Headed to Mars? Remember to pack your snow gear. Turns out there are snowstorms on the Red Planet at night, according to a new paper.
The findings, published this week in the journal Nature Geoscience, could shed light on the dynamics of the planet's ancient climate — and reveal that Mars remains a more dynamic world than some scientists expected.
Today, the Red Planet seems dusty, rusty and dry, with an atmosphere that's about 100 times thinner than Earth's. But scientists say that early in its history, Mars probably looked a lot like Earth, with a thick atmosphere, puffy clouds and liquid water. That's part of why researchers study Mars — to understand why our next-door neighbor turned out so differently than our planetary home.
Even now, Mars has some thin clouds, as well as water-ice deposits on and beneath its surface. (It's cold enough to have carbon dioxide ice deposits too.) A laser instrument on NASA's Phoenix Mars Lander even discovered signs of actual snowfall, years ago. But many scientists figured that if snow was contributing to that subsurface ice, it was doing so very slowly, building up gradually over time.
Aymeric Spiga, a planetary scientist at the Laboratoire de Météorologie Dynamique in Paris, and his colleagues wondered whether some other phenomenon was at work. Thanks to data from NASA's Mars Reconnaissance Orbiter and Mars Global Surveyor, they noticed strange temperature patterns beneath the Martian water-ice clouds that hinted at a surprising amount of air movement in the atmosphere.
"It was like the temperature profiles were showing very strong mixing and were representative of very strong winds below the clouds, and it was at night," said Spiga, the lead author of the new study.
The understanding at the time, he added, "was that water-ice clouds on Mars were not supposed to create very strong winds, especially at night, and the winds at night were supposed to be very calm."
After developing models that simulated these temperature patterns, Spiga and his colleagues realized that the natural explanation for these patterns was brief but strong snowstorms, triggered by radiative cooling at night.
Snowfall on Mars, it turns out, could be much more dramatic than expected.
"It seems quite satisfying that data acquired quite a few years ago from the Phoenix lander can so nicely be explained by the model," said Paul Mahaffy, a planetary scientist at NASA's Goddard Space Flight Center who was not involved in the work.
These snowstorms aren't quite like those on Earth, Spiga pointed out. For one thing, the "snow" probably isn't made of delicate, crystalline snowflakes; instead, it's probably more like tiny chunks of ice just a few micrometers thick. But the snow would be coming down fast, he added — about as fast as during a moderate thunderstorm on Earth.
"The amount of water overall is quite small — so you won't be able to build any snowmen on Mars with that, and you won't be able to put up a ski station," Spiga quipped.
Still, the fact that so little water in such a thin atmosphere could have such a pronounced effect on the mixing of air shows that far more remains to be learned about the dynamics of the Martian atmosphere, he said.
Understanding the influence of these storms will also help researchers better understand the Red Planet's dynamics many millions of years ago, when its axial tilt toward the orbital plane was more pronounced. That meant that the poles received far more sunlight back then than they do now, resulting in a very different climate.
Mahaffy, the lead scientist in charge of instruments on NASA's Mars Curiosity rover and the MAVEN spacecraft, agreed.
"It's a little piece of the puzzle in our understanding of Mars," he said.
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