Could snow on Mars harbour life? Perhaps, thanks to a form of greenhouse effect that creates liquid water beneath an icy crust.
As far as anyone can tell, liquid water is rare on Mars. At the equator, temperatures can rise above freezing, but any snow or ice that melts would quickly evaporate due to the low atmospheric pressure. Near the poles, water is abundant but permanently frozen.
New calculations by of the German Aerospace Center in Berlin suggest that these frozen deposits could contain liquid water, at least during the day. According to M枚hlmann, the heat from sunlight penetrating into ice or snow should get absorbed by any embedded dust grains, warming the dust and the surrounding ice. This heat mostly gets trapped because ice absorbs infrared radiation.
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This effect melts the interior of ice and snow deposits in Antarctica, and so may do the same on Mars, an idea first proposed by Gary Clow of the US Geological Survey in 1987. But Clow assumed the liquid water would form within porous snow. On Mars, such water would still be subject to the low pressure of the atmosphere and so prone to evaporation.
M枚hlmann鈥檚 calculations assumed an impermeable upper crust of solid ice, which would form as water vapour diffused into pores and refroze. Such a seal would prevent evaporation and trap heat more effectively inside a snow bank, causing it to start melting in a zone that begins a few centimetres below the icy surface and extends a further 10 metres down, he says (Icarus, ).
鈥淢artian snow might melt in a zone that begins a few centimetres below the icy surface鈥�
of Arizona State University in Tempe says the idea has merit. 鈥淚f I was going to search for life on Mars I would certainly include landing and looking at some of these potential snow deposits,鈥� he says.
