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Moon and Mars

December 4, 2015

Winter arrives here in the northern hemisphere in less than three weeks, so the north pole is cloaked in darkness. On Mars, though, it’s almost the start of northern summer, so its north pole is basking in sunlight. That allows telescopes on Earth to watch one of the planet’s most striking features: the north polar ice cap, which covers an area bigger than Texas.

Most of the cap is made of frozen water. In fact, that’s pretty much all we see during summer. During winter, though, the entire cap gets a fresh veneer of dry ice — frozen carbon dioxide that condenses out of the atmosphere.

But when spring arrives, the Sun shines on the ice cap once again. It warms the carbon dioxide, causing it to vaporize and flow back into the atmosphere. As it does so, it creates winds and eddies that can stir up dust storms. At times, these storms can cover most of the planet.

By summer, the carbon dioxide is gone, leaving only the frozen water. It’s deposited in layers that form spirals. And a giant canyon runs down the center of the ice cap. It’s as long as the Grand Canyon here on Earth, and more than a mile deep — a spectacular canyon of ice on the Red Planet.

And Mars is in the morning sky right now, shining like a moderately bright orange star. It’s in especially good view the next couple of days, because the Moon slips past it. Mars is close to the lower left of the Moon at dawn tomorrow, and to the upper right of the Moon on Sunday.

Script by Damond Benningfield, Copyright 2015

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