The Japan Aerospace Exploration Agency (JAXA) is preparing a bold sample‑return mission that could rewrite what we know about Mars and its tiny moons. The MMX (Martian Moons eXploration) spacecraft is designed to collect at least 10 grams of material from the surface of Phobos and bring it back to Earth — the first rocks ever returned from a Martian moon.
The timeline is long: MMX will spend about one year cruising to Mars, then operate in the Martian system for roughly three years before embarking on another year‑long journey home. If everything works, scientists should have Phobos samples in hand around 2031.
How did Mars’ moons form?
MMX targets one of planetary science’s big open questions: the origin of Phobos and Deimos. Two main scenarios compete:
- They condensed from debris after a giant impact on Mars.
- They are captured asteroids from the outer solar system.
The moons are dark and have reflectance spectra similar to water‑ and carbon‑rich asteroids, but their nearly circular, equatorial orbits fit better with the giant‑impact model. Comparing Phobos material with existing Martian surface samples could finally tip the balance.
Autonomous landing on a tiny world
At launch, MMX will mass about 4,480 kg (9,900 lb), more than half of which is fuel split into three reserves for outbound cruise, exploration, and return. Near Mars, the outbound module will be discarded; after a flyby of Deimos, the exploration module will also be jettisoned.
The main spacecraft, built by Mitsubishi Electric, must then land on Phobos, which has a radius of only ~11 km (Earth’s Moon is >1,700 km). Phobos’ gravity is about 300× weaker than the Moon’s but 50× stronger than that of asteroid Ryugu, where JAXA has already demonstrated small‑body landings. Hover‑style descent, used on tiny asteroids, would burn too much fuel here.
Instead, MMX carries high‑precision autonomous navigation to cope with up to 20 minutes of one‑way radio delay. During descent, the probe will continuously compare camera images with detailed topographic maps of Phobos’ craters, adjusting its trajectory toward the target site. Below 300 m altitude it will detect elevation changes, flag hazardous areas, and, if needed, divert or abort and climb away.
Just before touchdown, the IDEFIX rover — developed by the French and German space agencies — will be released to the surface for about 100 days of independent scouting, helping to validate terrain safety and science targets before the main spacecraft commits to landing.
Source: Wired
