Astronomers Think They've Discovered a New Dwarf Planet in Our Solar System

Newsweek

26-05-2025

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A team of astronomers believe they may have discovered a new dwarf planet—just like Pluto—on the edge of our solar system.
The object—which orbits out beyond Neptune—has been named "2017 OF201" by the team, which was led by Sihao Cheng of the Institute for Advanced Study in Princeton, New Jersey.
Cheng and colleagues estimate that the body has a diameter of more than 430 miles, which means that it may be large enough to qualify as a dwarf planet.
While further observations are required to determine its exact size, current estimates suggest that 2017 OF201 is the second-largest known object in such a wide orbit.
So-called "trans-Neptunian objects" (TNOs) like 2017 OF201 can vary dramatically in size—from as large as 1,477 miles in diameter (i.e. Pluto) down to just 22 miles like the peanut-shaped Arrokoth.
A stock image showing the view of Pluto from space.
A stock image showing the view of Pluto from space.
buradaki/Getty Images
The region of space that TNOs occupy is commonly known as the Kuiper Belt, named after the Dutch-American astronomer Gerard Kuiper.
Indeed, the discovery of 2017 OF201 could suggest that the space beyond Neptune in the Kuiper Belt may not be empty after all.
Cheng said: "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. 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."
The extreme orbit of 2017 OF201 suggests that it could take approximately 25,000 years to go once around the sun. This could highlight a complex history of gravitational interactions, the researchers suggest.
Cheng and his colleagues used advanced computational methods to identify the TNO's trajectory.
"2017 OF201 spends only one percent of its orbital time close enough to us to be detectable. 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," Cheng continued.
The potential dwarf planet was announced by the International Astronomical Union's Minor Planet Center on May 21, 2025.
Cheng was able to identify the TNO by pinpointing bright spots in an astronomical image database from the Victor M. Blanco Telescope and Canada France Hawaii Telescope. He was then able to connect possible groups of such spots that appeared to move across the sky in the way a TNO could also do.
By using a computationally efficient algorithm, Cheng was able to identity 2017 OF201 across 19 different exposures over seven years.
The researchers suggest that the discovery of another dwarf planet like Pluto could have significant implications for our understanding of the outer solar system.
Newsweek has contacted Cheng and the Institute for Advanced Study via email for comment.
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Reference
Cheng, S., Li, J., & Yang, E. (2025). Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201 (arXiv:2505.15806v1 [astro-ph.EP]). arXiv. https://arxiv.org/abs/2505.15806