NASA Ames Research Center, Moffett Field, California.
Astrobiology. 2020 Feb;20(2):163-166. doi: 10.1089/ast.2019.2136.
There has been considerable attention on how to detect life on other worlds by searching for biomolecules. However, there has been much less clarity as to when it becomes warranted to focus a mission on the search for life on another world. At a minimum, a life-detection mission should follow convincing evidence of (1) Liquid water of suitable salinity, past or present; (2) Carbon in the water; (3) Biologically available N in the water; (4) Biologically useful energy in the water; (5) Organic material that can possibly be of biological origin and a plausible strategy for sampling this material. Based on these prerequisites, the most promising targets for a life search are currently the plume of Enceladus and the subsurface of Mars-in equatorial lake bed sediments and in polar ice-cemented ground. Neither the surface of Europa nor the clouds of Venus meet the criteria listed here but may with further exploration.
人们一直非常关注如何通过寻找生物分子来探测其他星球上的生命。然而，对于何时有必要将任务重点放在另一个世界的生命搜索上，却没有太多的明确性。至少，生命探测任务应该遵循以下令人信服的证据：（1）过去或现在有适宜盐度的液态水；（2）水中的碳；（3）水中可生物利用的氮；（4）水中有生物可用的能量；（5）可能具有生物起源的有机物质，以及对这种物质进行采样的合理策略。基于这些前提，目前最有希望进行生命搜索的目标是土卫二的羽状喷发物和火星的地下——赤道湖泊床沉积物和极地冰固结的地面。木卫二的表面和金星的云层都不符合这里列出的标准，但随着进一步的探索，可能会符合。
