ScienceCNA Explains: Mars’ two mysterious moons

The inner Solar System has only three moons: Earth’s Moon and the two orbiting Mars. Phobos and Deimos are smaller and irregularly shaped. Phobos is slowly spiralling toward Mars, moving about 1.8 metres closer every 100 years; in roughly 50 million years, it may collide with the planet or break apart into a debris ring.