styx (formerly known as s/2012 (134340) 1 and informally as p5) is a small moon of the dwarf planet pluto. it was discovered on june 26, 2012, using the hubble space telescope. it is the fifth moon of pluto discovered so far. the others are charon, discovered in 1978, nix and hydra, which were discovered in 2005, and kerberos, discovered in 2011.