Scientists say they’ve found a dwarf planet very far from the sun

A sizable world has been found in a part of the solar system that astronomers once thought to be empty. It probably qualifies as a dwarf planet, the same classification as Pluto.

Temporarily named 2017 OF201, it takes more than 24,000 years to travel around the sun just once along a highly elliptical orbit, coming as close as 4.2 billion miles and moving as far out as 151 billion miles. (Neptune is just 2.8 billion miles from the sun.)

And 2017 OF201 may have implications for the hypothesis of an undiscovered planet, nicknamed Planet Nine, in the outer reaches of the solar system.

“We discovered a very large trans-Neptunian object in a very exotic orbit,” said Sihao Cheng, a researcher at the Institute for Advanced Study in Princeton, New Jersey.

The findings, by Cheng and two Princeton University graduate students, Jiaxuan Li and Eritas Yang, have not yet been published in a peer-reviewed journal.

Estimated to be about 430 miles wide, 2017 OF201 is very likely to be massive enough for its gravity to pull it into a round shape — the criterion for a dwarf planet. The International Astronomical Union created this category in 2006 when it dropped Pluto from the roster of full-fledged planets.

Like Pluto, 2017 OF201 would not meet the threshold to be called a planet because it is not large enough to have “cleared its neighborhood” of other objects near its orbit.

Cheng became intrigued by the far out region of the solar system after listening to a talk last year by Mike Brown, an astronomer at the California Institute of Technology. In 2005, Brown discovered Eris, a Pluto-size world beyond Pluto, which set off a series of events leading to Pluto’s demotion.

The astronomical union has officially recognized only five dwarf planets: Pluto, Eris, the large asteroid Ceres and two other objects beyond Neptune, Haumea and Makemake. But according to Brown, more than 100 other solar system bodies are likely to qualify, although definitive evidence of roundness is unlikely anytime soon.

Brown also discovered Sedna, a surprisingly large world — more than 700 miles wide — that orbits the sun far beyond the orbit of Neptune. Over the years, more of these worlds, which are sometimes called extreme trans-Neptunian objects, have been identified.

Brown and Konstantin Batygin, also of Caltech, have asserted that the orbits seem to align in a particular direction, and have said that points to the gravitational tugging of an unseen planet several times larger than Earth — Planet Nine. But so far, searches for Planet Nine have come up empty.

Cheng decided to search, too. His co-author Li suggested delving into an archive of images taken by the Blanco telescope in Chile.

Cheng spent half a year writing a computer program to recognize that dots in different images taken months apart were actually the same object that had moved in the sky.

“The motion of these objects on the sky follow a particular pattern,” Cheng said. But the permutation of possible dots, which could also be closer objects like asteroids or random noise in the sensors, was daunting. He came up with a clever algorithm.

“It’s still a lot of computation,” Cheng said. “Just from impossible to possible.”

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