This is Scientific Americans 60 Second Science.

I'm Lee Billings.

Mars is a planet of outside splendor.

Despite being only half as big and a tenth as heavy as Earth,

it bears the solar system's tallest mountain, longest canyon, and largest

crater.

At 22 and 12 kilometers wide, however, its inner moon phobos and outer moon demos are figurative small potatoes.

Scientists suspect both formed much as Earth's single large moon did,

from a massive debris disk ejected into orbit by a giant impact eons ago.

But if Mars's moons formed like Earth's,

why are they so very much smaller?

The answer may be that they did not form alone.

New simulations from Pascal Rosenblad of the Royal Observatory of Belgium and colleagues

show how the debris disk from a giant impact on Mars could have generated additional moons

a few hundreds of kilometers in size.

After forming in the dense inner regions of the disk,

those larger moons would have stirred the disk's sparser outer reaches,

allowing smaller companions like Phobos and Demos to coalesce from the ripples.

The study appears in Nature Geo Sciences.

In this scenario, the reason we only see Phobos and Demos today is that the bigger moons were destroyed a few

million years after their formation.

Their low fast orbits outpaced Mars's rotation, creating a tidal pole that sent them spiraling down to crash into the planet.

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