Japan launches bold mission to explore Mars' mysterious moons and return samples by 2031

Before dawn on Tuesday, a Japanese spacecraft lifted off from Tanegashima Island carrying humanity's first serious attempt to land on and sample the moons of Mars. The five-year mission, called MMX for Martian Moons Exploration, represents an unusual moment in space exploration: five world space agencies—Japan leading, with NASA, France, Germany, and the European Space Agency in support—pooling resources and expertise toward a single, audacious goal. By 2031, if all goes as planned, samples of dust, soil, and rock from Phobos will be sitting in the Australian desert, having traveled nearly 140 million miles.

Phobos itself is an unprepossessing target: a lumpy, potato-shaped rock roughly 14 miles across, orbiting Mars in a tight, fast loop. No spacecraft has ever landed there. No one has ever collected samples from any Martian moon. NASA has successfully landed nine rovers and landers on Mars over the past five decades, and China achieved a touchdown in 2021, but Phobos and its smaller sibling Deimos remain untouched. Japan, however, arrives at this challenge with an advantage—two successful asteroid sample-return missions already completed, proof that the Japanese space agency knows how to retrieve material from distant worlds and bring it home.

The $578 million spacecraft, weighing five tons, will reach Mars by late summer 2027. Once there, it will synchronize with Phobos' orbit and deploy a rover called Idefix, named after the white dog in the Asterix comic books. Idefix is small—no larger than a microwave oven—and designed for an environment almost incomprehensibly hostile to Earth machines. Phobos' gravity is so weak that when Idefix lands, it will bounce for several minutes before settling. The rover moves at a glacial pace: one millimeter per second, or about 0.04 inches per second. This slowness is deliberate. If the rover's solar panels deploy and it lands upside down, it cannot right itself. Soft soil or a wedge between rocks could trap it permanently. For 100 days, Idefix will scout the terrain, mapping safe zones where the main lander can touch down.

That lander—a four-legged stationary platform—will arrive in late 2028 or 2029. It will have just two hours on Phobos' surface. In that window, it must drill and vacuum up at least 10 grams of material, then launch back into space. The mothership will also conduct a series of flybys of Deimos, Mars' smaller moon, before departing the Martian system in 2030 and beginning the long journey home.

The scientific stakes justify the risk. Phobos and Deimos are thought to hold clues to Mars' deep history. Scientists want to know whether these moons formed from the debris of an ancient collision between Mars and a large space rock, or whether they are stray asteroids captured by Mars' gravity billions of years ago. Either way, Phobos likely carries traces of Mars itself—material kicked up by impacts and deposited on the moon's surface. Samples would offer a two-for-one window into planetary formation and the conditions that might have supported life. The findings will inform future human missions to Mars, according to NASA's acting planetary science director Lindsay Hays.

The path to this moment is littered with failure. Russia attempted three missions to Phobos and failed at all three. Japan's only previous Mars mission failed to achieve orbit. Even NASA, with its track record of success on Mars, has experienced setbacks in the broader effort to answer whether life ever existed on the red planet. The moons themselves carry ominous names—Phobos means fear, Deimos means dread, both sons of Ares, the god of war. Yet the scientific community views this mission as a once-in-a-lifetime opportunity, in the words of the German Space Agency's rover chief Markus Grebenstein.

Japan is not alone in pursuing Martian samples. China plans to launch its own sample-return mission to Mars in 2028, also targeting a 2031 return. NASA is still working out how to retrieve more than 30 sample tubes collected by the Perseverance rover, which holds the record for distance traveled by any off-Earth vehicle. The race is on, and the stakes—both scientific and geopolitical—are high. Japan is investing $350 million in MMX. NASA contributes $87 million, France about $68 million, Germany about $56 million, and the European Space Agency $17 million. The next five years will determine whether this coalition succeeds in bringing home the first samples ever collected from the Martian system.