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首页> 外文期刊>Astrobiology >Energy, Chemical Disequilibrium, and Geological Constraints on Europa
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Energy, Chemical Disequilibrium, and Geological Constraints on Europa

机译：欧罗巴的能源，化学不平衡和地质限制

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Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO_2 to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO_2-rich ices yield CO and H_2CO_3; the reductants H_2CO, CH_3OH, and CH_4 are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O_2, H_2O_2, CO_2, SO_2, and SO_4~(2-)) are delivered only once every ～0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa's ocean could reach O_2 concentrations comparable to those found in terrestrial surface waters, even if ～10~9 moles yr~(-1) of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.
机译：欧罗巴是天体生物学的主要目标。全球地下液态水海洋的存在以及可能包含一系列生物成因的组合物的存在，使其成为寻找第二生命起源的引人注目的世界。但是，对于这些因素而言，至关重要的可能是欧罗巴生物过程的能源可用性。我们检查了欧罗巴上氧化剂和含碳还原剂的生产和可用性，以更好地了解地下海洋的可居住性。来自伽利略（Galileo）近红外光谱仪的数据用于将CO_2的表面丰度相对于水限制为0.036％。实验室结果表明，经辐射处理的富含CO_2的冰可产生CO和H_2CO_3。还原剂H_2CO，CH_3OH和CH_4最多为次要物种。我们分析了化学来源和汇，得出结论，即使表面氧化剂（O_2，H_2O_2，CO_2，SO_2和SO_4〜（2-）仅每〜释放一次），欧罗巴的经辐射处理的表面仍可用于维持海洋的氧化。 0.5 Gyr。如果交付期与观测到的地表年龄（30-70 Myr）相当，那么欧罗巴的海洋中O_2的浓度可以与陆地地表水中的O_2浓度相媲美，即使水热输送的还原剂约10〜9摩尔yr〜（-1）。消耗大部分的氧化剂流量。对于陆地海洋大型动物来说，这样的海洋将非常热情好客。还原剂的可用性可能是欧罗巴生物学上有用的化学能的限制因素。

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