Planet Nine may not exist, but Dwarf Planet Nine might

26 June 2025

The apparent discovery of an extremely distant dwarf-planet, known as 2017 OF201, might put paid to the speculated existence of a likewise far-flung Neptune-size planet, often referred to as Planet Nine, says Isaac Schultz, writing for Gizmodo:

Which brings us, inevitably, to Planet Nine, the theorized distant world posited as a gravitational explanation for the strange clustering of objects in the Kuiper Belt. Other ideas have been floated to explain the phenomenon — such as a ring of debris exerting gravitational influence, or even a primordial black hole — but nothing grips our human fascination like a distant planet, so far away from our solar system’s other worlds that it’s never been observed.

Unexpected variations in the orbits of numerous dwarf-planets and various other bodies, known as Trans-Neptunian Objects (TNO), usually located beyond the orbit of Pluto, have long puzzled scientists and astronomers. This has lead some of them to believe the solar system hosts a larger planet, which they call Planet Nine.

This body possibly orbits the Sun elliptically, at an average distance of two-hundred-and-fifty astronomical units (AU), or thirty-seven billion KM (compared with an average six billion or so KM for Pluto), and takes ten to twenty thousand years to do so. But its theorised presence might account for the odd orbital behaviour of some TNOs.

But this is where things become intriguing. A 2013 NASA survey of the area surrounding the solar system, apparently detected no indication of any reasonably large planetary bodies beyond the orbit of Pluto. This despite the ability of their technology to perceive Saturn-size objects a tenth of a light year distant.

This discovery of 2017 OF201, which leisurely orbits the Sun once every twenty-five thousand years, and ventures as far away as sixteen-hundred AU, makes sense in this context. It also opens the door to locating potentially many more highly distant dwarf-planets.

The presence of 2017 OF201 however does not completely eliminate the possibility Planet Nine exists, the 2013 NASA study notwithstanding. Sihao Cheng, who participated in finding 2017 OF201, still hopes Planet Nine turns out to be there.