Japan's MMX mission aims to bring back first samples from Mars's Moon Phobos

Japan is preparing to attempt something no space agency has done: landing on a Martian moon, collecting at least 10 grams of its surface material, and returning it to Earth. The spacecraft, MMX (Martian Moons eXploration), is targeting Phobos, a lumpy, potato-shaped moon less than thirty kilometres long that orbits Mars closer than any other known moon orbits its planet. If successful, laboratories on Earth would hold the first physical sample taken from the Mars system.

Why does it matter?

The origin of Mars's two moons, Phobos and the smaller Deimos, remains unknown. They could be asteroids captured by Mars's gravity or debris thrown into orbit when a massive object struck the planet. Each explanation points to a different history of the early solar system, and only laboratory analysis of a sample can resolve the question.

The Japan Aerospace Exploration Agency (JAXA), which led the Hayabusa missions that returned grains from two asteroids, is heading the project. NASA, France's CNES, Germany's DLR and the European Space Agency are partners. JAXA describes it as the largest international planetary mission Japan has led.

"The Martian moon Phobos remains an unexplored frontier for humankind," said MMX project manager Kawakatsu Yasuhiro in a JAXA statement. He said returning samples could help explain how the moons formed, how the Mars sphere evolved, and how water and organic materials on terrestrial planets originated.

All about MMX spacecraft

MMX is about nine metres long and consists of three stacked modules: a propulsion module to brake into Mars orbit, an exploration module with landing legs and sampling equipment, and a return module to carry the sample home. According to ESA, it carries 11 science instruments, seven on the main spacecraft and four on a small rover.

Because Phobos's gravity is less than a thousandth of Earth's, MMX will use a quasi-satellite orbit. It technically circles Mars but moves in step with Phobos, appearing to loop around the moon. From there, the TENGOO telescopic camera can resolve features about 40 centimetres across. The OROCHI wide-angle camera, a laser altimeter, the French infrared spectrometer MIRS and NASA's MEGANE gamma-ray and neutron instrument will map the terrain, minerals and chemical elements.

Before the main spacecraft attempts a landing, it will release Idefix, a 25-kilogram rover built by CNES and DLR. It will drop from 40 to 100 metres above the surface, right itself and operate for about 100 days. On Phobos, it will weigh roughly as much as 15 grams does on Earth.

The exploration module will then land, staying on the surface for around two and a half hours, and may touch down a second time at another site. Its main sampling tool is a corer on a robotic arm that drills about 2 centimetres deep, enough to reach material not chemically altered by sunlight and solar radiation.

A NASA-supplied backup system uses a jet of nitrogen gas to blast surface grains into a container, the same principle OSIRIS-REx used at asteroid Bennu. In Phobos's weak gravity, however, the jet carries a small risk of tipping the spacecraft.