Japan Prepares Mission to Bring Home First-Ever Samples From a Martian Moon
JAXA plans to launch its MMX probe in October to collect at least 10 grams of material from Mars' moon Phobos, with samples expected back on Earth in 2031. The mission aims to help resolve how Mars' moons formed and may also capture traces of Martian dust.
Japan's space agency, JAXA, is preparing to launch a probe called MMX, short for "Martian Moons eXploration," designed to bring back the first-ever rock samples from a moon of Mars. The target is Phobos, one of the planet's two moons, and the goal is to collect at least 10 grams of material.
The journey will take roughly a year to reach Mars, followed by three years of exploration in orbit around the planet, and another year for the return trip to Earth. If the mission goes as planned, scientists expect to have the samples in hand by 2031.
An Open Question About Origins
One of the central mysteries MMX could help resolve is how Phobos and Deimos, Mars' two moons, came to exist. Researchers have proposed two competing explanations: that the moons formed from debris thrown off after a massive collision with Mars, or that they are captured asteroids originally from the outer solar system. The moons' dark coloring and reflective properties resemble asteroids rich in water and carbon, but their nearly circular orbits along Mars' equatorial plane point more toward the impact scenario. Comparing the new samples with material already collected from Mars' surface could help settle the debate.
Engineering Hurdles
At launch, the spacecraft will weigh 4,480 kilograms, with fuel making up more than half that mass across three separate reserves for the outbound trip, exploration phase, and return journey. Landing on Phobos, which has a radius of only about 11 kilometers, poses unique challenges: its gravity is far weaker than that of Earth's moon but noticeably stronger than that of the asteroid Ryugu, where JAXA has landed probes before. Because radio signals can take up to 20 minutes to travel between Earth and the probe, MMX relies on autonomous navigation to handle descent, landing, and takeoff without real-time human guidance, including the ability to reroute or abort if hazards are detected.
Shortly before the main spacecraft lands, a rover called IDEFIX, developed jointly by the French and German space agencies, will be deployed to Phobos' surface to spend about 100 days scouting the terrain and helping ensure a safer landing site. Samples will be gathered both by a robotic drilling arm and by a device that uses nitrogen gas to capture fine surface dust. Scientists estimate that roughly 0.1 percent of the collected material could actually be debris from Mars itself, deposited on the moon by past meteorite impacts.
The mission carries a price tag of about $345 million and marks Japan's first Mars probe launch in 28 years. MMX is scheduled to lift off from the Tanegashima Space Center on October 20, 2026.
