Named 2017 OF201, the newly-discovered trans-Neptunian object is one of the most distant visible objects in our Solar System and is likely large (about 700 km in diameter) enough to qualify as a dwarf planet.
Cutout images of all 19 detections of 2017 OF201. Image credit: Cheng et al., arXiv: 2505.15806.
Trans-Neptunian objects (TNOs) are minor planets that orbit the Sun at a greater average distance than the orbit of Neptune.
After 30 years of the discovery of the first TNOs other than Pluto, various survey programs have been conducted to explore the vast region of the outer Solar System, and more than 5,000 TNOs have been discovered so far.
The newly-discovered TNO is special for two reasons: its extreme orbit and its large size.
“The object’s aphelion — the farthest point on the orbit from the Sun — is more than 1,600 times that of the Earth’s orbit,” said Dr. Sihao Cheng, an astronomer at the Institute for Advanced Study and Perimeter Institute.
“Meanwhile, its perihelion — the closest point on its orbit to the Sun — is 44.5 times that of the Earth’s orbit, similar to Pluto’s orbit.”
“This extreme orbit, which takes the object approximately 25,000 years to complete, suggests a complex history of gravitational interactions.”
“It must have experienced close encounters with a giant planet, causing it to be ejected to a wide orbit,” added Princeton University astronomer Dr. Eritas Yang.
“There may have been more than one step in its migration.”
“It’s possible that this object was first ejected to the Oort cloud, the most distant region in our Solar System, which is home to many comets, and then sent back.”
“Many extreme TNOs have orbits that appear to cluster in specific orientations, but 2017 OF201 deviates from this,” said Dr. Jiaxuan Li, also from Princeton University.
“This clustering has been interpreted as indirect evidence for the existence of another planet in the Solar System, Planet X or Planet Nine, which could be gravitationally shepherding these objects into their observed patterns.”
“The existence of 2017 OF201 as an outlier to such clustering could potentially challenge this hypothesis.”
The astronomers estimate 2017 OF201’s diameter to be 700 km, which would make it the second largest known object in such a wide orbit.
“2017 OF201 spends only 1% of its orbital time close enough to us to be detectable,” Dr. Cheng said.
“The presence of this single object suggests that there could be another hundred or so other objects with similar orbit and size; they are just too far away to be detectable now.”
The researchers discovered 2017 OF201 as part of an ongoing research project to identify TNOs and possible new planets in the outer Solar System.
The object was identified by pinpointing bright spots in an astronomical image database from the Victor M. Blanco Telescope and Canada France Hawaii Telescope (CFHT), and trying to connect all possible groups of such spots that appeared to move across the sky in the way a single TNO might.
The scientists identified 2017 OF201 in 19 different exposures, captured over 7 years.
“Even though advances in telescopes have enabled us to explore distant parts of the Universe, there is still a great deal to discover about our own Solar System,” Dr. Cheng said.
The team’s paper was posted online on arXiv.org.
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Sihao Cheng et al. 2025. Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201. arXiv: 2505.15806
