Winter is Coming – Could it Snow on Mars?

Given that there are ambitious plans to colonize Mars in the near future, it is surprising how much we still have to learn about what it would be like to actually live on the planet. Take the weather, for instance. We know there are wild fluctuations in Mars’s climate and that it is very windy and at times cloudy (though too cold and dry for rainfall). But does it snow? Might settlers on Mars be able to see the red planet turn white? A new study surprisingly suggests so.

The study, published in Nature Geoscience, has found a way in which tiny specks of water-ice could travel down to the ground without the strange frozen carbon dioxide coat. If correct, this would mean genuine snow on Mars, just like that on Earth. The team used measurements from two orbiting spacecraft (the Mars Global Surveyor and Mars Reconnaissance Orbiter) to study how temperature varies with height in the Martian atmosphere.

The planet’s atmosphere is of low pressure and very dry. Although it is still possible for clouds to form at an altitude of several kilometres, until now it has been generally believed that any true snowfall would not reach the ground. The clouds, resembling Earth’s cirrus clouds, are believed to form when the small amount of water vapour in the atmosphere condenses (directly from vapour to ice) on to grains of dust lofted skywards during storms.

Fast-falling snowstorms may rage at night in certain regions of Mars. The phenomenon hasn’t been seen directly, but a group of researchers believe such storms are happening based on new computer models of the Martian atmosphere. These models suggest that it gets cold enough at night for ice particles to fall rapidly from thin clouds in the sky. This would lead to rapid downdrafts of air, travelling at about 10 metres per second, which could carry ice crystals to the surface too quickly for them to “evaporate”. However, the snow layer would probably be thin and not last too long before it sublimes back into the atmosphere, where it could form new clouds and snowfall.

The phenomenon is similar to what is known on Earth as a microburst, when a localised 60mph (97km per hour) downdraft below a thunderstorm can be powerful enough to flatten trees. The same process can also be responsible for intense snowfall at a particular location, by carrying snowflakes ground ward in a blast, punching through the near-surface layer of air that would normally be warm enough to melt them.

Snow has not yet been observed in the process of actually reaching the ground on Mars, but it has been seen falling through the sky. NASA’s Phoenix lander, which landed at 68⁰ N in 2008 and became famous for finding ice below the surface when it scraped the dirt away, studied the sky above too. It used a LIDAR (like radar but relying on reflections from a laser beam) to probe the atmosphere, and on at least two nights observed curtains of falling snow hanging below the cloud layer.

Mars emerged from its most recent ice age about 400,000 years ago. Since then, its polar caps have been small, and any ice surviving near the equator has been buried under dust.

As awesome as this is, it’ll be a long time until we’re shredding the mountains of Mars!