HR: 17:15h
AN: P34A-06    [Abstracts]
TI: Time Scales for Discharge of Near-Equatorial WEH on Mars: Implications for a Recent Climate Change
AU: * Feldman, W C
EM: wfeldman@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545 United States
AU: Mellon, M T
EM: mellon@lasp.colorado.edu
AF: Laboratory-Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 United States
AU: Nelli, S
EM: snelli@nmsu.edu
AF: New Mexico State University, Department of Astronomy, Las Cruces, NM 88003 United States
AU: Murphy, J R
EM: murphy@nmsu.edu
AF: New Mexico State University, Department of Astronomy, Las Cruces, NM 88003 United States
AU: Maurice, S
EM: sylvestre.maurice@cesr.fr
AF: Centre d'Etude Spatiale des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31400 France
AU: Gasnault, O
EM: Olivier.Gasnault@cesr.fr
AF: Centre d'Etude Spatiale des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31400 France
AB: Geomorphic studies of Martian mid-latitude features suggest that Mars has recently experienced an ice age. A mid-latitude water-ice cover could result from enhanced sublimation of residual water ice that presently covers portions of both polar caps. Such a change could be driven by changes in the orbital state of Mars, or in atmospheric conditions that led to a removal of the present residual south-polar CO2-ice veneer. Regardless of origin, such conditions would lead to the filling of near-surface pore volumes with water ice. After a change back to the present orbital or atmospheric state where low to mid latitude water-ice deposits are unstable, the pore-filling water ice would sublimate, and the ice table (the top of the ice-cemented layer) would recede downward. If the water-equivalent hydrogen (WEH) now observed at low to mid latitudes of Mars reflects such a process, then we can predict the time of the change from stable to unstable conditions as a function of surface temperature and apparent abundance of WEH. Resultant time scales range from about one hundred to 5000 Martian years. Such short time scales rule out an interpretation of the presently observed WEH distribution in terms of water-ice deposits from past obliquity cycles. If removal of the south polar CO2-ice veneer cannot increase the average hydration state of the atmosphere by a factor of two or more, then the measured low to mid latitude WEH distribution most likely does not reflect water ice. Instead, it must reflect the existence of one or more hydratable minerals.
DE: 5405 Atmospheres (0343, 1060)
DE: 5410 Composition (1060, 3672)
DE: 5416 Glaciation
DE: 5462 Polar regions
SC: Planetary Sciences [P]
MN: Fall Meeting 2005