MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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http://www.jpl.nasa.gov

Guy Webster, (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Donald Savage (202) 358-1727
NASA Headquarters, Washington

RELEASE: 2003-165 December 8, 2003

ODYSSEY STUDIES CHANGING WEATHER AND CLIMATE ON MARS

Mars may be going through a period of climate change, new findings
from NASA's Mars Odyssey orbiter suggest.

Odyssey has been mapping the distribution of materials on and near
Mars' surface since early 2002, nearly a full annual cycle on Mars.
Besides tracking seasonal changes, such as the advance and retreat of
polar dry ice, the orbiter is returning evidence useful for learning
about longer-term dynamics.

The amount of frozen water near the surface in some relatively warm
low-latitude regions on both sides of Mars' equator appears too great
to be in equilibrium with the atmosphere under current climatic
conditions, said Dr. William Feldman of Los Alamos National
Laboratory, N.M. He is the lead scientist for an Odyssey instrument
that assesses water content indirectly through measurements of neutron
emissions.

"One explanation could be that Mars is just coming out of an ice age,"
Feldman said. "In some low-latitude areas, the ice has already
dissipated. In others, that process is slower and hasn't reached an
equilibrium yet. Those areas are like the patches of snow you
sometimes see persisting in protected spots long after the last
snowfall of the winter."

Frozen water makes up as much as 10 percent of the top meter (three
feet) of surface material in some regions close to the equator. Dust
deposits may be covering and insulating the lingering ice, Feldman
said. He and other Odyssey scientists described their recent findings
today at the fall meeting of the American Geophysical Union in San
Francisco.

"Odyssey is giving us indications of recent global climate change in
Mars," said Dr. Jeffrey Plaut, project scientist for the mission at
NASA's Jet Propulsion Laboratory, Pasadena, Calif.

High latitude regions of Mars have layers with differing ice content
within the top half meter (20 inches) or so of the surface,
researchers conclude from mapping of hydrogen abundance based on
gamma-ray emissions.

"A model that fits the data has three layers near the surface," said
Dr. William Boynton of the University of Arizona, Tucson, team leader
for the gamma-ray spectrometer instrument on Odyssey. "The very top
layer would be dry, with no ice. The next layer would contain ice in
the pore spaces between grains of soil. Beneath that would be a very
ice-rich layer, 60 to nearly 100 percent water ice."

Boynton interprets the iciest layer as a deposit of snow or frost,
mixed with a little windblown dust, from a cold-climate era. The
middle layer could be the result of changes brought in a warmer era:
The ice down to a certain depth dissipates into the atmosphere. The
dust left behind collapses into a soil layer with limited pore space
for returning ice.

Information from the gamma-ray spectrometer alone is not enough to
tell how recently the climate changed from colder to warmer, but an
estimated range might come from collaborations with climate modelers,
Boynton said.

Other Odyssey instruments are providing other pieces of the puzzle.
Images from the orbiter's camera system have been combined into the
highest resolution complete map ever made of Mars' south polar region.
"We can now accurately count craters in the layered materials of the
polar regions to get an idea how old they are," said Dr. Phil
Christensen of Arizona State University, Tempe, principal investigator
for the camera system.

Temperature information from the camera system's infrared imaging has
produced a surprise about dark patches that dot bright expanses of
seasonal carbon-dioxide ice. "Those dark features look like places
where the ice has gone away, but thermal infrared maps show that even
the dark areas have temperatures so low they must be carbon-dioxide
ice." Christensen said. "One possibility is that the ice is clear in
these areas and we're seeing down through the ice to features
underneath."

Odyssey's high-energy neutron detector continues to monitor seasonal
changes in the amount of carbon-dioxide ice deposited in polar
regions, allowing tests of atmosphere-circulation models, said Dr.
Igor Mitrofanov of the Institute for Space Research, Moscow, Russia.

Measurements by an instrument for monitoring the radiation environment
at Mars show the level of radiation hazard that Mars-bound astronauts
might face, including levels during a period of unusually intense
solar activity, said Dr. Cary Zeitlin of the National Space Biomedical
Research Institute, Houston.

JPL manages Mars Odyssey for NASA's Office of Space Science,
Washington. Investigators at Arizona State University, Tempe;
University of Arizona, Tucson; NASA's Johnson Space Center, Houston;
the Russian Aviation and Space Agency, Moscow; and Los Alamos National
Laboratory, Los Alamos, N.M., built and operate Odyssey science
instruments. Information about the mission is available on the
Internet at: http://mars.jpl.nasa.gov/odyssey.

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