THE LUNAR THERMAL ICE PUMP
THE LUNAR THERMAL ICE PUMP
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月球热冰泵
DOI：
10.1088/0004-637x/788/2/169
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
O. Aharonson
中科院分区：
文献类型：
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作者：
N. Schorghofer;O. Aharonson
长期以来，人们一直认为水冰可以存在于月球两极附近的极冷地区，那里的升华损失可以忽略不计。含氢风化层的地理分布显示只有部分或模糊的相关性与永久阴影区，从而表明，另一种机制可能有助于当地提高水的浓度。我们表明，在适当的条件下，水分子可以泵入风化层的昼夜温度周期，导致富集的H2O超过表面浓度。理想的抽气条件进行了估计，发现发生在平均表面温度低于105 K和峰值表面温度高于120 K。这些条件补充了经典冷阱的那些条件，经典冷阱大致由低于120 K的峰值温度定义。在今天的月球上，估计有0.8%的全球表面积经历这种温度变化。通常情况下，抽水发生在小面积的面向极点的斜坡上，但在每个极点的几度范围内，面向赤道的斜坡是首选。虽然预计在累积的大面积上泵送水分子，但这种泵的绝对产量很低;充其量，输送到表面的H2O的百分之几可能以这种方式积累在近地表层中。冰的量随着蒸汽扩散率的增加而增加，因此在具有大孔隙空间的风化层中更高。
It has long been suggested that water ice can exist in extremely cold regions near the lunar poles, where sublimation loss is negligible. The geographic distribution of H-bearing regolith shows only a partial or ambiguous correlation with permanently shadowed areas, thus suggesting that another mechanism may contribute to locally enhancing water concentrations. We show that under suitable conditions, water molecules can be pumped down into the regolith by day–night temperature cycles, leading to an enrichment of H2O in excess of the surface concentration. Ideal conditions for pumping are estimated and found to occur where the mean surface temperature is below 105 K and the peak surface temperature is above 120 K. These conditions complement those of the classical cold traps that are roughly defined by peak temperatures lower than 120 K. On the present-day Moon, an estimated 0.8% of the global surface area experiences such temperature variations. Typically, pumping occurs on pole-facing slopes in small areas, but within a few degrees of each pole the equator-facing slopes are preferred. Although pumping of water molecules is expected over cumulatively large areas, the absolute yield of this pump is low; at best, a few percent of the H2O delivered to the surface could have accumulated in the near-surface layer in this way. The amount of ice increases with vapor diffusivity and is thus higher in the regolith with large pore spaces.