The following new images taken by the Mars Global Surveyor spacecraft are now available:
The images reside on the Mars Global Surveyor website.
Ron Baalke
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Flight controllers for NASA's Mars Global Surveyor mission are continuing to work toward isolating what caused a hinge on the spacecraft's high-gain telecommunications antenna to stop moving last week.
This afternoon, engineers received the results of a test they conducted earlier in the day that moved the hinge one-half of a degree from side to side. The information from the spacecraft shows that the hinge moves freely in one direction, but it's motion appears to be obstructed in the opposite direction. The tests are designed to help engineers determine if the obstruction is internal to the motor mechanism, or external, such as a thermal blanket or cable obstruction. Flight controllers continue to analyze the test results and will send additional commands to the spacecraft tomorrow that will attempt to move the hinge a little bit more -- one full degree -- in each direction.
The spacecraft remains in good health and the science instruments are turned off while engineers continue to define the hinge.
There are two hinges at the end of the boom that connect to the high-gain antenna. One hinge, called the azimuth hinge, moves the antenna from side to side; the other hinge, called the elevation hinge, moves the antenna up and down. The azimuth hinge stopped moving midway between its "parked" position and the position its in when it is transmitting data to Earth.
Mars Global Surveyor 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.
SPACEMAIL
April 20, 1999
The antenna can still be used even if the hinge doesn't work. But that requires periodically halting the collection of science data and turning the entire spacecraft to point the antenna at Earth.
The spacecraft put itself into a so-called contingency mode when the problem occurred, shutting down all science instruments and shifting communication with flight controllers to its smaller antenna.
Sometime Monday engineers planned to command Mars Global Surveyor to transmit recorded data they hope would reveal what was happening on the spacecraft when the hinge stopped moving.
The spacecraft was launched in November 1996 and has been orbiting Mars since September 1997 as part of a mapping mission of Earth's neighboring planet.
The hinge is one of two at the end of a boom on which the main antenna is mounted. One allows the antenna to move from side to side. The other one, which moves the antenna up and down, is the one that became stuck.
The hinges were designed to allow the antenna to keep pointing at Earth during communications sessions while the orbiting spacecraft keeps its instruments pointed at Mars to collect a continuous stream of images and data for mapping.
Engineers do not believe the problem is related to the March 28 deployment of the boom because the hinge had functioned properly since then.
Deployment of the boom from the folded position it had been in since the launch was a concern because of worries that a device to cushion the force would not work properly.
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
NASA's Mars Global Surveyor spacecraft executed an automatic response to place itself in a "contingency" mode last night after a hinge that allows the spacecraft's high-gain telecommunications antenna to point toward Earth stopped moving as planned.
When the spacecraft is in a contingency mode, it shuts down all the science instruments and initiates communications with flight controllers through its smaller low-gain antenna. Contingency mode is an intermediate step that is not as severe as when a spacecraft goes into a so-called "safe" mode.
Flight controllers at JPL in Pasadena, CA, and Lockheed Martin in Denver, CO are in the process of diagnosing the problem to determine when the antenna stopped moving. This diagnostic process will continue throughout the weekend.
There are two hinges at the end of the boom that connect to the high-gain antenna. One hinge, called the azimuth hinge, moves the antenna from side to side; the other hinge, called the elevation hinge, moves the antenna up and down. The azimuth hinge appears to have stopped moving midway between its "parked" position and its "earth-tracking" position.
The on-board sequence commands the hinge to the "earth- tracking" position before the daily communications downlink. At the end of the communication session the sequence commands the hinge to the "parked" position to minimize the gravity force on the antenna.
The hinge has functioned as planned since the antenna deployment on March 28, indicating to project engineers that the problem is not related to that event.
Mars Global Surveyor began its full-scale, two-year mapping mission of the red planet on March 9.
In its deployed and steerable position, the high-gain antenna allows the spacecraft to simultaneously make measurements of Mars and communicate with Earth without turning the spacecraft. Information from the science instruments are recorded 24 hours per day on solid-state recorders onboard the spacecraft. Then the data are transmitted to Earth once a day, during a 10-hour tracking pass over a Deep Space Network antenna.
Mars Global Surveyor 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 is on the Internet.
