It’s Snowing on the Red Planet!
Bit by bit, feature by feature, Mars is slowly revealing itself to us. A century ago, it was thought of as a planet crisscrossed by a network of canals — surely the great irrigation channels of a highly advanced race. Then we flew by for a first close look in the early 1960s and saw nothing but a cratered wasteland, little better than our own moon, save for the rusty color. But closer study has revealed much more. Mars was indeed once wet, as the dry seabeds and riverways that score its surface attest. Indeed, it still has some water, as new sightings of seasonal streaking down mountain faces caused by springtime ice melt show.
Now comes word from NASA’s Mars Reconnaissance Orbiter (MRO) that it’s snowing on the Red Planet — a lot. A massive, 310-mile-diameter (500 km) cloud persists all winter long over the planet’s south polar cap, dumping snow to blizzard-level depths. The catch: this snow isn’t made from water crystals, but carbon dioxide, and that’s just a little bit of what makes the new findings — and the way they were uncovered— so intriguing.
Don’t expect captivating snowflake patterns on Mars, however. Though the scientists aren’t certain what shape the falling snow takes, Earth-based experiments suggest they are solid particles — and they’re nasty ones too. Catch one of these on your tongue and you’ve got instant frostbite.
This isn’t the first snowfall found on Mars; NASA’s Phoenix Lander mission detected falling water-ice at the planet’s northern regions in 2008. But until now, researchers had only indirect evidence of falling CO2 snow: a bed of CO2 ice on the surface, temperatures cold enough for CO2 to freeze, and satellite-based scans suggesting the presence of dense CO2 clouds. “We had all those different lines of evidence,” Hayne says, “but this is the first direct three-dimensional observation of the cloud and the composition information.”
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Image Credit: NASA/JPL/Mars Global Surveyor