Single asteroid impact may explain Deimos's smooth surface

New research suggests that a single asteroid impact reshaped Deimos, Mars's smaller moon, giving it its unusually smooth, dusty surface and a large depression at its south pole. The findings, published in Nature Astronomy, are based on images from the European Space Agency's Hera mission, which flew past Mars in March 2025, combined with impact simulations.

The impact scenario

Using a smoothed particle hydrodynamics code, researchers modeled about 100 impact scenarios. The best match was a 320-meter asteroid striking Deimos at a 45-degree angle at high speed. This impact created a 10-kilometer-wide basin at the south pole and ejected vast amounts of material that blanketed the moon in regolith, hiding older craters. Source: Gizmodo

Why it matters

Deimos, about 12 kilometers in diameter, orbits Mars every 30 hours. Unlike its cratered sibling Phobos, Deimos has a smooth, dusty surface that has puzzled scientists since the Viking 2 orbiter first revealed it in 1977. The new study offers a plausible explanation and provides testable predictions for the Japanese space agency's MMX mission, scheduled for launch later this year, which aims to study both moons and return samples from Phobos. Source: CNN

Disagreement and uncertainty

While the impact hypothesis is compelling, the origin of Mars's moons remains unconfirmed. Some scientists propose they are captured asteroids, while others suggest they formed from debris ejected by impacts on Mars. The study's authors note that their model supports the latter idea, but they acknowledge that further observations are needed. Source: Gizmodo