JAXA’s MMX Mission Will Study Mars’ Moons and Return Phobos Samples

JAXA’s Martian Moons eXploration (MMX) is a planned, Japan-led mission to investigate Phobos and Deimos and return a sample from Phobos to Earth. Its central scientific question is deceptively fundamental: are Mars’ moons captured asteroids, or did they form from debris thrown up by a major impact on ancient Mars?

If the current schedule holds, MMX will launch from Japan in October 2026, reach the Mars system about a year later, spend roughly three years surveying the moons and their environment, and return its sample capsule to Earth in 2031.

MMX launch date and mission timeline

JAXA has scheduled MMX’s launch aboard H3 Flight 10 for October 20, 2026, at 4:41:03 a.m. Japan Standard Time. The launch site is the Yoshinobu Launch Complex at the Tanegashima Space Center. The reserved launch period runs from October 21 through November 7, 2026.

The mission is designed as an approximately five-year round trip. Its main milestones are:

• 2026: Launch aboard the H3 rocket from Tanegashima.
• 2027: Arrival in the Mars system after about one year of interplanetary travel and insertion into an orbit that allows repeated observations of the moons.
• 2027–2030: Surveying Phobos, Deimos, Mars and the surrounding environment, including close approaches and planned Phobos landing operations.
• 2030: Departure from the Mars system after the observation and sampling phase.
• 2031: Return of the sample capsule to Earth, with the current recovery plan targeting the Australian desert in July.

These are mission plans rather than completed events. Launch opportunities, spacecraft health, navigation and surface conditions could affect the schedule or the eventual science return.

What the MMX spacecraft will do

MMX combines an orbiter, a lander and a sample-return spacecraft in one mission. It will first use remote sensing and orbital operations to characterize the Mars system and identify suitable conditions for work at Phobos. The spacecraft is expected to operate in quasi-satellite orbits near the Martian moons rather than simply making a single flyby.

Its primary target is Phobos, the larger and closer of Mars’ two moons. MMX plans to attempt landings on Phobos and collect regolith—surface rock and dust—using two sampling mechanisms. The complementary systems, known as the C-Sampler and P-Sampler, are intended to improve the chances of obtaining scientifically useful material.

The sample will be sealed in a return capsule for transport to Earth. JAXA’s sample-return approach builds on technology and experience developed through the Hayabusa2 asteroid mission.

Deimos will be studied remotely

Deimos is not the sample-collection target. MMX will instead observe it from orbit and during planned encounters, gathering comparative information about its surface, composition, topography and broader geological context. Studying both moons matters because their similarities and differences could help distinguish competing explanations for their origin.

The sample-return goal: more than 10 grams from Phobos

MMX aims to return more than 10 grams of Phobos material to Earth, making it the first mission intended to bring samples back from the Martian region.

The returned regolith could answer questions that remote observations alone cannot resolve. Laboratory analysis may reveal the moon’s mineral and chemical composition, provide clues about the presence of water-related materials or organic compounds, and test whether Phobos resembles a primitive asteroid or material associated with Mars.

Because Phobos may have accumulated material ejected from Mars, its regolith could also preserve indirect evidence of Martian surface history. That possibility makes the mission more than a study of a small moon: it could provide another way to investigate the evolution of Mars and the early terrestrial planets.

The main science question: captured asteroid or impact debris?

Scientists have long considered two broad formation scenarios for Phobos and Deimos:

1. Captured asteroids: The moons may be primitive bodies that formed elsewhere and were later captured by Mars’ gravity.
2. Impact fragments: They may have formed from debris produced when a large body struck early Mars and the material later reassembled.

MMX will compare the moons’ physical and chemical properties while also examining Mars’ influence on their surfaces and environments. The sample from Phobos is especially important because laboratory measurements can test composition and structure at a level that spacecraft instruments cannot fully replicate.

International contributions to MMX

Although JAXA leads MMX, the mission is an international project involving NASA, France’s CNES, Germany’s DLR and ESA.

France and Germany: the IDEFIX rover

CNES and DLR developed IDEFIX, a small rover designed to operate on Phobos. It is planned to be released before the main spacecraft’s surface operations and to measure the moon’s surface and regolith properties. Those measurements can help researchers understand the terrain and reduce risks for MMX’s landing and sampling activities. The rover’s planned surface mission is about 100 days.

NASA: the MEGANE instrument

NASA provided MEGANE, short for Mars-moon Exploration with GAmma rays and NEutrons. The instrument uses gamma-ray and neutron measurements to investigate the elemental composition of the moons. Its results will contribute directly to the question of whether Phobos is an asteroid captured by Mars or material produced by an impact.

JAXA’s role

JAXA is responsible for the spacecraft and the mission’s core operations, including navigation, remote sensing, Phobos landing attempts, sample collection, Earth return and sample curation. The mission draws on the agency’s previous sample-return experience while applying it to the more complex environment of the Mars system.

Why Phobos matters for future human missions

Phobos is also relevant to long-term Mars exploration planning. Because it orbits close to Mars, it has been discussed as a possible bridgehead or staging location for future crewed missions. A mission operating from Phobos could potentially avoid some of the challenges involved in landing on Mars and then launching back through the planet’s atmosphere.

MMX will not construct or operate a crewed station. Its contribution is more practical and preliminary: it can improve knowledge of Phobos’ surface properties, terrain, gravity environment, hazards, composition and operational accessibility. Those data could help future planners assess whether Phobos is a viable location for infrastructure, transportation or mission support.

The bottom line

MMX is significant because it combines three investigations in one campaign: a comparative survey of both Martian moons, surface operations on Phobos, and a sample return to Earth. The scheduled October 20, 2026 launch is the first step in a mission that could deliver Phobos material in 2031, clarify the moons’ origin and provide useful operational knowledge for future Mars exploration.

The most important qualification is that MMX remains a planned mission. Its headline achievements—the landing, the collection of more than 10 grams and the return of samples to Australia—are objectives, not results already secured.