Japan's Martian Moons Exploration (MMX) mission, scheduled for launch in late 2026, targets Phobos—the larger and innermost of Mars' two tiny moons. The spacecraft will orbit the moon and deploy a lander to collect surface samples, with the primary goal of decoding its internal structure and settling a long-standing debate about its origin.
Phobos, measuring just 27 kilometers across at its widest, has long puzzled planetary scientists. Its low density and spectral properties suggest either a captured asteroid or a chunk of Mars blasted into space by an ancient impact. The MMX mission will carry a ground-penetrating radar and a suite of spectrometers to map the moon's composition and subsurface layers.
The launch window opens in late 2026, with arrival at Mars expected in 2027. The mission will spend about three years in the Martian system, performing multiple flybys of Phobos before attempting a landing to retrieve at least 10 grams of regolith. Samples are slated to return to Earth by 2031.
Resolving Phobos' origin carries profound implications for understanding Mars' early history and the broader dynamics of the inner solar system. If Phobos is a captured asteroid, it would preserve primitive material from the solar system's formation; if it is a Martian fragment, its composition could reveal crustal material otherwise inaccessible.
A key caveat remains: even with MMX's advanced instrumentation, the mission can only analyze the surface and immediate subsurface. Without drilling deeper than a few meters, the hypothesis that Phobos is a rubble pile of mixed origin—part captured asteroid, part Martian ejecta—may remain untestable.