Introduction
Japanese scientists are preparing a mission to retrieve samples from Mars' moons, a venture that could unlock clues about the origins of the solar system and life on Earth. The unmanned Martian Moons eXploration (MMX), scheduled to blast off from Tanegashima Space Center in the coming months, faces a competitive timetable: a rival Chinese mission aims to return samples before Japan's spacecraft does.
The spacecraft, revealed to the media last Thursday, will spend around three years in Mars' orbit, attempting to land on Phobos, the larger of the red planet's two moons. It will collect at least 10 grams (0.35 ounces) of material from Phobos' surface, while the IDEFIX rover—named after the French name for comic hero Asterix's dog—conducts surface observations. MMX will also observe Deimos, the other Martian moon, without landing, before a return capsule heads back to Earth to land in Australia in around 2031.
Scientific goals: origin of Mars' moons
The Japan Aerospace Exploration Agency (JAXA) hopes the mission will reveal how Mars and its moons formed, a key piece of knowledge in understanding how the solar system was born. Two competing theories exist: the "giant impact" hypothesis, which suggests the moons formed after a celestial body collided with Mars, and the "capture" hypothesis, which posits that they are asteroids from the outer solar system captured by Mars' gravity.
Determining which hypothesis is correct, JAXA said, will help reveal "how a habitable environment for life might have arisen on the terrestrial planets"—the four rocky worlds closest to the sun: Mercury, Venus, Earth, and Mars.
Patrick Michel, a French astrophysicist working on IDEFIX, said MMX would "shed light on the transport mechanisms that delivered water, volatiles, and organic compounds from the outer solar system to the inner rocky planet region—processes that may have played a key role in making these worlds habitable." He added that if Phobos and Deimos are remnants of these early delivery systems, they may hold clues to the origins of life or the transport of materials key to life on rocky planets.
The mission also looks beyond pure science: JAXA said it will explore the possibility of using Phobos as a "natural space station" for crewed Mars exploration, potentially laying the groundwork for human visits to the red planet.
Technical and collaborative aspects
MMX is a collaboration involving France's CNES, Germany's DLR, NASA, and ESA, as well as universities and technology companies. Akinari Uehara, an engineer at Mitsubishi Electric, described the challenge of developing the landing legs for a touch-down on Phobos, where gravity is extremely low.
Japan's space agency brings recent experience in sample-return missions and resilient landers. JAXA's Hayabusa-2 returned 5.4 grams of rock and dust from an asteroid in 2020, and its SLIM "Moon Sniper" lander tipped over after touching down on the Moon in 2024 but still transmitted data and survived several two-week lunar nights.
The competitive and geopolitical landscape
The race to bring back samples from Mars' moons is not only scientific. China's Tianwen-3 spacecraft is scheduled for launch around 2028 and aims to return samples from Mars to Earth around 2031—potentially earlier than MMX's timeline. China's Tianwen-1 mission landed the Zhurong rover on Mars in 2021, signalling the country's growing capabilities in deep-space exploration.
Meanwhile, NASA's Perseverance rover, which has been roaming Mars since 2021 and has collected samples ready for return to Earth, has effectively been cancelled by the administration of President Donald Trump following a U.S. Congress vote in January. This shift in U.S. plans leaves Japan's mission as one of the few near-term efforts to bring Martian material back to Earth.
The MMX mission represents a significant step for Japan in planetary science, combining sample-return precision with the audacity of landing on a low-gravity body. Its outcome will likely shape our understanding of the solar system's evolution and the potential for life beyond Earth.