Enceladus: Evidence and Unsolved Questions for an Ice-Covered Habitable World
Enceladus: Evidence and Unsolved Questions for an Ice-Covered Habitable World
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土卫二：冰雪覆盖的宜居世界的证据和未解决的问题
DOI：
10.1007/978-981-13-3639-3_25
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Kamata Shunichi
中科院分区：
文献类型：
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作者：
Sekine Yasuhito;Shibuya Takazo;Kamata Shunichi
土卫二是土星的一颗中等大小的冰冷卫星，自从发现其剧烈的地质活动以来，它已成为天体生物学的中心。从土卫二南极附近的冰壳上的温暖裂缝中喷发出的富含水的羽状物来自与岩石核心相互作用的全球地下海洋。卡西尼号飞船对羽流的现场测量表明，海洋中含有溶解的气体种类，如CO2，NH3，CH 4和H2，它们可以提供不平衡的氧化还原能量来支持产甲烷生命。羽流的盐成分表明海洋的pH值为碱性（pH值约为9至11）。羽流还含有大量有机物质，包括高分子量有机化合物，但其来源仍不清楚。温度高于90 °C的热液活动极有可能存在于海底或岩石核心内，这可能在维持海洋内的化学不平衡方面发挥作用。这些观测结果表明，土卫二是一个行星体，目前符合可居住性和生命的基本要求-液态水，有机物质和生物可利用的能量-超越地球。
The icy midsized satellite of Saturn—Enceladus—has become the central to astrobiology since the finding of its dramatic ongoing geological activity. The water-rich plumes erupting from the warm fractures on the icy crust near the South Pole of Enceladus originate from its global subsurface ocean that interacts with the rocky core. In situ measurements of the plume by the Cassini spacecraft showed that the ocean contains dissolved gas species, such as CO2, NH3, CH4, and H2, which can provide disequilibrium redox energy to support methanogenic life. The salt composition of the plume indicates an alkaline pH of the ocean (pH ~9 to 11). The plume also contains significant amounts of organic matter, including high-molecular-weight organic compounds, although its origin remains unclear. Ongoing hydrothermal activity at temperatures greater than 90 °C is highly likely to exist on the seafloor or within the rocky core, which could play a role in sustaining the chemical disequilibrium within the ocean. These observations suggest that Enceladus is a planetary body thus far that currently meets the fundamental requirements for habitability and life—liquid water, organic matter, and bioavailable energy—beyond Earth.