Japan launches ambitious mission to explore Mars' mysterious moons

Before sunrise on Tuesday, a Japanese spacecraft lifted off from Tanegashima Island carrying humanity's first serious attempt to land on and sample Mars' moons. The five-year mission, called MMX for Martian Moons Exploration, represents an unusual moment in space exploration: five agencies—Japan leading, with NASA, France, Germany, and the European Space Agency in support—pooling resources and expertise toward a single, audacious goal. The spacecraft itself weighs five tons and carries a budget of $578 million. It will reach Mars by late summer next year.

What makes this mission unprecedented is not just its ambition but its target. While NASA has successfully landed nine spacecraft on Mars over the past half-century and China achieved a touchdown in 2021, no one has ever set foot—robotic or otherwise—on either of Mars' two moons, Phobos or Deimos. No one has brought back samples from Mars itself, much less from its satellites. The Japan Aerospace Exploration Agency is betting that it can do both. The agency has already proven its mettle with two successful asteroid sample return missions, giving it credibility for an undertaking this complex.

Phobos, the target, is a lumpy, potato-shaped rock roughly 14 miles across. It orbits Mars in a tight embrace, and the plan calls for the spacecraft to synchronize with that orbit before releasing a rover named Idefix—a nod to the white terrier from the Asterix comics, and a collaboration between French and German engineers. Idefix is small, no larger than a microwave oven, and will have to contend with Phobos' extraordinarily low gravity. When it lands, it will bounce for several minutes before settling. The rover is engineered to right itself if it lands upside down, a crucial feature given the uncertainty of the terrain. But once its solar panels deploy, that self-righting ability is lost, which is why Idefix will move at a glacial pace—one millimeter per second—across the moon's surface for roughly 100 days.

The rover's job is reconnaissance. It will scout for safe landing zones, avoiding powdery soil and jagged terrain where the main lander might get stuck. That lander, a four-legged stationary platform, will descend in late 2028 or 2029 and spend just two hours on Phobos. In that brief window, it will drill and vacuum up at least one-third of an ounce of material—10 grams of dust, soil, and rock—before launching back into space. The spacecraft will then conduct a series of flybys of Deimos, Mars' smaller moon, before departing the Martian system in 2030 and racing back to Earth. If all goes as planned, the samples will arrive in the Australian desert in 2031.

The scientific stakes are substantial. Phobos and Deimos carry secrets about Mars' own formation. Scientists want to know whether these moons coalesced from the debris of an ancient collision between Mars and a large space rock, or whether they are stray asteroids that Mars' gravity captured long ago. Either way, the moons likely bear traces of Mars itself—material ejected during impacts and re-accreted over billions of years. Studying samples from Phobos could illuminate not just how Mars' moons formed, but how moons form elsewhere in the solar system. It could also reveal whether Mars ever harbored life, a question that has driven planetary science for decades. NASA's acting planetary science director, Lindsay Hays, has said the findings will shape future Mars missions, including those carrying astronauts.

But this is not a race Japan is running alone. China plans to launch its own Mars sample return mission in 2028, also targeting a 2031 delivery. NASA, meanwhile, is still working out how to retrieve more than 30 sample tubes collected by its Perseverance rover, which has become the distance champion for off-Earth driving. The competition is real, and the stakes are high. Japan is investing $350 million in MMX. NASA is contributing $87 million, France about $68 million, Germany about $56 million, and the European Space Agency some $17 million. Together, they are betting that the payoff—understanding the Martian system at a level never before possible—justifies the risk.

That risk is not theoretical. The moons themselves carry ominous names: Phobos means fear in Greek, Deimos means dread. They are named for the twin sons of Ares, the god of war. The history of Mars exploration is littered with failures. Russia has stumbled in all three of its attempts to reach Phobos, along with many other Mars missions. Japan itself failed to get a spacecraft into orbit around Mars in its only previous attempt. Even NASA, the most successful Mars explorer by far, has experienced its share of setbacks in pursuit of answers about the red planet. The path to Phobos is treacherous. But if Japan succeeds, it will have opened a door that no one has ever opened before.