Thermal creep efficiently transports gas through
Martian soil. To quantify the Martian soil pump we carried
out laboratory analog experiments with illuminated granu-
lar media at low ambient pressure. We used samples of 1 μm
to 5 μm SiO 2 (quartz), basalt with a broad size distribution
between 63 μm and 125 μm, and JSC-Mars 1A with a size
fraction from 125 μm to 250 μm. The mean ambient pres-
sure was varied between 50 Pa and 9000 Pa. Illumination
was varied between 100 W/m 2 and 6700 W/m 2 . The ex-
periments confirm strong directed gas flows within granular
and dusty soil and local sub-soil pressure variations. We find
that Martian soil pumps can be described with existing mod-
els of thermal creep for capillaries, using the average grain
size and light flux related temperatures.

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• Gas flow within Martian soil: experiments on granular Knudsen compressors