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
March 29, 1999
"Having a deployed, steerable high-gain antenna is like switching from a garden hose to a fire hose in terms of data return from the spacecraft," said Joseph Beerer, flight operations manager for Mars Global Surveyor at NASA's Jet Propulsion Laboratory.
"Up until now, we have been using the high-gain antenna in its stowed position, so periodically during the first three weeks of our mapping mission, we had to stop collecting science data and turn the entire spacecraft to transmit data to Earth," Beerer explained. "Now that the high-gain antenna is deployed and steerable, we have the ability to simultaneously study Mars and communicate with Earth."
The antenna was deployed at about midnight EST, Sunday, March 28. It had been stowed since launch in November 1996 to reduce its chances of being contaminated by exhaust from the spacecraft's main engine, which was fired periodically throughout the mission. The spacecraft entered orbit around Mars in September 1997 and used a technique called aerobraking to gradually lower the spacecraft's altitude to the desired orbit for mapping. The mapping mission began March 9; full-scale mapping begins April 4.
Because engineers were uncertain that a device intended to dampen the force of the deployment would work correctly, engineers used the antenna in its stowed configuration for the first three weeks of mapping. This allowed the team to meet the mission's minimum science objectives before risking the antenna deployment.
Last night, the dish-shaped high-gain antenna, 5 feet in diameter, was deployed on a 6.6-foot-long boom and was pushed outward from the spacecraft by a powerful spring. The suspect dampening device worked as it should have, cushioning the force of the spring and limiting the speed of the deployment, similar to the automatic closer on a screen door. With the antenna successfully deployed, Mars Global Surveyor will return a nearly constant stream of observations of Mars for the next two years.
Information from the science instruments is recorded 24 hours a day on solid state recorders on board the spacecraft. Once a day, during a 10-hour tracking pass over a Deep Space Network antenna, the data are transmitted to Earth. In addition, every third day a second tracking pass is used to transmit data "live" at a very high rate directly to Earth without being put on the recorder. These data, which will contain high-resolution images of Mars, will be transmitted at rates between 40,000 and 80,000 bits per second.
Mars Global Surveyor is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. Lockheed Martin Astronautics of Denver developed and operates the spacecraft. The Jet Propulsion Laboratory is a division of the California Institute of Technology.
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
The Mars Global Surveyor spacecraft successfully began its prime mapping mission at 4 p.m. Pacific time March 8, 1999.
The spacecraft is executing a sequence of commands with its high-gain antenna in a fixed position. During this sequence, Global Surveyor records science data for nine orbits (about 18 hours) when all the instruments are pointed at Mars and then spends three orbits (about six hours) pointed at Earth playing back the data. The playbacks occur roughly between 9 a.m. and 3 p.m. Pacific time each day.
During the playback orbits, the flight team can receive data from Global Surveyor only when the spacecraft is in view of Earth. For about half of each orbit, there is no communication with the spacecraft because it is behind Mars and out of view. The data, when received on the ground, are one day old. For example, the data being returned today were recorded between 4 p.m. Pacific time on Monday and 9 a.m. Pacific time on Tuesday.
New images from Global Surveyor taken during last week's camera calibration will be released each day for the rest of this week. Starting next week, new images from the mapping phase will be posted to the Internet on Tuesdays and Thursdays. The images are available at:
http://www.msss.com/mars/global_surveyor/camera/images/index.html
and
http://photojournal.jpl.nasa.gov
There will be no new images during the week of March 29 when
the deployment of the spacecraft's high gain antenna is scheduled
to occur.
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
February 20, 1999
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.
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
October 14, 1997
The spacecraft's current 35-hour orbit around Mars, which was taking it down to 75 miles (121 kilometers) above the Martian surface during each of its closest passes over the planet, has been raised to 105 miles (170 kilometers). The orbit was raised Oct. 12 by the operations team at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, and Lockheed Martin Astronautics, Denver, CO, by performing a brief, 5.15-mile-per-hour (2.3-meter-per-second) propulsive burn at the farthest point of the spacecraft's orbit around Mars. The panel's performance has had no effect on spacecraft power.
"We're taking a hiatus from aerobraking for the next few weeks while we study data to try to model and understand the apparent deflection of the solar panel that never fully deployed and latched in place after launch," said Glenn E. Cunningham, Mars Global Surveyor project manager at JPL. "This delay in the aerobraking process will probably change the spacecraft's final mapping orbit from the originally planned 2 p.m. local Mars time passage over the planet's equator to another time, and we are studying several other orbits that will give us nearly the same quality of science results."
