In May 2025, astronomers announced the discovery of a new (potential) dwarf planet: 2017 OF201. This trans-Neptunian object (TNO) resides far beyond Pluto and offers fresh insights into the outer solar system. Its unique characteristics challenge existing theories and open new avenues for exploration.
Discovery of 2017 OF201
A team led by Sihao Cheng from the Institute for Advanced Study identified 2017 OF201. They analyzed archival data from the Dark Energy Camera (DECam) and the Canada-France-Hawaii Telescope. Over the course of seven years, they tracked the object’s movement across 19 sets of images. On May 21, 2025, the International Astronomical Union’s Minor Planet Center confirmed the discovery.
Physical characteristics
2017 OF201 is estimated to be approximately 700 kilometers (435 miles) in diameter, making it a strong candidate for dwarf planet status. Its size suggests that it is likely spherical, and its composition is presumed to be icy, similar to that of other objects in the Kuiper Belt.
Orbital dynamics
2017 OF201 exhibits an extremely elongated orbit. At its closest approach to the Sun (perihelion), it is about 44.9 astronomical units (AU) away, similar to Pluto’s distance. At its farthest point (aphelion), it extends up to approximately 1,630 AU, reaching into the inner Oort Cloud. This orbit takes around 25,000 years to complete. As of 2025, 2017 OF201 is located about 90.5 AU from the Sun. Its highly eccentric orbit suggests complex gravitational interactions, possibly involving Neptune or the Milky Way‘s tidal forces.
Significance of the discovery
The detection of 2017 OF201 is noteworthy for several reasons. It spends only about 1% of its orbital time close enough to Earth to be detectable, indicating that many similar distant objects may remain undiscovered. Its discovery hints at a potentially large population of similar objects in the outer solar system, challenging the notion of an empty region beyond the Kuiper Belt.
Is it Planet Nine?
Some have wondered whether 2017 OF201 could be the mysterious Planet Nine. The answer is no. This minor planet is far too small. Planet Nine, if it exists, is predicted to be several times more massive than Earth. In contrast, 2017 OF201 is likely only 700 kilometers wide. That’s much smaller than even Earth’s Moon. In addition, its orbit does not match what scientists expect from Planet Nine. Planet Nine is thought to shape the orbits of several distant objects in a specific way. But 2017 OF201 does not fit that pattern. Its orbit is anti-aligned with those objects, which challenges the influence of a massive, unseen planet. Also, simulations show that if Planet Nine did exist, it would likely disrupt 2017 OF201’s orbit. That disruption is not observed. So, based on current evidence, this minor planet is not Planet Nine and may even argue against its existence.
The discovery of 2017 OF201 enriches our understanding of the solar system’s outer regions. Its unique orbit and characteristics challenge existing models and underscore the need for continued exploration. As technology advances, further discoveries may reshape our cosmic perspective.
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