We Just Discovered Snow On Mars

Two snowflakes seen close up. These only appear on Mars at night. Alexey Kljatov/Flickr; CC BY-NC 2.0

Winter is coming – to Mars. In fact, according to a new Nature Geoscience study, it appears that it snows every night on the Red Planet, but not in the way you might expect.

Rather than having widespread snow cover, the rusty red soil sees explosions of snow known as “ice microbursts” – something that only occurs in the shadows. Think less White Christmas idyllic expansive snow clouds, and more along the lines of snow ambushes.

Even weirder still, the clouds have to be pretty low – about 1 to 2 kilometers (0.61 to 1.24 miles) above the surface  – or else the snow particles will be annihilated before they reach the rusty soil. This is because the air pressure increases rapidly as you head downwards, which in turns boosts the local temperature and causes the snow to reach evaporation-ready temperatures.

Until this point, it was thought that “snow precipitation occurs only by the slow sedimentation of individual particles,” the authors explain in their study. However, their research indicates that this isn’t the case, and that this sudden snow explosion mechanism must have affected “Mars’ water cycle, past and present”.

Thanks to its incredibly thin atmosphere, the thermal insulation on Mars is pretty low. At night, on the surface, the mercury on Mars can plunge to temperatures as low as -73°C (-100°F) on the equator and -125°C (-195°F) at the poles.

When exposed to sunlight, however, water at the equator is given just enough energy to evaporate and form low-pressure clouds – something that NASA’s Curiosity rover keeps an eye on from time to time.

A team of researchers, led by Aymeric Spiga – a planetary scientist at the National Center for Scientific Research in Paris (CNRS) – wanted to know if snowstorms could be produced by these clouds.

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Mars' ice caps are mainly composed of dry ice - frozen carbon dioxide - and not water. NASA/JPL

As aforementioned, at night, the temperature of Mars drops considerably. CNRS’s atmospheric models reveal that these clouds of water ice suddenly experience a rapid crystallization event.

At the same time, thanks to this rapid and localized redistribution of heat, the air currents around them become unstable – and both conspire to cause those water ice crystals to dramatically fall out.

Some reach the surface, but if it’s left to heat up for too long as it falls, it sublimates into a gas. These ephemeral streaks of snowfall that fail to reach their destination are known as “virgas”.

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