleans, Louisiana, and Point Barrow, Alaska, in the northern hemisphere; and Sydney, Australia, to much of the Antarctic coast in the south.
The water supply is believed to be about 100 to 400 meters (300 to 1300 feet) below the surface, and limited to specific regions across the planet. Each flow that came down each gully may have had a volume of water of, roughly, 2500 cubic meters (about 90,000 cubic feet) -- about enough water to sustain 100 average households for a month or fill seven community-sized swimming pools. The process that starts the water flowing remains a mystery, but the team believes it is not the result of volcanic heating.
"I think one of the most interesting and significant aspects of this discovery is what it could mean if human explorers ever go to Mars," said Malin. "If water is available in substantial volumes in areas other than the poles, it would make it easier for human crews to access and use it -- for drinking, to create breathable air, and to extract oxygen and hydrogen for rocket fuel or to be stored for use in portable energy sources."
"This latest discovery by the Mars Global Surveyor is a true 'watershed'--that is, a revolution that pushes the history of water on Mars into the present," said Dr. Jim Garvin, Mars Program Scientist, NASA Headquarters. "To follow up on this discovery we will continue the search with Mars Global Surveyor and its rich array of remote sensing instruments, and in 2001, NASA will launch a scientific orbiter with a high spatial resolution middle- infrared imaging system that will examine the seepage sites in search of evidence of water-related minerals.
"Furthermore, NASA is in the process of evaluating two options for a 2003 mission to Mars, both of which could provide independent information concerning the remarkable sites identified by Malin and Edgett."
The NASA "better, faster, cheaper" spacecraft known as Mars Polar Lander was last heard of as it prepared to enter Mars's atmosphere on December 3. Unfortunately, neither it nor the two probes have been heard from since, in spite of many tries to contact them. At first it was hoped that the Lander's antenna was simply misoriented or that the spacecraft was in a "safe" mode, but as the days wore on and no word was received, finally hope was lost.
Following the loss of Mars Climate Orbiter a couple of months earlier, the problem raises questions about understaffing and cutting corners as a result of the "faster, cheaper" part of NASA's current mantra. The whole Mars program will now be restudied along with an investigation of the problem with the Mars Polar Lander, and a delay of the 2001 missions to Mars may occur. It is not clear whether the current date of 2008 for the return of a sample from Mars will be changed. Since no news was received from the spacecraft, scientists and engineers have little to go on in diagnosing the problem. Future spacecraft will probably have more robust communications with Earth during the crucial periods.
A failure to recognize and correct an error in a transfer of information between the Mars Climate Orbiter spacecraft team in Colorado and the mission navigation team in California led to the loss of the spacecraft last week, preliminary findings by NASA's Jet Propulsion Laboratory internal peer review indicate.
"People sometimes make errors," said Dr. Edward Weiler, NASA's Associate Administrator for Space Science. "The problem here was not the error, it was the failure of NASA's systems engineering, and the checks and balances in our processes to detect the error. That's why we lost the spacecraft."
The peer review preliminary findings indicate that one team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit.
"Our inability to recognize and correct this simple error has had major implications," said Dr. Edward Stone, director of the Jet Propulsion Laboratory. "We have underway a thorough investigation to understand this issue."
Two separate review committees have already been formed to investigate the loss of Mars Climate Orbiter: an internal JPL peer group and a special review board of JPL and outside experts. An independent NASA failure review board will be formed shortly.
"Our clear short-term goal is to maximize the likelihood of a successful landing of the Mars Polar Lander on December 3," said Weiler. "The lessons from these reviews will be applied across the board in the future."
Mars Climate Orbiter was one of a series of missions in a long-term program of Mars exploration managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO. JPL is a division of the California Institute of Technology, Pasadena, CA.
Contact with the Mars Climate Orbiter was lost on the morning of September 23 as it went behind Mars preparatory to going into orbit. It was to go into an elongated elliptical orbit and then, through aerobraking, go into a more circular orbit. It was to act as a relay for a few months for the Mars Polar Lander, scheduled for December 23, and then to carry out a mapping mission.
MAGNETIC STRIPES PRESERVE RECORD OF ANCIENT MARS
NASA's Mars Global Surveyor has discovered surprising evidence of past movement of the Martian crust, further evidence that ancient Mars was a more dynamic, Earth-like planet than it is today.
Scientists using the spacecraft's magnetometer have discovered banded patterns of magnetic fields on the Martian surface. The adjacent magnetic bands point in opposite directions, giving these invisible stripes a striking similarity to patterns seen in the crust of Earth's sea floors. On the Earth, the sea floor spreads apart slowly at mid-oceanic ridges as new crust flows up from Earth's hot interior. Meanwhile, the direction of Earth's magnetic field reverses occasionally, resulting in alternating stripes in the new crust that carry a fossil record of the past hundreds of million years of Earth's magnetic history, a finding that validated the once-controversial theory of plate tectonics.
