Japan launches historic mission to bring samples back from Mars moon Phobos

Japan has successfully launched an ambitious spacecraft toward Mars in an attempt to land on the mysterious moon Phobos, collect samples from its surface and return them to Earth in a mission that could resolve a decades-old scientific debate about how Mars acquired its two unusual moons.

The Japan Aerospace Exploration Agency launched its Martian Moons eXploration spacecraft, known as MMX, aboard an H3 rocket from the Tanegashima Space Center at 4:41 a.m. Japan Standard Time on October 20. JAXA confirmed that the rocket completed its planned flight and successfully separated the spacecraft approximately one hour and 11 minutes after liftoff, placing MMX onto the trajectory that will eventually carry it toward Mars.

The spacecraft is expected to reach the Martian system in August 2027 before spending years studying both Phobos and Deimos, the two small moons orbiting Mars. MMX will concentrate primarily on Phobos, where it plans to deploy a rover, land on the moon itself and collect at least 10 grams of surface material from two locations before beginning the long journey back to Earth.

If successful, the mission would accomplish something no country has done before: return physical material from one of Mars’ moons. Scientists hope those samples will reveal whether Phobos and Deimos are captured asteroids or fragments created by an enormous ancient impact involving Mars, while potentially offering new clues about how water and organic material were distributed through the early solar system.

Japan’s H3 rocket successfully sends MMX spacecraft on five-year journey to Mars

MMX lifted off from Tanegashima in southwestern Japan in the early hours of Tuesday morning, beginning a mission that JAXA has spent years developing. The H3 rocket followed its planned trajectory before releasing the roughly five-ton spacecraft into space, with JAXA confirming that MMX separated normally and was successfully inserted onto its intended flight path.

The launch was also an important milestone for Japan’s H3 rocket program. The rocket suffered a highly publicized failure during its inaugural flight in March 2023, when controllers were forced to destroy the vehicle after its second-stage engine failed to ignite. Subsequent launches restored confidence in the system, and the MMX mission marks the H3’s first attempt to send a spacecraft on an interplanetary journey.

Japan has substantial experience with sophisticated sample-return missions despite operating a smaller space program than the United States or China. Its Hayabusa spacecraft returned particles from asteroid Itokawa in 2010, while Hayabusa2 delivered samples from asteroid Ryugu to Earth in 2020 after an exceptionally complex mission.

MMX builds directly on that expertise but presents a considerably larger challenge. Rather than visiting an asteroid relatively close to Earth, the spacecraft must travel to Mars, maneuver around another planet, operate near an irregularly shaped moon with extremely weak gravity and eventually leave the Martian system carrying scientifically valuable material back toward Earth.

MMX will travel to Mars before spending years examining Phobos and Deimos

The spacecraft is scheduled to reach Mars in August 2027 and begin operating around Phobos the following month. Rather than immediately attempting a landing, MMX will spend an extended period examining the moon’s surface, gravity, composition and internal structure so scientists can identify safe areas for later operations.

Phobos is the larger of Mars’ two moons but remains tiny compared with Earth’s moon. It measures only about 27 kilometers across at its widest point and travels around Mars at an altitude of roughly 6,000 kilometers above the planet’s surface, making it one of the closest-orbiting moons to its parent planet anywhere in the solar system.

Its irregular shape and extremely weak gravity make operating near the surface particularly difficult. A spacecraft cannot approach Phobos in the same way it would land on a large planet or moon because even relatively small movements can significantly change its trajectory.

MMX will therefore conduct extensive reconnaissance before attempting to touch down. Cameras, spectrometers and other instruments will map Phobos while simultaneously collecting information about Deimos and the surrounding Martian environment, providing scientists with a far more detailed view of the two moons than previous spacecraft have been able to obtain.

Scientists want to solve the mystery of how Mars acquired its two moons

One of the mission’s central objectives is resolving the origin of Phobos and Deimos, an issue planetary scientists have debated for decades. Their small size, dark surfaces and irregular shapes resemble asteroids, leading to a long-standing theory that Mars captured the objects from elsewhere in the solar system.

