By day, Mars is an arid desert. But by night, the Red Planet might have its own winter wonderland, as snow falls from the thin Martian clouds.
By John Wenz
Yes, snow on Mars, much like the frozen water crystals that fall on us in the chilly winter months. In a paper published today in Nature Geoscience, French researchers have made sense of a decades-old mystery first noticed by the Mars Phoenix lander. The laser on board that craft seemed to detect signs of precipitation, but there’s never been a definitive explanation of what was happening.
The new study used Phoenix data as well as global weather information from the Mars Reconnaissance Orbiter and Mars Global Surveyor to solve the puzzle. Gusts of wind during cold nights can hit clouds of water vapour in the Martian atmosphere with just enough force that the water vapour briefly turns into icy particles, causing “microbursts” of rapidly falling snow. Those quick snow flurries create more convection and churn up winds that sweep across the planet’s surface. The snow may not fall, but the storms have an effect on the ground.
However, few, if any, of the snowflakes actually reach the surface. The snowflakes are a thousandth of a millimetre across, and Mars’s atmosphere is so thin that the icy crystals sublimate back to vapour before they can reach the surface. In fact, it is the thin Martian atmosphere that allows the clouds to form in the first place, even though there is only a small amount of water vapour on Mars compared to Earth.
“On Earth, the snowfall you can see with the naked eye, and we have snow crystals that you can actually see, while the snowflakes on Mars are much smaller,” lead author Aymeric Spiga of Sorbonne University says of the discovery.
The Phoenix lander touched down in the north polar region of Mars in 2008, looking for signs of water ice. The spacecraft noted the unique cloud formations that Spiga and his team identified as the source of small Martian snowflakes. The clouds were thought to be water ice in nature, and they seemed to only form at northern latitudes. They can, however, originate at the equator and move north. The clouds require extremely cold temperatures, which typically come at night during the winter, as Martian summers can bring downright balmy days.
“At places where the atmosphere gets cold enough, then you will start to form clouds,” Spiga says.
Tanya Harrison, director of research for Arizona State University’s Space Technology and Science (“NewSpace”) Initiative, extensively studies weather phenomena on Mars. “The model they put forth provides an interesting alternative explanation for the detection of snow with the Phoenix Meteorological Station (MET) LiDAR instrument,” she says.
So now we know: Some nights, Mars might have a white Christmas—if only briefly.
From: PM USA