145452 Ritona

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145452 Ritona is a large object in the Kuiper belt, a distant region beyond Neptune. It is a classical (hot) Kuiper belt object and is big enough that some scientists consider it a possible dwarf planet.

Discovery and naming
- Discovered on 10 September 2005 by Andrew Becker, Andrew Puckett, and Jeremy Kubica at Apache Point Observatory, New Mexico.
- Precovery images go back to 1954.
- Minor Planet Center number: 145452. It was named Ritona after the Celtic goddess of river fords; the name was officially announced in 2025.

Orbit and distance
- Orbits the Sun about every 267 years.
- Semi-major axis: about 41.5 astronomical units (AU).
- Eccentricity: about 0.0226 (nearly circular).
- Inclination: about 19.3 degrees relative to the solar system plane.
- Distance from the Sun ranges roughly from 40.6 AU at perihelion to 42.5 AU at aphelion.
- Part of the classical Kuiper belt (also called a cubewano) in the 39–48 AU region.

Size and brightness
- Diameter: about 679 kilometers (with some uncertainty).
- Geometric albedo (reflectivity): about 0.11.
- Absolute magnitude and apparent brightness indicate a dark, reddish surface.

Rotation and shape
- Rotation period is not firmly fixed: estimates give either about 6.95 hours (single-peaked light curve) or 13.89 hours (double-peaked).
- Very little brightness variation has been observed, suggesting Ritona may be nearly spheroidal with small surface color differences.
- No moons or natural satellites are known to orbit Ritona.

Surface composition
- Surface seen as dark and reddish.
- JWST observations (2022) show a surface made of water ice, carbon dioxide ice (CO2), carbon monoxide ice (CO), and organic compounds.
- CO2 ice is more abundant than water ice, indicating a thin CO2 frost layer on the surface.
- CO ice is also present; ultraviolet light from the Sun may help create CO from CO2 on Ritona’s surface.

Temperature
- Surface temperature around 43 K near perihelion (very cold, far from the Sun).

In short, Ritona is a large, distant, ice-covered world in the hot classical Kuiper belt, with a likely dwarf-planet status, a mostly featureless rotation, and a surface rich in CO2 ice alongside water ice, CO, and organics.