2003 UB 313, formerly known as Xena, is a dwarf planet larger than Pluto. It just officially got a name. "ERIS"

From the article
"In mythology, Eris caused a quarrel among goddesses that sparked the Trojan War. In real life, Eris forced scientists to define a planet that eventually led to Pluto getting the boot. Soon after Pluto's dismissal from the planet club, hundreds of scientists circulated a petition protesting the decision."

So when you are drawing the solar system, you can remember to leave some space to put Eris way on out there....