HR: 16:30h
AN: C12C-03 INVITED     [PDF]
TI: Theory of Ground Ice on Mars and Implications to the Neutron Leakage Flux
AU: * Mellon, M T
EM: mellon@argyre.colorado.edu
AF: University of Colorado, Laboratory for Atmospheric and Space Physics University of Colorado, Boulder, CO 80309 United States
AU: Feldman, W C
AF: Los Alamos National Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Prettyman, T H
AF: Los Alamos National Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AB: Near-surface ground ice (subsurface ice in the upper several meters of the surface) is an important component of the global cycles of water and the behavior of the martian climate. It represents a substantial reservoir of water that can dynamically exchange with the atmosphere on timescales comparable to that of oscillations in the planet's orbit. As the martian obliquity increases or decreases, the global atmospheric humidity also increases or deceases. In response to this and changes in the regolith temperatures, ground ice can undergo cycles of sublimation and condensation, such that the upper meter or two of the martian regolith can become alternately ice-saturated and desiccated. The rate of sublimation and condensation is fast enough to respond to orbital changes, but slow enough that the distribution of ice in one year may not reflect the climate conditions of that year, but instead reflect an average over the previous thousand or so years. Therefore, the present day distribution of ground ice reflects some measure of the longer-term martian climate. In this work we present new calculations of the geographic and depth distribution of ground ice on Mars and draw comparisons with the inferred distribution of ice from Mars Odyssey Neutron Spectrometer observations of the neutron leakage flux. We find that ground ice is stable at relatively shallow depths on Mars, at an ice table such that ice-cemented soil occurs beneath a dry-soil layer, similar to the configuration of ground ice found in the Antarctic Dry Valleys. Predicted ice-table depths vary, but values average around a few centimeters. We also find that the measured geographic distribution of leakage neutrons in the martian southern hemisphere is extremely consistent with a presence of ground ice at a depth in diffusive equilibrium with atmospheric water vapor. The amount of water vapor that best corresponds to the measured neutron flux is near 20 precipitable micrometers, somewhat more water vapor than is presently observed on an annual average basis. This water vapor content corresponds to a longer-term average of a thousand or so year
DE: 1823 Frozen ground
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Cryosphere [C]
MN: 2003 Fall Meeting