Martian moon may have come from impact on home planet

Phobos, the larger of Mars' two tiny satellites, is the darkest moon in the solar system. This dark aspect inspired the hypothesis that the close-orbiting moon may be a captured asteroid, but its orbital dynamics seemed to disagree. A new study suggests Phobos' composition may be more like the volcanic crust of the Red Planet than it appears, consistent with an origin for the moon in an ancient, violent impact on Mars.

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