It is an evocative idea: a huge and mysterious planet is lurking in the darkness at the edge of our solar system, evading all our efforts to spot it. Some astronomers say the strange, clustered orbits of icy rocks beyond Neptune indicate that something big is out there, which they have dubbed “planet nine.”
Now, a US-based trio hunting this elusive world has instead stumbled on what appears to be a new dwarf planet in the solar system’s outer reaches and the existence of this new kid on the block could challenge the planet nine theory.
Named 2017 OF201, the new object is about 700km across, according to a preprint study, which has not been peer-reviewed.
Photo: AFP / Caltech / Robert Hurt
That makes it three times smaller than Pluto, said the study, which was published online last week.
However, that is still big enough to be considered a dwarf planet, said Cheng Sihao (程思浩) of the Institute for Advanced Study in New Jersey, the lead author.
The object is three times farther away from Earth than Neptune, although its elongated orbit swings out more than 1,600 times the distance between the Earth and the sun, taking it into the hypothesized ring of icy rocks around the solar system called the Oort cloud.
It goes so far out that it could have passed by stars other than our sun, Cheng said.
During its 25,000-year orbit, the object is only close enough to Earth to be observed about 0.5 percent of the time, he said.
“It’s already getting fainter and fainter,” Cheng said.
The discovery suggests “there are many hundreds of similar things on similar orbits” in the Kuiper Belt beyond Neptune, Cheng said.
After taking a risk spending more than half a year sorting through a difficult dataset in search of planet nine, Cheng said he was “lucky” to have found anything at all.
The researchers are requesting time to point the James Webb, Hubble and ALMA telescopes at their discovery.
However, Sam Deen, a 23-year-old amateur astronomer from California, has already been able to track the dwarf planet candidate through old datasets.
“OF201 is, in my opinion, probably one of the most interesting discoveries in the outer solar system in the last decade,” Deen told reporters.
The icy rocks discovered in the Kuiper belt tend to have a clustered orbit going in a particular direction. Two decades ago, astronomers proposed this was due to the gravitational pull of a world up to 10 times larger than Earth, naming it planet nine.
In 1930, astronomers were searching for planet nine when they discovered Pluto, which became the solar system’s ninth planet before it was demoted to dwarf planet status in 2006.
There are four other officially recognized dwarf planets and Cheng believes 2017 OF201 could join their ranks.
When the researchers modeled its orbit, they found it did not follow the clustered trend of similar objects, which could pose a problem for the planet nine theory, although Cheng said that more data are needed.
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