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Moon and Mars

November 5, 2016

For the last couple of decades, NASA’s mantra for exploring Mars has been “follow the water.” Since water is a critical ingredient for life, one of the main goals for most Mars missions has been to find evidence of water, past or present. The water can then tell us where conditions are comfortable for life today, or where they might have been comfortable in the past

But following the water can be a lot easier said than done. Consider small “gullies” found on the slopes of craters and other features.

Early studies suggested these features were formed by flowing water. The idea was that water in underground chambers might gush to the surface during spring and summer, when conditions are warm, and rush downhill, carving the gullies. The water wouldn’t stick around, though; in the thin Martian atmosphere, it would quickly boil away.

But more recent studies suggest otherwise. They found that the gullies probably are formed not by flowing water, but by carbon dioxide frost. The C-O-2 freezes on the surface when conditions are cold, and vaporizes when it warms up.

There’s still plenty of evidence of water in other places on Mars — frozen in the polar ice caps and beneath the surface, for example. Yet the Martian gullies appear to have come up dry.

Look for Mars in the evening sky right now. The planet looks like a fairly bright orange star. It’s especially easy to find tonight, because it stands close to the left of the crescent Moon.

Script by Damond Benningfield

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