(202421) 2005 UQ513

is a large classical Kuiper belt object located in the trans-Neptunian region of the Solar System. It was discovered on 21 August 2005 by American astronomers Mike Brown, David Rabinowitz, and Chad Trujillo at the Palomar Observatory in California.

Thermal observations by the Herschel Space Telescope estimate its diameter to be , which makes it among the top 34 largest known trans-Neptunian objects. It has a highly reflective geometric albedo of , which is higher than average for typical hot classical Kuiper belt objects. completes one rotation relatively quickly every 7.03 hours. Visible spectroscopy observations show that has a featureless spectrum with no detected absorption bands. However, its surface is very red due to a spectral slope of 18.1 ± 2.0%/100 nm, indicating a surface rich in complex organics. Models classify its orbit as dynamically stable over a period of 1 billion years. The Hubble Space Telescope is scheduled to observe the object in 2026 to search for potential moons. If a moon is found, it will allow scientists to directly calculate the mass and density of .

History Discovery

was discovered on 21 October 2005 by American astronomers Mike Brown, David Rabinowitz and Chad Trujillo at the Palomar Observatory in California, United States. At the time, they were searching for distant trans-Neptunian objects using the observatory's 1.2-meter Samuel Oschin telescope. It has been observed 750 times over 28 oppositions with precovery images back to 1990.

Further observations Following its discovery, was tracked by multiple stations, including the Apache Point-Sloan Digital Sky Survey, Purple Mountain Observatory, and Pic du Midi Observatory. As of 2026, the object has been observed 750 times over an observation arc of 13,112 days. is scheduled for observation with the Hubble Space Telescope in 2026; if those observations discover a moon, they could lead to a measurement of the mass and density of .

Provisional designation and numbering The object was formally given the provisional designation by the Minor Planet Center on 1 September 2007. The provisional designation of indicates its discovery date, the first letter represents the second half of October and the second letter and numbers means that it is the 12,842nd object discovered during that half-month. was assigned its permanent number 202421 in December 2008.

Orbit and classification

is a trans-Neptunian object that orbits the Sun at a distance of 36.8–49.6 AU with an semi-major axis or average orbital distance of 43.2 AU once every 284.1 years (for reference, Neptune's orbit is at 30 AU). Its orbit has an eccentricity of 0.15 and an inclination of 25.7° with respect to the ecliptic. As of December 2018, it is currently 48.0 AU from the Sun. It will come to perihelion in 2123.

is located in the classical region of the Kuiper belt 39–48 AU from the Sun, and is classified as a classical Kuiper belt object (also known as a "cubewano"). The high orbital inclination (25.7°) of it makes it a dynamically "hot" member of the classical Kuiper belt. The Minor Planet Center (MPC) also classifies it as a classical Kuiper belt object (cubewano) The Deep Ecliptic Survey (DES) classifies it as ScatExt (scattered-extended). Dynamically, it would have been a good candidate to be a member of the Haumea collisional family. However, given its red spectrum, it is probably not.

Orbital stability In a 2021 study, scientists analyzed the orbital stability of over a period of 1 billion years. Models calculated a diffusion time of 67.717 billion years, predicting its orbit to be very stable. In the full 1 billion year simulation, 199 out of 200 tracked test particles maintained regular orbits, leading that study to classify as dynamically stable.

Physical characteristics Size, Mass and density

A 2014 study based on thermal wavelengths have measured 's size to be at in diameter, making it approximately ⁵/9 the size of the dwarf planet Sedna. is a very large trans-Neptunian object and is among the top 34 largest known TNOs. is not known to have any natural satellites or moons, which means there is currently no way to measure its mass and density.

's size is large enough that Mike Brown classify it as a possible dwarf planet, putting it in the 'very likely' zone. Based on its size of approximately , it belongs to the proposed class of "mid-sized" TNOs between in diameter, which are believed to represent the transition between small, low-density TNOs and large, high-density dwarf planets. Planetary scientists have hypothesized that mid-sized TNOs should have highly porous and unheated interiors, because TNOs in this size range (such as Uni and Gǃkúnǁʼhòmdímà) have been found to have low densities around .

Surface Composition, spectrum and color

Spectroscopy observations show that has a featureless spectrum with no detected absorption bands. The surface is very red, displaying a spectral slope of 18.1 ± 2.0%/100 nm, which makes it likely too red to be in the Haumea family. These measurements indicate that the surface contains a decent amount of processed materials composed of complex organics.

Albedo, brightness and visibility from Earth has a visual absolute magnitude (Hv) of 3.91 according to the Jet Propulsion Laboratory, which was later refined to by the Herschel survey. This brightness is similar to that of Varda. Thermal observations by the Herschel Space Telescope show that the object has a geometric albedo of . This albedo value is higher than the average for typical hot classical Kuiper belt objects. However, due to its very far distance from Earth, it has a dim apparent magnitude of 20.8 when viewed from Earth.

Rotation has a relatively fast rotation period of 7.03 hours, with its brightness varying by magnitudes during each rotation, indicative of an approximate spheridal shape. For comparison, such rotation period is similar to the large plutino 208996 Achlys.

Origin

The hot classical Kuiper belt objects like are believed to have been scattered by Neptune's gravitational influence during the Solar System's early history. 's orbital position matches with the group very well, hence, it was considered a candidate for the Haumea family. However, has a red surface spectrum and not a water-ice surface, making likely an interloper that did not originate from the Haumea family impact.

Exploration concepts

has not been visited by any spacecraft. A 2019 study on flyby mission opportunities between 2025 and 2040 calculated hypothetical trajectories to TNOs with H brighter than 4.0 including using planetary gravity assists. A trajectory using a Saturn swingby has a launch window from 2025 to 2029, with a minimum travel time of 12.5 years. Trajectories using a Jupiter swingby have launch windows between 2031 and 2034, with a shorter flight duration of 10.4 years. Other than that, a combined Jupiter and Neptune swingby pathway makes launch options from 2032 to 2034, requiring a longer travel time of at least 23.4 years.

(202421) 2005 UQ513

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