Mars once had many moons

Phobos, Deimos all that’s left of larger family formed in wake of asteroid impact, simulation suggests

Martian moons

MANY MOONS AGO  Mars’ moons, Deimos (left) and Phobos (right), might have formed out of rocks blasted off the Red Planet by a large asteroid, a new study suggests.

Deimos: JPL-Caltech/NASA, U. Arizona; Phobos: ESA, DLR, FU Berlin, CC-BY-SA IGO 3.0

Mars’ misshapen moons, Phobos and Deimos, might be all that’s left of a larger family that arose in the wake of a giant impact with the Red Planet billions of years ago, researchers report online July 4 in Nature Geoscience.

The origin of the two moons has never been clear; they could be captured asteroids or homegrown satellites. But their orbits are hard to explain if they were snagged during a flyby, and previous calculations have had trouble reproducing locally sourced satellites. The new study finds that a ring of rocks blown off of the planet by a collision with an asteroid could have been a breeding ground for a set of larger satellites relatively close to the planet. Those moons, long since reclaimed by Mars, could have herded remaining debris in the sparsely populated outer part of the ring to form Phobos and Deimos.

Pascal Rosenblatt, a planetary scientist at the Royal Observatory of Belgium in Brussels, and colleagues ran computer simulations to show how the helper moons formed, did their duty and then fell to Mars, leaving behind a pair of moons similar to Phobos and Deimos.

The rain of moons is not over. While Deimos is in a stable orbit, Phobos is developing stress fractures as it slowly inches toward the Red Planet (SN: 12/12/15, p. 11).

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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