- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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).
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- Additional information about these findings
and other exciting new results from the Mars Global Surveyor mission is
available at the following Internet sites:
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- http://mars.jpl.nasa.gov/mgs/ http://emma.la.asu.edu/
http://ltpwww.gsfc.nasa.gov/tharsis/mola.html
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- 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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