The Martian Moons Exploration mission plans to visit the moons of Mars, and collect samples from the inner moon, Phobos.
This sample is expected to reveal information about how the moons formed, and the transfer of material between the inner and outer Solar System, including water and organics.
But MMX is not expected to collect only moon material.
Throughout their history, the planets have been bombarded with meteorites.
This has occurred all over Mars’s surface and back to a time when Mars may have supported liquid water and potentially even life.
While these collisions are not as large as the impacts thought to have created the Earth’s moon and possibly Phobos and Deimos, they can eject material from Mars's surface into space.
These fragments of the Martian surface may even travel as far as the Earth to become Martian meteorites.
However, the interplanetary journey is long and only a few fragments from Mars make it to the Earth.
Of those the Martian fragments that do make the journey, many will burn up in the Earth’s atmosphere.
This leaves us with only hard igneous rocks from Mars on Earth.
All other material, including softer rocks that would contain clues to Mars’s wet past, are lost.
However, Phobos is far closer to Mars than the Earth and lacks an atmosphere.
This makes for a far easier journey from the Martian surface to the surface of Phobos.
The small moon should therefore to be coated with material that originated from all over Mars throughout the planet’s long history.
Some of these Martian grains are expected to be gathered into the samples collected by the MMX spacecraft.
Such a sample will complement material gathered by the NASA/ESA Mars Sample Return program, which will collect a larger sample from a known geographic location.
When MMX returns to the Earth in 2029, it will bring not only information about Martian moons,
but also the first grains to be collected from our neighbouring world.