On this date Mars Express made its closest approach of Mars’ largest moon, Phobos, flying just 67 kilometres
(41 miles) above its surface. During this brief window of opportunity Mars Express was able to conduct a gravity experiment and produce some outstanding images.
Although it wasn’t able to study Mars' other moon, Deimos, as closely, the information collected on Phobos was enough for astronomers to rethink its origins. Originally it was thought that these moons were captured asteroids. However, after density and mineral composition analysis, it is thought that these moons – and Phobos in particular – formed during a reaccretion of rocky material in Mars’ orbit.