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Mars Global Surveyor Unveils Its First Portrait Of Mars

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Contact: Diane Ainsworth

FOR IMMEDIATE RELEASE                         October 3, 1997

MARS GLOBAL SURVEYOR UNVEILS ITS FIRST PORTRAIT OF MARS 

     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.

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