Japan prepares MMX probe launch for historic round-trip mission to Mars moon Phobos

What happened

Japan is preparing to launch the Martian Moons eXploration (MMX) probe on a historic round-trip mission to retrieve physical samples from Mars’s moon Phobos. The unmanned spacecraft, carried by Japan’s flagship H3 rocket, is scheduled to lift off from the Tanegashima Space Center at 4:41 am local time on Tuesday (1941 GMT Monday).

The Japan Aerospace Exploration Agency (JAXA) aims to execute the world’s first sample-return journey to the Martian system. The mission seeks to answer long-standing questions about the formation of the Solar System and how life-supporting ingredients reached Earth.

How the MMX mission will explore Phobos

After a one-year voyage to reach Mars, the probe will spend up to three years orbiting Phobos while conducting detailed observations. Before MMX lands, a small rover named IDEFIX — developed in partnership with French and German space agencies — will deploy to inspect the surface and ensure a safe landing site.

The main probe will then touch down to collect at least 10 grams of sand and rock before blasting off to return to Earth. MMX will also observe Mars’s second moon, Deimos, from orbit.

"The sampling from Phobos is of course the world's first, but it means this is the first round trip to the Martian system," said Yasuhiro Kawakatsu, MMX project manager.

Escaping the deep gravitational field of Mars presents a significant technical hurdle compared to previous asteroid missions. Gravity on Phobos itself is extremely weak, requiring specialised landing legs designed to prevent the probe from bouncing off or tipping over.

Unlocking the origins of the Solar System

Scientists believe samples from Phobos could resolve two competing theories regarding how the Martian moons came to be:

• The giant impact hypothesis, which suggests the moons formed from debris after a celestial body struck Mars.
• The capture hypothesis, which posits that Mars’s gravity trapped two passing asteroids.

If Phobos formed from a planetary collision, its dust will contain material swept up from early Mars. Patrick Michel, an astrophysicist working on the IDEFIX rover, noted that these materials may reveal how water and organic compounds were transported to the inner rocky planets.

The global race for Martian samples

Japan's venture comes amid shifting international efforts to retrieve material from the Martian environment. NASA’s Perseverance rover has been gathering rock cores on the Red Planet since 2021, but its return mission was effectively cancelled following a vote in the US Congress in January. Meanwhile, China plans to launch its Tianwen-3 mission around 2028, targeting a Mars sample return as early as 2031.

JAXA also views the MMX mission as an opportunity to assess Phobos as a potential staging ground for future crewed exploration, testing the round-trip capability required for eventual human flights to Mars.