Japan is preparing to launch an ambitious mission to collect material from Phobos, the larger of Mars’s two moons. The Japan Aerospace Exploration Agency calls the project Martian Moons eXploration, or MMX. Its spacecraft will survey both moons, land on Phobos, gather rocks, and send a capsule back to Earth. If successful, MMX will deliver the first samples taken directly from a Martian moon. Researchers expect those grains to preserve evidence about the moon’s origin and the early solar system. The mission also offers a new way to study Mars without landing on the planet.
The Launch and Interplanetary Journey
MMX will travel aboard Japan’s H3 rocket from Tanegashima Space Center in southern Japan. JAXA moved the mission from an earlier launch window after delays affected H3’s development schedule. The revised plan targets the 2026 Earth-to-Mars opportunity, with arrival around Mars during 2027. After departure, controllers will track the probe and refine its route through interplanetary space. Solar arrays will supply electricity, while antennas maintain communications across growing distances. That cruise phase prepares MMX for the difficult work waiting near Mars.
Navigating Near Phobos
Mars presents an unusual navigation problem because Phobos possesses very little gravity. The irregular moon measures roughly 27 kilometers across along its longest dimension. It circles Mars about 6,000 kilometers above the planet’s surface, completing each orbit in under eight hours. A conventional orbit around Phobos would become unstable under Mars’s powerful gravitational influence. Instead, MMX will follow carefully designed paths around Mars that remain close to Phobos. These quasi-satellite orbits will support mapping, gravity measurements, landing-site selection, and repeated approaches. With that orbital foundation established, the mission can address its central scientific mystery.
The Question Behind the Mission
Scientists still debate how Phobos and smaller Deimos formed. One hypothesis says Mars captured primitive asteroids that wandered inward from the outer solar system. Their dark surfaces and spectral properties resemble carbon-rich asteroids, supporting that possibility. However, capture into their nearly circular, equatorial orbits requires a mechanism that removes substantial energy. Another model proposes that a large impact blasted debris around ancient Mars. That debris could have formed a disk, which later assembled into the two surviving moons. Chemical composition, mineral structure, and isotopic ratios can distinguish between these competing histories. A returned sample gives laboratories much greater precision than remote observations alone. This question reaches beyond Mars, since moon formation accompanies planetary growth throughout the solar system.
Collecting Material in Weak Gravity
MMX aims to retrieve at least 10 grams of material from the surface of Phobos. The spacecraft will descend slowly and touch down in the moon’s extremely weak gravity. Landing legs will stabilize the vehicle while collection hardware reaches into the regolith. JAXA developed a coring sampler that gathers material mechanically from beneath the immediate surface. A second pneumatic system uses gas to move loose grains into a sample container. NASA supported development of that pneumatic sampler, adding redundancy and a different collection method. Engineers designed the operation to limit contact time and avoid an uncontrolled rebound. After sampling, MMX will lift away and secure its cargo for the homeward journey.
Instruments Build the Geological Record
Sampling represents the mission’s defining task, but orbital instruments provide essential context. High-resolution and multiband cameras will map geology, boulders, grooves, craters, and surface colors. A near-infrared spectrometer will identify minerals and examine how composition varies across Phobos. The MEGANE instrument will measure gamma rays and neutrons linked to elemental abundances. The Johns Hopkins University Applied Physics Laboratory leads MEGANE with Japanese and international partners. A laser altimeter will chart topography and help determine the moon’s shape and gravitational field. Other sensors will examine dust, ions, and the plasma environment around Mars. Together, these measurements will connect each returned grain with a documented geological setting.
IDEFIX Tests the Surface
Before the main spacecraft attempts its landing, it will deploy a compact rover onto Phobos. The German Aerospace Center and France’s CNES developed the rover, named IDEFIX. Phobos’s weak gravity creates movement conditions that no rover has previously experienced directly. IDEFIX will test controlled driving while examining surface texture, thermal behavior, and mechanical properties. Its cameras will photograph grains and terrain at scales unavailable from orbit. Wheel interactions will reveal whether the surface acts like firm soil, fluffy dust, or coarse rubble. Those observations can reduce risk for the larger spacecraft’s touchdown and sampling sequence. They also provide engineering knowledge for future missions to small bodies. The rover therefore bridges scientific exploration and practical preparation.
Science Beyond the Landing Site
MMX will also observe Deimos and Mars during its extended operations. Deimos orbits farther away and has a smoother appearance than Phobos. Comparing both moons may reveal whether they share one origin or record different events. Its sensors will also track the Martian atmosphere, including dust, clouds, and escaping particles. Phobos may add another archive because impacts can throw Martian rocks onto its surface. Some ejecta could survive there for long periods, mixed among native grains. Laboratories might therefore find small fragments representing several locations and ages on Mars. That possibility increases the sample’s value, although identifying Martian debris will require careful analysis.
Bringing the Sample Home
After completing observations, MMX will leave Mars and begin its return to Earth. The revised mission schedule calls for sample delivery in 2031, following several years near Mars. Approaching Earth, the spacecraft will release a protected reentry capsule on a precise trajectory. The capsule will endure intense heating before descending to a designated recovery area. Recovery teams will locate it, secure it, and transport the sealed contents to specialized facilities. Scientists will document every particle while controlling terrestrial contamination and preserving material for future work. JAXA gained relevant experience through Hayabusa and Hayabusa2, which returned asteroid samples successfully. MMX builds on that heritage, but Mars operations and Phobos landings create distinct challenges. Only after recovery will the mission’s most detailed investigations begin.
What Laboratories Can Reveal
Laboratories can study returned material with microscopes, mass spectrometers, and other instruments too large for spacecraft. Teams will measure isotopes, elemental chemistry, mineralogy, organic compounds, grain ages, and exposure to space. Multiple laboratories can repeat measurements, compare methods, and reserve pristine portions for improved technology. Hayabusa2 samples from asteroid Ryugu demonstrated the power of careful curation and international access. MMX researchers plan similar cooperation while protecting the scientific record of each grain. Results could confirm asteroid capture, support impact formation, or reveal a more complicated history. They could also clarify how water-bearing materials moved through the young solar system. The findings will influence models of Mars, small moons, and planet formation. That broad scientific reach explains why a modest sample can carry exceptional importance.