"The discovery of this pattern on Mars could revolutionize current thinking of the red planet's evolution," said Dr. Jack Connerney of NASA's Goddard Space Flight Center, Greenbelt, MD, an investigator on the Global Surveyor's magnetometer team. "If the bands on Mars are an imprint of crustal spreading, they are a relic of an early era of plate tectonics on Mars. However, unlike on Earth, the implied plate tectonic activity on Mars is most likely extinct."
Alternate explanations for the banded structure may involve the fracturing and breakup of an ancient, uniformly magnetized crust due to volcanic activity or tectonic stresses from the rise and fall of neighboring terrain.
"Imagine a thin coat of dried paint on a balloon, where the paint is the crust of Mars," explained Dr. Mario Acuna of Goddard, principal investigator on the Global Surveyor magnetometer. "If we inflate the balloon further, cracks can develop in the paint, and the edges of the cracks will automatically have opposite polarities, because nature does not allow there to be a positive pole without a negative counterpart."
Peer-reviewed research based on the observations were published in the April 30 issue of the journal Science.
The observations of the so-called magnetic stripes were made possible because of Mars Global Surveyor's special aerobraking orbit. This process of dipping into the upper atmosphere of Mars to gradually shape the probe's orbit into a circle was extended due to a problem with a solar panel on the spacecraft. The lowest point of each elliptically shaped orbit curved below the planet's ionosphere, allowing the magnetometer to obtain better-than- planned regional measurements of Mars.
"At its nominal orbit more than 200 miles high, the instruments face too much magnetic interference, and they do not have the resolution to detect these features," Acuna noted. "We began with misfortune, and ended up winning the lottery."
The bands of magnetized crust apparently formed in the distant past when Mars had an active dynamo, or hot core of molten metal, which generated a global magnetic field. Mars was geologically active, with molten rock rising from below cooling at the surface and forming new crust. As the new crust solidified, the magnetic field that permeated the rock was "frozen" in the crust. Periodically, conditions in the dynamo changed and the global magnetic field reversed direction. The oppositely directed magnetic field was then frozen into newer crust.
"Like a Martian tape recorder, the crust has preserved a fossil record of the magnetic field directions that prevailed at different times in the ancient past," Connerney said. When the planet's hot core cooled, the dynamo ceased and the global magnetic field of Mars vanished. However, a record of the magnetic field was preserved in the crust and detected by the Global Surveyor instrument.
The mission's map of Martian magnetic regions may help solve another mystery -- the origin of a striking difference in appearance between the smooth, sparsely cratered northern lowlands of Mars and the heavily cratered southern highlands. The map reveals that the northern regions are largely free of magnetism, indicating the northern crust formed after the dynamo died.
"The dynamo likely died a few hundred million years after Mars' formation. One possibility is that later asteroid impacts followed by volcanic activity heated and shocked large areas of the northern crust, obliterating any local magnetic fields and smoothing the terrain," Acuna said. "When the crust cooled, there was no longer a global magnetic field to become frozen in again."
The map also identifies an area in the southern highlands as the oldest surviving unmodified crust on Mars. This area on Mars is where the magnetic stripes are most prominent. The bands are oriented approximately east-to-west and are about 100 miles wide and 600 miles long, although the longest band stretches more than 1,200 miles.
"The bands are wider than those on Earth, perhaps for a couple of reasons," Connerney said. "The Martian crust could have been generated at a greater rate, causing a given magnetic field to be imprinted over a wider area before it reversed direction. Second, the Martian magnetic field may have reversed direction less frequently, which would have given more time for any one field direction to imprint itself in the steadily moving crust, resulting in wider bands.
"In order to call this pattern a crustal spreading center like that observed in the mid-oceanic ridges on Earth, we need to find a point of symmetry, where the pattern on one side matches the pattern on the other. We have not yet found evidence of this type of symmetry," Connerney added.
NASA's Mars Global Surveyor spacecraft will begin its primary mapping mission within the next two weeks, following a successful firing of its main engine on Feb. 19 to fine-tune its path around the red planet into a nearly circular, Sun-synchronous orbit.
The final "transfer to mapping orbit" burn lowered Global Surveyor's closest approach over Mars from 253 miles (405 kilometers) to approximately 229 miles (367 kilometers). Later this week, the flight team will turn on, focus and calibrate the spacecraft's camera and power up several other science instruments, including the thermal emission spectrometer and laser altimeter.
"Reaching our mapping orbit has been a long time coming for all involved. We are delighted to finally be able to do this mission as it was designed, in the proper mapping orbit with all the instruments working at their full potential," said Dr. Arden Albee, the Mars Global Surveyor project scientist at the California Institute of Technology, Pasadena, CA.
