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.





May, 1998


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