Just when you thought you knew all the worlds in the solar system, astronomers go and discover a new object that could rewrite the space map. 

This icy world, temporarily named 2017 OF201, could be a distant cousin of Pluto — and scientists mean “distant” quite literally. At its farthest point, it’s more than 1,600 times the distance of Earth from the sun. At its closest, it’s still 44.5 times farther than Earth.

What makes 2017 OF201 stand out is its very stretched-out path around the sun, which takes an incredible 25,000 Earth-years to complete. For comparison, Pluto makes a lap around the sun every 248 Earth-years. 

How this world got to the edge of the solar system is a mystery — perhaps the result of close encounters with a giant planet like Jupiter or Neptune that tossed it out into a wide orbit. Or maybe when it was originally ejected, it ended up in the so-called Oort Cloud before returning. The Oort Cloud is thought to be a sphere of ancient, icy objects surrounding the solar system. NASA says the cloud remains a theory because the comets there have been too faint and distant to be directly observed.

The International Astronomical Union’s Minor Planet Center, which catalogs new moons and other small bodies in the solar system, announced the discovery on May 21. At roughly 435 miles wide, 2017 OF201 could qualify as a dwarf planet, the same designation Pluto has had since its demotion from ninth planet in 2006. 

“Even though advances in telescopes have enabled us to explore distant parts of the universe,” said Sihao Cheng, the Institute for Advanced Study researcher who led the discovery, in a statement, “there is still a great deal to discover about our own solar system.”

Cheng, along with Princeton University graduate students, found the possible dwarf planet while searching for a potential “Planet 9,” a hypothetical hidden world whose gravitational effects could be responsible for a strange clustering of far-flung objects beyond Neptune.

The team used computer programs to look through years of space pictures taken by the Victor M. Blanco Telescope in Chile and the Canada France Hawaii Telescope. By connecting bright spots that moved slowly across the sky, they were able to identify it.

These are the current orbits of Pluto, Neptune, and 2017 OF201.
Credit: Jiaxuan Li / Sihao Cheng infographic

But 2017 OF201 is a strange outlier because it doesn’t follow the clustering pattern of other trans-Neptunian objects.

“The existence of 2017 OF201 might suggest that Planet 9 or X doesn’t exist,” said Jiaxuan Li, one of the collaborators, on his personal website. Their research is available now on the arXiv pre-print server. 

The discovery also challenges many scientists’ notion of the outer solar system. The area beyond the Kuiper Belt, where the object is located, has previously been thought of as fairly empty. NASA’s New Horizons probe, which snapped pictures of Pluto and its moons in 2015, has since more than doubled that distance, though surprisingly, it still hasn’t reached the edge of the belt. 

That could mean the spacecraft will travel billions of more miles before reaching interstellar space, a region that is no longer influenced by the sun’s radiation and particles. In 2019, New Horizons snapped photos of an icy red dumbbell-shaped thing, named Arrokoth, the farthest object a spacecraft has ever encountered. 

If 2017 OF201 only spends 1 percent of its orbit close enough for people to detect it, that may imply what lies outside the Kuiper Belt is not so empty after all. 

“The presence of this single object suggests that there could be another hundred or so other objects with similar orbit and size, ” Cheng said. “They are just too far away to be detectable now.”