Transient liquid water and water activity at Gale crater on Mars
Transient liquid water and water activity at Gale crater on Mars
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DOI：
10.1038/ngeo2412
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发表时间：
2015-05-01
影响因子：
18.3
通讯作者：
Vaniman, David
中科院分区：
文献类型：
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作者：
Martin-Torres, F. Javier;Zorzano, Maria-Paz;Vaniman, David
正如我们所知，水是生命的必需品。从赤道火星上的轨道飞行器观测到的瞬态液态水的间接证据(2)，与大规模气候模型的预期相反。高氯酸盐的存在降低了水的冰点温度，这是好奇号火星车在火星赤道的盖尔环形山探测到的。此外，高氯酸盐可以通过潮解吸收大气中的水蒸气形成稳定的水合化合物和液体溶液（6,7）。在这里，我们分析了“好奇号”漫游者在盖尔陨石坑的相对湿度、空气温度和地面温度数据，发现这些观测结果支持夜间在地下最上面5厘米处形成瞬态液态盐水，然后在日出后蒸发。我们还发现，根据“好奇号”的测量，在地下最上层15厘米内盐的水化状态的变化与大气-土壤界面上活跃的水交换是一致的。然而，水的活度和温度可能太低，无法支持陆地生物(8)。高氯酸盐在火星表面广泛存在(9)，我们预计，在大气湿度较高、温度较低的赤道地区以外，液态盐水也会大量存在。
Water is a requirement for life as we know it(1). Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars(2), in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover(3,4), lowers the freezing temperature of water(5). Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence(6,7). Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere-soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms(8). Perchlorates are widespread on the surface of Mars(9) and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.