It was named after the charecter of Greek mythology of the same name, his brother being Phobos. Deimos was discovered in 1877 by Asaph Hall, who also discovered Phobos in the same year. It was photographed in 1977 by the craft Viking 2.
An oddly shaped, irregular moon, it has some impact craters, of which two are named - Swift and Voltaire.
- Dimensions: 15 × 12.2 × 10.4 km
- Mass: 1.48×1015 kg
- Semimajor axis: 23,460 km
- Orbital period: 1.26244 days
- Inclination: 0.93° (To Mars' equator)
- Orbital eccentricity: 0.000 2
- Discovered: 1877
- Host planet: Mars