Mars has surprisingly powerful snowstorms, which form at night.
Although the planet has relatively little water vapour in its atmosphere, clouds of water-ice crystals can still develop. A team led by Aymeric Spiga of the Laboratory of Dynamic Meteorology in Paris used a high-resolution atmospheric model to study how those clouds behave over the Tharsis Montes region of Mars.
After sunset, when the air cools, water-ice clouds radiate away heat — a process that creates strong downward- and upward-flowing winds. This atmospheric churning carries water-ice particles downward, where they precipitate out as snow.
Spacecraft orbiting Mars have detected this night-time atmospheric mixing, and NASA’s Phoenix lander also spotted streaks suspected to be snow on the ground beneath a night-time cloud. The latest work ties those observations together.
Researchers had thought that snow formation on Mars was a slow and gentle process, and will now have to rethink their ideas about the Martian water cycle.