The Martian Moons Exploration (MMX) is a robotic space probe set for launch in 2024 to bring back the first samples from Mars' largest moon Phobos.[2][4] Developed by the Japanese Aerospace Exploration Agency (JAXA) and announced in 9 June 2015, MMX will land and collect samples from Phobos once or twice, along with conducting Deimos flyby observations and monitoring Mars' climate.[5][6]

The mission aims to provide key information to help determine whether the Martian moons are captured asteroids or the result of a larger body hitting Mars.

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The spacecraft will enter orbit around Mars, then transfer to Phobos,[7] and land once or twice and gather sand-like regolith particles using a simple pneumatic system.[8] The lander mission aims to retrieve a minimum 10 g (0.35 oz) of samples.[3][9] The spacecraft will then take off from Phobos and make several flybys of the smaller moon Deimos before sending the Sample Return Capsule back to Earth, arriving in July 2029.[7][2]

The mission architecture uses three modules: propulsion module (1,800 kg), exploration module (150 kg) and the return module (1,050 kg).[1] With the mass of Deimos and Phobos being too small to capture a satellite, it is not possible to orbit the Martian moons in the usual sense. However, orbits of a special kind, referred to as quasi-satellite orbits, can be sufficiently stable to allow many months of operations in the vicinity of the moon.[1][10]

NASA, ESA, and CNES[11] are also participating in the project, and will provide scientific instruments.[12][13] The U.S. will contribute a neutron and gamma-ray spectrometer called MEGANE (an acronym for Mars-moon Exploration with GAmma rays and NEutrons, which also means "eyeglasses" in Japanese),[7][14] and France (CNES) the Near IR Spectrometer (NIRS4/MacrOmega).[9][15] France is also contributing expertise in flight dynamics to plan the mission's orbiting and landing manoeuvres.[8]

Development and testing of key components, including the sampler, is ongoing.[16] As of 2017, MMX is scheduled to be launched in 2024, and will return to Earth five years later.[9]

Additionally, the Gravity GradioMeter (GGM), Laser-Induced Breakdown Spectroscope (LIBS), Mission Survival Module (MSM) are proposed as additional instruments.[17]
The CNES team is also conducting a study of the feasibility of including a small rover.[8]

For sample collection, the mission opted to use an air gun to puff pressurised gas, pushing about 10 grams of soil into the sample container.[18] The spacecraft will then take off from Phobos and make several flybys of the smaller moon Deimos before sending the Sample Return Capsule back to Earth, arriving in July 2029.[7][2]