Kerberos is a small natural satellite of Pluto, about 19 km (12 mi) in its longest dimension. Kerberos is also the second-smallest moon of Pluto, after Styx. It was the fourth moon of Pluto to be discovered and its existence was announced on 20 July 2011. It was imaged, along with Pluto and its four other moons, by the New Horizons spacecraft in July 2015. The first image of Kerberos from the flyby was released to the public on 22 October 2015.
Kerberos imaged by New Horizons on 14 July 2015 from a distance of 396,100 km
Hubble discovery images of Kerberos
The dwarf planet Pluto has five natural satellites. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, and Hydra. Charon, the largest, is mutually tidally locked with Pluto, and is massive enough that Pluto and Charon are sometimes considered a binary dwarf planet.
Charon and Pluto, to scale. Photo taken by New Horizons on approach.
The Hubble discovery image of Nix and Hydra
Discovery image of Styx, overlaid with orbits of the satellite system
Formation of Pluto's moons. 1: a Kuiper belt object approaches Pluto; 2: it collides with Pluto; 3: a dust ring forms around Pluto; 4: the debris aggregates to form Charon; 5: Pluto and Charon relax into spherical bodies.