Massive Asteroid Impact May Have Reshaped Mars’ Potato-Shaped Moon Deimos

A massive asteroid impact may have dramatically changed Deimos, one of Mars’ two small and mysterious moons.

New research published in Nature Astronomy suggests a single asteroid collision could explain Deimos’ unusual smooth surface, distinctive potato-like shape and a large impact basin near its southern pole.

Deimos is about 7.5 miles across and orbits roughly 14,913 miles above Mars. Unlike its more heavily cratered sibling, Phobos, Deimos has a relatively smooth surface covered by a thick layer of dust and rubble known as regolith.

Researchers used computer simulations to recreate possible asteroid impacts and compared the results with close-up images captured during the European Space Agency’s Hera mission flyby in March 2025.

The simulations identified a likely scenario involving an asteroid approximately 1,050 feet wide that struck Deimos at a 45-degree angle.

According to the researchers, the collision would have released enough debris to spread across the moon's surface, burying existing features under as much as 656 feet of material. The impact was powerful enough to reshape Deimos but apparently not strong enough to destroy it.

Researchers believe Deimos’ fractured interior helped absorb the impact's energy, allowing older craters to remain visible beneath the debris.

The findings could help scientists answer a larger question: Where did Mars’ moons come from?

Scientists have debated whether Phobos and Deimos are asteroids captured by Mars’ gravity or whether they formed from material blasted away from Mars during ancient impacts.

Japan’s Martian Moons eXploration, or MMX, mission could provide important answers. The spacecraft is expected to reach Mars’ moons in 2027 and spend about two years studying Phobos before collecting samples for return to Earth. The mission will also observe Deimos.

A sample from Phobos is expected to reach Earth in 2031.

Researchers say the MMX mission could provide the observations needed to test whether the asteroid-impact scenario accurately explains Deimos’ unusual appearance and potentially shed light on the origins of both Martian moons.

CNN contributed to this report.

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