Japan heads for Mars moon Phobos as ‘Idefix’ prepares the way for first samples

Japan has begun a five-year journey to the Martian system. On Tuesday, 20 October, the MMX spacecraft lifted off aboard an H3 rocket from Tanegashima spaceport in south-western Japan, bound for the Mars moon Phobos. It aims to bring the first soil samples from the moon back to Earth in 2031. Travelling aboard is Idefix, a German-French rover that will explore the surface before sampling begins.

MMX, short for Martian Moons eXploration, is Japan’s largest mission yet to explore the solar system. For Europe’s space industry, it also marks a closer partnership with a country combining scientific ambition with the development of new businesses in space.

Ten grams to answer a big question

At the mission’s heart is a mystery: how did Mars’s two moons, Phobos and Deimos, form? They may be asteroids captured by Mars. Alternatively, they could have formed from material thrown into space by an impact on the planet. Examining samples could help distinguish between these explanations.

Both moons are small and irregularly shaped. Phobos measures just under 27 kilometres at its widest point, Deimos about 15 kilometres. Material from Phobos could illuminate not only its own history, but also the formation of Mars and the solar system.

Japan’s space agency, Jaxa, wants to retrieve at least ten grams of material from a depth of at least two centimetres. That sounds modest, but samples brought to Earth can be examined with laboratory instruments that cannot readily be carried on a spacecraft. They also remain available for future analysis using new methods.

Japan already has experience of sample-return missions. Hayabusa2, launched in 2014, brought material from the asteroid Ryugu back to Earth six years later. That mission also carried Mascot, a lander jointly developed by the German Aerospace Centre, DLR, and France’s space agency, CNES.

Idefix faces an almost weightless landscape

The rover is roughly the size of a drinks crate and weighs about 25 kilograms. In 2029, the main spacecraft is due to release it above Phobos from a height of around 40 to 100 metres. It must then right itself independently and begin work, with 100 days of exploration planned.

The exceptionally weak gravity makes this particularly challenging. Gravity on Phobos is less than one-thousandth of that on Earth. No wheeled vehicle has ever driven on a celestial body under such conditions. “Landing and driving on Phobos is completely uncharted territory for robotics,” says DLR project manager Markus Grebenstein.

Before launch, Idefix was tested for resistance to extreme temperatures. On Phobos, these can range from minus 170 to plus 70 degrees Celsius. Operations will be managed through control centres in Cologne and Toulouse, but the vehicle must handle key stages of landing and movement largely autonomously.

Its measurements will prepare the way for the spacecraft’s later landing to collect samples. The rover will examine the surface’s properties, using equipment including the RAX Raman spectrometer for material analysis. The development team reduced its weight to 1.5 kilograms; comparable instruments typically weigh four to seven kilograms. Such savings matter because every additional kilogram has to be transported.

From scientific research to a commercial market

MMX also serves an industrial strategy. Mitsubishi Heavy Industries supplies the launch rocket, while Mitsubishi Electric developed and built the spacecraft. The experience is intended to help the group enter lunar and space logistics. Guidance, navigation and control technology, in particular, can be used for further projects.

A diverse space economy is emerging around Japan’s government programmes. Honda tested a reusable rocket capable of landing itself in 2025. Nissan is developing an uncrewed lunar rover, while Toyota is working on a vehicle for astronauts on the Moon. Other companies are developing space-debris removal or transport services; insurers already offer policies for lunar transport.

European companies are seeking a foothold. Bremen-based space company OHB is advising Toyota on its lunar vehicle and considering opening an office in Japan. It sees opportunities both in space exploration and in satellites with civilian and military applications, including communications and Earth observation.

For Switzerland, the relevance lies chiefly in its place within European space activities. Switzerland is a founding member of the European Space Agency, ESA, and Swiss research institutions and companies have long participated in international space programmes. That does not, however, establish any Swiss involvement in MMX. This mission’s specific European contribution is the German-French collaboration on the rover.

The decisive stages still lie ahead

MMX is due to reach the Martian system in 2027, after roughly a year’s flight. It is scheduled to spend about three years there before beginning the return journey. The timetable follows strict astronomical constraints: Earth and Mars are favourably aligned for a transfer only about once every 26 months.

The successful launch therefore leaves the most difficult stages ahead: arrival at Mars, deploying Idefix on Phobos, collecting samples and returning them safely to Earth. The rover’s exploration is intended to prepare for the sampling operation, while the mission as a whole depends on completing each stage of the journey.

If it succeeds, Japan will have brought home material from a destination never previously sampled. It will also have tested technologies intended to make further journeys to moons and planets possible.