Like our moon, Deimos is tidally locked to Mars, meaning the same side always faces the planet—the only side visible to rovers on the Martian surface. The only way to see Deimos’ far side up close is for a probe like Hera to fly behind it, making such images more of a rarity.

On the way to investigate the scene of a historic asteroid collision, a European spacecraft swung by Mars and captured rare images of the red planet's mysterious small moon Deimos, the European Space Agency said Thursday.

A European spacecraft on a journey to study NASA's asteroid crash site did a quick pop-in of Mars on its way, capturing unprecedented images of Mars' lesser-known moon, Deimos. Mars has two moons, Phobos and Deimos,