Japan Launches MMX Mission to Grab Piece of Mars's Moon Phobos

A Japanese spacecraft is set to launch Monday on a mission to collect 10 grams of dust from Phobos, the larger of Mars's two moons, and carry it back to Earth, according to BBC News. The Mars Moons Exploration (MMX) mission, run by the Japan Aerospace Exploration Agency (JAXA), will take until August 2027 to reach Mars, with the sample capsule not due back on Earth until 2031.

If the capsule lands as planned in Australia's Woomera desert, it would mark the first time material from Mars or its moons has been returned to Earth for laboratory analysis, the BBC reports.

What Is the MMX Mission Launching This Week?

The spacecraft departs from Japan on Monday and will first study Deimos, the smaller of Mars's two moons, as it arrives in the Mars system, before turning its full attention to Phobos. Phobos measures roughly 20 kilometers (12 miles) across; Deimos is about half that size, at roughly 10 kilometers (six miles), according to the BBC. Both moons are irregularly shaped.

How Will the Spacecraft Collect Phobos Dust?

MMX will first deploy a small rover to scout a landing site on Phobos, a maneuver Prof. Sara Russell of the Natural History Museum, the mission's deputy for sample analysis, says has never been attempted on a body this small. "The moon itself doesn't have very much of its own gravity," Russell told the BBC, "but it's next to an enormous planet that's got a much higher gravity, and that makes it much harder to get a rover onto the surface." Once the rover identifies a site, the spacecraft itself will land and use a robotic arm with two samplers to gather the moon dust.

How Much Material Will Return to Earth, and When?

The mission will bring back just 10 grams of Phobos material, packed into a capsule scheduled to land in Woomera, South Australia, in 2031. Dr. Chrysa Avdellidou of Leicester University, who works with the Japanese team, said the tiny haul is still enough for extensive research.

"It's a very small [amount] actually," Avdellidou said. "However we can do several studies even on individual grains… You don't need to have kilos back from a surface in order to do science. So it's worth every gram."

Why Does Phobos's Origin Matter to Scientists?

Mars acquired its two moons roughly 4.5 billion years ago, but researchers have never confirmed how, per the BBC. One theory holds that an impact on Mars early in its history flung out debris that coalesced into Phobos and Deimos. The competing theory holds that both moons were originally wandering asteroids captured by Mars's gravity. Russell said the sample should settle the question: "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. It should be pretty much immediately obvious."

What Could Go Wrong Before Sample Return?

No mission has previously landed, let alone returned material from, Phobos, and the rover-first landing strategy on a body with minimal gravity next to a much larger planet has no precedent, according to the BBC's reporting. Russell called the overall effort "incredibly ambitious." The roughly five-year gap between launch and sample return in 2031 leaves multiple mission phases — Deimos flyby, rover landing-site survey, sample collection and the return trip — that must each succeed in sequence.

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