Douglas Isbell
Headquarters, Washington, DC                     May 27, 1998
(Phone: 202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 98-90

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.