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首页> 外文期刊>Icarus: International Journal of Solar System Studies >Recent rheologic processes on dark polar dunes of Mars: Driven by interfacial water?
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Recent rheologic processes on dark polar dunes of Mars: Driven by interfacial water?

机译：火星黑暗极地沙丘上的最新流变过程：受界面水驱动？

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In springtime on HiRISE images of the Southern polar terrain of Mars flow-like or rheologic features were observed. Their dark color is interpreted as partly defrosted surface where the temperature is too high for CO_2 but low enough for H_2O ice to be present there. These branching streaks grow in size and can move by an average velocity of up to about 1 m/day and could terminate in pond-like accumulation features. The phenomenon may be the result of interfacial water driven rheologic processes. Liquid interfacial water can in the presence of water ice exist well below the melting point of bulk water, by melting in course of interfacial attractive pressure by intermolecular forces (van der Waals forces e.g.), curvature of water film surfaces, and e.g. by macroscopic weight, acting upon ice. This melting phenomenon can be described in terms of "premelting of ice". It is a challenging consequence, that liquid interfacial water unavoidably must in form of nanometric layers be present in water ice containing soil in the subsurface of Mars. It is the aim of this paper to study possible rheologic consequences in relation to observations, which seem to happen at sites of dark polar dunes on Mars at present. The model in this work assumes that interfacial water accumulates at the bottom of a translucent water-ice layer above a dark and insolated ground. This is warmed up towards the melting point of water. The evolving layer of liquid interfacial water between the covering ice sheet and the heated ground is assumed to drive downward directed flow-like features on slopes, and it can, at least partially, infiltrate (seep) into a porous ground. There, in at least temporarily cooler subsurface layers, the infiltrated liquid water refreezes and forms ice. The related stress built-up is shown to be sufficient to cause destructive erosive processes. The above-mentioned processes may cause change in the structure and thickness of the covering ice and/or may cause the movement of dune grains. All these processes may explain the observed springtime growing and downward extension of the slope streaks analyzed here.
机译：春季在火星南极地形的HiRISE图像上观察到了流状或流变特征。它们的深色被解释为部分除霜的表面，其中温度对于CO_2而言过高，但对于其中存在H_2O冰而言则足够低。这些分支条纹的大小会增大，并且可以以高达约1 m / day的平均速度移动，并可能终止于池塘状的堆积特征。该现象可能是界面水驱动流变过程的结果。在存在水冰的情况下，液体界面水可以通过分子间力（例如范德华力），水膜表面的曲率和例如水蒸气等在界面吸引力的压力下熔融，从而大大低于散装水的熔点。通过宏观重量作用在冰上。这种融化现象可以用“冰的预融化”来描述。一个具有挑战性的结果是，在火星表面下的含有土壤的水冰中不可避免地必须以纳米层的形式存在液态界面水。本文的目的是研究与观测有关的可能的流变学后果，目前看来，这可能发生在火星上黑暗极地沙丘上。这项工作中的模型假设界面水积聚在一个黑暗且阳光充足的地面上方的半透明水冰层的底部。将其加热至水的熔点。假设在覆盖的冰盖和加热的地面之间的液体界面水的演化层在斜坡上驱动向下的流动状特征，并且它可以至少部分地渗透（渗入）多孔地面。在那里，至少在暂时较冷的地下层中，渗入的液态水重新冻结并形成冰。已显示出相关的应力累积足以引起破坏性的侵蚀过程。上述过程可能会导致覆盖冰的结构和厚度发生变化，并且/或者可能导致沙丘颗粒的运动。所有这些过程都可以解释这里分析的观察到的春季生长和斜坡条纹的向下延伸。

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