NASA / JPL-Caltech / UTA / UA / MSSS / ESA / DLR / JPL Solar System Visualization Project
Until now, it's been thought that clouds on Mars don't move water in a way that allows snow to form but new mathematical models published in Nature Geoscience today suggest it is indeed possible for convection snowstorms to occur in the Martian atmosphere — at night.
Why it matters: Researching snow on Mars has been important to understanding water on the planet and the Martian climate. "There [are] a couple of holy grails in Mars science," Hanna Sizemore, an expert on ground ice on Mars at the Planetary Science Institute who wasn't involved in the research, told Axios. "One of them is life, biology, and one of them, which is linked to the first, is understanding the water cycle." The authors say their study shows snow precipitation may have "played a key role in forming tropical and mid-latitude glaciers on Mars."
Why it happens at night and not during the day: At night there's no sunlight shining on the clouds and the ice particles floating around, so they cool down. And when they cool down, they're denser and heavier, so they fall. During the day, they're a little stabler because "warm air is moving upward in convection, but the ice clouds are being warmed from above and no cooling can take place," Isaac Smith, who works with the U.S. SHARAD team, said. Since the clouds are neither cooling nor heating, the unstable layers that drive the snowstorms can't form.
"One of the reasons this wasn't understood earlier is because this is occurring at night. Our observational data is fairly limited to daytime observations," an expert on Mars' climate history , Nathaniel Putzig, said. "It's kind of hard to catch it in the act."
What's next: Nicholas Heavens from Hampton University suggested future research might try modeling different time periods on Mars to see if those different climate conditions persisted and could have resulted in snowfall to the surface to form glaciers. Ultimately, he notes the need for "more observations to firmly demonstrate that this is happening on Mars," not just a model.