Japanese scientists are preparing a mission to the moons of Mars to collect samples that could reveal the origins of the solar system and life on Earth, although a rival Chinese mission aims to return first. The Unmanned Martian Moon eXploration (MMX), scheduled to launch from the Tanegashima Space Centre in the coming months, could also lay the groundwork for humans to visit the red planet.
The spacecraft, revealed to the media last week, will remain in orbit around Mars for approximately three years and will attempt to land on Phobos. It will collect at least 10 grammes of material from Phobos's surface, while the IDEFIX rover—named after the comic character who accompanies Asterix—will conduct observations on the surface. The spacecraft will also observe Deimos, the other moon of Mars, but without landing, before a return capsule comes back to Earth to land in Australia around 2031.
Japan's Aerospace Exploration Agency (JAXA) hopes the mission will reveal how Mars and its moons formed, key knowledge for understanding how the solar system was born. One theory about the origin of Mars's moons—the "giant impact hypothesis"—holds that they formed after a celestial body collided with Mars. The "capture hypothesis", by contrast, posits that the moons are asteroids from the outer solar system that were captured by Mars's gravity.
Determining which is correct will help reveal "how a habitable environment for life could have emerged on terrestrial planets", JAXA stated, referring to the four rocky worlds closest to the sun: Mercury, Venus, Earth and Mars. "MMX will shed light on the transport mechanisms that delivered water, volatiles and organic compounds from the outer solar system to the inner rocky planet region, processes that could have played a key role in making these worlds habitable", said Patrick Michel, French astrophysicist working on IDEFIX. "If Phobos and Deimos are indeed remnants of these early delivery systems, they could contain clues about the origins of life itself, or to be more precise, about the transport of materials that were key to the emergence of life on rocky planets", he added in remarks to AFP.
JAXA indicated that the mission will also explore the possibility of using Phobos as a "natural space station" by establishing the technology required for a round trip to Mars, something "essential for crewed exploration of Mars". MMX is a collaboration with France's National Centre for Space Studies (CNES), Germany's Aerospace Centre (DLR), NASA and the European Space Agency (ESA), as well as several universities and technology companies.
The development of the spacecraft's landing legs was particularly difficult, since gravity on Phobos is extremely low, according to Akinari Uehara, an engineer at Mitsubishi Electric. "We have to prevent the probe from falling by having the legs cushion the landing impact", said Uehara. Japan's unmanned lunar lander Smart Lander for Investigating Moon (SLIM), known as the "Lunar Sniper", tipped over after touching down on the Moon in 2024, but still transmitted data and survived several fortnights of lunar nights.
Japan also has experience in bringing samples back from space, including JAXA's unmanned Hayabusa-2, which returned 5.4 grammes of rock and dust collected from an asteroid several hundred million kilometres from Earth in 2020. But MMX is not the only Mars mission attempting to bring material back. NASA's Perseverance rover, which has been exploring the red planet since 2021, has already collected samples ready to be returned to Earth. However, the mission has been effectively cancelled by President Donald Trump's administration following a vote by the United States Congress in January.
China has also announced that its Tianwen-3 spacecraft is scheduled to launch around 2028 and will return samples from Mars to Earth around 2031, potentially earlier than MMX's sample return. China's Tianwen-1 mission already placed a rover called Zhurong on Mars's surface in 2021, in one of the biggest successes of Beijing's space programme.