Challenges of Landing on Phobos: The MMX Mission
Last August, looking up from the edge of an ancient river delta on Mars, the Perseverance rover’s electronic eye spied an oblong shadow crossing the distant, glowing Sun. Phobos, the Martian moon named for the Greek god of fear and panic, was transiting the solar disk. The tiny moon, with its murky origins, is an enigma, and one whose makeup and history could tell us much about Mars and the wider solar system. The international Martian Moons eXploration (MMX) mission, which successfully launched on 20 October, seeks to explore that mystery with an unprecedented series of landings on Phobos.
This mission brings unusual challenges, such as designing an orbit to study a microgravity moon and assessing how to land on this low-gravity pile of loosely assembled dirt and rock. “I often say that landing on Phobos is like trying to land a balloon,” says Yasuhiro Kawakatsu, project manager of MMX at JAXA.
Why Phobos Is Such a Strange Moon
Phobos is one of two small Martian moons; the other is Deimos. Their origins are unclear, with theories suggesting they were captured asteroids or formed from debris after a celestial impact on Mars. Scientifically, Phobos is considered a rubble pile, shaped like a lumpy potato, roughly 27 kilometers long, with only 1/1,800th of Earth’s gravity.
MMX launched on Japan’s H3 rocket from Tanegashima spaceport on 20 October 2026, carrying scientific payloads from several space agencies, including NASA, and a new rover called Idefix, developed by CNES and DLR in collaboration with JAXA.
MMX consists of three modules: a propulsion module, an exploration module carrying the rover and scientific instruments, and a return module for samples. After collecting samples on Phobos, the exploration module will be jettisoned, and the return module will head back to Earth.
If successful, MMX will deliver a 10-gram sample to Earth in 2031, facing challenges like navigating complex orbits and landing while Mars periodically blocks communications with Earth. “It’s the most complex mission I have ever seen,” says Patrick Michel, director of research at CNRS.
How MMX Will Orbit Phobos
After reaching low Earth orbit, MMX will cruise to Mars, requiring a carefully timed engine burn to be captured by Mars’ gravity. It will then enter a quasi-satellite orbit, allowing it to keep pace with Phobos while moving around it. This unique orbit will enable MMX to map the surface in high resolution and identify candidate landing sites.
Martian Maneuvers
MMX will loop around Phobos at varying distances to gather detailed images. During its two-year remote sensing campaign, it will prepare for the rover’s descent to the surface.
Idefix Rover: The First Penguin
The Idefix rover will be released during a low-altitude pass in 2028 or early 2029. It will freefall and is expected to touch down at a velocity of less than 1 meter per second. Idefix will operate at a maximum speed of one millimeter per second, using specialized wheels for traction in Phobos’s microgravity.
Idefix’s findings will inform the main spacecraft’s landing strategy. The rover will provide insights into the regolith’s properties, aiding in understanding Phobos’s composition.
How MMX Will Land and Collect Samples
After Idefix’s exploration, MMX will attempt to land its larger exploration module on Phobos. The descent will be controlled until about 10 meters above the surface, after which it will free fall. A successful landing will initiate a crucial sampling phase.
MMX will utilize two sampling devices: a coring sampler developed by JAXA and a pneumatic sampler provided by NASA. The coring sampler will reach at least 2 centimeters below the surface, while the pneumatic sampler will capture grains stirred up by injected nitrogen gas. This dual system provides redundancy against uncertainties in Phobos’s surface conditions.
MMX also aims to collect Martian ejecta, potentially returning the first Martian samples to Earth. The samples will be stored in a capsule for the return journey, which will begin in November 2030. The sample capsule will reenter Earth’s atmosphere in 2031, aiming to provide valuable insights into Phobos and the early solar system.
“MMX is a mission to understand the Mars system and shed light onto how terrestrial planets like Earth develop a habitable environment,” Kawakatsu says. “Mars sits at the gateway between the inner and outer solar system, making its moons valuable witnesses to the processes that shaped potentially habitable worlds.”
Related link: science.nasa.gov
Source: IEEE Spectrum