28978 Ixion (ik-sye'-un; Latin Ixīōn, Greek Ιξίων) is a Kuiper belt object discovered on May 22 2001 with a diameter of < 822 km and a semimajor axis of about 39.5 AU. Ixion is a Plutino, meaning it has a 3:2 orbital resonance with Neptune.

Little is known about Ixion. The latest spectroscopy results indicate that it has a surface that is a mixture of dark carbon and tholin, which is a heteropolymer formed by irradiation of clathrates of water and organic compounds (such as methane or ethane).

28978 Ixion is named after Ixion, a figure from Greek mythology. It previously had the provisional designation 2001 KX₇₆.

Reference

• Pre-print about Ixion's surface from the Planetary Systems Research group of the University of Helsinki.