PSO J318.5-22, or PSO for short, is a SolarBalls character, a sub-brown dwarf, and a rogue planet. His atmosphere is thought to be purplish. He is slightly larger than Jupiter and is about 80 light years away from the Sun in real life. PSO appears mostly cocky upon his debut and meeting with Planet X, as he makes fun of Planet X, calling him a "blueberry". Yet, he seems to get annoyed at Planet X when he called him an "onion". He also likely says something he should not say when he mentions the Rogue Planet Army to Planet X, which makes him question the Rogue Planets.