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.
Mars' ice caps are mainly composed of dry ice - frozen carbon dioxide - and not water.
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.
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”. The atmospheric conditions on Mars are simply too unstable and mercurial to allow regular snow to fall. Unlike Earth, the Red Planet is a world of extremes – and right now, only robots, not humans, get to experience it for real.
Sadly though, most of the robots on Mars are unable to see these storms in person.
“Snowstorms could be occurring above Curiosity or other rovers – undetected!” Spiga said, adding that, indirectly, “snow precipitation has been spotted solely by the Mars Phoenix lander at night, using LIDAR laser sounding.”
You may be wondering about the ice caps on Mars too. They contain more ice than Earth’s Greenland Ice Sheet, but they’re not just made of water ice, but frozen carbon dioxide. Could you get sudden nighttime snowstorms of carbon dioxide too, instead of only water?
“You might. The convection in CO2 snowstorms would be triggered by the energy released when CO2 vapor condenses into CO2 ice particles; kind of like thunderstorms on Earth with the condensation of water.” Spira said.
Mars isn’t the only extraterrestrial world that experiences snow, by the way. Jupiter’s volcanic moon Io experiences a global sulfuric snowstorm when it moves into the gas giant’s shadow.