Japan has launched one of its most ambitious space exploration missions: Martian Moons eXploration, better known as MMX.
On October 20, 2026, the Japan Aerospace Exploration Agency (JAXA) sent the spacecraft toward Mars aboard an H3 rocket from the Tanegashima Space Center.
Its destination is Phobos, the larger of Mars’ two small moons.
Unlike conventional Mars missions, MMX will not focus primarily on exploring the planet’s surface. Instead, it will investigate its mysterious moons, collect material from Phobos, and bring those samples back to Earth.
If successful, MMX will become the first mission to return samples from a moon of Mars.
The five-year mission could answer fundamental questions about how Phobos and Deimos formed and reveal new details about the early history of the Solar System.
What Is the MMX Mission?
MMX stands for Martian Moons eXploration.
The mission is led by JAXA, with scientific and technical contributions from NASA, the European Space Agency, and research organizations in France and Germany.
Its main objectives include:
- Studying the surfaces and composition of Phobos and Deimos
- Investigating how the two moons formed
- Deploying a small robotic rover on Phobos
- Collecting at least 10 grams of surface material
- Returning the samples to Earth in 2031
MMX is a sample-return mission, meaning it is designed to collect material from another celestial body and deliver it to laboratories on Earth.
This approach allows scientists to perform detailed investigations using instruments too large or sensitive to send into space.
Why Is Phobos So Interesting?
Phobos is a small, irregularly shaped moon measuring approximately 27 kilometers along its longest dimension.
Its average diameter is about 22 kilometers.
It orbits extremely close to Mars, approximately 6,000 kilometers above the planet’s surface.
Phobos completes one orbit in only about 7 hours and 39 minutes, traveling around Mars faster than the planet rotates.
Its surface is covered with craters, loose dust, and rocky material known as regolith.
The enormous Stickney crater is one of its most recognizable geological features.
Unlike Earth’s Moon, Phobos has extremely weak gravity.
This makes landing, sampling, and operating robotic equipment particularly challenging.
Where Did Mars’ Moons Come From?
Scientists have debated the origins of Phobos and Deimos for decades.
One possibility is that both moons were once asteroids captured by Mars’ gravitational field.
Another suggests that they formed from material thrown into orbit after an enormous collision with early Mars.
This second explanation involves an impact-generated debris disk, a collection of fragments that could gradually accumulate into small moons.
Both ideas have supporting evidence, but important questions remain.
The moons’ dark surfaces resemble some primitive asteroids, while their nearly circular orbits close to Mars present challenges for simple asteroid-capture explanations.
The chemical composition of Phobos could provide crucial evidence for distinguishing between competing formation theories.
How Will MMX Reach and Explore Phobos?
Following its October 2026 launch, MMX is expected to reach the Martian system in August 2027.
The spacecraft will then begin observing Phobos and its surrounding environment.
Instead of following a conventional close orbit directly around the tiny moon, MMX will use a quasi-satellite orbit.
In this arrangement, the spacecraft orbits Mars while remaining close to Phobos and appearing to circle it from the moon’s perspective.
This allows detailed mapping and repeated observation without depending on a stable, very low orbit around such a small body.
Scientists will examine the moon’s shape, surface composition, geological features, and potential landing locations.
A Small Rover Will Explore the Surface
One of the mission’s most exciting components is Idefix, a compact robotic rover developed by the French space agency CNES and the German Aerospace Center DLR.
The rover is designed to operate in Phobos’ extremely weak gravitational environment.
It will carry cameras and scientific instruments to study the surface and its physical properties.
Its equipment includes an instrument that uses Raman spectroscopy, identifying minerals by examining how laser light interacts with matter.
A miniature radiometer will investigate surface temperature and thermal behavior.
The rover is expected to explore Phobos for approximately 100 days.
Its observations will also help scientists understand the challenges of operating machinery on small, low-gravity celestial bodies.
How Will MMX Collect Samples?
MMX plans to collect material from two locations on Phobos during controlled surface operations.