Preliminary data from the panel indicate that it has moved past what would have been its fully deployed and latched position, Cunningham said. In addition, the panel has shown some movement, rather than maintaining its rigid position during aerobraking. These changes occurred during the spacecraft's fifteenth close approach to Mars, on Oct. 6, when the density of the Martian atmosphere doubled unexpectedly.
During the next few weeks, the Mars Global Surveyor flight team will leave the spacecraft's orbit in the current, 35-hour revolution around Mars, which will not take the spacecraft through the upper atmosphere of Mars, while they analyze data and simulate conditions in the Martian atmosphere to understand the behavior of the solar panel. This hiatus also means the spacecraft's solar panels will not be reconfigured for each close pass over Mars, but will remain in the normal cruise position.
"We can't yet explain what has happened," Cunningham said. "We saw the unlatched panel move past the latched-up position, and it remains past that point now. By raising the spacecraft's orbit above the upper atmosphere, the panel should not shift further because it will not be exposed to the aerodynamic forces of the Martian atmosphere."
Several other mapping orbits are available to Mars Global Surveyor to carry out its science objectives. The flight team will explore alternatives in the next few weeks to accomplish the lowest orbit possible and achieve a "sun-synchronous" orbit that will allow Global Surveyor to fly over the Martian equator at the same local solar time each orbit. These sun-synchronous orbits are designed so that the spacecraft's instruments always see Mars at the same lighting angle on every pass over the surface.
"As we step back from aggressive aerobraking temporarily, we will have the opportunity to study the situation until we fully understand it. We will take advantage of this opportunity to return some spectacular data from the camera and laser altimeter," Cunningham said. "The thermal emission spectrometer and magnetometer/electron reflectometer also will continue to collect data while we remain in this holding pattern."
The Mars Global Surveyor atmospheric advisory group reported that the Martian atmosphere has more than doubled in thickness in the last week. Global Surveyor is designed to withstand more than a 50 percent increase in atmospheric density, but began showing movement in the solar panel last week, during the fifteenth close approach on Oct. 6.
JET PROPULSION LABORATORY October 3, 1997
"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 or the Global Surveyor project home page.
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.
Office of the Flight Operations Manager
Mars Surveyor Operations Project
NASA Jet Propulsion Laboratory
Friday, 3 October 1997
For more information about these initial findings, please visit the following science page on the Mars Global Surveor web site.
This page contains links to explanations about the initial science results, graphical illustrations used by the scientists at the press conference, and a download archive of images taken by the camera since orbit insertion.
Meanwhile, aerobraking continues to proceed smoothly after 13 revolutions around the red planet. At the start of aerobraking operations two weeks ago, the altitude of the orbit's high point was 33,570 miles (54,025 km). As of today, that height has dropped down to 30,304 miles (48,770 km). Over the next four months, the high-point altitude will shrink all the way down to 280 miles (450 km).
Passes through the atmosphere now occur once every 39 hours as the spacecraft skims through the low point of its orbit 68.4 miles (110 km) above the Martian surface. At this altitude, air resistance slows Surveyor by about 6.7 m.p.h. (3 meters per second) on each orbit. Although aerobraking deeper in the atmosphere will accelerate the process of shrinking the orbit, spacecraft safety constraints prohibit passes at altitudes significantly lower than the current value.
In addition to shrinking the size of Surveyor's orbit, aerobraking has also had a positive effect on the solar panel that deployed about 20 degrees short of its final position just after launch. This position discrepancy resulted when part of the panel's deployment mechanism broke and wedged into the hinge connecting the panel to the spacecraft. During the most recent atmospheric passes, the force of the oncoming air flow has been strong enough to force the panel back into position despite the presence of debris in the hinge. The panel is now less than one degree from its proper position.
After a mission elapsed time of 330 days from launch, Surveyor is 167.81 million miles (270.07 million kilometers) from the Earth and in an orbit around Mars with a period of 39.25 hours. The spacecraft is currently executing the P14 command sequence, and all systems continue to be in excellent condition.
Headquarters, Washington, DC.
