A Newly Discovered Dwarf Planet at the Solar System’s Frontier

A newly discovered distant dwarf planet lies beyond Neptune, challenging the existence of the hypothetical Planet 9 or Planet X.

Sihao Cheng and colleagues first spotted this object, initially recognized in 2017, while reviewing data from the Victor M. Blanco telescope in Chile.

The 2017 OF201 measures roughly 700 km in diameter, qualifying it as a dwarf planet similar to Pluto, which is about three times larger. Currently, it is positioned approximately 90.5 astronomical units (AU) away from Earth, roughly 90 times the distance from the Earth to the Sun.

Classified as a Trans-Neptunian Object (TNO), 2017 OF201 has an average orbital distance from the Sun that exceeds Neptune’s orbit. It travels beyond Neptune and through the Kuiper Belt, a region of icy bodies on the outskirts of the solar system.

Researchers analyzed 19 observations collected over seven years at the Canada-France-Hawaii Telescope. They determined that the next close approach of 2017 OF201 to the Sun would occur at perihelion, positioned at 44.5 AU, which is reminiscent of Pluto’s orbit. Its furthest point from the Sun lies at about 1600 AU, beyond our solar system.

This distant orbit may have resulted from an encounter with a large planet that ejected the dwarf planet from the solar system, according to researchers.

“This is a fascinating discovery,” says Kevin Napier from the University of Michigan. He explains that objects can interact with various stars in the galaxy as they move beyond our solar system and can also interact within our own solar system.

Many extreme TNO trajectories seem to be converging toward a specific direction, which some interpret as evidence for a hidden ninth planet within the Oort Cloud—a vast shell of icy rocks that surrounds the solar system. The speculation is that the gravitational pull of this ninth planet may be influencing TNOs into specific orbital paths.

However, the trajectory of 2017 OF201 does not align with this observed pattern. “This object is certainly an outlier among the observed clustering,” notes Erita Yang at Princeton University.

Cheng and his team also conducted simulations of object orbits concerning Planet 9. “With Planet 9, objects get ejected over hundreds of millions of years. Without it, they remain stable,” states Napier. “This is not evidence supporting the existence of Planet 9.”

Nevertheless, until more data is available, the matter remains unsettled, according to Cheng. “I hope that Planet 9 is real because it would be even more intriguing.”

This candidate dwarf planet takes approximately 25,000 years to complete its orbit, meaning we detect it for only about 1% of that time. “These objects are faint and very challenging to locate, and their elongated orbits make them visible only when they are near the Sun, resulting in a brief window for observation,” explains Napier.

It is possible that hundreds of such objects exist in the outer solar system. The upcoming Vera C. Rubin Observatory is expected to start operating later this year and may delve deeper into the universe to find more objects like this.