How the Next Mars Mission Will Work: Japan’s Bold Journey to Phobos

Mars exploration is entering a new and unusually ambitious phase. The next major mission aimed at the Mars system is not simply another rover crawling across the planet’s surface. Japan’s Martian Moons eXploration mission—better known as MMX—will travel to Mars, study its two mysterious moons, land on Phobos, collect material from its surface, and return those samples to Earth. If it succeeds, MMX will become the first mission to bring samples back from the Mars region and one of the most technically demanding robotic expeditions ever attempted.

Mars has fascinated humanity for centuries because it appears both familiar and unreachable. It has deserts, mountains, valleys, polar ice, weather, and a day that is only slightly longer than Earth’s. Yet the planet is also hostile: its atmosphere is thin, its surface is cold and dusty, and radiation bombards everything exposed to the sky. Reaching Mars is difficult, but landing safely is harder. Returning material from Mars or one of its moons is harder still.

MMX takes a different route. Instead of immediately landing on Mars, the spacecraft will investigate Phobos, the larger and closer of the planet’s two small moons. Scientists hope that Phobos may preserve clues about how Mars formed, how its moons originated, and whether some of its surface material was blasted from Mars by ancient impacts. The mission may therefore answer questions not only about Mars, but also about the birth of planets throughout the Solar System.

The Mission’s Central Question
The most important question behind MMX is simple to ask but difficult to answer: where did Phobos come from?

Phobos is an irregular, dark, cratered object only about 27 kilometres across at its longest dimension. It orbits extremely close to Mars, completing a journey around the planet in less than eight hours. Deimos, the smaller outer moon, travels farther away. Both moons look unlike Earth’s large, round Moon, and their origins remain uncertain.

There are two leading explanations. The first is that Phobos and Deimos are captured asteroids. In this scenario, they formed elsewhere in the Solar System and were later caught by Mars’s gravity. Their dark appearance has encouraged comparisons with carbon-rich asteroids.

The second explanation is that the moons formed from material ejected when a large object struck Mars. A powerful impact could have thrown rocks and dust into orbit, eventually allowing the debris to gather into moons. If this theory is correct, Phobos could contain material directly connected to Mars.

Remote observations from orbiters and telescopes cannot fully settle the debate. Instruments can measure colour, surface composition, mineral signatures, gravity, and shape, but they are limited by distance and by the complex effects of space weathering. A laboratory on Earth can examine a sample far more carefully than a spacecraft can analyse it millions of kilometres away.

That is why sample return is the heart of MMX. The spacecraft will not merely photograph Phobos. It will bring pieces of the moon to Earth, where researchers can study them with instruments that are too large, delicate, or powerful to send into space.

What Makes Phobos Valuable?
At first glance, collecting samples from a tiny moon may seem less important than collecting them from Mars itself. However, Phobos may act as a natural archive of the Martian system.

The moon’s surface could contain three types of material:

Rock that formed as part of Phobos itself.

Dust and fragments thrown from Mars by meteorite impacts.

Material deposited by asteroids, comets, and space debris.

A returned sample may allow scientists to separate these sources. If Phobos contains unmistakable Martian minerals, researchers could examine material from Mars without having to land on the planet, drill through its surface, launch a rocket from Mars, and return the material directly to Earth.

Phobos also experiences a weak-gravity environment. A spacecraft can land and depart from it using much less energy than would be needed to launch from Mars. This makes the moon scientifically interesting and strategically important. Future astronauts or robots could potentially use Phobos as an observation platform, communications station, or staging point for Mars operations.

Yet Phobos is not an easy destination. Its gravity is weak enough that ordinary movement becomes dangerous. A spacecraft approaching too quickly could bounce away from the surface or collide with it. Dust and loose soil may behave differently from soil on Earth. The moon’s irregular shape makes navigation and landing more complicated than it would be on a spherical world.

MMX must therefore perform a carefully choreographed sequence of orbital manoeuvres, observations, surface operations, sample collection, and departure.

Step One: Leaving Earth
The mission is scheduled for launch during Japan’s fiscal year 2026 aboard the H3 rocket from Tanegashima Space Center. The launch window matters because Earth and Mars are constantly moving around the Sun. A spacecraft cannot simply point at Mars and fly in a straight line. It must be placed on an efficient trajectory that allows the spacecraft and Mars to arrive at the same region of space at approximately the same time.

The spacecraft will leave Earth with several major components integrated into one vehicle. Its design includes systems for propulsion, communication, navigation, scientific observation, landing, sample storage, and atmospheric re-entry.

The launch vehicle’s task is to provide the initial energy needed to escape Earth’s gravity and enter a heliocentric path. Once MMX is on its interplanetary trajectory, the spacecraft’s own engines will make adjustments. Small errors at launch can become large positional errors after millions of kilometres, so trajectory correction manoeuvres will be essential.

