![]() Ritona imaged by the Hubble Space Telescope on 25 April 2010 | |
Discovery [1] | |
---|---|
Discovered by | |
Discovery site | Apache Point Obs. |
Discovery date | 10 September 2005 |
Designations | |
(145452) Ritona | |
Pronunciation | /ˈrɪtənə/ |
Named after | Ritona |
2005 RN43 | |
Orbital characteristics (barycentric) [5] | |
Epoch 5 May 2025 (JD 2460800.5) | |
Uncertainty parameter 0 [2] | |
Observation arc | 70+ yr |
Earliest precovery date | 2 June 1954 |
Aphelion | 42.450 AU |
Perihelion | 40.575 |
41.512 AU | |
Eccentricity | 0.0226 |
267.29 yr (97,627 d) | |
352.812° | |
0° 0m 13.275s / day | |
Inclination | 19.274° |
186.989° | |
≈ 15 June 2029 [6] | |
172.899° | |
Physical characteristics | |
679+55 −73 km [3] | |
| |
0.107+0.029 −0.018 [3] | |
Temperature | 43.2 K (perihelion) [8] : 11 |
≈ 20 (average) [1] [11] : 5 | |
145452 Ritona (provisional designation 2005 RN43) 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 679+55
−73 km, 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 (tholins). 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. [13] : 1, 3
Ritona was discovered by astronomers Andrew Becker, Andrew Puckett and Jeremy Kubica on 10 September 2005, during observations for the Sloan Digital Sky Survey. [1] [14] The discovery observations were made using the 2.5-meter telescope at Apache Point Observatory in Sunspot, New Mexico. [14] The discoverers continued observing Ritona by November 2005 and found the object in precovery observations from dates as early as June 2001. [14] The discovery of Ritona was announced by the Minor Planet Center on 23 July 2006. [14] Since then, Ritona has been found in even earlier precovery observations dating back to June 1954. [1]
The object is named after Ritona, the Celtic goddess of river fords. [15] : 24 The naming of this object was announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 21 July 2025. [15] : 24 Before Ritona was officially named, it was known by its provisional designation 2005 RN43, [1] which indicates the year and half-month of the object's discovery date. [16] Ritona's minor planet catalog number of 145452 was given by the Minor Planet Center on 5 December 2006. [17] : 160
Ritona is a trans-Neptunian object orbiting the Sun at a semi-major axis or average distance of 41.5 astronomical units (AU). [5] [b] It follows a moderately inclined and nearly circular orbit, [7] : 2537 with a low eccentricity of 0.02 and inclination of 19.3° with respect to the ecliptic. [5] 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. [5] Ritona last passed perihelion in November 1760 and will make its next perihelion passage on 15 April 2029. [19] [6]
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 (sometimes known as a "cubewano"). [3] : 2–3 The high orbital inclination of Ritona makes it a dynamically "hot" member of the classical Kuiper belt. [3] : 3 The hot classical Kuiper belt objects are believed to have been scattered by Neptune's gravitational influence during the Solar System's early history. [20] : 230
Ritona has a diameter of 679 km (422 mi) (full range 606 to 734 km or 377 to 456 mi when including uncertainties), according to thermal emission measurements by the infrared Herschel Space Observatory. [3] Ritona is large enough that some astronomers consider it a possible dwarf planet. [21] : 178 [13] : 1 [22] : 397
In visible light, the surface of Ritona appears dark and reddish in color, [9] [10] with a geometric albedo of about 0.11. [3] : 10 Spectroscopic observations by the James Webb Space Telescope (JWST) in 2022 have shown that Ritona's surface is composed of water ice, carbon dioxide (CO2) ice, carbon monoxide (CO) ice, and various organic compounds (tholins). [23] : 2 This composition is common among Kuiper belt objects. [23] Analysis of JWST's spectroscopic observations has shown that Ritona's surface is more abundant in CO2 ice than water ice, which suggests that Ritona's surface is covered with a thin (a few micrometres thick) layer of fine, micron-sized CO2 ice particles. [23] : 1–2 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. [23] : 1 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 CO2 molecules, and leaves the CO trapped within the surrounding CO2 ice. [23] : 1, 5 A similar scenario has been hypothesized for (84522) 2002 TC302 , another CO2-rich Kuiper belt object observed by JWST. [23]
As of 2018 [update] , observations of Ritona's brightness over time indicate it has a rotation period of either 6.946 or 13.892 hours, depending on whether the object's brightness variability is caused by surface albedo variations or an elongated shape. [a] [7] : 2537, 2542 Studies from 2010 to 2018 have consistently shown that Ritona exhibits very little brightness variation (less than 0.06 magnitudes), which makes it difficult to accurately determine its rotation period. [7] : 2539 The small brightness variations of Ritona can be explained if it has a spheroidal shape with small albedo variations across its surface. [21] : 177–178