Planet nine stays hidden, but the solar system has a new mystery guest

Astronomers have discovered a new dwarf planet far beyond Neptune. Named 2017 OF201, the object measures roughly 700 kilometres across and lies three times farther from Earth than Neptune. Its elongated orbit swings out over 1,600 times the distance between Earth and the Sun, taking it deep into the Oort cloud—a distant shell of icy objects surrounding the solar system.

The new find comes from a US-based research team that had been searching for the mysterious Planet Nine. While they didn’t locate the long-theorised giant planet, their work led to the unexpected discovery of 2017 OF201.

What makes 2017 OF201 different

According to lead author Sihao Cheng of the Institute for Advanced Study in New Jersey, the orbit of this object spans 25,000 years. During that time, it is visible from Earth for only around 0.5 percent of its orbit—about one century.


“It’s already getting fainter and fainter,” Cheng said.

Despite being three times smaller than Pluto, the object is likely large enough to qualify as a dwarf planet. Pluto itself, once considered the ninth planet, was reclassified as a dwarf planet in 2006.


Amateur astronomer Sam Deen, aged 23, independently traced 2017 OF201 using archival data. “OF201 is, in my opinion, probably one of the most interesting discoveries in the outer solar system in the last decade,” he said.

A challenge to the Planet Nine theory

The theory of Planet Nine originated from observations that icy objects in the Kuiper Belt tend to move in clustered orbits. Scientists suggested this pattern might be caused by the gravitational pull of an undiscovered planet, possibly up to 10 times the size of Earth.

However, 2017 OF201 does not follow the clustered pattern seen in those earlier discoveries. This raises questions about whether the clustering is really due to an unseen planet.

Cheng acknowledged this, saying the object’s orbit could “pose a problem for the Planet Nine theory,” though he added that more data is required before drawing firm conclusions.

Samantha Lawler, an astronomer at the University of Regina in Canada, described the find as a “great discovery” and added that it weakens the original argument for Planet Nine. “The original argument for Planet Nine is getting weaker and weaker,” she said.

Despite the doubts, Cheng remains hopeful. “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.”

The researchers are now requesting time on high-powered observatories, including the James Webb Space Telescope and the Hubble, to study the object further.

Meanwhile, astronomers are also looking ahead to the Vera Rubin Observatory, due to become operational in Chile this year. Deen is optimistic. “With Vera Rubin on the horizon I don’t think we’ll have to wonder about its existence for much longer,” he said.

(With inputs from AFP)