Deimos

Deimos is the smaller and more distant of the two moons of Mars. Like Phobos, it was discovered by Asaph Hall in August 1877. It orbits Mars every 30.3 hours at an altitude of about 23,460 km.

Deimos’s surface is far smoother in appearance than Phobos’s because a thick regolith partly fills its craters. Only two named craters exceed 2 km in diameter: Swift and Voltaire. In 2023 the UAE’s Hope orbiter captured the first detailed images of Deimos’s far side, revealing details of its trailing hemisphere never before seen.

Unlike Phobos, Deimos is outside Mars’s synchronous orbit, meaning tidal forces push it slowly outward — it will eventually escape Mars entirely. Its density and spectral properties are consistent with a C- or D-type carbonaceous asteroid, suggesting it may be a captured main-belt object rather than a body that formed in Mars’s orbit.