Mars once had rings and a much bigger moon, new evidence suggests

Mars may have once had a giant ring that eventually got smooshed to form one of its oddly-shaped moons, new research suggests.

Mars has two small, lumpy moons, Phobos and Deimos. Phobos orbits closer to the Red Planet and follows the line of Mars’ equator. Deimos orbits farther away, along an orbit that’s tilted by 2 degrees off the plane of the Martian equator. The wonky orbit adds evidence to the idea that Phobos may once have been a giant ring that eventually coalesced into its present shape.In 2017, a team of researchers argued in the journal Nature Geoscience that the Martian moons go through cycles — ripped apart into thin rings by the planet’s gravity, then eventually forming moons again. In each cycle, the moon formed from the ring is smaller than its former self, with bits of the rings falling out of orbit and drifting out into space. Over billions of years, generations of moons would have gone through these cycles of ring-moon-ring, scientists suspect. 

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