The martian soil as a planetary gas pump
Microgravity experiments on a dust bed in a ‘drop tower’ set-up reveal the ability of martian soil to act as an efficient gas pump when heated by the Sun. 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...
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Veröffentlicht in: | Nature physics 2014-01, Vol.10 (1), p.17-20 |
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Zusammenfassung: | Microgravity experiments on a dust bed in a ‘drop tower’ set-up reveal the ability of martian soil to act as an efficient gas pump when heated by the Sun.
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 CO
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atmosphere is rather tenuous. Aeolian processes on the surface such as drifting dunes, dust storms and dust devils are nevertheless still active
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,
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,
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. The transport of volatiles below the surface, that is, through the porous soil, is unseen but needs to be known for balancing mass flows
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,
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. 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. |
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ISSN: | 1745-2473 1745-2481 |
DOI: | 10.1038/nphys2821 |