Japan has launched the Martian Moons eXploration mission, known as MMX, an ambitious effort to study Mars’ two small moons and return material from the surface of Phobos to Earth. The Japan Aerospace Exploration Agency said the spacecraft lifted off on October 20, 2026, at 4:41:03 a.m. Japan Standard Time aboard the tenth flight of the H3 rocket from the Yoshinobu Launch Complex at the Tanegashima Space Center.
According to Reuters, the uncrewed spacecraft is expected to reach Mars in August 2027. Its central objective is to collect at least 10 grams of material from Phobos, the larger of the two Martian moons, and send a protected sample capsule back to Earth in 2031. If the mission succeeds, scientists will receive the first material ever returned from a moon of Mars.
Testing two competing origin theories
The origin of Phobos and its smaller companion, Deimos, has remained unsettled. One possibility is that the irregular bodies are asteroids captured by Mars’ gravity. Another is that they formed from debris thrown into orbit after a massive collision involving the planet. Detailed laboratory analysis of the returned material could reveal mineral and chemical signatures that distinguish between those explanations.
Phobos is an irregular body measuring roughly 27 by 22 by 18 kilometres and orbits about 6,000 kilometres above the Martian surface. Reuters reports that it circles Mars about three times each day. Its close orbit also raises the possibility that the moon’s surface contains fragments ejected from Mars by ancient impacts, adding another layer of scientific value to the samples.
International instruments and the Idefix rover
Although JAXA leads MMX, the mission includes substantial international participation. The Associated Press reports contributions from NASA and European space organisations. A compact rover named Idefix, developed by France’s CNES and Germany’s DLR, will be released onto Phobos to examine the terrain. Its observations are intended to help the main spacecraft assess the surface before attempting short operations to collect material.
The mission plan combines extended observations around Phobos, detailed mapping and more than one sampling attempt. MMX will also conduct flybys of Deimos, allowing researchers to compare Mars’ two moons. The collected material will be sealed inside a return capsule for delivery to laboratories on Earth, where instruments far more capable than those carried by a spacecraft can examine it.
A first interplanetary mission for H3
The launch is also a major milestone for Japan’s H3 rocket. MMX is the launcher’s first interplanetary mission. H3’s debut flight failed in 2023 when its second-stage engine did not ignite, but the programme subsequently completed a series of mostly successful missions. Sending MMX beyond Earth orbit is therefore an important test of the vehicle’s role in Japan’s future scientific exploration plans.
The scientific payoff will take years. MMX must first complete its cruise to Mars, enter the required trajectory, study Phobos and carry out surface operations before beginning the return journey. The sample capsule is scheduled to reach Earth in 2031. Success depends on a chain of demanding steps, including navigation across interplanetary space, operations in Mars orbit, safe contact with a very low-gravity surface, preservation of the sample and a precise return to Earth.
If those stages are completed, the mission could resolve a long-running debate about the Martian moons and offer a new record of conditions in the early solar system. The result would also extend Japan’s experience in sample-return missions after the Hayabusa programmes, while demonstrating technologies relevant to future robotic exploration around Mars.
