These two views of Mars were made with data taken by the neutron spectrometer component of NASA's Mars Odyssey gamma ray spectrometer suite. These maps show epithermal neutron flux, which is sensitive to the amount of hydrogen present.
The first view was made shortly after the Mars Odyssey science mission began in Feb. 2002, during late summer in the south. The magenta region in the south is due to large amounts of water ice buried a fraction of a meter beneath the surface. The amount of ice is approximately 60 percent by volume. At that time the buried ice in the north was not visible because it was covered with a thick cap of carbon dioxide (dry-ice) frost.
The second view was made in November 2002 as Mars enters summer in the north. In this view the ice-rich regions in the north are now visible because the thick carbon dioxide frost has evaporated, and the ice-rich regions in the south are beginning to be obscured by the formation of wintertime seasonal frost. The ice content in the north is even greater than it is in the south, though it is not yet known by how much.
JPL, a division of the California Institute of Technology in Pasadena, manages the 2001 Mars Odyssey mission for NASA's Office of Space Science in Washington, D.C. Investigators at Arizona State University in Tempe, the University of Arizona in Tucson and NASA's Johnson Space Center,Houston, operate the science instruments. The gamma-ray spectrometer was provided by the University of Arizona in collaboration with the Russian Aviation and Space Agency, which provided the high-energy neutron detector, and the Los Alamos National Laboratories, New Mexico, which provided the neutron spectrometer. 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 from JPL.