Deimos is the smaller and outer of the two natural satellites of Mars, the other being Phobos. Deimos, likely an asteroid captured by Mars' gravity, is highly non-spherical with a mean diameter of 12.5 km (about 57% the size of Phobos) and it orbits 23,460 km from Mars (Deimos' orbit is slowly getting larger and it is expected to eventually escape Mars' gravity). Escape velocity from the surface of Deimos is only 5.6 m/s so a human can basically jump off of it.
In the universe of The Expanse TV series (a political sci-fi drama set in mid-24th century when humans have colonized the entire Solar system) Deimos hosts military facilities and a deep radar station for Martian Congressional Republic - one of the three competing powers in The Expanse, along with the United Nations (based on Earth) and the Belt.
Concept art of Deimos in The Expanse by Canadian designer Lee Fitzgerald:
In early season 2 of The Expanse Deimos is destroyed with nuclear missiles in a "moon for a moon" retaliatory strike by the United Nations (Earth) after the Martian assault cruiser destroyed Earth's research base on Saturn's moon Phoebe along with the consequent destruction of the moon itself. The destruction of Deimos killed 17 Martians and the moon disintegrated forming the "Deimos Ring" around Mars.
Concept art of Martian Deep Radar Station on Deimos before the missile strike by Lee Fitzgerald:
News coverage of the destruction of Deimos:
