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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars
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A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars

机译：沃斯托克湖替代起源的数值模型及其对火星的生物学影响

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In connection with recent Galileo images of the Jovian satellite Europa, there has been a significantly increased interest in the subglacial Lake Vostok in central East Antarctica. Since the theoretical prediction by Zotikov [1961] of the existence of lakes (one of which later was named Vostok) under similar to4 km of ice in Antarctica and its confirmation by radar measurements from aircraft in 1974 [Robin et al., 1977] and from the ERS-1 satellite in 1993, it was tacitly assumed that the lake originated from the basal melting of ice [e.g., Zotikov, 1961, 1977, 1986; Kapitsa et al., 1996]. Recently, Zotikov and Duxbury [2000] proposed an alternative hypothesis that Lake Vostok had existed on the surface before the Antarctic perennial glaciation began 5-30 Myr ago, then it was buried under the thermally protecting ice and never froze all the way to the bottom. In this study we support our hypothesis by comprehensive numerical modeling and evaluate its interesting implications for Mars and exobiology. Our numerical experiments on the sensitivity of the freezing depth to different upper boundary temperatures and different internal heat flows and the recent Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA) data support our model of the origin of possible subpolar water on Mars versus the old basal melting hypothesis. We also propose here experimental tests for our hypothesis. As a result of our computations, we conclude that Lake Vostok has survived the Antarctic glaciation without freezing completely, if it were initially an open lake with a surprisingly small water depth (greater than similar to 53 m). The current water depth at a single point is as much as 500 m [Verkulich et al., 1996]. This maximum freezing depth of similar to 53 m was reached in only 3300 years when the total upper ice cover was only similar to 600 m. The computed critical water depth is applicable to other Antarctic lakes under a thick ice cover. For the Martian internal heat flow we have computed the critical water depth to be similar to 63 m. The existence of the lake before the accumulation of ice in Antarctica implies that possible microorganisms and their remnants in the lake can be older than the Antarctic ice sheet, i.e., older than 5-30 Myr. If future observations find water under the Martian polar caps, this subpolar water, according to our model, has originated from lakes that were on the Martian surface before the formation of Mars' polar caps and have not completely frozen. Such environments would be ideal candidates for extant or extinct life on the red planet. This argues for a drilling mission at the Martian polar caps. [References: 38]
机译：关于木星欧罗巴的伽利略卫星的最新图像，人们对南极东部中部的冰下沃斯托克湖的兴趣大大增加。自Zotikov [1961]对南极洲接近4 km冰的湖泊（其中一个后来被称为Vostok）的存在进行理论预测以来，并于1974年通过飞机的雷达测量结果对其进行了确认[Robin等，1977];根据1993年的ERS-1卫星，人们默认地认为该湖起源于冰的基础融化[例如Zotikov，1961年，1977年，1986年; Kapitsa等，1996]。最近，Zotikov和Duxbury [2000]提出了另一种假设，即在南极多年生冰期开始于5-30 Myr之前，沃斯托克湖已经存在于地表，然后将其埋在热保护冰下，从未结冰至底部。在这项研究中，我们通过全面的数值模型来支持我们的假设，并评估其对火星和外生物学的有趣意义。我们关于冻结深度对不同的上限温度和不同的内部热流的敏感性的数值实验以及最新的Mars Global Surveyor火星轨道激光高度计（MOLA）数据支持了我们关于火星与旧基底的可能亚极水起源的模型假说。在此，我们还为我们的假设提出了实验检验。根据我们的计算结果，我们得出的结论是，如果沃斯托克湖最初是一个开阔的湖，水深出乎意料地小（大于53 m），就可以在南极冰川中幸存下来而没有完全冻结。当前单点水深达500 m [Verkulich等，1996]。当总的上层冰盖只有600 m时，仅3300年就达到了大约53 m的最大冻结深度。计算得出的临界水深适用于厚冰层下的其他南极湖泊。对于火星内部热流，我们计算出的临界水深类似于63 m。在南极洲的冰层积聚之前，该湖的存在意味着该湖中可能存在的微生物及其残留物可能早于南极冰盖，即早于5-30 Myr。如果未来的观察发现在火星的极地帽下​​有水，那么根据我们的模型，这种亚极水起源于火星的极地帽形成之前位于火星表面的湖泊，并且尚未完全冻结。这样的环境将是红色星球上现存或灭绝生命的理想人选。这表明在火星极地盖进行钻探任务。 [参考：38]

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