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.

Rob has been producing internet content since the mid-1990s. He was a writer, editor and Director of Site Operations at Space.com starting in 1999. He served as Managing Editor of LiveScience since its launch in 2004. He then oversaw news operations for the Space.com's then-parent company TechMediaNetwork's growing suite of technology, science and business news sites. Prior to joining the company, Rob was an editor at The Star-Ledger in New Jersey. He has a journalism degree from Humboldt State University in California, is an author and also writes for Medium.