Deimos reshaping: Asteroid impact explains Mars moon features

New research published in Nature Astronomy suggests that a single, violent asteroid impact significantly reshaped Deimos, one of Mars’ two moons. By analyzing imagery from the European Space Agency’s Hera mission flyby in March 2025, scientists have proposed a new explanation for the moon’s unique physical characteristics.

Deimos, a potato-shaped moon approximately 12 kilometers in diameter, is notably smoother and more covered in dust than its heavily cratered sibling, Phobos. Researchers, led by Sabina Raducan from the University of Bern, used high-resolution impact simulations to model the event. The findings suggest that a roughly 320-meter asteroid struck the moon at a 45-degree angle. This oblique collision created the large impact basin observed at the southern pole and ejected material that eventually settled back onto the surface, forming a global layer of regolith that can be over 200 meters deep.

The study indicates that Deimos likely possesses a porous, fractured internal structure that helped absorb the impact's energy without destroying the moon. These findings provide concrete predictions for the upcoming Japan Aerospace Exploration Agency (JAXA) Martian Moons eXploration (MMX) mission, which aims to conduct detailed observations and potentially return samples from the Martian moons.