University of Kent tests show Mars rocks can reach and be preserved on Phobos

University of Kent researchers ran collision experiments and simulations showing that rocks blasted off Mars by large impacts can reach Phobos’s surface and remain preserved there, findings reported Nov. 12, 2026. |

The findings touch a central question for the Martian Moons Exploration mission: is Phobos a captured asteroid or debris from a giant impact on Mars? Scientists debate the two origins, and the impact scenario fits the moons’ orbits while raising composition questions. Preserved Martian rock on Phobos could help distinguish a captured-asteroid origin from giant-impact debris, a central goal of MMX. |

Earlier observations have shaped that debate. The Soviet Phobos 2 spacecraft in 1989 and NASA’s Infrared Telescope Facility in the 2010s found that Phobos resembles dark, primitive D-type asteroids from the outer solar system. Those observations hint at the moon’s origins, though explaining how Mars could capture two separate asteroids would be difficult. |

The Kent team fired projectiles with a light-gas gun, a device that launches projectiles at high speed, at material simulating Phobos’s surface under both proposed formation scenarios. They studied how crater formation changes with impact speed and object size, and they found the process possible under conditions that replicate natural impact processes and speeds. Europlanet, a society supporting planetary scientists, provided financial support for the experiments. |

The work is being submitted to Monthly Notices of the Royal Astronomical Society (MNRAS), and a related study on Martian grains in Phobos’s surface layer is under revision in the same journal. Dr. Emelia Branagan-Harris of the University of Oxford, Dr. Ben Rider-Stokes of The Open University, and Dr. Vassi Spathis of the Institute for Space in Leicester collaborated on detecting those Martian grains. They presented their findings at the Europlanet Science Congress in The Hague, Netherlands, in September. |

Identifying foreign material remotely would help scientists interpret observations and choose soil samples that provide the most useful information for return to Earth. University of Leicester researchers in the Hard Rocks group are preparing experiments to search for organic material on Phobos. Organic material would not by itself signal life, since nonbiological chemistry or asteroid delivery can create it, yet such material can still reveal Phobos’s past and the way the moons came to be. |

About 10 years before the Nov. 12, 2026 reports, experiments and simulations showed that colliding objects can leave material on a planetary body’s surface even at low impact velocities.

In 2023, MMX selected the lead researcher as a participating scientist on its surface science and geology science strategy team. The work centers on the processes shaping the moons’ surfaces, especially impacts, and aims to study crater numbers and sizes using observations from different spacecraft instruments. A goal is establishing whether researchers can identify foreign material on Phobos. |

Japan launched the Martian Moons Exploration mission aboard an H3 rocket from Tanegashima Space Center in southern Japan on Oct. 19, 2026, with liftoff at 3:41 p.m. EDT (4:41 a.m. Japan Standard Time). The $578 million mission began a five-year expedition to land on Phobos, Mars’s larger moon, and return soil samples to Earth, the world’s first sample return from the Martian moons. It separated from the rocket about 71 minutes after liftoff for a 10-month voyage to Mars. |

The 63-meter (207-foot) H3 is Japan’s flagship launch vehicle, and the MMX configuration used four strap-on solid boosters, full-throttle main engines, and an extended shroud. Ars Technica described the flight as Japan’s heaviest and most ambitious interplanetary mission to date. The upper stage accelerated MMX to more than 24,000 mph, enough to break free of Earth’s gravitational pull. The spacecraft weighs nearly 9,900 pounds (4.5 metric tons), with two-thirds of its mass made up of propellant. |

Ground controllers received MMX’s first signal confirming that the spacecraft was communicating normally about two weeks before the Nov. 12, 2026 reports. JAXA President Hiroshi Yamakawa declared the launch a success.

A long journey of five years has just started

Hiroshi Yamakawa, Ars Technica

Yamakawa said. Project manager Yasuhiro Kawakatsu reported that MMX established contact, unfurled its solar panels, and was in a very stable condition soon after separation. |

Japan’s science minister Yoshihiro Seki called MMX a challenging mission aiming for the world’s first sample return from the Martian moons and said he hoped its results would aid Japan’s space science and exploration technology. MMX builds on Japan’s Hayabusa and Hayabusa 2 missions, the first two spacecraft to return pristine asteroid specimens. Scientists believe Phobos could be an asteroid captured into orbit around Mars billions of years ago, and one of MMX’s science goals is determining whether that theory is correct. |

MMX will investigate both Martian moons and bring samples back from Phobos, where distinct compositions could reveal a captured-asteroid or giant-impact origin. If the moons formed from a giant impact on Mars, they could contain fragments of Martian rock and of the colliding object, evident in distinct compositions of the returned material. Direct asteroid strikes on Phobos can leave fragments behind, and scientists call material delivered to the moon from elsewhere exogenous material. |

Recovering Martian rock or asteroid material on Phobos could help reconstruct the moon’s impact history and shed light on where it came from. An alternative proposal holds that Mars captured fragments of an asteroid torn apart by its gravity, with the fragments forming a disk from which the moons evolved, a middle path between outright asteroid capture and giant-impact debris that raises the question of how an outer-solar-system object reached Mars. |