In a new paper published in Nature Geoscience, Aymeric Spiga from the University of Paris and co-authors show that snowfall can occur on Mars—in the form of microbursts, which also are seen on Earth. Microbursts happen when cold, dense air from a cloud is moving rapidly toward the ground.
This is astounding, because the Martian atmosphere is very thin, and temperatures are well below freezing. However, because of that thin atmosphere, little water is needed to saturate the air, which results in the formation of water-ice clouds. In fact, such clouds are quite common on Mars.
Spiga demonstrated with the help of numerical simulations that microbursts and associated snowfalls should occur on Mars, too. But they would happen only at night, and would last for just a few minutes rather than hours as on Earth.
The new results are supported by previous observations from the LIDAR instrument on the Mars Phoenix mission, which detected icy crystals below a water-ice cloud during the night. The case for the existence of snowfalls is now very strong, as it is now backed up by both, observation and theoretical explanation.
These new insights have consequences for understanding the distribution of water on Mars, particularly with respect to the formation of glaciers in the equatorial regions and the planet’s evolution from a much wetter past to today’s extreme dryness. In most regions on Mars, the deposited snow would sublimate away very quickly, meaning that the snow would change to the gaseous phase directly, without ever becoming liquid. Thus, it is unlikely that these deposits of snow, even snow “storms,” would have a direct benefit on (putative) Martian life. And they are expected to occur only rarely. Nevertheless, it shows that water is available on Mars in a previously unexpected way. And it makes us wonder what other surprises the Red Planet may still have in store for us.