DPS 34th Meeting, October 2002
Session 11. Mars Odyssey Symposium
Invited, Chair: J.J. Plaut, Tuesday, October 8, 2002, 8:30-10:00am and 10:30am-12:00noon, Ballroom

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[11.03] Recession of the North-Polar CO2 Cap During Early Spring: Results from the Mars Odyssey Gamma-Ray Spectrometer

W.C. Feldman, R.L. Tokar, T.H. Prettyman (Los Alamos National Laboratory), W.V. Boynton (University of Arizona, Lunar Planetary Laboratory)

Neutron and gamma-ray fluxes measured using the Mars Odyssey Gamma-Ray Spectrometer are used to map the recession of the CO2 frost deposit that covered the region poleward of about 60 degrees N latitude during late winter. This signature is most evident in the thermal neutrons, but can also be readily followed using epithermal and fast neutrons as well as using the hydrogen capture gamma-ray line at 2.223 MeV and the Potassium line at 1.468 MeV. There are three salient features of this recession. First, the thickness of the center of the cap decreases monotonically with time. Preliminary evidence shows there may be a sharply enhanced reduction rate between Ls = 15 and 27 degrees, similar to that found in an analysis of the MOLA data [Smith et al., Science, 294, 2141-2146, 2001]. Second, the edge of the cap steadily moves poleward between Ls = 351 and 41 degrees from about 60 to about 70 degrees N latitude, respectively. And lastly, a lane of CO2 ice deposit north of about 55 degrees N latitude that is centered on 35 degrees W longitude diminishes steadily during this period. This work was funded by NASA and conducted under the auspices of the U.S. DOE and the U. of Arizona. The Odyssey mission is managed by the Jet Propulsion Laboratory for NASA.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.