JAXA’s MMX Enroute to Mars To Return Samples of Phobos

The Japan Aerospace Exploration Agency successfully launch the Martian Moons eXploration (MMX) mission this afternoon EDT. MMX will not land on Mars, but instead explore its two moons, Phobos and Deimos, returning samples of Phobos to Earth in 2031. Japan and the U.S. have returned samples of asteroids, but this will be the first from a moon other than our own and could solve the mystery of whether Phobos is an asteroid captured by Mars’s gravity or a piece of Mars ejected by a collision.

MMX lifted off on a Mitsubishi Heavy Industries H3 rocket at 3:41 pm EDT today, Monday, October 19, 2026 — the early hours (4:41 am) of Tuesday, October 20, at the Tanegashima launch site.

MMX is headed to Mars, but instead of landing it will enter a Quasi-Satellite Orbit or QSO. That will enable it study the moons Phobos and Deimos including a landing on Phobos to collect samples for return to Earth.

The two small moons are a scientific mystery.

The larger of the two, Phobos, is just 22 kilometers (14 miles) in diameter. Deimos is even smaller, 12 km (7.5 mi). Are they asteroids captured by the gravity of Mars, or ejecta from a collision between Mars and another celestial object eons ago? The asteroid belt with its millions of asteroids — rocks left over from the formation of the solar system — lies between Mars and Jupiter. But the orbits of Phobos and Deimos are circular and aligned with Mars’s equator, not tilted. That suggests to others they weren’t randomly pulled into orbit around Mars, but instead that an impact on Mars might have ejected material into orbit where it collected into these moons.

Today’s launch was just the first leg of the journey, which will last five years. MMX will arrive at Mars in August 2027 and descend to land on Phobos no earlier than December 2028.  The samples will come back to Earth in 2031, landing in Australia just like JAXA’s two previous asteroid sample missions, Hayabusa from Itokawa in 2010 and Hayabusa2 from Ryugu in 2020.

Those two missions gave JAXA experience in landing on asteroids, which have virtually no gravity. That included rovers on the Hayabusa2 mission that explored Ryugu in 2018. One of those was a German/French “hopper” named MASCOT that operated for 17 hours. Germany’s DLR and France’s CNES teamed up again for MMX and developed a larger (25 kg) four-wheeled rover, Idefix, with solar panels and a rechargeable battery that will spend as many as 100 hours on Phobos scouting areas for MMX to land.

Idefix is just one of 13 scientific instruments on MMX, including two from NASA: the Mars-moon Exploration with GAmma rays and NEutrons (MEGANE ) spectroscopy instrument developed by the Johns Hopkins University Applied Physics Lab (APL), and the Pneumatic collection mechanism (P-Sampler) from Honeybee Robotics, part of Blue Origin.

During a pre-launch press conference last week, NASA explained MEGANE (meh-GAH-nay) will study Phobos as MMX flies close to the surface to measure the moon’s elemental composition using gamma-ray neutron spectroscopy. P-sampler is on one of the landing legs and will collect surface samples in a matter of seconds.

JAXA’s own Core sampler (C-Sampler) will drill deeper down into the Phobos surface. Other JAXA instruments include cameras to take high resolution images of the global topography of Phobos, an infrared spectrometer to study mineral composition, and others to investigate the environment around Mars globally.

JAXA isn’t the only country to return samples from elsewhere in the solar system. Six NASA Apollo crews brought back 382 kilograms (842 pounds) of Moon rocks and NASA completed its own asteroid sample return mission in 2023 with OSIRIS-REx bringing back 121.6 grams (4.29 ounces) of material from Bennu. In addition, samples of the solar wind were retrieved on NASA’s Genesis mission and dust from a comet on Stardust.