2017 OF₂₀₁

2017 OF₂₀₁
	2017 OF201 imaged by the Canada–France–Hawaii Telescope on 31 August 2011
Discovery
Discovered by	Sihao Cheng, Jiaxuan Li, Eritas Yang
Discovery site	Cerro Tololo Inter-American Observatory
Discovery date	23 July 2017 (date of first observation)
Designations
MPC designation	2017 OF201
Minor planet category	TNO, SDO and eTNO
Orbital characteristics (barycentric)
	Epoch 5 May 2025; (JD 2460800.5)
	Uncertainty parameter 3
Observation arc	14.11 yr (5,153 days); (based on 25 observations)
Earliest precovery date	21 Sep 2004
Aphelion	1612 AU (barycentric); 1632±14 AU (preliminary); 1693±6 AU (heliocentric)
Perihelion	44.91±0.01 AU
Semi-major axis	840 AU
Eccentricity	0.946
Orbital period (sidereal)	23800 yr (barycentric); 24300 years (preliminary); 26000±1300 yr (heliocentric)
Mean anomaly	1.3°
Mean motion	0° 38m 7.8s / day
Inclination	16.21°
Longitude of ascending node	328.7°
Time of perihelion	1930 November 13 ± 3 days
Argument of perihelion	338.2°
Known satellites	0
Physical characteristics
Mean diameter	≈700 km (est. at 0.13 albedo); 560~850 km (for albedo 0.10–0.25)
Geometric albedo	0.13 (predicted)
Spectral type	B–V = 0.96±0.09; g–r = 0.77±0.08; r–i = 0.56±0.07
Apparent magnitude	22.6 (r band)
Absolute magnitude (H)	3.72±0.09 (V band); 3.49±0.45 (JPL);

2017 OF₂₀₁ is an extreme trans-Neptunian object and dwarf planet candidate, estimated to be around 500 to 900 kilometres (300 to 600 miles) in diameter. It was announced in 2025 by Sihao Cheng, Jiaxuan Li, and Eritas Yang, who discovered the object in archived telescope images from 2011 to 2018. With an absolute magnitude between 3~4, 2017 OF₂₀₁ is one of the brightest known objects in the Solar System that does not have a directly measured size. The orbit of 2017 OF₂₀₁ is extremely large and elongated, bringing it from 45 to 1,610 astronomical units (0.00071 to 0.02546 ly) away from the Sun. 2017 OF₂₀₁ is not considered a sednoid because its perihelion or closest point to the Sun is below 60 AU, which means that the object comes close enough to Neptune that the planet's gravitational influence affects the orbit of 2017 OF₂₀₁.

2017 OF₂₀₁ has not yet been imaged by high-resolution telescopes, so it has no known moons. The Hubble Space Telescope is planned to image it in 2026, which should determine if it has significantly sized moons, whose orbital motion would allow reliable determination of its mass, and possibly its size as well.