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Distribution and habitability of (meta)stable brines on present-day Mars
Nature Astronomy ( IF 14.1 ) Pub Date : 2020-05-11 , DOI: 10.1038/s41550-020-1080-9
Edgard G. Rivera-Valentín , Vincent F. Chevrier , Alejandro Soto , Germán Martínez

Special Regions on Mars are defined as environments able to host liquid water that simultaneously meets certain temperature and water activity requirements that allow known terrestrial organisms to replicate1,2 and therefore could be habitable. Such regions would be of concern for planetary protection policies owing to the potential for forward contamination (biological contamination from Earth). Pure liquid water is unstable on the Martian surface3,4 but brines may be present3,5. Experimental work has shown that brines persist beyond their predicted stability region, leading to metastable liquids6,7,8. Here we show that (meta)stable brines can form and persist from the equator to high latitudes on the surface of Mars for a few percent of the year for up to six consecutive hours, a broader range than previously thought9,10. However, only the lowest eutectic solutions can form, leading to brines with temperatures of less than 225 K. Our results indicate that (meta)stable brines on the Martian surface and its shallow subsurface (a few centimetres deep) are not habitable because their water activities and temperatures fall outside the known tolerances for terrestrial life. Furthermore, (meta)stable brines do not meet the Special Region requirements, reducing the risk of forward contamination and easing threats related to the exploration of the Martian surface.



中文翻译:

当今火星上(亚)稳定盐水的分布和可居住性

火星上的特殊区域被定义为能够容纳液态水的环境,该环境同时满足一定的温度和水活度要求,使已知的陆地生物能够复制1,2,因此可以居住。由于存在潜在的正向污染(来自地球的生物污染),此类地区将受到行星保护政策的关注。纯液态水在火星表面3,4不稳定,但盐水3,5可能存在。实验工作表明,盐水持续超出其预测的稳定区域,导致形成亚稳液体6,7,8。在这里,我们表明,(亚)稳定的盐水可以从赤道形成并持续到火星表面的高纬度,一年中的百分之几,连续六个小时,比以前认为的要大9,10。但是,只能形成最低的共晶溶液,导致盐水温度低于225K。我们的结果表明,火星表面及其浅表层(几厘米深)上的(亚)稳定盐水不适合居住,因为它们的水活动和温度超出了已知的地球生命容忍度。此外,(亚)稳定盐水不符合特别地区的要求,从而降低了前向污染的风险,并减轻了与火星表面勘探有关的威胁。

更新日期:2020-05-11
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