Ixion

28978 Ixion /ɪkˈsaɪ.ən/, provisional designation 2001 KX76, is a large trans-Neptunian object and a possible dwarf planet. It is located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Ixion is classified as a plutino, a dynamical class of objects in a 2:3 orbital resonance with Neptune. It was discovered in May 2001 by astronomers of the Deep Ecliptic Survey at the Cerro Tololo Inter-American Observatory, and was announced in July 2001. The object is named after the Greek mythological figure Ixion, who was a king of the Lapiths. In the visible spectrum, Ixion appears moderately red in color while it appears neutral in the near-infrared, likely as a result of the presence of dark organic compounds on its surface. Water ice has been also suspected to be present on Ixion's surface, albeit in trace amounts as most of the water ice is expected to be hidden underneath a thick layer of organic compounds on Ixion's surface. Ixion's diameter is estimated at 617 km (383 mi), making it the fourth-largest known plutino. Several astronomers have considered Ixion to be a possible dwarf planet under the expectation that it is large enough to have assumed a round shape under hydrostatic equilibrium, although studies in 2019 suggest that objects around the size of Ixion may retain significant internal porosity and thus represent a transitional zone between small Solar System bodies and dwarf planets. Ixion is currently not known to have a natural satellite, thus its mass and density remain unknown.