Japan is preparing to launch a spacecraft that will collect soil from Mars' largest moon in part by blasting it with high-pressure nitrogen gas. The Martian Moons eXploration mission, known as MMX, is targeted for liftoff at 3:41 p.m. EDT on Monday, Oct. 19, from Tanegashima Space Center, according to NASA.

The Japan Aerospace Exploration Agency leads the mission, with NASA supplying a science instrument, the gas-powered sampler technology, and deep-space communications. If all goes to plan, a capsule carrying Phobos material will return to Earth in 2031.

The goal is to settle a long-running puzzle. Scientists still do not know whether Phobos and its smaller sibling, Deimos, are debris from a giant impact on Mars or asteroids that the planet captured billions of years ago.

A Sampler That Blows Soil Into a Container

The sampling plan uses two tools. A pneumatic sampler mounted on one of the lander's legs fires bursts of high-pressure nitrogen gas into the surface, lifting loose material into a collection chamber, according to NASA. A second JAXA-built coring device will dig a few inches deeper to capture material from below the top layer.

NASA's role in the gas sampler is a technology demonstration. The mechanism was developed by Honeybee Robotics, a Blue Origin company, under NASA's Discovery Program. Gas-based sampling is attractive on a small moon because Phobos has extremely weak gravity, which makes pushing a drill into the ground tricky.

The mission aims to bring back about 10 grams (roughly a third of an ounce) of Phobos material, Space.com reported. NASA will receive and curate about 15% of the returned sample at the Johnson Space Center's astromaterials lab in Houston.

Impact Debris or Captured Asteroids

Both main explanations for the moons' origin have support. Their dark, carbon-rich appearance resembles some asteroids, pointing to capture. Their nearly circular orbits close to Mars' equator are easier to explain if they formed from a disk of debris thrown up by a massive collision.

Tom Statler, NASA's MMX program executive and program scientist, said in the agency's announcement that the moons "may be the remains of a massive impact on Mars." Samples could tip the balance, because impact debris should carry chemical fingerprints of Mars itself, while captured asteroids should look like material from elsewhere in the solar system.

NASA's MEGANE instrument, built by the Johns Hopkins Applied Physics Laboratory, will help from orbit. It measures gamma rays and neutrons coming off Phobos to map which elements make up its surface, giving scientists context for where the sample came from.

The answer also matters for the early solar system. NASA said the findings may help explain how the inner planets, including Earth, acquired much of their water and organic compounds.

A Small Rover and a Long Road Home

MMX also carries a passenger. Idefix, a 55-pound (25-kilogram) rover built by Germany's space agency DLR and France's CNES, will be dropped onto Phobos and spend about three months studying its surface, DLR said. It will help scientists understand how loose and grainy the ground is, which matters for any future landings.

The timeline is long. After launch on JAXA's H3 rocket, the spacecraft is expected to reach Mars in August 2027 and begin surveying both moons. Phobos sample collection is planned for no earlier than December 2028, with the return to Earth in 2031, according to NASA.

The schedule has already slipped once. Launch was originally planned for 2024 but was delayed by problems with the H3 rocket, Space.com reported. Because Earth and Mars line up for efficient launches only about every 26 months, the current window runs from Oct. 19 to Nov. 7.

Weather and Rocket Readiness Could Shift the Launch

Launch dates for interplanetary missions can change because of weather, technical checks or range conditions. The Oct. 19 target is the first day of the window, so a delay of a day or more would not end the mission's chances this year. Readers should check JAXA and NASA updates for the latest timing.

For U.S. viewers, the launch time falls in the afternoon on the East Coast and late morning or midday in the West. JAXA typically streams its launches online, and NASA will support the mission's communications and navigation through its Deep Space Network of large radio antennas, which tracks spacecraft across the solar system. That support will continue through the multi-year cruise, the Phobos operations and the trip home.

The mission also connects to NASA's broader planetary goals. Phobos has been studied as a possible staging point for future human missions to Mars, and learning what its surface is made of and how it behaves could inform those plans, though no such mission is scheduled.

There are real risks. Landing and sampling on a small, low-gravity moon is technically demanding, and Japan's earlier asteroid sample-return missions, Hayabusa and Hayabusa2, both faced setbacks before succeeding. Scientists will not know whether MMX meets its sampling target until the spacecraft reaches Phobos late in the decade.

Nicky Fox, who leads NASA's Science Mission Directorate, said in the NASA announcement that the samples are expected to deliver paradigm-shifting science on the Mars system for generations.

Nature World News will report on the launch and on the mission's major milestones, including arrival at Mars in 2027.

The bottom line is that a few grams of dust could answer one of planetary science's more stubborn questions. If MMX succeeds, scientists will finally be able to hold pieces of a Martian moon in the lab and test where it came from.

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What Readers Want to Know

When does MMX launch?

The target is 3:41 p.m. EDT on Monday, Oct. 19, 2026, from Japan's Tanegashima Space Center. The launch window runs through Nov. 7.

How will MMX collect samples from Phobos?

A pneumatic sampler fires bursts of high-pressure nitrogen gas to lift surface material into a container, while a separate corer digs a few inches deeper.

How much material will it bring back?

The mission aims for about 10 grams of Phobos material. NASA will curate about 15% of the returned sample.

When will the samples reach Earth?

The return is planned for 2031.

What question is MMX trying to answer?

Whether Phobos and Deimos formed from debris after a giant impact on Mars or are captured asteroids.

What is NASA contributing?

The MEGANE instrument, the gas sampler technology demonstration, Deep Space Network support, and funding for U.S. scientists.