A spacecraft launched from Japan is now on its way to Phobos, one of Mars's two small moons, where it will attempt something no mission has ever managed: landing a rover on the moon's surface, scooping up a sample of its dust, and bringing it back to Earth for analysis. If it succeeds, it would be the first time material from Mars or either of its moons has ever been returned to a laboratory on Earth.
The Mars Moons Exploration mission, led by the Japan Aerospace Exploration Agency, is scheduled to arrive in the Mars system in August 2027. "There hasn't yet been a successful mission to go to Phobos and bring a bit back to Earth," said Professor Sara Russell of the Natural History Museum, the mission's deputy for sample analysis. "I think this is an incredibly ambitious and fun mission."
A Puzzle 4.5 Billion Years Old
Mars's two moons, Phobos and Deimos, are tiny and irregularly shaped — Phobos is about 20km across, Deimos roughly 10km — and scientists have never been sure how they formed. One theory holds that a space rock smashed into Mars early in its history and the moons coalesced from the debris; the other holds that they are captured asteroids, wanderers from the outer solar system grabbed by the planet's gravity. "When we get the sample back, we'll be able to look in detail at its chemistry and its mineral composition, and the two hypotheses will produce very distinct results," Russell said. "It should be pretty much immediately obvious."
The spacecraft will first study Deimos as it arrives, then focus on Phobos, deploying a small rover to scout a landing site — no small task, since, as Dr Chrysa Avdellidou of Leicester University put it, "the moon itself doesn't have very much of its own gravity," making it far harder to set a rover down safely than on a larger body. The mission will then collect roughly 10 grams of surface material using a robotic arm and two samplers, a tiny haul by Earth standards but, Avdellidou said, "worth every gram" given how much can be learned from individual grains. There is also a chance of an unplanned bonus: because Phobos orbits so close to Mars, scientists believe impacts on the Martian surface may occasionally implant grains of actual Mars material onto the moon itself.
The sample capsule is due to land in the Woomera desert of South Australia in 2031. The mission comes as Nasa's own Mars Sample Return project, designed to retrieve samples already gathered by the Perseverance rover, has been effectively cancelled after Congress halted its funding — leaving Japan's smaller, cheaper mission as the most advanced active attempt to bring any piece of the Martian system home. China has said it plans its own Mars sampling mission, targeting a 2028 launch and a 2031 return.