Japan will launch its uncrewed Martian Moons Exploration probe on October 20, 2026, aiming to bring the world’s first surface samples from the Martian moon Phobos back to Earth. The flagship mission seeks to resolve long-standing debates over how Mars and its moons formed.
The Launch Window and Spacecraft Design
The Japan Aerospace Exploration Agency scheduled the liftoff of the Martian Moons eXploration probe for 4:41 a.m. on October 20, 2026, at the Tanegashima Space Center. The mission relies on the flagship H3 rocket, which has achieved consecutive successful flights recently, most notably placing a quasi-zenith satellite into orbit. Should weather or technical checks scrub the primary attempt, reserve days run from October 21 through November 7, 2026.
The mission was originally slated for 2024 but faced delays following the initial failure of the H3 rocket in 2023. Because planetary alignment permits direct interplanetary journeys only once every two years, the team had to wait for the next optimal launch window.
Led by Mitsubishi Electric, the spacecraft stands approximately 5.3 meters tall and spans about 9 meters wide with its solar arrays deployed. With a mass of roughly 4.2 to 4.5 tons at launch—carrying a total propellant load that makes up more than half its weight—it represents the largest lunar or planetary probe ever launched by Japan.
Journey to Mars and Module Separation
During its initial flight out of Earth orbit, the spacecraft operates as a combined stack consisting of three distinct modules: a propulsion module, an exploration module, and a return module. The propulsion module manages initial navigation and guidance before exhausting its propellant and being jettisoned in the Martian sphere.
The craft will take approximately one year to reach the Red Planet. Once established in Mars orbit, the mission will spend roughly three years mapping and observing both Phobos and Deimos. While the spacecraft will study Deimos extensively through remote observation, it will not land on it. Instead, the focus centers entirely on Phobos, the larger and closer moon, which measures about 14 miles across compared to Deimos at 7.8 miles wide.
Communication hardware supplied by the European Space Agency will maintain links with Earth via the return module, while scientific instruments—including the NASA-supplied MEGANE spectrometer—will gather detailed composition data.
Autonomous Landing and the Idefix Rover
Landing on Phobos presents severe engineering hurdles due to its tiny size and weak gravitational pull, which is about 50 times greater than that of the asteroid Ryugu but vastly weaker than Earth’s moon. Prolonged hovering, a technique used during JAXA’s previous asteroid missions, would burn too much fuel under Phobos’ gravitational influence.
To solve this, the probe features high-precision autonomous navigation capable of compensating for the 20-minute radio signal delay between Earth and Mars.
The mission includes the French-German rover Idefix, which will be deployed onto the surface of Phobos to conduct independent exploration.
Just before the main spacecraft touches down, it will deploy the French-German rover called Idefix—named after the comic hero Asterix’s dog—to conduct approximately 100 days of independent surface observations.
Sample Collection and the Road to 2031
Following the rover’s reconnaissance, the main probe will make contact with the surface of Phobos and collect at least 0.35 ounces of material. The samples will be sealed inside an inverted-bowl return capsule equipped with high-definition cameras developed jointly by JAXA and NHK.
The mission schedule projects departure from Mars orbit in 2030, with the return capsule landing in Australia in fiscal 2031.
The total development cost for the project stands at ¥55.3 billion. Beyond sample recovery, JAXA aims to evaluate whether Phobos could eventually serve as a natural space station to support crewed exploration of Mars.
Unlocking Solar System Origins
Scientists remain divided over whether Phobos and Deimos formed from debris ejected during a massive impact between a giant body and early Mars, or if they are captured carbon- and water-rich asteroids from the outer solar system. Analyzing pristine material in terrestrial laboratories will provide definitive chemical markers.
“could yield significant information about how water and organic matter were transported to planets within the solar system.”
Kawakatsu Yasuhiro, Project Manager
With development complete, project teams prepare for the autumn launch window. If successful, the mission will close a major chapter in planetary science by providing the first direct physical evidence from the Martian moon system.
