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Monday 19 December 2016

The Universe in 101 words: Does it snow on Mars?

Above: Wintry frost on Mars, photographed by the Viking mission.
I'm a bit... obsessed... with snow*. So it’s important I ask: Mars gets frosts in winter - but does it snow? 

In fact, it snows twice! Wispy clouds have been caught dropping falls of Earth-like ‘diamond dust’ snow. But a Martian water-ice snow fall is puny, a few tiny flakes here and there: The real Martian snow is the CO2 snow - cubic flakes formed by the planet's atmosphere itself freezing in the bitter Martian winter. 

Mars is the only world where we've seen this strange snow, and in the winter of 2008 the two kinds entombed the Phoenix spacecraft...

* Blame it on Britain's ability to be freezing yet snow-less all winter, for years in a row.

Above: Crystals of the two kinds of Martian snow - H2O on the left an CO2 on the right - side by side in an electron microscope super close up..

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