Earth vs. Mars

Mars is the most Earth-like other world known, yet the two planets are really a world apart and many mysteries remain. Here's what's known:

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Looks blue from outer space, due to being two-thirds water.

Looks ruddy from outer space, due to being covered in oxidized iron. Earthlings call this "rust."

Two natural ones, Phobos and Deimos, plus two sent by NASA and more on the way.

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