The longstanding mystery of Mars' moons—and the mission that could solve it

The two small moons of Mars, Phobos (about 22km in diameter) and Deimos (about 13km in diameter), have been puzzling scientists for decades, with their origin remaining a matter of debate. Some have proposed that they may be made up of residual debris produced from a planet or large asteroid smashing into the surface of Mars (#TeamImpact).