During the cruise, mission controllers will monitor the spacecraft’s health. They will check its power systems, computers, instruments, antennas, thermal control, and propulsion system. The spacecraft will rely primarily on solar power, although the amount of sunlight available changes with distance from the Sun and spacecraft orientation.

Interplanetary travel is not an empty pause between exciting events. It is an engineering phase in which every system must remain reliable for years. A computer fault, a damaged instrument, a leak, or an antenna problem could threaten the mission long before MMX reaches Phobos.

Step Two: Entering the Mars System
According to the mission plan, MMX will spend approximately one year travelling to the Mars region and is expected to arrive around 2027. It will not immediately land on Phobos. First, it must become part of the Mars system.

This involves a series of precise gravitational and engine-assisted manoeuvres. Mars has a strong gravitational field compared with Phobos, so the spacecraft must approach at the correct speed and angle. If it arrives too fast, it may fly past Mars. If it approaches incorrectly, it may enter an unwanted orbit or use too much fuel correcting its path.

Once near Mars, MMX will begin a long period of scientific observation. It will study both Phobos and Deimos, measuring their shapes, surfaces, internal structures, compositions, and gravitational environments. These observations will help mission controllers select safe locations for surface operations.

Mapping will be especially important. Phobos is covered with craters, ridges, slopes, boulders, and areas of loose material. A landing zone must be scientifically valuable but also operationally safe. The spacecraft must avoid terrain that could tip it, trap its landing gear, or interfere with its sampling mechanism.

The spacecraft’s instruments will also examine how Phobos responds to the gravity of Mars. Tiny changes in its orbit can reveal information about its internal structure. A moon that is solid rock will behave differently from one containing substantial fractures, voids, or loosely bound material.

This is one of MMX’s unique strengths: it combines planetary science with orbital mechanics. Scientists will study not only what Phobos is made of, but also how the moon moves and responds to its environment.

Step Three: Deploying the IDEFIX Rover
MMX will carry a small rover called IDEFIX, developed through cooperation involving the French space agency CNES and Germany’s DLR. The rover will be deployed onto Phobos before the main spacecraft attempts its own surface operation.

IDEFIX is important because Phobos is unlike any planetary surface previously explored by a rover. Its terrain is uncertain, its gravity is extremely weak, and ordinary driving techniques may not work as expected.

A rover on Earth can press its wheels into the ground because gravity holds it down. On Phobos, the rover’s weight is tiny. If it accelerates too quickly, strikes a rock, or climbs a steep slope, it could lose contact with the surface. Rather than driving like a car, it may need to move slowly and carefully, using specially designed wheels and mobility techniques.

The rover will help test the physical properties of the surface. Its wheels can reveal whether the soil is firm, powdery, rocky, or unstable. Cameras will document the surrounding landscape. Other instruments will investigate the texture and composition of the surface material.

This information will guide the larger MMX spacecraft. A landing system that appears safe from orbit may become hazardous when examined at ground level. IDEFIX can act as a pathfinder, providing information that cannot be obtained from distant images alone.

The rover also demonstrates an important principle for future exploration: complex missions can reduce risk by combining different machines. An orbiter can survey a large region, a rover can investigate the surface, and a stationary spacecraft can collect samples. Each vehicle performs the job for which it is best suited.

Step Four: Landing on Phobos
The most dramatic stage will be MMX’s descent to Phobos.

The spacecraft is not designed to land once and remain permanently on the surface. Instead, it must descend, make contact, collect samples, and later take off again. This is more like a controlled touch-and-go operation than a conventional planetary landing.

Before descent, the spacecraft will be placed into an orbit or trajectory that brings it close to the chosen sampling region. Controllers will use navigation data, images, and onboard sensors to refine the approach. Because communication signals take time to travel between Earth and Mars, MMX cannot be flown manually like a drone. The spacecraft must execute many actions autonomously or according to commands sent well in advance.

At the surface, the mission faces several dangers. Phobos’s gravity is weak, so the spacecraft could rebound after contact. Its surface may contain unexpected slopes or rocks. Dust could interfere with instruments or moving parts. The spacecraft may also experience forces that are difficult to reproduce perfectly in Earth-based tests.

The landing mechanism must therefore be carefully controlled. MMX needs to make contact gently enough to remain stable but firmly enough to allow sampling. The spacecraft’s position and attitude must be monitored throughout the operation.

The goal is to collect more than 10 grams of material from Phobos. That amount may seem small, but it is scientifically valuable. A few grams can contain thousands of individual grains, mineral crystals, organic compounds, and microscopic traces of geological history.

