The Earth got its Moon when a small planet collided with our planet more than four billion years ago. This impact hurled molten rock into space, which eventually coalesced to form the satellite we can see every night from across our planet.

But what of our neighbour, Mars? The red planet has two small, irregularly shaped moons called Phobos and Deimos. There are several theories on how these natural satellites formed, but no clear front-runner. Soon, a Japanese-led space mission called Martian Moons Exploration (MMX) will begin its hunt for the answer.

On Monday October 19, MMX is due to lift off on an H3 rocket from Tanegashima Space Center in southern Japan. The mission will aim to land on Phobos and collect a sample of soil. The spacecraft will then send this precious payload to Earth, for study in laboratories.

Of the two Martian moons, Phobos is the largest and orbits closer to the planet. It has a mean diameter of 22.2km and a mass of 10,637 million million kg. Deimos has a mean diameter of 12.5km and a mass of 1,480 million million kg.

The moons were discovered during a six-day window in 1877 by the American astronomer Asaph Hall, who was working at the US Naval........

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