145452 Ritona
145452 Ritona is a large trans-Neptunian object orbiting the Sun in the Kuiper belt. It was discovered on 10 September 2005 by astronomers Andrew Becker, Andrew Puckett and Jeremy Kubica at Apache Point Observatory in Sunspot, New Mexico. Ritona has a measured diameter of, which is large enough that some astronomers consider it a possible dwarf planet.
Ritona has a dark and reddish surface made of water ice, carbon dioxide ice, carbon monoxide ice, and various organic compounds. Observations by the James Webb Space Telescope have shown that carbon dioxide ice is more abundant than water ice in Ritona's surface, which suggests that there is a thin layer of carbon dioxide ice covering Ritona's surface. Ritona is not known to have any natural satellites or moons, which means there is currently no way to measure its mass and density.
History
Discovery
Ritona was discovered by astronomers Andrew Becker, Andrew Puckett and Jeremy Kubica on 10 September 2005, during observations for the Sloan Digital Sky Survey. The discovery observations were made using the 2.5-meter telescope at Apache Point Observatory in Sunspot, New Mexico. The discoverers further observed Ritona until November 2005 and found the object in precovery observations from dates as early as June 2001. The discovery of Ritona was announced by the Minor Planet Center on 23 July 2006. Since then, Ritona has been found in even earlier precovery observations dating back to June 1954.Name and number
The object is named after Ritona, the Celtic goddess of river fords. The naming of this object was announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 21 July 2025. Before Ritona was officially named, it was known by its provisional designation, which indicates the year and half-month of the object's discovery date. Ritona's minor planet catalog number of 145452 was given by the Minor Planet Center on 5 December 2006. The Kuiper belt objects 145451 Rumina and come before and after Ritona's number in the minor planet catalog, respectively.Orbit
Ritona is a trans-Neptunian object orbiting the Sun at a semi-major axis or average distance of 41.5 astronomical units. It follows a moderately inclined and nearly circular orbit, with a low eccentricity of 0.02 and inclination of 19.3° with respect to the ecliptic. In its 267-year-long orbit, Ritona comes as close as 40.6 AU from the Sun at perihelion and as far as 42.5 AU from the Sun at aphelion. Ritona last passed perihelion in November 1760 and will make its next perihelion passage on 15 April 2029.Ritona is located in the classical region of the Kuiper belt 39–48 AU from the Sun, and is thus classified as a classical [Kuiper belt object]. The high orbital inclination of Ritona makes it a dynamically "hot" member of the classical Kuiper belt. The hot classical Kuiper belt objects are believed to have been scattered by Neptune's gravitational influence during the Solar System's early history.
Physical characteristics
Size
Ritona has a diameter of , according to thermal emission measurements by the infrared Herschel Space Observatory. Ritona is large enough that some astronomers consider it a possible dwarf planet.Surface
In visible light, the surface of Ritona appears dark and reddish in color, with a geometric albedo of about 0.11. Spectroscopic observations by the James Webb Space Telescope in 2022 have shown that Ritona's surface is composed of water ice, carbon dioxide ice, carbon monoxide ice, and various organic compounds. Ritona shares this composition with the -type trans-Neptunian objects, which are commonly found on dynamically excited orbits such as those in the hot classical Kuiper belt.Analysis of JWST's spectroscopic observations has shown that Ritona's surface is more abundant in ice than water ice, which suggests that Ritona's surface is covered with a thin layer of fine, micron-sized ice particles. CO ice is also abundant in Ritona's surface, contrary to theoretical predictions that CO should sublimate and escape from Ritona's surface at its temperature and distance from the Sun. Planetary scientists Michael E. Brown and Wesley C. Fraser have hypothesized that the Sun's ultraviolet light produces CO in Ritona's surface by irradiating and breaking down molecules, and leaves the CO trapped within the surrounding ice. A similar scenario has been hypothesized for, another -rich Kuiper belt object observed by JWST.