Japan to launch first mission to bring back samples from a moon of Mars

A Japanese spacecraft is preparing to head to one of the solar system's least-understood bodies — Phobos, a potato-shaped moon of Mars roughly 27 kilometres across — on a five-year mission that will attempt, for the first time, to bring back samples from the Martian system.

The Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) probe is set to lift off from the Tanegashima Space Center on October 20 at 4:41 a.m. local time aboard a new H3 rocket, according to JAXA. The spacecraft is expected to reach the Mars region around August 2027, spend up to three years orbiting and studying Phobos, land to collect at least 10 grams of material, and return the samples to Earth in 2031 — landing in Australia before being sent on to Japan.

The sampling (from) Phobos is of course the world's first, but it means... this is the first round trip to the Martian system.— Yasuhiro Kawakatsu, MMX Project Manager, JAXA

The central scientific question the mission hopes to settle is deceptively simple: where did Phobos and its sibling moon Deimos come from? Two competing theories have divided scientists for decades. The 'giant impact' hypothesis holds that a large celestial body collided with Mars, flinging debris into orbit that eventually coalesced into the two moons. The 'capture' hypothesis argues the moons are asteroids that wandered too close to Mars and were snared by its gravity. The answer matters well beyond planetary science.

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 may have played a key role in making these worlds habitable.— Patrick Michel, French astrophysicist working on IDEFIX

If Phobos and Deimos are indeed remnants of these early delivery systems, they may hold clues to the origins of life itself or, to be more correct, to the transport of the materials that were key to the emergence of life on rocky planets.— Patrick Michel, French astrophysicist working on IDEFIX

JAXA scientists note that Phobos was chosen over Deimos partly because its closer orbit to Mars means its soil is likely to contain more Martian material — roughly 0.1% of what MMX collects is expected to originate from Mars itself. Scientists say collecting samples from multiple locations on Phobos also increases the chances of finding any traces of past microbial life from the planet.

We can almost certainly come to a conclusion by analysing soil samples.— Kiyoshi Kuramoto, Principal Investigator, MMX mission

The mission is a genuinely international effort. MMX carries 13 instruments contributed by partners including NASA, the European Space Agency, France's National Centre for Space Studies (CNES), and the German Aerospace Center (DLR), along with roughly 20 universities and technology companies. NASA is providing a sampling device that uses pressurised gas to lift surface dust into a container, as well as an instrument to measure gamma rays and communications support. ESA is contributing a deep-space communications device. A Japanese radiation monitor will gather data relevant to future crewed missions.

The most visible international contribution is a small rover called IDEFIX — named after Asterix's dog in the French comic series — jointly developed by France and Germany. IDEFIX is scheduled to land on Phobos first, conducting a roughly 100-day surface survey around 2029 to identify a safe, level landing site for the main spacecraft. The rover has wheels designed for traction in near-zero gravity, can right itself if it tips over, and moves, in JAXA's own description, 'at a snail's pace.'

Landing on Phobos is one of the mission's most demanding engineering challenges. The moon has just one two-thousandths of Earth's gravity, meaning a spacecraft risks bouncing off the surface rather than settling on it. To counter this, MMX's exploration module is fitted with four-legged landing gear incorporating shock absorption. Once down, JAXA aims to collect samples using two methods: NASA's pressurised-gas device for surface dust, and a Japanese coring tool that reaches about 2 centimetres underground. The plan calls for two separate landings.

Going deep into what we call the 'gravity well' is difficult.— Yasuhiro Kawakatsu, MMX Project Manager, JAXA

JAXA has relevant experience: its Hayabusa2 probe returned 5.4 grams of rock and dust from an asteroid hundreds of millions of kilometres from Earth in 2020. But the MMX mission adds a layer of difficulty that asteroid missions did not face — the spacecraft must operate deep within Mars's gravitational field and then escape it to return home. Previous attempts to reach Phobos have failed; multiple Russian missions, including one launched in 2011, never made it.

Beyond the science, JAXA has framed the mission as groundwork for eventual human exploration of Mars. The agency says establishing the requirements for a round trip to the Martian system is 'essential for crewed Mars exploration,' and has raised the possibility of using Phobos as a 'natural space station.' A Japanese radiation monitor aboard MMX will collect data directly relevant to that goal.

Despite their potential importance, Martian moons have never been fully investigated. They are known as the most important unclimbed mountains in the solar system.— Yasuhiro Kawakatsu, MMX Project Manager, JAXA

MMX is entering a newly competitive arena. China has announced its Tianwen-3 spacecraft is scheduled for launch around 2028, with the goal of returning samples from the Martian surface itself as early as 2031 — the same year MMX is due back. NASA's Perseverance rover has already collected surface samples on Mars, but the US Mars sample-return mission was cancelled earlier this year following a congressional vote and a decision by the Trump administration. JAXA scientists argue that Phobos soil may actually offer a wider variety of material than Mars surface samples alone, particularly if the moon formed from a collision with the planet.

Why it matters — The first sample return from the Martian system could resolve a decades-old debate about how Mars's moons formed and whether the same processes that seeded rocky planets with water and organic compounds also made life on Earth possible — while laying technical groundwork for future human missions to Mars.

Reported by theguardian.com, newscientist.com, straitstimes.com