The mapping orbit was designed so that Surveyor passes over a given part of Mars at the same local time each orbit. At about 2 p.m. local Mars time, the spacecraft will cross the equator flying northward on the daytime side and about 2 a.m., it will cross the equator flying southward on the nighttime side. This timing is essential for effective interpretation of atmospheric and surface measurements, because it allows scientists to separate local daily variations from longer-term seasonal and annual trends.
"We still have a few minor adjustments to fine-tune the orbit during the next few weeks. Our plan at this point is to conduct the first three one-week mapping cycles with Surveyor's high-gain communication antenna in the stowed position. After we have these first mapping cycles completed, we plan to deploy the antenna and continue mapping in that configuration," said Glenn E. Cunningham, deputy director of the Mars Exploration Program at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
Launched in November 1996 and in Mars orbit since September 1997, Mars Global Surveyor carries a dish-shaped high-gain antenna that will be deployed on a 6.6-foot-long boom. The antenna was stowed during launch and the early orbital phase at Mars to reduce the chances of its being contaminated by the exhaust plume from the spacecraft's main engine.
During deployment, the boom is pushed outward by a powerful spring. A damper mechanism cushions the force of the spring and limits the speed of the deployment, somewhat like an automobile shock absorber or the piston-like automatic closer on a screen door. Last year, engineers became aware of problems with similar damper devices on deployable structures such as solar panels on other spacecraft.
"Until we deploy the antenna, we must turn the entire spacecraft periodically to transmit data to Earth," Cunningham explained. "This means that we have to stop acquiring science data. The advantage of deploying the high-gain antenna is that we can then use its gimbals to point the antenna at Earth and send science data back at the same time the instruments are pointed at Mars."
The first phase of the primary mapping mission is scheduled to begin on March 8. The deployment of high gain antenna is currently scheduled for March 29, pending approval by NASA Headquarters officials in mid-March.
Mars Global Surveyor is the first mission in a long-term program of Mars exploration known as the Mars Surveyor Program that is managed by JPL for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology.
Further information about the mission, including a link to the "Top 10" images of Mars returned by Global Surveyor so far, is available on the Internet at:
http://mars.jpl.nasa.gov/mgs/index.html
The Japanese Nozomi probe to Mars won't get to Mars until the end of 2003
or the beginning of 2004. A swing-by of the Earth, meant to take it out of Earth
orbit, failed in early 1999, and now Nozomi must orbit the sun three times before
trying another swing-by. Once at Mars, Nozomi will be in orbit for two years
to analyze Mars's atmosphere.
[based on information from Nature, 21 January 1999, 397, p. 193]
NASA's Mars Global Surveyor spacecraft will soon begin its primary mapping mission after it successfully fired its main rocket engine early this morning and raised its orbit completely out of the Martian atmosphere to end the aerobraking phase of the mission.
The burn was executed at 12:11 a.m. Pacific time when the flight team determined that the farthest point in the spacecraft's orbit had dropped to 450 kilometers (279 miles) above the Martian surface. During the next two weeks, the spacecraft's closest approach to Mars will slowly drift south until it has moved into a circular Sun-synchronous orbit, in which the spacecraft will cross the Martian equator at about 2 a.m. local solar time.
The start of the primary mapping mission has been delayed by about a year due to a structural problem with the spacecraft's solar panel that required the flight team to take a more cautious approach to aerobraking to ensure that the weakened panel was not overstressed.
In addition to making a photographic map of the entire planet during one full Martian year (687 Earth days), Mars Global Surveyor will study the planet's topography, magnetic field, mineral composition and atmosphere.
"Global Surveyor will become our first weather satellite at Mars. During the extended aerobraking phase, the spacecraft was able to acquire some "bonus" science data that has yielded some spectacular new findings about Mars. We now have a profile of the planet's northern polar cap and information about the unique nature of its remnant magnetic fields," Cunningham said.
During the aerobraking technique, the spacecraft uses frictional drag as it skims through the planet's thin upper atmosphere to alter the shape of its orbit around the planet. First tested in the final days of the Magellan mission to Venus in 1994, the technique is an innovative way of changing the spacecraft's orbit while carrying less onboard fuel.
When Global Surveyor arrived at Mars in September 1997, it initially entered a looping, elliptical orbit around the planet that has been gradually circularized through aerobraking. Its winged solar panels -- which feature a Kapton flap at the tip of each wing for added drag -- supply most of the surface area that slowed the spacecraft by a total of more than 1,200 meters per second (about 2,700 miles per hour) during the entire aerobraking phase. Since the start of aerobraking, Surveyor's orbit around Mars has shrunk from an initial elliptical orbit of 45 hours to the now nearly circular orbit taking less than two hours to complete.
Flight controllers will again fire the spacecraft's main engine on February 18 and perform a final "transfer to mapping orbit" burn, which will lower Global Surveyor's closest approach over Mars from 405 kilometers (253 miles) to approximately 379 kilometers (237 miles). After a short period of calibrating the science instruments, mapping will begin in early March.
