The two moons that orbit Mars, Phobos and Deimos, are pretty dinky as far as moons go, clocking in at just 14 and 7.7 miles wide respectively and known for being rather pathetic potato-shaped bodies that more closely resemble asteroids. And so astronomers have hypothesized that they are in fact asteroids coaxed into orbit by the planet's gravitational pull, reports Space.com. Problem is, this would likely have resulted in irregular orbits, but the moons cut a nearly circular path around the Martian equator. Now, there's a new hypothesis. "Our results pave a new path to re-understand the Martian system in a context of formation similar but not identical to [that of] our own moon," says Pascal Rosenblatt of the Royal Observatory of Belgium, whose team just published the new hypothesis in the journal Nature Geoscience.
In their simulations, the team found that much like the formation of Earth's moon, Phobos and Deimos were created when a massive debris disk was ejected into orbit thanks to an impact of astronomical size. They're so small, and a pair instead of a single moon, because they were actually among many moons created by the impact, some of which may have been quite wide, reports Scientific American. The moons would have formed in the dense innards of the ejected disk, then stirred its less dense outer regions, where smaller objects like Phobos and Deimos would have formed. But due to the planet's tidal pull, the larger, inner moons would have fallen back to Mars, likely around 5 million years ago, and scientists are now looking for the enormous craters that would pockmark its surface as a result. (Here's why NASA lit a huge fire in space.)