Japan has begun an ambitious five-year mission to retrieve material from Phobos, the larger of Mars' two moons, in a bid to answer long-standing questions about the formation of the Martian system. The Martian Moon Exploration (MMX) spacecraft lifted off before dawn on Tuesday from the Tanegashima Space Center in Kagoshima prefecture, and mission controllers confirmed an hour later that it had separated cleanly from the rocket's upper stage.
The €578 million mission is backed by five space agencies, including the European Space Agency, and carries a small rover named Idefix, developed jointly by France and Germany. The four-wheeled rover, about the size of a microwave oven, will be released onto Phobos' surface, where it will bounce for several minutes before settling in the moon's extremely low gravity. Its name, taken from the white terrier in the Asterix comics, reflects the light-hearted spirit of a project that is anything but trivial.
A first for the Martian system
No spacecraft has ever landed on Phobos or its companion Deimos, and no mission has returned samples from Mars or its moons. NASA has landed nine probes on the red planet over the past half-century, and China achieved a touchdown in 2021, but all have stopped short of bringing material back. Japan, however, has a proven track record in asteroid sample returns, having completed two such missions, which analysts say gives it a distinct edge.
“There’s a lot of adrenaline and a lot of excitement and a lot of wow,” said NASA astrophysicist Tom Statler, who is involved in the project. The mission's scientific payoff could be substantial: Phobos is a lumpy, potato-shaped rock about 22 kilometres across, and studying it may reveal whether the moons are remnants of an ancient collision between Mars and a large space rock, or stray asteroids captured by the planet's gravity. Either way, scientists expect to find traces of Mars on Phobos, making the samples a two-for-one prize that could help demystify planetary formation and even the origins of life.
Rover's cautious crawl
Idefix will serve as a “scout for safety,” according to Julien Baroukh of the French Space Agency (CNES). It will move at a glacial 1 millimetre per second, deliberately slow to avoid sinking into soft soil or getting wedged between rocks. Once its solar panels deploy, the rover can no longer right itself if it flips over, so the cautious pace is essential. The rover will spend 100 days prowling the surface, mapping safe zones for the mothership—a four-legged stationary lander—to descend in late 2028 or 2029.
The lander will spend just two hours on Phobos, drilling and vacuuming up at least 10 grams of material before launching back into space. It will then perform a series of flybys of Deimos, leave the Martian neighbourhood in 2030, and deliver the samples to the Australian desert in 2031. The mission's risks are underscored by the moons' names: Phobos means 'fear' and Deimos 'dread', fitting for the twin sons of Ares, the god of war.
European collaboration and competition
Europe's involvement is significant. The German Space Agency (DLR) contributed the rover's design and operations, with Markus Grebenstein, its rover chief, calling the mission “a once-in-a-lifetime chance. We are part of the first sample return mission from the Martian system.” The French Space Agency provided key components, and the European Space Agency is supporting the mission with tracking and communications. Japan is investing $350 million (€308 million), with NASA contributing $87 million (€77 million), CNES about $68 million (€60 million), DLR about $56 million (€49 million), and ESA some $17 million (€15 million).
The mission is not without competition. China plans to launch its own Mars sample return mission in 2028, and both Japan and China are targeting 2031 for delivery. NASA, meanwhile, is still debating how to retrieve the more than 30 sample tubes collected by its Perseverance rover. The outcome of these efforts will shape future Mars exploration, including crewed missions, said Lindsay Hays, NASA's acting planetary science director.
For now, the MMX team is celebrating a successful start. The spacecraft is expected to reach Mars by late next summer, where it will match Phobos' tight orbit before deploying Idefix. The mission's success would mark a historic first for Japan and for planetary science, and a testament to international collaboration in space exploration.
