Scientists have proposed a new explanation for the odd, lumpy appearance of Mars’ outermost moon, Deimos. By comparing high‑resolution images from the European Space Agency’s Hera spacecraft with dozens of impact simulations, the team concluded that a single, sizable asteroid collision reshaped the moon.
What the research found
Deimos, roughly 7.5 miles (12 km) across, looks like a potato and is covered in a thick layer of dust and rubble called regolith. Unlike its sibling Phobos, Deimos is relatively smooth, except for a 6.2‑mile‑wide (10 km) basin at its south pole. The study, published in Nature Astronomy, suggests that an asteroid about 1,050 feet (320 meters) wide struck the moon at a 45‑degree angle. The impact would have thrown debris across the surface, burying older craters under up to 656 feet (200 meters) of material.
Simulations indicate the collision was powerful enough to redistribute material globally but not so violent that it shattered Deimos. The moon’s porous, “rubble‑pile” interior likely absorbed much of the shock, preserving the underlying crater patterns visible in Hera’s images.
How the theory will be tested
Japan’s Martian Moons eXploration (MMX) mission, slated for launch by the end of this year, aims to orbit both Phobos and Deimos, map their surfaces in detail, and return samples from Phobos to Earth. The mission’s scientists say the new model provides concrete predictions for what MMX’s instruments should observe, especially regarding the depth and composition of Deimos’ dust layer.
“Our study offers clear expectations for the MMX mission,” said lead author Dr. Sabina Raducan, a senior fellow at the Free University of Brussels. “This helps the mission plan its observations and sample‑collection strategies.”
Broader implications
The findings add to a long‑standing debate about whether Mars’ moons are captured asteroids or fragments ejected from the planet by ancient impacts. The porous nature of Deimos suggested by the simulations aligns with the idea that it may be a loosely bound collection of rocks rather than a solid body.
Future observations from MMX, scheduled to arrive at the moons in 2027, could confirm the impact scenario and shed light on the early history of the solar system, when large planets’ gravity frequently redirected space rocks toward one another.
Original reporting: KEYT (Ventura/Santa Barbara) — read the source article.
