Plans are in place for a mission to Phobos, one of the two moons orbiting Mars, with the goal of retrieving physical samples that researchers hope will shed light on the origins of the planet and its natural satellites. Scheduled for Tuesday, JAXA's Martian Moons eXploration mission — known as MMX — is designed to scoop no fewer than 10 grams of surface material from Phobos before delivering that sample back to Earth by 2031.

Phobos and Deimos — the pair of compact natural satellites orbiting Mars — are also on the agenda, with researchers aiming to piece together how each body formed and changed over time. Researchers working on MMX hope the probe would mark the first time samples have been brought back from a Martian moon, opening a path toward hands-on laboratory analysis of material drawn directly from that part of the solar system.

Scheduled for launch from the Tanegashima Space Center atop Japan's H3 rocket, the spacecraft will make its way toward the Martian system. Phobos is the target of planned close-range study once the spacecraft arrives in 2027, with researchers aiming to map the moon's surface relief, probe its interior architecture, analyse its material makeup, and measure the pull of its gravity.

Gathering specimens from a low-mass moon — where gravitational pull is too faint to anchor conventional collection methods — stands as the defining technical hurdle ahead of the mission. A compact rover, the product of a joint engineering effort between Germany's DLR and France's CNES, is slated for deployment aboard MMX to gather surface data and advance on-site exploration.

Two distinct mechanisms will handle sample retrieval aboard the spacecraft: one bores beneath the surface to extract subsurface material through a coring action, while the other fires bursts of pressurised nitrogen gas to dislodge and draw loose surface particles up into a dedicated collection vessel. Samples collected from two separate sites on Phobos are the target, with the probe designed to bring back no fewer than 10 grams of surface material.

Gathered samples will be loaded into a re-entry vessel destined for Earth, with touchdown in South Australia's Woomera test range pencilled in for 2031.

Gaps in scientific knowledge about Phobos and Deimos place the two Martian moons at the outer edge of what researchers have managed to characterise within the inner Solar System. Researchers pursuing the question of how Mars acquired its moons are weighing two competing explanations: that the moons are captured asteroids once drifting independently through space, or that debris thrown outward by an ancient planetary collision eventually settled into orbit around Mars.

Ground-based laboratory work on those samples stands as one path toward telling these competing explanations apart. Mineral makeup, chemical fingerprints, and other properties that onboard spacecraft instruments struggle to pin down conclusively will all fall under the team's laboratory scrutiny.

Debris launched from Mars during ancient impact events could be present within the collected samples, potentially offering researchers a view into the planet's early geological record and the raw materials that once influenced its environmental conditions.

Four space agencies — NASA, ESA, DLR, and CNES — are pooling resources behind the MMX mission, which operates under JAXA's overall coordination. Alongside its research goals, the flight will put to the test a suite of technologies required for touching down on compact celestial objects, gathering surface material, and ferrying those samples back through deep space.

A completed MMX mission would place the Martian system among the few destinations from which physical samples have been brought back to Earth. Data gathered through the mission could deepen scientific understanding of how Mars and its two moons took shape over time, while also laying groundwork for future expeditions aimed at reaching the planet and gauging whether conditions there ever supported life.