At minus 100 degrees Celsius, it is certainly cold enough for ice to form in the Mars atmosphere, but these scientists relied on NASA’s Phoenix lidar to finally answer the question.
From an article in Discover by Tom Yulsman.
First, what about those clouds in the image above? If you live somewhere with wide open vistas, you’ve probably seen the phenomenon yourself: darkish streaks appearing to hang from a cloud deck.
This is called “virga” — precipitation falling from the clouds but mostly not reaching the ground. I’ve seen virga many times before, but usually in summer. This is when temperatures are high and humidity near the surface can be relatively low, causing shafts of rain falling from clouds to evaporate before the drops reach the ground.
But I shot the photo above on December 19th, two days before the winter solstice and well into meteorological winter. At the elevation of the cloud deck, temperatures were almost certainly well below freezing. So the virga probably consisted of little ice crystals. As they fell toward the ground, they simply sublimated — meaning they went from the frozen state to water vapor without first condensing into liquid.
I decided to write a post about it here at ImaGeo, and as I did my research, my mind wandered far from Colorado. All the way to Mars, which I knew had its own clouds.
I began wondering whether Martian clouds feature ice crystals streaming downward to form virga. Do ice crystals actually reach the ground as snow? And what might all of this look like from the surface?
I haven’t been the only person to think about these things. In their quest to confirm that frozen water exists on the surface of Mars, and also to learn the role it has played in the planet’s geologic history, scientists have sought answers to those very same questions.
Among them is Jim Whiteway of the Centre for Research in Earth and Space Science at York University in Toronto. He led a team of Canadian researchers that used observations from NASA’s Phoenix spacecraft to address those questions using the Phoenix lidar.
The panel on the left from the Phoenix lidar reveals a cross section of sorts of an ice fog hugging the surface, as well as a cloud above 3 kilometers in the atmosphere. The panel on the right shows what happened about an hour and a half later. Fall streaks have formed, and these ribbons of ice crystals are indeed falling all the way to the surface.
“This is our evidence that it does snow on Mars,” Whiteway says.
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