That explanation creates its own difficulties because the moons travel in relatively circular, stable orbits around Mars. Capturing passing asteroids into such orderly trajectories would require a mechanism capable of removing substantial amounts of energy, and scientists have struggled to explain exactly how that could have occurred.

An alternative theory proposes that a large object collided with ancient Mars, throwing material into orbit around the planet. Debris from that impact could then have formed one or more moons, somewhat resembling theories about the formation of Earth’s own moon.

Samples from Phobos could provide a much clearer answer. Material resembling primitive asteroids would support the capture theory, while rocks showing strong chemical similarities to Mars could indicate that Phobos formed from debris blasted off the planet during an ancient collision.

Japan plans to collect at least 10 grams of material from Phobos

The most technically demanding phase of the mission will involve landing MMX on Phobos and extracting physical samples from the moon’s surface. JAXA intends to collect at least 10 grams of material from two different locations, providing scientists with enough material to conduct numerous laboratory studies after the samples return to Earth.

Ten grams may sound insignificant, but planetary scientists can extract enormous amounts of information from extremely small quantities of extraterrestrial material. Japan’s Hayabusa missions demonstrated that microscopic grains can reveal the age, chemical composition and geological history of distant objects when analyzed with sophisticated laboratory instruments.

Collecting material from two locations should also reduce the risk that scientists receive an unrepresentative sample from one unusual patch of terrain. Researchers will be able to compare material from different areas and determine whether major chemical or structural differences exist across the surface.

MMX is expected to perform its sampling operation after years of orbital observations and surface reconnaissance. The spacecraft must approach Phobos carefully, touch the surface without bouncing away in the moon’s extremely weak gravity and successfully transfer the collected material into a protected return capsule.

French-German rover Idefix will scout Phobos before main spacecraft lands

Before MMX performs its primary sampling operation, it will deploy a small rover developed jointly by the French space agency CNES and the German Aerospace Center. The rover, named Idefix, will descend to Phobos and explore the surface independently.

Idefix weighs roughly 25 kilograms and will analyze soil properties while helping researchers understand how a wheeled vehicle behaves in the moon’s extremely low gravity. Information collected by the rover can assist mission planners in assessing terrain and preparing for the larger spacecraft’s later landing attempts.

The rover also demonstrates the international nature of the project. Although JAXA leads MMX, NASA, the European Space Agency, France’s CNES and Germany’s DLR are contributing instruments, hardware and scientific expertise.

NASA is providing instruments including the Mars-moon Exploration with Gamma Ray and Neutrons experiment, known as MEGANE. The instrument will measure gamma rays and neutrons emitted from Phobos to help determine which elements are present in its surface material, providing another method of testing competing theories about the moon’s origin.

Phobos samples could contain material that originally came from Mars

Scientists are interested in Phobos for another unusual reason: its surface may contain small amounts of material blasted off Mars by asteroid impacts over billions of years. Some of that debris could have escaped the planet’s gravity temporarily before eventually landing on the nearby moon.

If such fragments are present in the samples collected by MMX, researchers could potentially study ancient Martian material without having to land directly on Mars and launch a rocket from its surface. That possibility gives the mission scientific value extending well beyond understanding Phobos itself.

Ancient Martian fragments could preserve evidence about the planet during periods when its environment was dramatically different from today. Mars once possessed rivers, lakes and a much wetter climate, and scientists continue investigating whether conditions may once have been suitable for microbial life.

JAXA describes the mission more broadly as an attempt to understand how habitable environments and the ingredients associated with life emerged in the inner solar system. Researchers hope Phobos can preserve clues about how water, carbon-rich material and other substances were transported among planets and smaller bodies during the solar system’s early history.

