MEDIA RELATIONS 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 RELEASEMay 27, 1998
SURVEYOR DATA REVEAL MORE EVIDENCE OF ABUNDANT WATER, THERMAL
ACTIVITY IN MARS' PAST
New mineralogical and topographic evidence suggesting that
Mars had abundant water and thermal activity in its early history
is emerging from data gleaned by NASA's Mars Global Surveyor
spacecraft.
Scientists are getting more glimpses of this warmer, wetter
past on Mars while Global Surveyor circles the planet in a
temporary 11.6-hour elliptical orbit. Findings from data gathered
during the early portions of this hiatus in the mission's orbital
aerobraking campaign are being presented today at the spring
meeting of the American Geophysical Union in Boston.
Among many results, the Thermal Emission Spectrometer
instrument team, led by Dr. Philip Christensen of Arizona State
University, Tempe, has discovered the first clear evidence of an
ancient hydrothermal system. This finding implies that water was
stable at or near the surface and that a thicker atmosphere
existed in Mars' early history.
Measurements from the spectrometer show a remarkable
accumulation of the mineral hematite, well-crystallized grains of
ferric (iron) oxide that typically originate from thermal
activity and standing bodies of water. This deposit is localized
near the Martian equator, in an area approximately 300 miles (500
kilometers) in diameter.
Fine-grained hematite, with tiny particles no larger than
specks of dust, generally forms by the weathering of iron-bearing
minerals during oxidation, or rusting, which can occur in an
atmosphere at low temperatures. The material has
been previously detected on Mars in more dispersed concentrations
and is widely thought to be an important component of the
materials that give Mars its red color. The presence of a
singular deposit of hematite on Mars is intriguing, however,
because it typically forms by crystal growth from hot, iron-rich
fluids.
Meanwhile, the Mars Orbiter Laser Altimeter instrument
is giving mission scientists their first three-dimensional views
of the planet's north polar ice cap. Principal Investigator Dr.
David Smith of NASA's Goddard Space Flight Center, Greenbelt, MD,
and his team have been using the laser altimeter to obtain more
than 50,000 measurements of the topography of the polar cap in
order to calculate its thickness, and learn more about related
seasonal and climatic
changes.
These initial profiles have revealed an often striking
surface topology of canyons and spiral troughs in the water and
carbon dioxide ice that can reach depths as great as 3,600 feet
below the surface. Many of the larger and deeper
troughs display a staircase structure, which may ultimately be
correlated with seasonal layering of ice and dust observed by
NASA's Viking mission orbiters in the late 1970s.
The laser data also have shown that large areas of the ice
cap are extremely smooth, with elevations that vary only a few
feet over many miles. At 86.3 degrees north, the highest
latitude yet sampled, the cap achieves an elevation of 6,600 to
7,900 feet (1.25 to 1.5 miles or 2-2.5 kilometers) over the
surrounding terrain. The laser measurements are accurate to
approximately one foot (30 centimeters) in the vertical
dimension.
In June, the ice cap's thickness will reach a maximum during
the peak of the northern winter season. Thickness measurements
from April will be compared to those that will be taken in June,
contributing to a greater understanding of the Martian polar
cap's formation and evolution.
In addition, the Global Surveyor accelerometer team, led by
Dr. Gerald Keating of George Washington University, Washington,
DC, has discovered two enormous bulges in the upper atmosphere of
Mars in the northern hemisphere, on opposite sides of the planet
near 90 degrees east latitude and 90 degrees west longitude.
These bulges rotate with the planet, causing variations of nearly
a factor of two in atmospheric pressure, and systematic
variations in the altitude of a given constant pressure of about
12,000 feet (four kilometers).
Additional information about these findings and other
exciting new results from the Mars Global Surveyor mission is
available at the following Internet sites:
http://mars.jpl.nasa.gov/mgs/
http://emma.la.asu.edu/
http://ltpwww.gsfc.nasa.gov/tharsis/mola.html
After a month-long period during which the Sun was between
Earth and Mars and thus degraded communications with Global
Surveyor, the spacecraft has resumed taking scientific data in
its temporary elliptical orbit. In September, it will once again
begin dipping into the upper atmosphere of Mars each orbit in a
process called aerobraking. The drag from this procedure will
allow the spacecraft to reach a low circular orbit and begin its
primary two-year global mapping mission starting in March 1999.
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5/27/98 DEA
#9850