Oh, hello there! Are you the tiniest moon of Pluto, Kerberos? It’s so lovely to finally meet you, and complete our family portrait of all of Pluto’s little moons.
The smallest moon of Pluto is Kerberos, this lumpy little mess of rock that looks like two moons got stuck together and now go by the hyphenate hybrid-name Ker-Beros as an inseparable celebrity couple. The moon is 12 kilometers (7.4 miles) across the longest dimension and 4.5 kilometers (2.8 miles) across its shortest dimension with an apparent double-lobe shape. It also looks suspiciously like the double-lobed comet 67P currently being explored by Rosetta, leading us to wonder if the Solar System is working from a limited set of fixed shapes for its small icy worlds.
Of course, this is Pluto’s system, so you know that something had to be weird about the wee moon. All the small moons have fairly high reflectivity (approximately 50%), an attribute that suggests a fairly clean icy surface. This is surprising for Kerberos: the faint little moon exerts a relatively high gravitation wallop on its orbital neighbours, leading researchers to initially theorize that it was larger but darker. Instead, it’s weirdly shiny and smaller, so we’ll need to come up with new theories as to why it has so much pull with the other moons.
Pluto’s moons to scale: Charon at 1,212 kilometer (751 mile) diameter, Nix and Hydra at approximately 40 kilometers (25 miles) across their longest dimension, and Kerberos and Styx at 10 to 12 kilometers (6-7 miles) across their longest dimension. Image credit: NASA/JHUAPL/SwRI
Kerberos is the last of Pluto’s moons to be imaged. The largest is Charon, the moon so massive it swings Pluto about its barycenter in our first known binary dwarf planet system. Next are the moderately-sized Nix and Hydra. Finally, the diminutive Styx and Kerberos are so small that scientists didn’t even discover them until New Horizons had already launched and was well on its way across the solar system. All four smaller moons are elongated with bright surfaces indicative of water ice. Together they make a weird little system whirling around on the outer edge of the solar system.