Japan launches MMX mission to bring back Phobos moon dust

Japan has launched a spacecraft bound for Phobos, one of Mars’s two moons, on a mission to collect surface dust and return it to Earth. The Mars Moons Exploration (MMX) mission, led by Japan’s space agency, is due to arrive at Phobos in August 2027.

What is the MMX mission trying to do?

The MMX spacecraft will study Deimos as it arrives in the Mars neighbourhood before focusing on Phobos. It plans to set down a small rover to explore the terrain and scout a landing site so the spacecraft itself can later touch down. Once on the surface, it will deploy a robotic arm and two samplers to grab moon dust.

If successful, it would be the first time a sample has been returned from Mars or its moons for analysis in laboratories on Earth.

How big are Mars’s moons?

There are only three moons in the inner Solar System: Earth’s Moon, and Phobos and Deimos. Phobos is about 20km (12 miles) across and Deimos about 10km (six miles) across. Both are irregularly shaped.

Why is landing a rover on Phobos difficult?

Prof Sara Russell, from the Natural History Museum, is the MMX mission’s deputy for sample analysis. She said no one has ever landed a rover on such a small moon. “The moon itself doesn’t have very much of its own gravity,” she said. “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.”

When does the sample come back, and how much is it?

The material will be packed into a small capsule scheduled to return to Earth in 2031, landing in the Woomera desert of South Australia. The amount coming back is tiny: 10g. “It’s a very small [amount] actually,” said Dr Chrysa Avdellidou, from Leicester University, who is working with the Japanese mission. “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,” she said.

What will the sample reveal about how Mars’s moons formed?

Scientists believe the sample will shed light on where Mars’s moons came from. There are two competing ideas: either a space rock smashed into Mars early in its history and Phobos and Deimos were created from the debris, or the moons are two wandering asteroids from the outer Solar System that were grabbed by the Red Planet’s gravity.

Russell said the two hypotheses will produce very distinct results. “It should be pretty much immediately obvious.. whether it’s the product of this dramatic impact or whether it’s a captured asteroid. So we’ll find that out really quickly,” she said.

Could the sample contain pieces of Mars?

Russell said Phobos is so close to the Mars surface that whenever there is an impact on Mars, little grains might become implanted into Phobos. “And that means that the sample we get back may actually contain grains of Mars as well,” she said. “So it can give us really direct information about the composition and history of Mars.”

What other missions are collecting Mars samples?

Nasa’s Perseverance rover, which has been exploring Mars since 2021, has been collecting samples and storing them in canisters. A second Nasa/ESA mission, Mars Sample Return, that would have picked up and returned those canisters has been effectively cancelled after its funding was halted by the US Congress. China is planning its own sampling mission to Mars, set to launch in 2028 and to attempt to return Martian material to Earth in 2031.

Fragments of Mars do exist on Earth as Martian meteorites, pieces blasted off the surface by asteroid strikes. They are extremely rare and become contaminated as soon as they land, mixing with air, dust, soil and water.

Frequently asked questions

When will the MMX mission arrive at Phobos?

The Mars Moons Exploration spacecraft is scheduled to arrive at Phobos, one of Mars’s two moons, in August 2027.

How much material will the MMX mission bring back from Phobos?

The mission aims to return just 10g of moon dust, packed into a small capsule that is due to land in the Woomera desert of South Australia in 2031.

Why are scientists interested in Phobos samples?

Researchers say the chemistry and mineral composition of the sample will show whether Phobos and Deimos formed from debris after an impact on Mars or were captured asteroids, and may include grains of Mars itself.

Is Nasa still bringing Mars samples back to Earth?

Nasa’s Perseverance rover has stored samples in canisters on Mars, but the Nasa/ESA Mars Sample Return mission that would have collected them has been effectively cancelled after its funding was halted by the US Congress.

With reporting from BBC News.

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