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.
