NASA spots dry ice and gullies in a Martian crater

From over 100 miles above the surface, a NASA satellite spotted dry ice and gullies inside a Martian crater.

It gets quite chilly on Mars during its winter — NASA's rovers contend with temperatures of -140 degrees Fahrenheit, though it gets much colder at the poles — allowing carbon dioxide in the atmosphere to condense into dry ice.

In this image, wintertime CO2 frost is found closer to the equator, where it's usually a bit too "warm" for dry ice to exist. Yet inside parts of the crater that receive less sunlight, frost has formed.

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But that's not all. Also visible is another curious sight on Mars: gullies. These are channels or trenches cut into the surface. The CO2 frost can act like a fluid and flow in, or form, gullies.

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Mars contains some water ice, too. In the planet's frigid Korolev crater, ice brims inside this deep basin year-round.

Planetary scientists have found evidence that water once flowed on Mars, perhaps as "recently" as 2 billion years ago. And perhaps some 4 billion years ago, it's possible Mars was even a largely blue world, with enough water to cover large swathes of the planet.

Today, the planet's surface is a harsh, dusty desert. NASA's robotic rovers are now sleuthing this arid world for any signs of primitive, past life.