Pluto and its moons Charon, Nix, Hydra, Kerberos and Styx
Luckily for planetary scientists, the New Horizons spacecraft flew by Pluto, Charon and the dwarf planet's myriad moons in July 2015. Data is still flowing in from the encounter, providing scientists reams of information about the moons that they are working to understand.
A recent release from SETI (the Search for Extraterrestrial Intelligence) summarizes some of the latest findings on Charon: it has red northern plains due to the molecule tholin, and some spots with ammonia ice. It doesn't appear to be as geologically active as Pluto, either, which surprised scientists by showing off mountains shortly after the encounter.
Scientists are also working to understand the origins of other moons discovered around Pluto. Charon was found in 1978, but its smaller moons Nix, Hydra, Kerberos and Styx were all discovered between 2005 and 2012.
Image credit: NASA-JHUAPL-SWRI