It snows on Mars at night, reports a paper published online this week in Nature Geoscience. The study simulates Martian meteorology to suggest that localized storms of rapidly falling snow - ‘microbursts’ of snowfall - can occur on Mars due to cooling of cloud water-ice particles during the night.

Because the atmosphere of Mars is cold and thin, water-ice clouds can form despite the limited amount of atmospheric water vapour compared to Earth. However, it had been thought that any snow precipitation that fell from these clouds did so as slowly settling particles, rather than in rapidly descending storms.

Here, Aymeric Spiga and colleagues use an atmospheric model to simulate the weather on Mars. They find that cooling of water-ice cloud particles during the cold Martian night can create unstable conditions within the cloud, triggering the development of a descending plume of snow. These turbulent storms, which can only form at night, act to vigorously mix the atmosphere and, in some places, deposit snow on the Martian surface. The proposed process also sheds light on the previously unexplained precipitation signatures detected by NASA’s Phoenix lander.

The authors propose that Martian snowstorms are analogous to small localized storms on Earth called microbursts, in which cold dense air carrying snow or rain is rapidly transported downwards from a cloud.