Chaos was an entirely fictional tenth planet of the Solar System composed primarily of dark matter. Chaos was the stronghold of the Pirate Clans, protected by both its unknown location (in fact, no one save the Pirates and the ones they trusted knew it existed at all) and the cloaking properties of the dark matter. The latter were also used by the Pirates to construct cloaking devices that kept their rather small fleet hidden from the Exofleet and later, the Neosapiens.
Clan-based society of Chaos was extremely unstable, partly because of the emotional instability caused by Dark Matter Syndrome which was typical for all Pirates, but eventually the constant danger of being eradicated by bigger enemies forced them to cooperate and to elect a ruler over all Clans. Jonas Simbacca was the leader of all Pirates during the war and when he allied the Clans with the Exofleet, Chaos became the first truly safe harbor for the Terrans.
Chaos vanished months after the end of the Neosapien War when an apparently aggressive and extremely powerful alien civilization from beyond the Solar System attacked it and appeared to absorb the planet. The only individual confirmed to have survived this event was Wing Commander J.T. Marsh. The Lyoko Warriors used the power of the Black Star Dragon Balls to save the planet Chaos by tricking Emperor Pilaf to wish for the new Alien race to be returned to the dimension, thus restoring Chaos.