Astronomers May Have Found New Dwarf Planet And It’s Casting Doubt On Planet Nine Theory

Last Updated:May 29, 2025, 20:43 IST

Spotted beyond Neptune, the newly identified object follows an odd path through space, one that complicates a decades-old theory about a giant planet lurking in the dark

A composite image showing the five dwarf planets recognized by the Astronomical Union, plus the newly discovered trans-Neptunian object 2017 OF201. Credit: Images of dwarf planets: NASA/JPL-Caltech; image of 2017 OF201: Sihao Cheng et al.

A Surprise In The Hunt For Planet Nine

In the vast, dark outskirts of our solar system, astronomers have long speculated about the existence of a massive, hidden world—Planet Nine—lurking beyond Neptune’s orbit. But while chasing this elusive celestial body, a team of US-based astronomers has instead discovered what could be a new dwarf planet.

Named 2017 OF201, the newly identified object is estimated to be around 700 kilometres wide—roughly a third the size of Pluto—according to a preprint study published online last week. Though not yet peer-reviewed, the finding is already raising fresh questions about the Planet Nine hypothesis.

Extreme Orbit In The Oort Cloud

The object is currently more than three times farther from Earth than Neptune. Its highly elongated orbit stretches over 1,600 astronomical units (AU) from the Sun—taking it deep into the icy ring of debris known as the Oort Cloud.

“It’s already getting fainter and fainter," said lead author Sihao Cheng of the Institute for Advanced Study in New Jersey, speaking to AFP. The object completes one full orbit around the Sun in about 25,000 years and is only visible from Earth for about 0.5 per cent of that time—roughly a century.

Cheng believes its discovery suggests “there are many hundreds of similar things on similar orbits" in the Kuiper Belt, the region beyond Neptune populated by icy bodies.

Tracked Through Old Data

Despite the fading visibility, the object has already been tracked independently by Sam Deen, a 23-year-old amateur astronomer from California, who located 2017 OF201 in older datasets. “OF201 is probably one of the most interesting discoveries in the outer solar system in the last decade," Deen told AFP.

Cheng and his team are now seeking observation time with major facilities such as the James Webb Space Telescope, the Hubble Space Telescope, and ALMA to study the object further. He called the find “lucky", especially after more than six months of combing through difficult data in the search for Planet Nine.

Challenging The Planet Nine Theory

Around two decades ago, astronomers noted that some icy rocks in the Kuiper Belt appeared to have clustered orbits, suggesting the influence of a massive unseen object. This gave rise to the theory of Planet Nine—also known as Planet X, a name dating back more than a century.

The theory gained traction due to the unusual alignment of these distant objects, thought to be shaped by the gravitational pull of a planet up to ten times the size of Earth.

However, when Cheng’s team modelled 2017 OF201’s orbit, they found it did not follow the expected clustering trend. This could pose a challenge to the Planet Nine hypothesis.

Astronomer Samantha Lawler of the University of Regina in Canada told AFP that this “great discovery" is yet another example that “the original argument for Planet Nine is getting weaker and weaker".

The Vera Rubin Telescope May Hold Answers

The upcoming Vera C. Rubin Observatory in Chile, expected to begin operations later this year, is likely to provide crucial data. Its deep-sky surveys may confirm or debunk the existence of Planet Nine once and for all.

Deen said it is discouraging that no trace of Planet Nine has been found so far. “But with Vera Rubin on the horizon, I don’t think we’ll have to wonder about its existence for much longer."

Still Hope For A Hidden Giant

Despite the complications raised by the discovery of 2017 OF201, Cheng remains hopeful that a massive planet could still be hiding in the solar system’s far reaches. “We’re in an era when big telescopes can see almost to the edge of the universe," he said. “But what is in our backyard still largely remains unknown."

With inputs from AFP.

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