The rocky planets of the solar system have only three moons among them: our own Moon, and the two much smaller moons of Mars – Phobos and Deimos. There have been no successful missions to either of the Martian moons, but now the Japan Aerospace Exploration Agency is sending a probe to Phobos to be launched in 2024, to land and collect material from its surface, and return it to Earth. But why Phobos?  What might we learn from such a mission?

Tomo Usui is a professor in the Department of Solar System Sciences at the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency.  He is leading the science team for the mission to Phobos.