Researchers at the Los Alamos National Laboratory, the University of Arizona Lunar Planetary Laboratory, Tucson,
Ariz., and Cornell University, Center for Radiophysics and Space Research,
Ithaca, N.Y., have discovered further evidence for the possible existence of
a changing, and perhaps predictable, Martian climate.

In presentations at the American Geophysical Union (AGU) 2002 meeting in San
Francisco, scientists unveiled thermal, epithermal, and fast neutron data
gathered from February through November 2002 by the Neutron Spectrometer
subsystem aboard NASA’s Mars Odyssey spacecraft.

The mapping of the Odyssey data indicates deposits of hydrogen in large
areas centered on Arabia Terra and 180 degrees east longitude near the
equator. The thermal and fast flux data also indicates that these deposits
are buried below a shallow layer of water-poor Martian soil.

According to Los Alamos’ principal investigator on the project, Bill
Feldman, this spatial distribution of hydrogen deposits cannot be explained
by the general north-south latitude gradient of water vapor that is in the
present Martian atmosphere, thereby requiring different climatic conditions
in the relatively recent past.

Maps of thermal, epithermal, and fast neutrons for the northern Martian
latitudes-northward of +45 degrees-were also studied to determine the time
variation of carbon dioxide frost at latitudes during late winter mid
summer. The data collected between February and November 2002, were broken
into sixteen, roughly two-week intervals of time. The edge of the carbon
dioxide frost cap is seen to steadily recede during the period, revealing
subsurface deposits of water-rich soil.

Previously, the Los Alamos’ neutron spectrometer had mapped the Martian
surface while it was summer in the south and winter in the north. That data
revealed the extent to which the northern and southern polar caps are
covered by a thick layer of carbon dioxide, or dry ice. During winter, the
carbon dioxide layers extend from the poles to within about 60 degrees of
the equator because the dry ice frost settles out of the atmosphere when
temperatures fall about 186 degrees below zero Fahrenheit. During the warmer
summer the carbon dioxide layer evaporates completely in the north but
remains as a thick cover of the residual polar cap in the south.

Thermal neutrons are low energy neutrons that are in thermal contact with
the soil. Epithermal neutrons are intermediate-energy neutrons that are
scattering down in energy after bouncing off of the soil material. Fast
neutrons are the highest energy neutrons produced in the interaction between
very high energy galactic cosmic rays and the soil.

The Jet Propulsion Laboratory, a division of the California Institute of
Technology, manages the Mars Odyssey mission for NASA’s Office of Space
Science. Investigators at Arizona State University in Tempe, the University
of Arizona in Tucson and NASA’s Johnson Space Center, Houston, operate the
science instruments. Additional science partners are located at the Russian
Aviation and Space Agency and at Los Alamos National Laboratory. Lockheed
Martin Astronautics, Denver, is the prime contractor for the project, and
developed and built the orbiter. Mission operations are conducted jointly
from Lockheed Martin and JPL.

Los Alamos National Laboratory is operated by the University of California
for the National Nuclear Security Administration (NNSA) of the U.S.
Department of Energy and works in partnership with NNSA’s Sandia and
Lawrence Livermore national laboratories to support NNSA in its mission.

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