9714161 Kastings The project involves theoretical modeling of the effect of methane and CO2 ice clouds on martian paleoclimate. Early Mars appears to have been warm and wet, yet existing climate models, which assume a C02-H20 atmosphere, have been unable to explain this. Preliminary calculations show that the addition of ~1% CH4 to the martian paleoatmosphere could have brought the mean global surface temperature above the freezing point of water early in the planet's history. Most of the warming is caused by the absorption of incoming solar radiation at visible and near-infrared wavelengths. Methane has a complex band structure in this wavelength region that needs to be accurately parameterized in order to do the climate calculation properly. C02 ice clouds also need to be included in the computer model to determine their effect on the planetary radiation balance. Calculations with an atmospheric photochemical model suggest that a CH4 mixing ratio of 1% by volume could have been maintained if there was a source of methane at the martian surface comparable in magnitude to the present biological flux of methane on Earth. Such a source could, in principle, have been provided by methanogenic bacteria living on the surface of early Mars or within basaltic rocks. The recent identification of possible fossilized bacteria in the martian meteorite ALH84001 is entirely consistent with this scenario. Finding a solution to the early Mars climate problem would help us to better understand Mars' history and may have implications for the prevalence of life on other planets both within and beyond our own Solar System. This award is jointly supported by Division of Atmospheric Sciences, Astronomy and the Directorate of Mathematical and Physical Sciences Office of Multidisciplinary Activities