After a one-day delay, NASA's Mars Climate Orbiter blasted off launch pad 17A at Cape Canaveral Air Station, FL, at 1:45 p.m. Eastern Standard Time today and hurtled skyward on a 9-1/2- month flight to Mars to embark on a study of the planet's climate and current water resources. The 24-hour launch delay will not change the spacecraft's arrival date at Mars on September 23, 1999, or alter its primary mapping mission.
The spacecraft shot through a breezy, cloud-laced midafternoon sky atop a Delta II launch vehicle on the second day of the primary launch period with new onboard software to guard against overcharging the spacecraft's battery. The orbiter team tested the new software using the Mars Polar Lander spacecraft at Kennedy Space Center, FL, as a testbed. Mars Polar Lander, which will join Mars Climate Orbiter at Mars in December 1999, is currently being processed for launch on January 3, 1999.
Sixty seconds after liftoff, the four solid-rocket boosters were jettisoned, two at a time, followed by first-stage separation and second-stage engine ignition. The second-stage burn lasted approximately 11 minutes, 22 seconds, placing the spacecraft in a low-Earth orbit at about 189 kilometers (117 miles) above Earth's surface.
Third-stage separation occurred at approximately 2:26 p.m. EST, followed by a burn of the third-stage engine for 88 seconds. Once out of Earth's gravitational grasp, the orbiter was jettisoned from the third stage using the spacecraft's onboard thrusters to remove all remaining motion. Four minutes later, the spacecraft's solar arrays were unfolded and pointed toward the Sun for power. NASA's Deep Space Network complex near Canberra, Australia, acquired the orbiter's signal at 2:45 p.m. EST. Spacecraft controllers at Lockheed Martin Astronautics in Denver, CO, and at the Jet Propulsion Laboratory in Pasadena, CA, are now assessing the spacecraft's initial performance.
Now on its way to Mars, the Climate Orbiter will rely on its low-gain and medium-gain antennas for communications with Earth during the first half of the journey to Mars. Ground-controllers will track the spacecraft 24 hours a day during the first week of cruise, then reduce tracking time to 12 hours a day using 34- meter (112-foot) antennas of the Deep Space Network. Twelve days into flight, one of the spacecraft's science instruments, the Pressure Modulator Infrared Radiometer, will be powered on and acclimated to the environment of space.
The first trajectory correction maneuver to remove errors in the spacecraft's flight path introduced at the time of launch will be performed 10 days into the cruise phase, on December 21, 1998. That thruster firing will be the largest and longest of all four trajectory correction maneuvers, lasting about 15 to 20 minutes and changing the spacecraft's velocity by about 30 meters per second (67 miles per hour).
Mars Climate Orbiter and Mars Polar Lander are the second set of spacecraft to be launched in NASA's long-term program of robotic exploration of Mars.
NASA's Mars Global Surveyor has captured some spectacular new views of Olympus Mons, the largest volcano in the solar system, and a system of giant channels on the red planet known as Kasei Vallis.
The new images are available on the Internet at
http://www.jpl.nasa.gov, http://photojournal.jpl.nasa.gov/
and at http://www.msss.com.
Taken on April 25, 1998, from a distance of about 900 kilometers (560 miles) above the surface, this wide-angle image of Olympus Mons captures the west side of the volcano on a cool, crisp winter morning. Olympus Mons is by far the tallest volcano in the solar system, rising higher than three Mount Everests and spanning the width of the entire Hawaiian island chain.
The images of Kasei Vallis, a system of giant channels thought to have been carved by catastrophic floods more than a billion years ago, illustrate the complexity of the planet's geologic history. These images were acquired on June 4, 1998, and reveal details of the 6-kilometer-diameter (4-mile) crater as it pokes out from beneath an "island" in the valley. The mesa was created in part by the flood and by its subsequent retreat, which caused small landslides of the scarp that encircles it. A "mote" or trench partly encircles the crater to the west and south. This moat formed were the turbulence of the floodwaters interacting with the crater rim eroded material in front of and alongside the crater.
When Mars Global Surveyor reaches its final mapping orbit in March 1999, the spacecraft's camera will be used to make daily global maps of Martian clouds and weather systems. The wide-angle images will resemble weather satellite pictures of Earth and will help the Mars Global Surveyor science teams plan their observations and test computer-driven prediction models of Martian weather.
New temperature data and close-up images of the Martian moon Phobos gathered by NASA's Mars Global Surveyor indicate the surface of this small body has been pounded into powder by eons of meteoroid impacts, some of which started landslides that left dark trails marking the steep slopes of giant craters.
New temperature measurements show the surface must be composed largely of finely ground powder at least one meter (three feet) thick, according to scientists studying infrared data from the thermal emission spectrometer instrument on the spacecraft. Measurements of the day and night sides of Phobos show such extreme temperature variations that the sunlit side of the moon rivals a pleasant winter day in Chicago, while only a few kilometers away, on the dark side of the moon, the climate is more harsh than a night in Antarctica. High temperatures for Phobos were measured at -4 degrees Celsius (25 degrees Fahrenheit) and lows at -112 Celsius (-170 degrees Fahrenheit).
