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The dwarf planet Pluto has a system of at least five moons, whose orbits imply that they were formed in the ancient past when another large Kuiper Belt Object crashed into the planet. The majority of the resulting debris coalesced into Pluto's largest moon, Charon, but the remainder formed four much smaller moons. Two of these, Hydra and Nix, are nonetheless relatively substantial, while the two remaining moons, Styx and Kerberos, are tiny bodies.
Kerberos appears to have been formed from two even smaller bodies, pulled together by gravity to form a curious double-lobed shape, with the two moonlets connected by a narrow neck. The resulting irregularly-shaped composite moon is still tiny, with its longest axis measuring no more than 19km from one lobe to the other. Kerberos is a highly reflective object, and this seems to indicate the presence of water ice on its undulating surface.
Kerberos is the second most distant of Pluto's moons, orbiting nearly sixty thousand kilometres from its parent planet, with only Hydra - a moon more than twice Kerberos' size - pursuing a more distant orbit. Currently, Kerberos rotates on its axis over a period of 5.3 days, and completes an orbit of Pluto in 32.2 days. The presence of two much more massive bodies in the system - Pluto and Charon - mean that this orbit is not stable over the longer term, and is subject to unpredictable changes.
By convention, the moons of the Pluto system are given names associated with the underworld, of which Pluto (or the Greek equivalent Hades) was the ruler. Kerberos takes its name from the three-headed dog said to guard the entrance to Pluto's domain. In English the name is more usually spelt Cerberus, but that name had long been established as the name of an asteroid (1865 Cerberus in the Apollo Group). What's more, the name is also used of a region on Mars, and for the star Eta Lupi. This moon's version of name therefore follows the original Greek Kerberos to avoid any potential confusion.
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