Successful mission would strengthen Japan’s position in global space exploration

The MMX launch comes as competition and cooperation in deep-space exploration accelerate among the world’s major space programs. The United States, China, Europe, India and Japan are all pursuing increasingly ambitious lunar, Martian and asteroid missions, often with overlapping scientific and strategic objectives.

Japan has generally emphasized specialized robotic missions rather than competing directly with the scale of NASA or China’s crewed space ambitions. Sample return has emerged as one of its strongest areas, allowing JAXA to undertake scientifically valuable missions that few other agencies have successfully completed.

A successful MMX mission would reinforce that reputation. Returning samples from Phobos would place Japan at the center of international research on the formation of the Mars system while demonstrating technologies relevant to future missions operating around small celestial bodies.

The H3 rocket is also strategically important. Japan developed the launcher as a lower-cost successor to the H-IIA and hopes to use it for government, scientific and commercial missions. Successfully sending MMX beyond Earth orbit gives the rocket program an important demonstration of its capability after the troubled first launch three years ago.

Mars sample-return ambitions are becoming an international race

MMX is launching during a period of intense interest in returning material from Mars and its surroundings. NASA and the European Space Agency have spent years developing plans to retrieve samples currently being collected by the Perseverance rover, although cost increases and technical challenges have repeatedly forced changes to that program.

China is independently developing its Tianwen-3 mission, which aims to collect material directly from the Martian surface and return it to Earth. Current schedules could place the return of Chinese Mars samples around the same period that Japan expects MMX to bring Phobos material home.

The missions are scientifically different because MMX will collect samples from a Martian moon rather than Mars itself. Even so, researchers could soon have access to multiple types of material from the Mars system, potentially transforming planetary science in the same way samples brought back from the Moon influenced research for decades.

The international competition also creates pressure to accomplish difficult engineering milestones first. Japan would secure a significant space-exploration achievement if MMX becomes the first mission to successfully land on Phobos, collect material and return it safely to Earth.

MMX is scheduled to return its Phobos samples to Earth in 2031

The journey will continue for approximately five years if the mission remains on schedule. After reaching Mars in 2027, MMX will spend several years conducting observations and preparing for its Phobos sampling operation before eventually leaving the Martian system.

The spacecraft is expected to begin its return journey after completing its scientific work and send a dedicated capsule containing the samples toward Earth. JAXA currently plans for that capsule to arrive in 2031, completing one of the longest and most technically complex sample-return missions ever attempted.

Much can happen before then. MMX must survive the interplanetary journey, enter the Martian system successfully, navigate around Phobos, deploy its rover, complete surface sampling, leave Mars and guide its return capsule safely through Earth’s atmosphere.

The successful October 20 launch therefore represents only the first major milestone. Scientists will now monitor MMX during its long cruise toward Mars before the most challenging phases begin next year.

If those phases succeed, a container holding roughly 10 grams of dark material from a small and mysterious Martian moon could eventually arrive in laboratories on Earth. From that modest amount of rock and dust, researchers hope to answer questions that have remained unresolved since Phobos and Deimos were discovered nearly 150 years ago.

Key takeaways from Japan’s MMX mission to Mars moon Phobos

• Japan successfully launched the MMX spacecraft aboard an H3 rocket from Tanegashima Space Center on October 20.
• JAXA confirmed that MMX separated successfully from the rocket approximately 71 minutes after liftoff.
• The spacecraft is expected to reach Mars in August 2027 and focus primarily on exploring the moon Phobos.
• MMX aims to collect at least 10 grams of rock and soil from two locations on Phobos before returning the samples to Earth.
• Scientists hope the material will determine whether Mars’ moons are captured asteroids or remnants of a massive ancient collision.
• A French-German rover named Idefix will explore Phobos and help characterize its surface before the main sampling operation.
• NASA, ESA and European space agencies are contributing instruments and expertise to the JAXA-led mission.
• MMX is scheduled to return to Earth in 2031, potentially completing the world’s first sample-return mission from the Martian system.