The extremely fast heat loss from day to night as Phobos turns in its seven-hour rotation can be explained if hip-deep dust covers its surface, said Dr. Philip Christensen of Arizona State University, Tempe, principal investigator for the experiment on the Mars Global Surveyor spacecraft.
"The infrared data tells us that Phobos, which does not have an atmosphere to hold heat in during the night, probably has a surface composed of very small particles that lose their heat rapidly once the Sun has set," Christensen said. "This has to be an incredibly fine powder formed from impacts over millions of years, and it looks like the whole surface is made up of fine dust."
New images from the spacecraft's Mars orbiter camera show many never-before seen features on Phobos, and are among the highest resolution ever obtained of the Martian satellites. A 10-kilometer-diameter (six-mile) crater called Stickney, which is almost half the size of Phobos itself, shows light and dark streaks trailing down the slopes of the bowl, illustrating that even with a gravity field only about 1/1000th that of the Earth's, debris still tumbles downhill. Large boulders appear to be partly buried in the surface material.
Infrared measurements of Phobos were made on August 7, 19 and 31 from distances ranging between 1,045-1,435 kilometers (648-890 miles), far enough away to capture global views of the Martian moon in a single spectrum. The instrument has been able to obtain the first global-scale infrared spectra of Earth and Mars in addition to the new Phobos data, bringing new insights about the composition of these three very different worlds.
"Of the three, Earth has the most complex infrared spectra, primarily due to the presence of carbon dioxide, ozone and water vapor in its atmosphere," Christensen said. "Mars, which is much colder than Earth because of its distance from the Sun, is less complex and shows only significant amounts of carbon dioxide. The spectrum of Phobos, however, has little structure because it has no atmosphere and the energy it emits is coming entirely from its surface."
NASA has downgraded the rover from its 2001 Mars mission from a long-distance wanderer (100 km path) gathering rocks to a local vehicle that will not gather samples. But international cooperation is rejuvenating the Mars program. For example, the Italian space agency may supply a communication satellite in Mars orbit relaying data back to Earth, and a 2003 launch of an Italian-American Mars radar to search for sub-Mars-surface water. France is to provide a 2005 launch on its Ariane 5 rocket for the sample-return mission and the Mars-orbiting spacecraft to receive the samples. [reference: Nature, 20 August 1998, p. 713]
Japan's Planet-B spacecraft to Mars, named Nozomi, was launched successfully on July 4, a date chosen to match the anniversary of the US's Mars Pathfinder. It carries 14 instruments from Japan, Canada, Sweden, Germany, and the United States. The spacecraft is orbiting the Earth for 5 months and then will travel to Mars, with arrival expected for October 1999. The spacecraft is a Mars orbiter.
PASADENA-Despite a 12-month delay in aerobraking into a circular orbit, the Mars Global Surveyor is already returning a wealth of data about the atmosphere and surface of the Red Planet. According to mission scientist Arden Albee of the California Institute of Technology, all scientific instruments on the Mars probe are fully functioning and providing good data. Early results from data collected during the 18 elliptical orbits in October and November are being reported in this week's issue of Science. "For the first time, a spacecraft has captured the start of a major dust storm on Mars and has followed it through its development and demise," Albee says. "Also, we've received a number of narrow-angle high-resolution images that are enough to put any planetary geologist into a state of ecstasy." These accomplishments are especially noteworthy when considering that the probe developed a glitch when it first began tightening up its orbit last September. For various reasons having to do with design and cost, Global Surveyor was set on a course that took it initially into a huge sweeping elliptical orbit of Mars. On its near approach in each orbit, the probe was to dip into the upper atmosphere of Mars in a maneuver known as "aerobraking," which would effectively slow the probe down and eventually place it into a near-circular orbit. But a solar-panel damper failed early in the mission, and damage to the solar panel forced the team to slow down the aerobraking. At the current rate of aerobraking, Mars Global Surveyor will enter its circular mapping orbit in March 1999.
This has delayed the systematic mapping of Mars, but Albee says that the new mission plan nonetheless permits the collection of science data in a 12-hour elliptical orbit, from March to September of this year. "Another exciting discovery is that the Martian crust exhibits layering to much greater depths than would have been expected," Albee says. "Steep walls of canyons, valleys, and craters show the Martian crust to be stratified at scales of a few tens of meters. "At this point, it is simply not known whether these layers represent piles of volcanic flows or sedimentary rocks that might have formed in a standing body of water," he adds.
The Mars Global Surveyor team has previously announced that the on-board magnetometer shows Mars to have a more complex magnetic field than once thought. Of particular interest is the fact that the magnetic field was apparently once about the same strength as that of present-day Earth. Many experts think that a strong magnetic field may be crucial for the evolution of life on a planet. Without a magnetic field, a planet tends to have any existing atmospheric particles blasted away by cosmic rays in a process known as "sputtering."
And finally, the Mars Orbiting Laser Altimeter (MOLA) has already sent back 18 very good topographic profiles of the northern hemisphere. "Characterization of these features is leading to a new understanding of the surface processes of Mars," Albee says. [Note to editors: Additional information and color images may be obtained from JPL. For these, please contact Diane Ainsworth at (818) 354-0850]
Contact: Robert Tindol
(818) 395-3631
tindol@caltech.edu
ITHACA, N.Y. -- After studying more than 9,500 images taken during the acclaimed Mars Pathfinder mission, scientists report in today's journal Science (Dec. 5) that surface photographs provide strong geological and geochemical evidence that fluid water was once present on the red planet.
"We now have geological evidence from the Martian surface supporting theories based on previous pictures of Mars from orbit that water played an important part in Martian geological history," said James F. Bell, Cornell senior research associate in astronomy and a member of the Mars Pathfinder imaging team.
Bell, along with lead author P. H. Smith of the University of Arizona; Robert J. Sullivan Jr., Cornell research associate in planetary science; and 23 other scientists authored the paper, "Results from the Mars Pathfinder Camera." The report is part of a complete Mars Pathfinder mission report published in Science.
During the first 30 days of the Mars Pathfinder mission, the Imager for Mars Pathfinder (IMP) returned 9,669 pictures of the surface. These pictures appear to confirm that a giant flood left stones, cobbles and rocks throughout Ares Vallis, the Pathfinder landing site. In addition to finding evidence of water, the scientists confirmed that the soils are rich in iron, and that suspended iron-rich dust particles permeate the Martian atmosphere.
Bolstering their evidence for once-present water, the imaging team found evidence for a mineral known as maghemite -- a very magnetic iron oxide. Bell explained that maghemite forms in water-rich environments on Earth and could likely be formed the same way on Mars. Bell explained that reddish rocks like Barnacle Bill, Yogi and Whale rock show evidence of extensive oxidation on their surfaces. He said the oxidation -- or the rusting of the iron -- is possible only if water existed on the surface at some time and played an important role in the geology and geochemistry of the planet.
But, where did all the water go?
"That's the golden question. No one knows," said Bell, explaining that several theories about the disappearing water exist, such as evaporation into space, or seepage into sub-surface ice deposits or liquid aquifers, or storage at the Martian poles. Bell said that robotic missions to Mars early in the next century, including a Cornell-led rover mission to be launched in 2001, will attempt to determine the water's whereabouts, as well as to determine whether the Martian environment may once have been more conducive to life.
Mars Pathfinder's camera also revealed that Mars' atmosphere is more dusty and dynamic than expected, Bell explained. Surprisingly, the scientists found wispy, blue clouds, possibly composed of carbon dioxide (dry ice), traveling through Mars' salmon-colored sky. White cirrus-like clouds, made of icy water vapor, also circulate throughout the thin Martian atmosphere.
"We were surprised to see such variations in the clouds, particularly since Mars has such a thin atmosphere," Bell said. "We figured the atmosphere would be the same everyday, but there is a lot of real weather occurring there. It's a small atmosphere, but a vigorous one."
Looking at Martian rocks like Yogi, Barnacle Bill and Scooby Doo reveals that the rocks have been sitting on the planet's surface for billions of years, enduring a slow-motion sandblasting from a usually weak, dusty Martian wind. To carve rock with such a weak wind force requires a vast amount of time, Bell explained.
"The slow, persistent weathering and erosion of the rocks is like water torture to the max," he said. "Mars really is an ancient world. We're still trying to sort it all out."
Mars Global Surveyor's first look at Mars is showing scientists a world devoid of an active core and anything more than the relic of an ancient magnetic field.
"Mars no longer has a global magnetic field generated by an internal energy source, like Earth and the other planets," said Dr. Jack Connerney, co-investigator of the magnetometer/electron spectrometer team, at an Oct. 2 Mars Global Surveyor press briefing at NASA's Jet Propulsion Laboratory. "It appears that the crust of Mars is strewn with multiple magnetic anomalies, which may represent the solidification of magma as it was coming up through the crust and cooling very early in Mars' evolution, but this is only the memory of a magnetic field."
Mars Global Surveyor went into orbit around Mars on Sept. 11 after a 10-month journey to the planet, and detected the presence of a weak magnetic field within a week of its arrival. Evidence of this faint magnetic field confirmed long-standing theories that the red planet had, at one time in its history, a liquid core able to support a dynamo. Scientists believe this core probably froze and solidified early in the planet's evolution.
The magnetometer data, acquired during one of the spacecraft's highly elliptical orbits around Mars during the week of Sept. 15-18, indicates that the planet's magnetic field is not globally generated in the planet's core, but is localized in particular areas of the crust, said Dr. Daniel Winterhalter, magnetometer experiment representative at JPL. Scientists plan to correlate these strong magnetic anomalies with topographical data obtained by Global Surveyor's camera and laser altimeter. That information may lead to the identification of particular topographic features in the crust.
