COLOGNE, Germany — Japan launched its Martian Moons eXploration (MMX) spacecraft on Oct. 19, sending a German-French rover toward Phobos as part of a mission to study Mars' two moons and return samples to Earth.
The Japan Aerospace Exploration Agency (JAXA) launched MMX aboard an H3 rocket from the Tanegashima Space Center. The spacecraft carries Idefix, a small rover developed by the German Aerospace Center (DLR) and the French space agency CNES.
The mission aims to determine how Phobos and Deimos formed. Scientists are trying to understand whether Mars captured the moons as asteroids or whether they developed from debris released by large impacts on the planet.
MMX is scheduled to reach Mars in summer 2027. The spacecraft will examine the moons from orbit before releasing Idefix toward the surface of Phobos around late 2028 or early 2029.
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Rover will operate in Phobos' low gravity
Idefix will attempt the first rover operations on the surface of a Martian moon. MMX plans to release the vehicle from approximately 40 to 100 meters above Phobos. Rather than using a powered landing system, the rover will fall to the surface and may bounce many times before coming to rest. It must then orient itself, deploy its solar panels and begin a planned 100-day exploration period.
The landing presents several engineering challenges. Phobos has less than one-thousandth of Earth's gravity, while temperatures can vary by more than 200 degrees Celsius during its roughly seven-hour day-night cycle.
Engineers designed Idefix to withstand these conditions while operating with limited direct control from Earth. Communication delays require the rover to perform some tasks autonomously.
The rover carries two DLR scientific instruments: the RAX Raman spectrometer and the miniRAD radiometer. Together, they will help researchers examine the mineral composition, temperature and physical characteristics of the moon's surface. The measurements will also help the MMX team evaluate potential sampling locations.
MMX plans to return samples to Earth in 2031
While MMX travels toward Mars, teams at DLR's Microgravity User Support Center in Cologne and a control center in Toulouse will prepare rover commands, conduct system checks and coordinate instrument calibrations. Mission planners also expect to update the rover's software during the flight.
After arriving at Mars, MMX will use eight scientific instruments to look at Phobos and Deimos. The spacecraft will later attempt to land on Phobos and collect at least 10 grams of surface material.
JAXA plans to return those samples to Earth in a capsule in 2031. If successful, the mission would give scientists their first opportunity to analyze material collected directly from a Martian moon in terrestrial laboratories.
