28978 Ixion is a Kuiper belt object that was found on 22 May, 2001. Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune) and could be a dwarf planet. Astronomers think that it has a diameter of about 800 km, which makes it the third biggest plutino. It is named after Ixion, a figure from Greek mythology. Before it was named Ixion, it had the provisional designation .