An Extreme Cousin for Pluto? Possible Dwarf Planet at Solar System Edge

Summary

A small team led by Sihao Cheng, Martin A. and Helen Chooljian Member in the Institute for Advanced Study’s School of Natural Sciences, has discovered an extraordinary trans-Neptunian object (TNO), named 2017 OF201, at the edge of our solar system.The TNO is potentially large enough to qualify as a dwarf planet, the same category as the much more well-known Pluto. The new object is one of the most distant visible objects in our solar system and, significantly, suggests that the empty section of space thought to exist beyond Neptune in the Kuiper Belt is not, in fact, empty at all.Cheng made the discovery alongside colleagues Jiaxuan Li and Eritas Yang from Princeton University, using advanced computational methods to identify the object’s distinctive trajectory pattern on the sky. The new object was officially announced by the International Astronomical Union’s Minor Planet Center on May 21, 2025, and in an arXiv pre-print shared today.Trans-Neptunian objects are minor planets that orbit the Sun at a greater average distance than the orbit of Neptune. The new 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 1600 times that of the Earth’s orbit,” explains Cheng. “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.” Jiaxuan Li and Sihao Cheng Image showing the current location of Pluto, Neptune, and 2017 OF201. 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,” says 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," Chen...