JAXA’s MMX Mission Aims to Secure the First-Ever Samples from a Martian Moon for Return to Earth

A Mars probe from the Japan Aerospace Exploration Agency (JAXA) promises to resolve enduring mysteries about the Red Planet and its satellites. The Martian Moons eXploration (MMX) mission seeks to gather a minimum of 10 grams of material from Phobos. Should the endeavor succeed, it will mark the inaugural delivery of rocks from a Martian moon to terrestrial laboratories.

The journey will be protracted. The MMX spacecraft requires roughly one year to traverse the void and reach Mars. Following arrival, it will spend three years in orbit conducting sample collection operations before embarking on a year-long return voyage. Barring any complications, researchers anticipate receiving the lunar specimens by 2031.

A primary scientific objective involves determining the origin of Mars’ moons, Phobos and Deimos. Two prevailing theories exist: either the moons coalesced from debris displaced by a colossal impact with Mars, or they were asteroids originating from the outer solar system that Mars’ gravitational pull subsequently captured.

Spectral analyses indicate that the moons are dark and share reflective properties with carbon- and water-rich asteroids. Conversely, their nearly circular orbits aligned with Mars’ equatorial plane and rotational direction strongly support the giant impact hypothesis. Analyzing these samples alongside those previously obtained from the Martian surface may definitively settle this scientific dispute.

Returning these extraterrestrial specimens presents formidable technical hurdles in both spaceflight and communications. At liftoff, the spacecraft will weigh 4,480 kilograms (9,900 pounds). Over half of this mass consists of fuel, strategically divided into three reserves for the outbound journey, the exploration phase, and the return leg. Upon reaching Mars, the outbound module will be discarded once its propellant is depleted; similarly, the exploration module will be jettisoned following the Deimos flyby.

Designed by Mitsubishi Electric, the probe must execute a precarious landing on Phobos, a diminutive moon with an approximate radius of merely 11 kilometers. For context, Earth’s moon spans a radius exceeding 1,700 kilometers. Landing techniques effective on Earth’s moon rely on significantly stronger gravity—roughly 300 times that of Phobos. While Phobos’ gravitational pull is about 50 times stronger than that of the asteroid Ryugu—where JAXA previously executed probe landings via prolonged hovering—the latter method is impractical for MMX due to the excessive fuel consumption required by Phobos’s stronger gravity.

To navigate these challenges, the probe relies on high-precision autonomous navigation systems. Given the communication delay of up to 20 minutes between Earth and the spacecraft, it must independently decide upon and execute descent, landing, and ascent sequences without real-time human intervention.

As the probe descends, it will cross-reference its surroundings with topographical data of Phobos’ craters to adjust its trajectory toward the designated landing site. Below an altitude of 300 meters, the onboard systems will detect any elevation changes in the surface, flagging significant anomalies as hazardous zones. This safety mechanism enables the probe to redirect to an alternate site or abort the landing entirely and temporarily ascend if necessary.

Shortly before the main spacecraft touches down, the IDEFIX rover—developed collaboratively by the French and German space agencies—will be deployed to Phobos’s surface. Over the course of approximately 100 days, the rover will conduct independent exploration. This preliminary reconnaissance serves as a vital scouting mission to guarantee a safer touchdown for the primary spacecraft.

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