(42301) 2001 UR163

(42301) 2001 UR₁₆₃ (provisional designation 2001 UR₁₆₃) is a resonant trans-Neptunian object located in the outermost region of the Solar System. The object measures approximately 352 kilometers (220 miles) in diameter with a high albedo and stays in an uncommon orbital resonance (4:9) with Neptune. It was discovered on 21 October 2001 by astronomers of the Deep Ecliptic Survey program at Kitt Peak National Observatory near Tucson, Arizona, United States. As of 2021^[update], it has not been named.^[1]

(42301) 2001 UR₁₆₃

Hubble Space Telescope image of 2001 UR163 taken in 2005
Discovery[1][2]
Discovered by	DES
Discovery site	Kitt Peak National Obs.
Discovery date	21 October 2001
Designations
MPC designation	(42301) 2001 UR163
Alternative designations	2001 UR163
Minor planet category	TNO[3] · 4:9 res[4][5] distant[1]
Orbital characteristics[3]
Epoch 1 July 2021 (JD 2459396.5)
Uncertainty parameter 2[1][3]
Observation arc	38.45 yr (14,045 d)
Aphelion	66.643 AU
Perihelion	36.987 AU
Semi-major axis	51.815 AU
Eccentricity	0.2862
Orbital period (sidereal)	372.98 yr (136,232 d)
Mean anomaly	80.814°
Mean motion	0° 0m 9.36s / day
Inclination	0.7531°
Longitude of ascending node	301.39°
Time of perihelion	8 October 1937
Argument of perihelion	344.50°
Physical characteristics
Mean diameter	352±85 km[4][6]: 26
Geometric albedo	0.209±0.08[4][6]
Spectral type	RR-U (very red)[7][8][6] B–V = 1.25±0.11[8] V–R = 0.88±0.06[8] V–I = 1.54±0.16[8]
Apparent magnitude	21.3[9]
Absolute magnitude (H)	4.21[1][3]

Classification and orbit

The object orbits the Sun at a distance of 37.0–66.6 AU once every 372 years and 12 months (136,232 days; semi-major axis of 51.82 AU). Its orbit has an eccentricity of 0.29 and an inclination of 1° with respect to the ecliptic.^[3] It came to perihelion on 8 October 1937, and has since been moving away from the Sun.^[3] In 2006, it moved beyond a distance of 50 AU and is at 53.7 AU as of 2021^[update].^[9] The body's observation arc begins with a precovery, published by the Digitized Sky Survey and taken at the Siding Spring Observatory in July 1982.^[1]

Numbering and naming

2001 UR₁₆₃ was numbered (42301) by the Minor Planet Center on 26 May 2002 (M.P.C. 45686).^[10] As of 2025^[update], it has not been named.^[1] According to the established naming conventions, it will receive a mythological or mythic name (not necessarily from Classical mythology), in particular one associated with creation.^[11]

Physical characteristics

Lightcurve analysis shows only small deviations, suggesting that 2001 UR₁₆₃ is a spheroid with small albedo spots.^[12] Observations with Spitzer's Infrared Array Camera were used to study the body's surface composition. The analyzed data indicate the presence of 20% water ice, 60% amorphous silicates, and 20% organic compounds, including complex ones such as tholins.^[6]: 20

Diameter and albedo

2001 UR₁₆₃ measures approximately 352 kilometers (220 miles) in diameter with a high albedo of 0.209.^[4][6]: 26

Based on previous estimates published on the Lightcurve Data Base and on Michael Brown's website, 2001 UR₁₆₃ measures between 531 km (330 mi) and 583 kilometers (360 miles), using an assumed intermediate surface albedo of 0.09 to 0.10 with an absolute magnitude of 4.49 and 4.4, respectively.^[7][13]

See also

• List of Solar System objects most distant from the Sun