HR: 0800h
AN: P11A-0964    [Abstracts]
TI: 3D simulations of the early Mars climate with a General Circulation Model
AU: * Forget, F
EM: forget@lmd.jussieu.fr
AF: LMD, CNRS, Universite Paris 6, BP99 4, place Jussieu, Paris, 75252 France
AU: * Forget, F
EM: forget@lmd.jussieu.fr
AF: NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000 United States
AU: Haberle, R M
AF: NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000 United States
AU: Montmessin, F
AF: NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000 United States
AU: Marck, E
AF: LMD, CNRS, Universite Paris 6, BP99 4, place Jussieu, Paris, 75252 France
AU: Colaprete, A
AF: NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000 United States
AB: The environmental conditions that existed on early Mars during the Noachian period are subject to debate in the community. While some authors suggest that the difference resulted from a stronger geothermalism during that period, and that a warm climate was not necessary to explain the valley network, others claim that a warm, wet early climate capable of supporting rainfall and surface runoff is the most plausible scenario for explaining the entire suite of geologic and mineralogical features in the Martian cratered highlands. The recent observations from the Mars Exploration Rovers, Mars Express and Mars Odyssey are more than ever raising the issue. To help understand this key issue in Mars science, we have developped a 3D general circulation model similar to the one used on current Earth or Mars to study the details of the climate today. Our first objective is to answer the following questions : how is the Martian climate modified if 1) the surface pressure is increased up to several bars (our baseline: 1 or 2 bars) and 2) if the sun luminosity is decreased by 25% like 3.8 Billion years ago. We did not take into account the heat possibly released by impacts during short periods, although it may have played a role. Preliminary results obtained assuming a 2 bars atmosphere suggest that, even without taking into account the radiative effect of CO$_2$ clouds, temperature near or above the freezing point of water may be obtained. In particular, the CO2 gas greenhouse effect may be stronger than usually expected because pressure induced absoprtion may have been underestimated in studies Moreover CO$_2$ ice clouds are found to form almost everywhere on the planet in the upper atmosphere above 40 km. Their radiative effect on the climate is very model dependent but, in our baseline simulation, correspond to a15 K warming of the surface. We found that above freezing temperatures are especially likely in the lower plains, due to the atmospheric adiabating warming. This would support a scenario were the lower northern plains would be filled by liquid water and the higher regions more or less covered by snow and glaciers. To better investigate the kind of water cycle one can expect in such conditions, we plan to apply parameterisations currently used in Earth models to simulate the water cycle on our planet.
DE: 5407 Atmospheres--evolution
DE: 5415 Erosion and weathering
DE: 5445 Meteorology (3346)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting