AIBRIEF
JAXA's MMX (Martian Moons eXploration) spacecraft is in cruise to Phobos, Mars's larger moon, where a 10 gram sample could settle the captured asteroid vs. impact debris debate — and may itself carry a piece of Mars.
Japan's space agency JAXA launched the Martian Moons eXploration (MMX) probe on October 20, 2026 from Tanegashima Space Center on the H3 rocket. JAXA confirmed separation about 71 minutes after liftoff and cleared the initial critical operations phase the next day. The spacecraft is now in cruise toward Mars.
The destination is Phobos, the larger of Mars's two small moons. MMX is built to land on Phobos, scoop at least 10 grams of regolith, and return the sample to Earth over a roughly five-year round trip. The central question is whether Phobos and its sibling Deimos are captured asteroids or shards from a giant impact on ancient Mars. Phobos's regolith may also contain material blasted off Mars itself: impact ejecta from ancient Martian craters is delivered to Phobos and mixed into its regolith, which would make the sample a piece of Mars without a Mars-surface mission.
That is the test now in flight: if the 10 grams carry no Martian signature, the ejecta shortcut is closed. If they do, the next decade of Mars sample science may not need a lander. Either answer comes back in a return capsule, after a five-year clock that started Tuesday.
MMX is a world-first mission led by JAXA, built in cooperation with major European and U.S. space agencies that contributed onboard equipment, on a spacecraft that builds on the experience gained through the successful Hayabusa2 mission to an asteroid. The H3 has an uneven record of its own: concerns about the rocket delayed the mission from its planned 2024 launch.