Step Five: Collecting the Sample
MMX is expected to use more than one sampling approach because no one can know exactly what the surface will be like before arrival.

One method is designed to collect loose surface material. This material may have been exposed to solar radiation, micrometeorites, and the vacuum of space for millions or billions of years. It could preserve evidence of how the surface changes under harsh conditions.

Another method may collect material from slightly below the surface. Subsurface grains can be scientifically important because they may be less altered by radiation and extreme space weathering. Comparing shallow and deeper material could show how Phobos’s surface evolves.

Once collected, the sample must be transferred into a sealed container. Contamination control will be essential. Researchers must distinguish between material that came from Phobos and particles accidentally introduced by the spacecraft, launch environment, or Earth-based handling.

The sample-return container will be kept secure during the remainder of the mission. It must survive launch from Phobos, years of travel, and high-speed re-entry into Earth’s atmosphere. The container will also need to preserve the sample in a condition suitable for laboratory analysis.

Sample return is not complete when the material is placed inside a capsule. It is complete only when scientists can open and study the material while protecting it from contamination and ensuring that any potentially sensitive compounds remain safely contained.

Step Six: Returning to Earth
After its observations and sample collection, MMX is planned to depart the Mars system around 2030 and return to Earth approximately one year later. The re-entry capsule is expected to separate from the spacecraft and enter Earth’s atmosphere during fiscal year 2031.

The return journey requires another sequence of navigation man oeuvres. MMX must leave Phobos, move away from Mars, and enter a trajectory that intersects Earth’s future position. A spacecraft launched toward Earth too early or too late could miss the planet entirely.

During the cruise, the mission team will continue checking the spacecraft and sample container. The spacecraft will also remain a scientific platform, potentially providing observations of Mars and its moons while preparing for the final phase.

The sample-return capsule will approach Earth at high speed. Its heat shield will absorb the energy generated as it passes through the atmosphere. Parachutes or other recovery systems will then slow the capsule before landing.

Recovery teams must locate the capsule quickly and transport it to a secure facility. The first priority will be preserving the sample and documenting the capsule’s condition. Scientists will then begin a carefully staged examination.

The returned material will probably be divided among laboratories in several countries. Some portions may be stored for future researchers because scientific instruments will continue improving. This is one of the lasting advantages of sample return: a sample can be tested repeatedly by generations of scientists.

Why Robots Are Sent First
MMX also illustrates why robotic missions are essential before humans travel to Mars.

Robots can survive long periods without food, water, oxygen, or psychological support. They can tolerate radiation levels that would be dangerous for people. They can also perform high-risk operations, such as landing on an unfamiliar moon, without placing astronauts in immediate danger.

A robotic mission can answer practical questions for future exploration. How stable is the surface? How much dust is present? How difficult is it to land and take off? How strong is the local radiation environment? Can communication be maintained? What resources might be available?

These questions matter because a human Mars mission would require a vast support system. Astronauts would need habitats, food, water recycling, power, medical equipment, radiation protection, spacesuits, spare parts, and a reliable return vehicle. Before humans arrive, robotic spacecraft can reduce uncertainty.

Phobos may become especially important in this context. Because it is close to Mars and has very weak gravity, it could serve as a place from which future missions observe the planet. It might also support communications or scientific operations. MMX will not build a human base, but it will provide information about whether such ideas are realistic.

Other Mars Missions on the Horizon
MMX is not the only important mission heading toward the Mars system. NASA’s ESCAPADE mission uses two identical spacecraft to study how the solar wind interacts with Mars’s magnetic environment and contributes to atmospheric escape. NASA describes ESCAPADE as a coordinated dual-spacecraft mission designed to observe the Martian environment from two locations.

The mission’s twin spacecraft are expected to arrive at Mars in September 2027. One of its scientific goals is to understand how the solar wind helps remove atmospheric particles from Mars. This research may help explain how Mars changed from a planet that once had more favorable conditions for liquid water into the cold, dry world observed today.

ESA’s Rosalind Franklin rover is another major planned mission. It is scheduled for launch between October and December 2028 and is intended to search for signs of past or present life using instruments designed for autonomous exploration and subsurface investigation.

The rover’s ability to examine material below the surface is particularly important. Mars’s surface is exposed to ultraviolet radiation and other damaging conditions. If biological traces exist, they may be better preserved underground than on the surface.

Together, these missions represent different approaches to the same broad problem. ESCAPADE studies the space environment around Mars. MMX investigates the planet’s moons and returns samples. Rosalind Franklin searches for evidence preserved beneath the Martian ground. No single mission can answer every question, but each can strengthen the scientific value of the others.

The Risks of the Journey
Every stage of MMX carries risk.

