Japan prepares to sample Phobos in search of the Martian moons’ origins

Mars has two small moons, but no agreed account of how they arrived. Were they asteroids caught by its gravity, or debris left by a giant collision? Japan’s MMX mission is preparing to look for an answer in material collected from Phobos itself.

In a 15 October update, NASA said the Japanese-led spacecraft was targeting launch from Tanegashima early on 20 October, Japan time. The mission will examine Phobos and Deimos and attempt to return a sample from Phobos. The update sets out a launch plan, rather than reporting a completed launch.

The journey will take years. Arrival at Mars is planned for August 2027. Detailed surveys would precede sampling, no earlier than December 2028, with the material due back on Earth in 2031.

Before collecting it, researchers need to understand the surface. NASA’s MEGANE instrument will measure gamma rays and neutrons to establish its elemental composition, supplying clues that laboratory analysis can later test.

Two sampling methods are planned. A Japanese device will collect material from below the surface, while a US-supplied pneumatic sampler uses bursts of high-pressure nitrogen to gather surface material.

NASA is to receive about 15% of the returned sample for curation in Houston and future research. If the mission succeeds, the debate over Phobos’s origins will gain evidence that telescopes alone cannot provide.

Sources

• NASA — MMX mission update, 15 October 2026