28978 Ixion

Lore & Background

Ixion was discovered on 22 May 2001 by a team of astronomers at the Cerro Tololo Inter-American Observatory in Chile, led by Robert L. Millis, through the Deep Ecliptic Survey. American astronomers James Elliot and Lawrence Wasserman identified Ixion in digital images taken with the 4-meter Víctor M. Blanco Telescope. The discovery was formally announced by the Minor Planet Center on 1 July 2001. Precovery images, the earliest from 17 July 1982, extended the observation arc, and Ixion received the permanent minor planet number 28978 on 2 September 2001. It is named after the Greek mythological figure Ixion, a king of the Lapiths sentenced to a burning solar wheel in the underworld, following the IAU naming convention for plutinos.

Ixion orbits the Sun with a semi-major axis of 39.5 AU, taking 248 years to complete one orbit, in a 2:3 mean-motion resonance with Neptune. Its orbit has an eccentricity of 0.24 and an inclination of 19.6° to the ecliptic. Ixion's distance from the Sun ranges from 29.9 AU at perihelion to 49.1 AU at aphelion, with perihelion occurring on 24 September 2070. In visible light, Ixion appears dark and moderately red due to organic compounds on its surface; water ice may exist in trace amounts beneath a thick layer of organics. Its rotation period is uncertain, with estimates ranging from 15.9±0.5 hours (2010) to 12.4±0.3 hours (2016), though the latter has a 1.2% probability of inaccuracy. Ixion is not known to have a natural satellite, so its mass and density are unknown.

Reader's Guide

Ixion's significance lies in its status as a large plutino and a transitional object between irregular bodies and dwarf planets. At the time of its discovery, it was thought to be among the largest trans-Neptunian objects, supporting suggestions that undiscovered large objects comparable to Pluto existed. Its discovery preceded the later discoveries of dwarf planets such as Haumea, Eris, and Makemake. Ixion's orbit closely resembles Pluto's, both being plutinos, and its physical characteristics—such as a dark, moderately red surface with possible trace water ice—provide insights into the composition of Kuiper belt objects. The lack of a detected satellite means its mass and density remain unknown, limiting understanding of its internal structure. Stellar occultation observations from 2020 to 2023 revealed a nearly spheroidal shape with a slight flattening, and no rings thicker than a kilometer were detected. Ixion's legacy includes its role in expanding knowledge of the outer Solar System and its contribution to the classification of trans-Neptunian objects.

Did You Know?

• Ixion is the fourth-largest known plutino, after Achlys, Orcus, and Pluto.
• Its rotation period is uncertain, with estimates of 15.9±0.5 hours (2010) and 12.4±0.3 hours (2016).
• Ixion's surface appears dark and moderately red due to organic compounds, with possible trace water ice underneath.
• No natural satellite has been detected for Ixion, so its mass and density are unknown.