The unusual orbit of a possible dwarf planet, known as 2017 OF201, makes it less likely that our solar system contains a hidden ninth “Planet X”
By Chris Simms
22 May 2025
The orbits of a potential dwarf planet called 2017 OF201 and the dwarf planet Sedna
Tony Dunn
A potential dwarf planet has been discovered in the outer reaches of our solar system, orbiting beyond Neptune. Its presence there challenges the existence of a hypothetical body known as Planet 9 or Planet X.
Sihao Cheng at the Institute for Advanced Study in Princeton, New Jersey, and his colleagues first detected the object, known as 2017 OF201, as a bright spot in an astronomical image database from the Victor M. Blanco Telescope in Chile.
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2017 OF201 is about 700 kilometres across – big enough to qualify as a dwarf planet like Pluto, which has a diameter about three times as big. The object is currently about 90.5 astronomical units (AU) away from us, or roughly 90 times as far from Earth as the sun is.
Because 2017 OF201’s average orbit around the sun is greater than that of Neptune, it is what’s known as a trans-Neptunian object (TNO). It passes through the Kuiper belt, a disc of icy objects in the outer solar system beyond the orbit of Neptune.
The researchers looked back over 19 observations, taken over seven years by the Canada France Hawaii Telescope, to determine that the closest 2017 OF201 gets to the sun – its perihelion – is 44.5 AU, which is similar to Pluto’s orbit. The furthest it gets from the sun is 1600 AU, way outside the solar system.