Kerberos

Kerberos is one of the smallest and most elusive members of Pluto’s satellite system. It was the fourth moon of Pluto to be discovered, but it wasn't spotted until 2011 by the Hubble Space Telescope during a search for rings around the dwarf planet.

Here is the lowdown on this tiny, icy world:

Physical Characteristics

Kerberos is notably small and has a very unusual shape. Data from the New Horizons flyby in 2015 revealed that it looks a bit like a double-lobed potato (similar to a comet).

• Size: It is roughly 12 miles (19 km) across its longest dimension.

• Reflectivity: Initially, scientists thought Kerberos was very dark, but New Horizons showed it is actually quite bright, reflecting about 50% to 80% of the sunlight that hits it. This suggests its surface is covered in relatively clean water ice.

• Shape: It appears to be a "contact binary," meaning it likely formed when two smaller icy objects drifted together and stuck at low speeds.

Orbit and Dynamics

Kerberos sits in a specific "groove" within the Pluto system:

• Location: It orbits between the moons Nix and Hydra.

• Distance: It circles Pluto at a distance of about 36,000 miles (57,800 km).

• Chaos: Like Pluto’s other small moons (Styx, Nix, and Hydra), Kerberos does not have a "tidy" rotation. Because the gravitational pull of Pluto and its large moon Charon is constantly shifting, Kerberos tumbles and wobbles unpredictably as it orbits, rather than keeping one face toward the planet.

Why the Name?

In keeping with the underworld theme of the Pluto system, Kerberos is named after the many-headed dog from Greek mythology (often spelled Cerberus) that guarded the gates of the underworld. The Greek spelling "Kerberos" was used to avoid confusion with an asteroid already named Cerberus.

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