Astronomers Discover a Possible Dwarf Planet Far Beyond Neptune, Where There Should Have Only Been Empty Space
As it orbits the sun once every 25,000 years, the celestial body 2017 OF201 travels beyond the Kuiper Belt into a region thought to be largely devoid of objects
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While the James Webb Space Telescope looks for the most distant galaxies ever seen, astronomers have discovered something new in our very own solar system.
Researchers from the U.S. and Canada have identified a celestial body with an enormous orbit that takes it around the sun once every roughly 25,000 years. With an estimated diameter of 435 miles, the object is potentially large enough to be classified as a dwarf planet like Pluto, though it’s more than three times smaller than the famously demoted planet.
Its existence, if confirmed, casts doubt on the idea that an undiscovered ninth planet might be lurking in the far reaches of our solar system, referred to as Planet X or Planet Nine.
“While searching for Planet X/Planet Nine, we found an extreme ‘cousin’ of Pluto,” Sihao Cheng, an astrophysicist at the Institute for Advanced Study, writes on his personal website. “Its orbit is extremely wide that it should come from the inner Oort cloud, a remote region in the solar system we still know little about.”
The International Astronomical Union’s Minor Planet Center announced the discovery last week, and Cheng is the lead author of a preprint study, which has not yet been peer-reviewed, posted on the arXiv server the same day.
The celestial body, officially named 2017 OF201, is a trans-Neptunian object (TNO)—a minor planet beyond Neptune’s orbit—and one of the most distant visible objects in the solar system. It travels even farther than the Kuiper Belt, a donut-shaped region of icy objects where researchers have identified thousands of TNOs, including Pluto, per Discover magazine’s Jack Knudson.
Notably, it orbits in a region astronomers had previously theorized to be empty.
“The object’s aphelion—the farthest point on the orbit from the sun—is more than 1,600 times that of Earth’s orbit,” Cheng explains in a statement. “Meanwhile, its perihelion—the closest point on its orbit to the sun—is 44.5 times that of Earth’s orbit, similar to Pluto’s orbit.”
According to the study, the last time 2017 OF201 reached its perihelion was likely in 1930, which is also the same year astronomers discovered Pluto. The object is now about twice as far from the sun as it was then, at around 90 times the distance of Earth’s orbit. In total, the celestial body is close enough for scientists to detect it for only 1 percent of its nearly 25,000-year orbit.
The researchers speculate that the newly discovered object’s extreme orbit may be the result of past gravitational interactions with other astronomical bodies, which ultimately launched it to the solar system’s farthest reaches.
“The presence of this single object suggests that there could be another hundred or so other objects with similar orbit and size; they are just too far away to be detectable now,” Cheng says in the statement.
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Cheng and his colleagues made the discovery by searching through astronomical images from the Victor M. Blanco Telescope and the Canada France Hawaii Telescope for bright spots that might represent a TNO. Using an algorithm developed by Cheng, the team identified 2017 OF201 in 19 separate observations spanning seven years.
“It’s a really cool discovery,” Kevin Napier, a researcher from the Michigan Institute for Data & A.I. in Society who was not involved in the study, tells New Scientist’s Chris Simms. Napier adds that the body might be interacting with other stars as much as it does with objects in our own solar system.
The finding has implications for understanding our solar system beyond the known planets—and the search for Planet Nine.
“The existence of 2017 OF201 might suggest that Planet Nine or X doesn’t exist,” Jiaxuan Li, a co-author of the study and a researcher at Princeton University’s Department of Astrophysical Sciences, writes on his website.
That’s because 2017 OF201’s orbit doesn’t follow a standard pattern seen in other TNOs, which form clusters in specific orientations that some researchers suggest might be caused by the gravity of a distant, undiscovered planet. That makes this new object an exception.
However, Konstantin Batygin, a planetary astrophysicist at the California Institute of Technology who did not participate in the study, doesn’t agree with that interpretation. “The object is unstable,” he suggests to Sky & Telescope’s David L. Chandler, “so it means virtually nothing for the Planet Nine hypothesis.” Despite this, Batygin, who co-authored the Planet X theory, says the study represents “a very sophisticated exercise.”
For his part, Cheng still hopes Planet Nine exists, “because that’ll be more interesting,” as he tells New Scientist.
