Department of Astronomy, University of Maryland, College Park, Maryland, USA.
Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
Astrobiology. 2022 Sep;22(9):1047-1060. doi: 10.1089/ast.2020.2432. Epub 2022 Aug 16.
Landed missions to icy worlds with a subsurface liquid water ocean must meet planetary protection requirements and ensure a sufficiently small likelihood of any microorganism-bearing part of the landed element reaching the ocean. A higher bound on this likelihood is set by the potential for radioisotope thermoelectric generator (RTG) power sources, the hottest possible landed element, to melt through the ice shell and reach the ocean. In this study, we quantify this potential as a function of three key parameters: surface temperature, ice shell thickness (., heat flux through the shell), and thickness of a porous (insulating) snow or regolith cover. Although the model we describe can be applied to any ocean world, we present results in the context of a landed mission concept to the south polar terrain of Saturn's moon Enceladus. In this particular context, we discuss planetary protection considerations for landing site selection. The likelihood of forward microbial contamination of Enceladus' ocean by an RTG-powered landed mission can be made sufficiently low to not undermine compliance with the planetary protection policy.
登陆到具有地下液态水海洋的冰冷世界的任务必须满足行星保护要求，并确保登陆部件的任何可能携带微生物的部分到达海洋的可能性足够小。这种可能性的上限由放射性同位素热电发生器 (RTG) 电源设定，这是可能到达的最热的登陆元件，有可能融化冰壳并到达海洋。在这项研究中，我们将这种可能性作为三个关键参数的函数进行量化：表面温度、冰壳厚度（.，通过壳的热通量）和多孔（隔热）雪或风化层覆盖物的厚度。虽然我们描述的模型可以应用于任何海洋世界，但我们在针对土星卫星土卫二南极地形的登陆任务概念的背景下展示了结果。在这种特殊情况下，我们讨论了登陆点选择的行星保护考虑因素。RTG 动力登陆任务对土卫二海洋的正向微生物污染的可能性可以降低到足以符合行星保护政策的程度。
