Distant Dwarf Planet Candidate Challenges Theories of Hidden Planet in Solar System

A newly identified object in the far reaches of the solar system, possibly a cousin of Pluto, is raising questions about long-standing theories surrounding a hypothetical ninth planet.

Astronomers have discovered a dwarf planet candidate named 2017 OF201, which travels in an exceptionally wide and elliptical orbit around the Sun. The object’s farthest point lies nearly 245 billion kilometers from the Sun — over 1,600 times the Earth’s distance — while its closest approach is around 7 billion kilometers, or 45 times Earth’s distance. The orbital period of this distant body is estimated to exceed 24,000 years.

The findings were detailed in a paper submitted on May 21 to arXiv.org by astrophysicist Sihao Cheng of the Institute for Advanced Study in Princeton, New Jersey, and his research team. The object was identified through public archival data comprising 19 telescope images taken between 2011 and 2018.

With an estimated diameter of 700 kilometers and a mass comparable to that of Earth’s moon, 2017 OF201 likely has sufficient gravity to maintain a rounded shape — a key criterion for classification as a dwarf planet, according to Cheng.

What makes 2017 OF201 particularly intriguing is that its orbit does not align with those of other distant solar system objects, many of which cluster in similar orientations. This clustering has been a cornerstone of the Planet Nine hypothesis, which proposes that an undiscovered massive planet is influencing the orbits of these remote bodies.

“This object’s orientation is about 90 degrees off from that clustering,” says Cheng. Simulations based on recently proposed orbits for Planet Nine suggest that 2017 OF201’s path is inconsistent with the presence of such a planet — at least in its currently theorized position.

However, Chad Trujillo, an astronomer at Northern Arizona University and a co-proposer of the Planet Nine hypothesis (though not involved in this new research), cautions against jumping to conclusions. “This object being incompatible with one [orbit] is not detrimental to Planet X,” he notes, highlighting the wide range of theoretical orbital paths that have been proposed.

Cheng and his team are now conducting further simulations to assess the long-term stability of 2017 OF201’s orbit and to explore whether alternative versions of the Planet Nine model could still account for its unusual trajectory.

While the discovery may complicate the search for Planet Nine, it also adds to the rich tapestry of celestial bodies in the solar system’s outer frontier — and opens new avenues for understanding the dynamics of these distant, icy worlds.