"The identification of these magnetic anomalies and their correlation with surface features may enable us to trace the history of the planet's interior, just as we are able to trace the history of Earth's interior using the magnetic anomalies that have been imprinted on the ocean floors," Winterhalter said.
Mars' very localized field also creates a new paradigm for the way in which it interacts with the solar wind, one that is not found with other planets. While Earth, Jupiter and other planets have large magnetospheres, and planets like Venus have strong ionospheres, Mars' small, localized magnetic fields are likely to produce a much more complicated interaction process as these fields move with the planet's rotation.
These observations and many more came just as the spacecraft finished the walk-in phase of aerobraking and was about to begin the main phase, which will last three months. All six of the spacecraft's science instruments had been turned on midway through the elliptical walk-in phase for calibration and engineering adjustments. Since its capture, the spacecraft's orbit has been reduced from 45 hours to 40 hours, 20 minutes. Through January 1998, the aerobraking and navigation teams will gradually circularize Surveyor's orbit into the final two-hour, 378-kilometer (234-mile) mapping orbit.
"The spacecraft and science instruments are operating magnificently," reported Dr. Arden Albee, of the California Institute of Technology, Pasadena, CA, who is the Mars Global Surveyor project scientist. "The initial science data we've obtained from the walk-in phase of aerobraking are remarkable in their clarity, and the combined measurements from all of the instruments over the next two years are going to provide us with a fascinating new global view of the planet."
Mars Global Surveyor carries six science instruments -- a camera, laser altimeter, magnetometer/electron reflectometer, thermal emission spectrometer and ultra-stable oscillator -- that will paint a global portrait of Mars, gathering data on the planet's atmosphere, surface and interior. The mission will enable scientists to determine Mars' current state and some of the major turning points in its evolution. Among a myriad of science objectives, Global Surveyor will study Mars' climate and its resources, and attempt to determine if life ever existed on the planet.
During the past three weeks, the spacecraft has been aerobraking through the upper atmosphere of Mars each time it passes closest to the surface. Aerobraking operations are continuing to proceed smoothly. The spacecraft has completed 12 revolutions around Mars, including nine aerobraking passes through the upper Martian atmosphere, said Dr. Richard Zurek, an investigator at JPL who is leader of the Mars Global Surveyor atmospheric advisory team. Each of these atmospheric passes takes place at the start and low point of the orbit, known as the periapsis, as Global Surveyor orbits at current altitudes of about 110 kilometers (70 miles).
. So far, the upper atmospheric density has varied according to daytime and nighttime measurements by as much as 70 percent, said Dr. Gerald Keating, on the atmospheric advisory team from George Washington University, Washington, DC, and densities are five times higher than they were when the Mars Pathfinder spacecraft entered the upper atmosphere on July 4. Density profiles are being acquired on a daily basis and used to help guide the aerobraking team's work to shrink and circularize the spacecraft's orbit. Although the thickness of the Martian atmosphere continues to run slightly higher than predicted, no major changes to the aerobraking strategy are being considered because the spacecraft was designed to tolerate up to a 70 percent increase in atmospheric thickness.
The first orbital images of the Martian surface in more than 20 years are showing geologic features that would dwarf some of the most spectacular features known to Earth. Initial science data show a canyon far deeper than Arizona's 1-mile-deep Grand Canyon and mountains standing much taller than Nepal's Mt. Everest. Vast expanses of smooth crustal flatlands in the northern hemisphere hint at a geologically younger portion of Mars, while new measurements of the planet's southern polar cap indicate drastically frigid temperatures of about minus 129 degrees Celsius (200 degrees Fahrenheit).
Mars Global Surveyor's camera revealed two regions of interest to geologists: a view of a highland valley network called Nirgal Vallis and an image of Labyrinthus Noctis, an area west of the Valles Marineris near the crest of a large updoming in the Martian crust. The images were presented by Dr. Michael Malin, of Malin Space Science Systems Inc., San Diego, CA, who is the principal investigator of the Mars Global Surveyor camera.
Nirgal Vallis is about 15 kilometers (9 miles) across by about 45 kilometers (27 miles) in length, with many small sand dunes and different aged craters in the vicinity, Malin said. The valley is located at 28.5 degrees south latitude, 41.6 degrees west longitude. Of interest to scientists are the processes that helped shape this canyon.
"The origin of this and many other canyons on Mars has been debated ever since the Mariner 9 mission," Malin said. "There are two leading theories: the first suggests that water flowing over the surface accumulated, as it does on Earth, then formed a drainage basin that allowed the water to flow further down into a larger channel. The alternative explanation was that ground water processes dissolved part of the subterranean materials on Mars, causing collapse and progressive deterioration of this particular region."
