Ritona has a dark and reddish surface made ofwater ice,carbon dioxide ice,carbon monoxide ice, and variousorganic compounds (tholins). Observations by theJames 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 anynatural satellites or moons, which means there is currently no way to measure its mass and density.[13]: 1, 3
Ritona was discovered by astronomersAndrew Becker,Andrew Puckett andJeremy Kubica on 10 September 2005, during observations for theSloan Digital Sky Survey.[1][14] The discovery observations were made using the 2.5-meter telescope atApache Point Observatory inSunspot, New Mexico.[14] The discoverers further observed Ritona until November 2005 and found the object inprecovery observations from dates as early as June 2001.[14] The discovery of Ritona was announced by theMinor Planet Center on 23 July 2006.[14] Since then, Ritona has been found in even earlier precovery observations dating back to June 1954.[1]
Diagram showing Ritona's inclined orbit (gray) around the Sun, with the outer planets shown. The vertical gray lines along Ritona's orbital path mark its positions above and below theecliptic plane.
Ritona is located in the classical region of theKuiper belt 39–48 AU from the Sun, and is thus classified as aclassical 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 beenscattered by Neptune's gravitational influence during the Solar System's early history.[20]: 230
Invisible light, the surface of Ritona appears dark and reddish in color,[9][10] with ageometric albedo of about 0.11.[3]: 10 Spectroscopic observations by theJames Webb Space Telescope (JWST) in 2022 have shown that Ritona's surface is composed ofwater ice,carbon dioxide (CO2) ice,carbon monoxide (CO) ice, and variousorganic 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 fewmicrometres 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 shouldsublimate and escape from Ritona's surface at its temperature and distance from the Sun.[23]: 1 Planetary scientistsMichael E. Brown andWesley C. Fraser have hypothesized that the Sun'sultraviolet 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 arotation 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 0.06magnitudes), 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
^abcThe rotation period of Ritona was measured by observing how its brightness changes over time, which is plotted as alight curve. If Ritona has a spheroidal shape, then its light curve should resemble a "single-peaked"sine wave, whereas if Ritona is elongated, then its light curve should resemble a "double-peaked" sine wave.[7]: 2539
^These orbital elements are expressed in terms of theSolar System Barycenter (SSB) as the frame of reference.[5] Due to planetaryperturbations, the Sun revolves around the SSB at non-negligible distances, so heliocentric-frame orbital elements and distances can vary in short timescales as shown inJPL-Horizons.[18]
^abcdeBelskaya, Irina N.; Barucci, Maria A.; Fulchignoni, Marcello; Lazzarin, M. (April 2015). "Updated taxonomy of trans-neptunian objects and centaurs: Influence of albedo".Icarus.250:482–491.Bibcode:2015Icar..250..482B.doi:10.1016/j.icarus.2014.12.004.
^Pinilla-Alonso, Noemí; Stansberry, John; Holler, Bryan (2020). "Chapter 18 - Surface properties of large TNOs: Expanding the study to longer wavelengths with the James Webb Space Telescope". In Prialnik, Dina; Barucci, Maria Antonietta; Young, Leslie (eds.).The Transneptunian Solar System. Elsevier. pp. 395–412.arXiv:1905.12320.Bibcode:2019arXiv190512320P.doi:10.1016/B978-0-12-816490-7.00018-7.ISBN978-0-12-816490-7.
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