Deimos, the outermost and smaller of Mars's two moons, bears a smooth, blanketed terrain shaped by a single massive asteroid impact, according to a study published Tuesday in Nature Astronomy.
How a Single Asteroid Impact Reshaped Martian Moon Deimos
For decades, scientists have debated the origins of the prominent depression on Deimos and its unusual, dust-covered surface. While its sibling moon, Phobos, features heavy cratering, Deimos appears remarkably smooth in orbital imagery captured since the 1970s, including a March 2025 flyby by the European Space Agency’s Hera mission. To solve the mystery, lead author Dr. Sabina Raducan and co-author Dr. Martin Jutzi ran roughly one hundred computer simulations using a hydrocode developed at the University of Bern over two decades.
The team tested various asteroid sizes, velocities, impact angles, and internal structures. They found that a 320-meter asteroid striking the moon at a 45-degree angle matched observational data from the Hera spacecraft. According to Dr. Jutzi, senior researcher at the University of Bern’s Space Research and Planetary Sciences Division, the impact was violent enough to redistribute material globally but not strong enough to destroy the 12-kilometer-wide moon entirely. The internal fracturing of Deimos helped dampen the shockwaves, preserving the faint outlines of older craters beneath the fresh debris layer.
Did you know? Deimos is named after the son of the Greek god Ares, translating to “dread” in ancient Greek, reflecting its mythological connection to the god of war.
Preparing for the JAXA MMX Mission to Mars
The new findings provide testable predictions for the Martian Moons Exploration (MMX) mission by the Japan Aerospace Exploration Agency (JAXA), scheduled for launch later this year. The MMX spacecraft aims to gather detailed observations of both Phobos and Deimos and return surface samples from Phobos to Earth.
While the study establishes that the impact occurred long after Deimos formed, the exact timing remains undetermined. Researchers will rely on upcoming missions like JAXA’s MMX to date the regolith and further clarify the evolutionary history of the Martian satellite system.
Frequently Asked Questions
How big is Deimos?
Deimos measures approximately 12 kilometers in diameter, making it the smaller and outermost of the two Martian moons.
What caused the smoothing of the surface on Deimos?
According to research published in Nature Astronomy, a single asteroid impact distributed a thick layer of dust and rubble up to 200 meters deep across the moon, smoothing over older craters.
When will the next mission to the Martian moons launch?
The Martian Moons Exploration (MMX) mission by the Japan Aerospace Exploration Agency is scheduled to launch later this year.
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