Labyrinthus Noctis, the second image presented Oct. 2, is near the crest of a large updoming of the Martian crust that is probably thousand of kilometers in diameter, and near very large, 2,000-meter-deep (6,500-foot) canyons bounded by faults. Debris shed from the steep slopes has moved down into the region after the canyons opened. Small dunes are seen in the lower portion of this area, beneath the high cliffs.
Global Surveyor's camera has acquired about a dozen high resolution images of Mars to date, which are being used to fine- tune the instrument in preparation for the start of mapping operations in March 1998. These first images were not the highest resolution expected during mapping because the spacecraft is not yet in the proper mapping orbit and the correct sunlight conditions have not yet been reached, Malin said. As the spacecraft moves into its Sun-synchronous orbit, in which it will cross the Martian equator at 2 p.m. local Mars time during each revolution, the Sun will be at a standard angle above the horizon in each image.
The spacecraft's thermal emission spectrometer recorded sub- freezing temperatures at the southern polar cap, said principal investigator Dr. Philip Christensen of Arizona State University, Tempe. The instrument, which takes infrared measurements on the surface, also recorded temperature highs of about -7 C (20 F) at the warmest parts of the planet and a very clear, dust-free atmosphere.
The laser altimeter, which fires 10 laser pulses a second at the surface, is also performing well, reported Dr. David Smith, principal investigator of the instrument and based at the NASA Goddard Space Flight Center, Greenbelt, MD. This experiment will measure the height of Martian surface features and provide elevation maps that will be precise to within 30 meters (98 feet) of surface features. From the 12,000 measurements already taken, Smith reported a notable inaccuracy in the location of some Martian features as shown on current maps based on Viking data. Global Surveyor will provide a much more accurate global map which will be used to guide future missions to the surface.
Additional information about the Mars Global Surveyor mission is available on the World Wide Web by accessing JPL's Mars news site at http://www.jpl.nasa.gov/marsnews or the Global Surveyor project home page at http://mars.jpl.nasa.gov .
Mars Global Surveyor is the first in a sustained program of Mars exploration, known as the Mars Surveyor Program. The mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology, Pasadena, CA.
NASA's Mars Global Surveyor, the first in a series of orbiters and landers to explore Mars in the next decade, performed a critical engine burn this evening and successfully entered orbit around the red planet.
The spacecraft executed a 22-minute engine burn at 01:17 Universal Time (6:17 p.m. Pacific Daylight Time) and slowed its speed by more than 3,200 kilometers per hour (2,000 miles per hour) to be captured in Martian orbit. (Because radio signals traveling at the speed of light take 14 minutes, 6 seconds to reach Earth from Mars, the start of the engine burn was detected by ground controllers at 6:31 p.m. PDT.) Doppler data after the burn indicated that the spacecraft is now in a highly elliptical orbit which takes it within about 250 kilometers (155 miles) of Mars at its closest point and about 56,000 kilometers (34,800 miles) at the most distant.
Global Surveyor is the first U.S. spacecraft to orbit Mars in more than 20 years and the first to use aerobraking rather than propulsive maneuvers to adjust its orbit upon arrival. The technique was demonstrated during the final months of the Magellan mission to Venus in the summer of 1993, and found to be a plausible design for circularizing a spacecraft's orbit while saving fuel.
Global Surveyor has arrived at Mars during fall in the northern hemisphere and spring in the southern hemisphere, which usually coincides with the start of the dust storm season. Although dust storms are a concern for the navigation team, the spacecraft will be able to raise its orbit and fly over these storms if it becomes necessary. Data from the surface of Mars, furnished by the highly successful Mars Pathfinder lander and rover mission, in addition to data from the orbiting Hubble Space Telescope and the National Radio Astronomy Observatory microwave antenna in Boulder, CO, will assist the Mars Global Surveyor team as they begin to dive into the upper atmosphere and understand the dynamics of the Martian environment.
Mars Global Surveyor will complete three revolutions around Mars in its initial, highly elliptical orbit, and gather some science data. On September 17, the spacecraft will perform its first aerobraking maneuver. Each time the spacecraft reaches the farthest point in its orbit around Mars--known as the apoapsis--it will perform an engine burn to trim the orbit. After four engine burns at apoapsis -- on September 17, 20, 22 and 24 -- Global Surveyor's orbit will be reduced to about three hours, meaning the spacecraft will be completing one revolution around Mars about every three hours.
During the next three months, the navigation team will continue to fine-tune the spacecraft's apoapsis and periapsis, or farthest and closest points over Mars, respectively. In January 1998, the navigation team will begin three weeks of final orbital adjustments. Then the science instruments will be turned on around March 10 and the mapping mission will begin on March 15, 1998.
Additional information and periodic updates at http://www.jpl.nasa.gov/marsnews or at the Global Surveyor project home page
Two new websites for the Mars probes:
Mars Global Surveyor
Mars Pathfinder
