MMX factsheet

Name: Martian Moons eXploration (MMX)
Mission: To explore Mars’s moons Phobos and Deimos, and bring back a sample from Phobos  
Planned launch: 2026
Partnership: MMX is led by the Japan Aerospace Exploration Agency (JAXA), in collaboration with NASA, the French space agency CNES, the German Aerospace Center (DLR), and ESA.

Why the martian moons?: Mars has two moons, Phobos (fear) and Deimos (terror), named after the sons of Greek war god Ares, the counterpart to the Roman war god Mars. Despite the large fleet of missions sent to the Red Planet, there is much we still wish to know about the Mars system.

The martian moons remain particularly mysterious, with major open questions about how they formed and what they are made of. So far, no spacecraft have dwelled near the martian moons for very long, so we know little more than what a few fly-by measurements have revealed.

MMX will be the first mission to not only collect detailed measurements of both moons, but also land on Phobos to collect a sample and return it to Earth for analysis.

The martian moons may also be important for future Mars missions. For example, landers on Phobos could serve as data relays to rovers or astronauts, perform scientific measurements, and monitor the space environment close to Mars

Science objectives: Mars is thought to have once had a surface environment more similar to young Earth’s, with the potential for life. MMX will help answer one of the key questions of ESA’s Cosmic Vision 2015–2025, namely What are the conditions for planet formation and the emergence of life?

Based on what we know now, Phobos and Deimos may be asteroids that were captured into orbit by Mars’s gravity, or they may be the remnants of debris thrown into orbit after a large object crashed into young Mars. Mirroring our continued investigations into how Earth’s Moon formed, uncovering the history of the martian moons can teach us about the history of our home planet and other terrestrial planets in the Universe.

If the moons were formed during collisions between Mars and gigantic asteroids, then they would be made of material that records the conditions on young Mars. Alternatively, if the moons are captured asteroids, their composition will be different to Mars. In this case, they could help clarify how compounds such as water have been transported throughout the Solar System.

We are also curious about how the surfaces of Mars and its moons have changed over time. The moons will likely be covered with material ejected from Mars over billions of years.

Engineering objectives: MMX will be the first mission that returns to Earth after visiting Mars, establishing the technology needed for such a round trip. Collecting a sample from Phobos also requires landing and manoeuvring in extremely low gravity conditions, and advanced techniques for collecting a sample on celestial objects. Finally, the mission will establish optimal communication technologies using a newly developed ground station at the JAXA Usuda Deep Space Centre.

Spacecraft: MMX comprises three modules: a propulsion module, a return module and an exploration module. The mass of the entire spacecraft, including fuel, is around 4200 kg.

The propulsion module uses a chemical propulsion system to bring the spacecraft to Mars. Aside from accelerating and decelerating the spacecraft, this module hosts the guidance, navigation and control subsystem to control the orientation of the spacecraft and keep track of its location.

A high-gain dish antenna on the return module allows the spacecraft to communicate with ground stations on Earth. Power is provided through two solar panel wings. This module has its own propulsion system, consisting of a 500 Newton class orbital manoeuvring engine and a 20 Newton class reaction control system.

The spacecraft lander, the exploration module, is equipped with four landing legs, two different sampling systems and various scientific instruments. MMX will also carry a rover named Idefix to explore the surface of Phobos that will be deployed before the main spacecraft lands.

Read more about the spacecraft here.

Instruments:

Read more about the MMX instruments here.

Journey and orbit: MMX is planned for launch on a H3 rocket from the Tanegashima Space Center in Japan Fiscal Year (JFY) 2026. After arriving at Mars around a year later, it will orbit around the martian moon Phobos for three years, collecting scientific data and gathering a sample from its surface. The spacecraft will return to Earth to deliver this sample in JFY 2031.

European contributions: ESA is providing the spacecraft’s deep space communication equipment, including a transponder and power amplifier. After launch, ESA will also provide ground station support from the Estrack network to send commands and receive telemetry from the spacecraft.

The MMX InfraRed Spectrometer (MIRS), one of the eleven scientific instruments on board the spacecraft, is being developed at LESIA-Paris Observatory in collaboration with four other French laboratories (LAB, LATMOS, LAM, IRAP-OMP) and in partnership with the French space agency CNES.

The MMX Idefix rover is jointly developed by CNES and the German Aerospace Center (DLR).

Furthermore, CNES is contributing its expertise in flight dynamics to plan the mission’s complex orbiting and landing manoeuvres, and DLR is providing test equipment including a drop tower and micro-gravity simulator.

MMX mission facts

MMX will be the first mission to land on Phobos, and the first to return a sample from the Mars system to Earth.

The gravity on Phobos is so low that the 25 kg MMX rover Idefix will only weigh the equivalent of 15 grams on the Phobos surface.

MMX is equipped with two sampling systems: a corer to collect cores from a depth of two centimetres, and a pneumatic sampler which uses pressurised gas to lift material from the surface into a sample container.

At least 10 grams of Phobos material will be brought back to Earth in the Sample Return Capsule (SRC), which is around 60 cm in diameter and has a heat shield to survive re-entering Earth’s atmosphere.

The SRC will land in Australia and then be transferred to the JAXA Institute of Space and Astronautical Science (ISAS) in Sagamihara, near Tokyo. There, the SRC will be disassembled inside a specialised laboratory, and the samples will be extracted, catalogued, and made available for scientific investigations.