Jet Propulsion Laboratory, Pasadena, CA
Goddard Space Flight Center, Greenbelt, MD
September 17, 1997
"Mars Global Surveyor has been in orbit for only a few days, yet it already has returned an important discovery about the Red Planet," said Vice President Al Gore. "This is another example of how NASA's commitment to faster, better, cheaper Mars exploration that began with Mars Pathfinder is going to help answer many fundamental questions about the history and environment of our neighboring planet, and the lessons it may hold for a better understanding of life on Earth."
The spacecraft's magnetometer, which began making measurements of Mars' magnetic field after its capture into orbit on Sept. 11, detected the magnetic field on Sept. 15. The existence of a planetary magnetic field has important implications for the geological history of Mars and for the possible development and continued existence of life on Mars.
"Preliminary evidence of a stronger than expected magnetic field of planetary origin was collected and is now under detailed study," said Dr. Mario H. Acuna, principal investigator for the magnetometer/electron reflectrometer instrument at NASA's Goddard Space Flight Center, Greenbelt, MD. "This was the first opportunity in the mission to collect close-in magnetic field data. Much more additional data will be collected in upcoming orbits during the aerobraking phase of the mission to further characterize the strength and geometry of the field. The current observations suggest a field with a polarity similar to that of Earth's and opposite that of Jupiter, with a maximum strength not exceeding 1/800ths of the magnetic field at the Earth's surface."
This result is the first conclusive evidence of a magnetic field at Mars. "More distant observations obtained previously by the Russian missions Mars 2,3 and 5 and Phobos 1 and 2 were inconclusive regarding the presence or absence of a magnetic field of internal origin," said Acuna.
The magnetic field has important implications for the evolution of Mars. Planets like Earth, Jupiter and Saturn generate their magnetic fields by means of a dynamo made up of moving molten metal at the core. This metal is a very good conductor of electricity, and the rotation of the planet creates electrical currents deep within the planet that give rise to the magnetic field. A molten interior suggests the existence of internal heat sources, which could give rise to volcanoes and a flowing crust responsible for moving continents over geologic time periods.
"A magnetic field shields a planet from fast-moving, electrically charged particles from the Sun which may affect its atmosphere, as well as from cosmic rays, which are an impediment to life," Acuna said. "If Mars had a more active dynamo in its past, as we suspect from the existence of ancient volcanoes there, then it may have had a thicker atmosphere and liquid water on its surface."
It is not known whether the current weaker field now results from a less active dynamo, or if the dynamo is now extinct and what the scientists are observing is really a remnant of an ancient magnetic field still detectable in the Martian crust.
" "Whether this weak magnetic field implies that we are observing a fossil crustal magnetic field associated with a now extinct dynamo or merely a weak but active dynamo similar to that of Earth, Jupiter, Saturn, Uranus and Neptune remains to be seen," Acuna said.
Mars Global Surveyor's magnetometer discovered the outermost boundary of the Martian magnetic field -- known as the bow shock -- during the inbound leg of its second orbit around the planet, and again on the outbound leg.
The discovery came just before Mars Global Surveyor began its first aerobraking maneuver to lower and circularize its orbit around Mars, said Glenn Cunningham, Mars Global Surveyor project manager at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
"This first 'step down' into the upper atmosphere was performed in two stages," Cunningham said. "On Sept. 16, during the farthest point in the spacecraft's orbit, called the apoapsis, the spacecraft fired its main engine for 6.5 seconds, slowing Global Surveyor's velocity by 9.8 miles per hour (4.41 meters per second). This maneuver lowered the spacecraft's orbit from 163 miles (263 kilometers) to 93 miles (150 kilometers) above the surface of the planet.
At its closest approach to Mars this morning, known as the periapsis, the spacecraft dipped into the upper fringes of the Martian atmosphere for 27 seconds, allowing the drag on its solar panels to begin the long aerobraking process of circularizing its orbit."
Mars Global Surveyor will continue aerobraking through the Martian atmosphere for the next four months, until its orbit has been circularized and it is flying about 234 miles (378 kilometers) above the Martian surface. All systems and science instruments onboard the spacecraft continue to perform normally after six days in orbit around the red planet.
Additional information about the magnetic field discovery and the Mars Global Surveyor mission is available on the World Wide Web by accessing the JPL home page or the Goddard Space Flight Center magnetometer site.
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