New Dwarf Planet 2017 OF201 Discovered Beyond Neptune: A Clue to the Solar System’s Secrets?

Princeton, May 24, 2025 – Astronomers have unveiled a new dwarf planet candidate, 2017 OF201, lurking in the distant reaches of our solar system, far beyond Neptune’s orbit. This intriguing object, roughly 435 miles (700 kilometers) in diameter, takes an astonishing 25,000 years to complete a single orbit around the Sun.

Discovered through meticulous analysis of archival telescope data, its extreme, elliptical path challenges existing theories about the outer solar system, including the elusive Planet 9 hypothesis. The find suggests that the region beyond the Kuiper Belt may be teeming with undiscovered objects, prompting scientists to rethink what lies in our cosmic backyard.

A Cosmic Discovery in Archival Data

On May 21, 2025, the International Astronomical Union’s Minor Planet Center officially recognized 2017 OF201, a trans-Neptunian object (TNO) identified by a team led by Sihao Cheng at the Institute for Advanced Study. Using data from the Victor M. Blanco Telescope in Chile and the Canada-France-Hawaii Telescope, researchers tracked the object across 19 observations spanning seven years, from 2011 to 2018.

Currently located 90.5 astronomical units (AU) from the Sun—over twice Pluto’s distance—this dwarf planet candidate boasts a highly eccentric orbit, swinging as close as 44.5 AU and as far as 1,600 AU, venturing into the inner Oort Cloud. Its last close approach to the Sun was in 1930, coinciding with Pluto’s discovery.

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An Outlier Orbit Challenging Planet 9

The orbit of 2017 OF201 is a cosmic anomaly, with an eccentricity of 0.95 and an inclination of 16.2 degrees, placing it near the boundary of the scattered disk and the Oort Cloud. Unlike many extreme TNOs, whose orbits cluster in patterns suggesting the gravitational influence of a hypothetical Planet 9, 2017 OF201 deviates significantly.

Simulations indicate that if Planet 9 exists, it would likely eject 2017 OF201 from the solar system within 100 million years, yet the object remains stable. This discrepancy, noted in a 2025 arXiv preprint, casts doubt on current Planet 9 models, though researchers caution that more observations are needed to confirm these dynamics.

Did You Know?
The Kuiper Belt, home to Pluto and 2017 OF201, is estimated to contain over 100,000 objects larger than 100 km, yet most remain undetected due to their faintness.

A Hidden Population in the Kuiper Belt?

The discovery of 2017 OF201, which is potentially the second-largest known extreme TNO after Pluto (2,377 km), suggests the Kuiper Belt and beyond may harbor a significant population of similar objects. With an estimated diameter of 550-850 km and a brightness indicating a reflective surface, it stands out among the 3,000 known TNOs.

Researchers estimate that 2017 OF201 is detectable only 1% of its orbital time, implying that hundreds of similar objects, totaling about 1% of Earth’s mass, could remain unseen. Recent online discussions highlight excitement over this find, with some speculating it could redefine our understanding of the solar system’s outer reaches.

What’s Next for 2017 OF201?

Further observations, possibly using radio telescopes, are planned to refine the object’s size and composition. Its discovery underscores the power of advanced computational methods, as Cheng’s team used algorithms to pinpoint its trajectory in archival data. This approach, accessible to researchers and citizen scientists alike, suggests more discoveries may await in existing datasets. As telescopes like the James Webb Space Telescope continue to probe the Kuiper Belt, 2017 OF201 could be a stepping stone to unraveling the mysteries of our solar system’s frontier.