What are the launch date, time, location, backup window, objectives, spacecraft and international partners, travel and operational timeline, sampling and rover plans, observations of Phobos and Deimos, expected sample return date and location, scientific questions about the moons

JAXA’s Martian Moons eXploration (MMX) is a planned first sample-return mission from the Martian system: it will survey Phobos and Deimos, land on Phobos, return its material to Earth, and test capabilities relevant to future Mars exploration. 613

• Launch: H3 Flight 10 is scheduled for 20 October 2026 at 04:41:03 JST from the Yoshinobu Launch Complex, Tanegashima Space Center, Japan. The backup period is 21 October–7 November 2026; liftoff time would be set separately for each backup day. 8

• Lead spacecraft and partners: JAXA leads MMX, an orbiter/lander/sample-return spacecraft carrying 11 science instruments and the French-German IDEFIX rover. International contributors include NASA, CNES, DLR, and ESA. 2615

• Primary objectives: Determine the origin and evolution of Phobos and Deimos; characterize their geology, composition, environment and interaction with Mars; and return Phobos material for high-precision laboratory studies. 34

• Why origins matter: The leading alternatives are that the moons are captured primitive asteroids or that they formed from debris generated by a giant impact on Mars. Their composition, isotopes and ages can discriminate between these models, constrain Mars’s early evolution, and potentially reveal material ejected from ancient Mars. 245

• Flight and operations timeline: The spacecraft is expected to take roughly one year to reach Mars, enter Mars orbit and rendezvous with Phobos in FY 2027. It is planned to spend about three years in the Martian system, using quasi-satellite orbits around the moons for remote sensing, reconnaissance and selection of a Phobos landing site before departing for Earth. The overall round trip is about five years. 1613

• Phobos sampling and rover: MMX is designed for up to two Phobos touchdowns at distinct sites, using independent coring and pneumatic collection systems to obtain more than 10 grams of regolith. IDEFIX is to land before the main spacecraft, measure the surface/regolith’s physical properties and help reduce landing and sampling risk. 115

• Observations of both moons: MMX will conduct extended remote sensing of Phobos, Deimos and the Mars environment. The detailed in-situ campaign and sample collection are at Phobos; Deimos is to be observed remotely rather than landed on. 3713

• Earth return: JAXA’s current planning target is FY 2031 for Earth return, carrying a sealed return capsule—the first returned sample from the Martian sphere. The current official material found specifies the return year but does not confirm a final Earth landing/recovery location; that should therefore be treated as not yet publicly fixed. 67

• Longer-term Mars-exploration value: MMX builds on Hayabusa2-style autonomous sampling and return, while demonstrating operations around and on a tiny, irregular, low-gravity body; precise navigation; surface mobility; and sample containment/re-entry. JAXA also frames understanding the moons’ environment and their possible use as a Mars-exploration base as part of the mission’s strategic value. 1215