Launch vehicles can fail. Deep-space electronics can malfunction. Navigation errors can accumulate. Communication with Earth can be interrupted. A spacecraft may arrive safely at Mars but fail during orbit insertion. A rover may be deployed successfully but become stuck. A sampling mechanism may collect too little material. The return capsule may be damaged during re-entry.

The weak gravity of Phobos creates a special challenge. Many conventional instincts about landing and driving come from experience on Earth, the Moon, or Mars. Phobos is different enough that an apparently minor movement could send a vehicle bouncing across the surface or into space.

The mission also depends on international cooperation. MMX includes participation from NASA, CNES, DLR, and ESA alongside Japan’s leadership. International missions benefit from shared expertise, but they also require careful coordination of schedules, hardware, software, testing, scientific priorities, and operational decisions.

The spacecraft must be tested for conditions that cannot be perfectly reproduced on Earth. Engineers can simulate low gravity, but a laboratory cannot fully recreate the combination of vacuum, radiation, irregular terrain, communication delay, and years of autonomous operation.

Success will therefore depend not on one spectacular invention, but on thousands of reliable systems working together.

What Scientists Will Do With the Samples
When the sample capsule reaches Earth, the scientific investigation will begin in stages.

First, researchers will document the sample’s physical appearance. They will examine grain size, color, shape, density, and structure. Microscopes and imaging systems will reveal whether the material is made of volcanic rock, impact debris, carbon-rich minerals, or a mixture of different sources.

Next, laboratories will determine its chemical and mineral composition. Isotope measurements may reveal when the material formed and where it originated. Some isotopes act like geological clocks, allowing researchers to estimate the age of minerals or the timing of major events.

Scientists will also search for evidence of water-related alteration. Minerals can preserve chemical signatures of past interaction with water, even when the water disappeared billions of years ago. If Phobos contains fragments from Mars, those fragments could reveal aspects of Martian history that are not exposed on the moon’s surface.

Organic chemistry will receive careful attention. Finding an organic molecule would not automatically prove life existed, because organic compounds can form through non-biological processes. However, their structure, distribution, and relationship to minerals could reveal more about the chemistry of Mars and its moons.

The samples may also help compare Phobos with asteroids visited by other missions. If Phobos resembles a captured asteroid, its composition may support an origin in the asteroid belt or another region of the early Solar System. If its material is closely related to Martian rocks, the impact-formation theory may become stronger.

The answer may not be completely one-sided. Phobos could have a complicated history involving both captured material and debris from Mars. Samples may reveal that the moon formed through a process more complex than either simple theory suggests.

A New Model of Exploration
The most unique aspect of MMX is not only that it returns samples. It changes the way we think about exploring a planet.

Traditional planetary missions often follow a simple pattern: launch, travel, enter orbit, land, conduct experiments, and send data home. MMX is more dynamic. It will explore a planetary system rather than a single surface. It will work around Mars, visit Phobos, deploy a rover, operate near the ground, collect material, and return to Earth.

This model resembles a carefully planned expedition involving several vehicles and several destinations. It combines remote sensing with direct contact, orbital science with surface exploration, and local autonomy with global mission control.

The mission also represents a shift from observing distant worlds to bringing them into terrestrial laboratories. Photographs and measurements from Mars have transformed planetary science, but physical samples provide another level of evidence. Scientists can preserve them, compare them, reanalyses them, and test new theories as technology develops.

In this sense, MMX is not merely a mission to a small moon. It is a demonstration of how humanity may explore increasingly complex destinations in the future.

The Meaning of the Next Mars Mission
The next Mars mission will not answer every mystery about the Red Planet. It will not land astronauts, establish a city, or immediately discover life. Its importance lies elsewhere: it will test a new path toward understanding Mars.

By studying Phobos, MMX may clarify how the moon formed. By collecting samples, it may reveal whether Martian material is present on its surface. By returning those samples to Earth, it will give scientists the opportunity to investigate the Mars system with unmatched precision.

The mission’s success will depend on patience. The spacecraft will spend years traveling, observing, sampling, and returning. The most important discoveries may come long after the spacecraft has completed its journey, when laboratories around the world analyses the material grain by grain.

Mars exploration is often described as a race to reach another planet. MMX suggests a more thoughtful idea: exploration is a process of reducing uncertainty. Each mission removes one layer of ignorance. One spacecraft studies the atmosphere, another searches for life, another maps the ground, and another brings pieces of the Mars region home.

The next Mars mission will therefore be more than a technological achievement. It will be a bridge between remote exploration and laboratory science, between one planet and another, and between today’s robotic missions and tomorrows human journeys.

When the sample capsule finally returns to Earth, it may carry only a small amount of dark dust and rock. But inside those grains could be clues to the origin of Mars’s moons, the evolution of the Martian environment, and the ancient history of our entire planetary neighborhood.