The mission aims to obtain at least 10 grams of samples.
This may seem like a very small quantity, but even a few grams of extraterrestrial material can contain enormous amounts of scientific information.
Researchers will examine mineral grains, chemical elements, and microscopic structures.
They may also investigate isotopic ratios, which compare the abundance of different forms of the same chemical element.
Such measurements can reveal clues about where a material originated and how it changed over time.
The collected samples will be sealed inside a return capsule for the journey home.
Could Phobos Contain Pieces of Ancient Mars?
One particularly fascinating possibility is that Phobos contains material originally blasted from Mars.
When meteorites strike a planet, some fragments can escape into space.
Because Phobos orbits so close to Mars, some of this ejected material may eventually accumulate on its surface.
Planetary scientist Ryuki Hyodo of JAXA has investigated how impact-generated material from Mars could reach Phobos.
His research suggests that such deposits might preserve information about ancient Martian environments.
MMX could potentially return microscopic fragments of Mars without landing directly on the planet.
However, identifying such material would require careful laboratory analysis.
What Scientific Instruments Does MMX Carry?
MMX is equipped with advanced imaging and measurement systems.
NASA contributes MEGANE, an instrument designed to investigate the elemental composition of Phobos by detecting gamma rays and neutrons.
Infrared observations will help scientists identify minerals and investigate surface properties.
High-resolution cameras will map geological structures and evaluate potential sampling locations.
MMX will also observe Deimos, Mars’ smaller and more distant moon, during its mission.
Comparing the two moons could help determine whether they share a common origin.
When Will the Samples Return to Earth?
After completing its observations and surface operations, MMX is scheduled to leave the Martian system in 2030.
The return journey will take approximately one year.
In 2031, a specially protected re-entry capsule containing the samples is expected to separate from the spacecraft and descend through Earth’s atmosphere.
Recovery is planned in Australia.
Scientists will then examine the material using advanced laboratory instruments.
Japan’s earlier Hayabusa and Hayabusa2 missions demonstrated the country’s experience with collecting and returning samples from small celestial bodies.
MMX builds on that heritage while attempting a significantly more distant and complex mission.
Why MMX Matters for Future Mars Exploration
The mission is about more than discovering the origin of two mysterious moons.
It will test technologies needed for navigating the Martian system, operating in low gravity, collecting samples, and returning safely to Earth.
Phobos could also become an important subject of study when planning future human exploration of Mars.
Understanding its surface conditions, composition, and environment may help evaluate possible future scientific operations near the Red Planet.
MMX represents a major step toward understanding Mars through the history preserved in its neighboring moons.
Interesting Facts
- Phobos completes an orbit around Mars in approximately 7 hours and 39 minutes.
- Phobos is gradually moving closer to Mars because of tidal interactions.
- The Stickney crater is approximately 9 kilometers across.
- MMX launched on October 20, 2026, Japan Standard Time.
- The spacecraft aims to return at least 10 grams of material from Phobos.
- The Idefix rover is designed to operate in an environment with extremely weak gravity.
- Phobos may contain tiny fragments of rock originally ejected from Mars.
- The mission is scheduled to return its samples to Earth in 2031.
- MMX will also investigate Deimos, the smaller of Mars’ two moons.
Glossary
- Sample-Return Mission — A space mission that collects material from another celestial body and returns it to Earth for laboratory analysis.
- Regolith — Loose rock fragments, dust, and other material covering the surface of a celestial body.
- Impact-Generated Debris Disk — A collection of fragments created by a major collision and distributed around a planet.
- Quasi-Satellite Orbit — An orbital arrangement in which a spacecraft follows a planet-centered path while remaining near a moon.
- Raman Spectroscopy — An analytical technique that identifies materials through changes in scattered laser light.
- Isotopic Ratios — Measurements comparing the abundance of different isotopes of a chemical element.
- Re-Entry Capsule — A protected spacecraft container designed to survive atmospheric entry and deliver its contents to Earth’s surface.
