The Japan Aerospace Exploration Agency (JAXA) has announced a mission to visit the two moons of Mars and return a rock sample to Earth. It’s a plan to uncover both the mystery of the moons’ creation and, perhaps, how life began in our Solar System.

The Solar System’s planets take their names from ancient Greek and Roman mythology. Mars is the god of war, while the red planet’s two moons are named for the deity’s twin sons: Deimos (meaning panic) and Phobos (fear).

Unlike our own Moon, Phobos and Deimos are tiny. Phobos has an average diameter of 22.2km, while Deimos measures an even smaller 13km. Neither moon is on a stable orbit, with Deimos slowly moving away from Mars while Phobos will hit the Martian surface in around 20 million years.

The small size of the two satellites makes their gravity too weak to pull the moons in spheres. Instead, the pair have the irregular, lumpy structure of asteroids. This has led to a major question about their formation: were these moons formed from Mars or are they actually captured asteroids?

The excitement for a Mars moon mission has led to strong international involvement in MMX. On April 10, JAXA president Naoki Okumura met his counterpart from France’s Centre National d’Etudes Spatiales (CNES), Jean-Yves Le Gall.

The meeting cemented a collaboration between the two space agencies. CNES will provide an instrument for MMX as well as combining expertise on flight dynamics for the tricky encounter with the Martian moons.