2017 OF201

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.