The martian soil as a planetary gas pump
The martian soil as a planetary gas pump
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DOI：
10.1038/nphys2821
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发表时间：
2014-01-01
期刊：
影响因子：
19.6
通讯作者：
Teiser, Jens
中科院分区：
文献类型：
--
作者：
de Beule, Caroline;Wurm, Gerhard;Teiser, Jens
火星有一个活跃的表面，有无所不在的小尘埃颗粒和较大的碎片。由于环境压力低于10毫巴，不到地球表面压力的1%，其二氧化碳大气相当稀薄。然而，地表的风成过程，如沙丘漂移、沙尘暴和沙尘暴仍然活跃（1-3）。挥发性物质在地表以下的迁移，即通过多孔土壤的迁移，是不可见的，但需要知道以平衡质量流（4，5）。在这里，我们描述了多孔土壤内的强制对流的机制。在平均环境气压为6毫巴的情况下，气体通过热蠕变流过火星的多孔地面是可能的，土壤充当（努森）泵。由太阳辐射的局部和时间变化提供的温度梯度导致系统的气体流动。我们的测量表明，流量可以超过扩散率。火星是太阳系中唯一可以自然发生这种情况的天体。我们的实验室实验表明，火星表面在土壤上下至少几厘米的地层中循环气体是有效的，周转时间只有几秒钟到几分钟。
Mars has an active surface, with omnipresent small dust particles and larger debris. With an ambient pressure below 10 mbar, which is less than 1% of the surface pressure on Earth, its CO2 atmosphere is rather tenuous. Aeolian processes on the surface such as drifting dunes, dust storms and dust devils are nevertheless still active(1-3). The transport of volatiles below the surface, that is, through the porous soil, is unseen but needs to be known for balancing mass flows(4,5). Here, we describe a mechanism of forced convection within porous soils. At an average ambient gas pressure of 6 mbar, gas flow through the porous ground of Mars by thermal creep is possible and the soil acts as a (Knudsen) pump. Temperature gradients provided by local and temporal variations in solar insolation lead to systematic gas flows. Our measurements show that the flow rates can outnumber diffusion rates. Mars is the only body in the Solar System on which this can occur naturally. Our laboratory experiments reveal that the surface of Mars is efficient in cycling gas through layers at least centimetres above and below the soil with a turnover time of only seconds to minutes.