LEXEN: Methanogenesis and the Climate of Early Mars

9714161卡斯廷斯该项目涉及甲烷和二氧化碳冰云对火星古气候影响的理论模拟。早期的火星看起来是温暖潮湿的，然而现有的气候模型，假设是C02-H20大气，一直无法解释这一点。初步计算表明，在火星历史早期，向火星古大气中添加~1%的甲烷可能会使全球表面平均温度高于水的冰点。大部分变暖是由吸收可见光和近红外波长的入射太阳辐射引起的。甲烷在这一波长区域具有复杂的能带结构，需要对其进行精确的参数化，以便正确地进行气候计算。计算机模型中还需要包括二氧化碳冰云，以确定它们对行星辐射平衡的影响。大气光化学模型的计算表明，如果火星表面存在数量与地球上目前生物甲烷通量相当的甲烷源，甲烷体积混合比率可能会保持在1%。原则上，这种来源可能是由生活在早期火星表面或玄武岩中的产甲烷细菌提供的。最近在火星陨石ALH84001中发现的可能的细菌化石与这一情景完全一致。找到早期火星气候问题的解决方案将有助于我们更好地了解火星的历史，并可能对我们太阳系内外其他行星上生命的普遍存在产生影响。该奖项由大气科学部、天文学司和数学和物理科学局多学科活动办公室联合支持

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