Washington, Oct. 7 (Reuters): It’s the biggest thing found orbiting the sun since astronomers discovered Pluto in 1930, but please do not call the frozen world a planet. Call it Quaoar.
At half the size of Pluto, Quaoar — pronounced KWAH-o-ar —is a large celestial object, but not large enough to be a planet, one of its discoverers said in a telephone interview.
Quaoar’s discovery also calls Pluto’s planet status into question, said Mike Brown of the California Institute of Technology (Caltech), who first detected the object on June 4. His findings were presented today to the American Astronomical Society’s planetary science division meeting in Birmingham, Alabama.
Still, Quaoar acts a lot like a planet. Circling the sun once every 288 years, Quaoar is located 1.6 billion km beyond Pluto, in an area loaded with icy orbiting objects called the Kuiper Belt.
The Kuiper Belt is where comets originate, and astronomers have long believed it harbours planet-shaped rocks like Quaoar. Over the last decade, more than 500 Kuiper Belt objects have been detected.
“In any realistic definition of a planet, you would have to say something like, a planet is significantly bigger than everything around it,” Brown said. “(Quaoar) is only 50 per cent bigger than the next biggest Kuiper Belt object, to me it’s not massive enough.”
Quaoar’s existence confirms that large orbiting bodies can reside at the very fringes of our solar system, and could give new insights on the primordial materials that formed planets like Earth some 5 billion years ago.
It also supports the theory that Pluto is not a planet at all, but rather a Kuiper Belt object. Pluto has a similarly long orbit — 248 years to make a complete trip around the sun — but is far more eccentric than Quaoar seems to be.
Instead of going around the sun in the same plane as the rest of the planets, Pluto’s orbit is tilted about 17 degrees. At one point, Pluto comes close enough to the sun to heat up the volatile substances on its surface, making it more reflective.
By contrast, Quaoar has a highly regular orbit, tilted only about 7.9 per cent, never getting close to the sun. Faint ultraviolet radiation over the ages has slowly changed the surface of this rock-and-ice object to a dark, tar-like substance.
Brown said Quaoar’s presence some 6.4 billion km from Earth casts doubt on Pluto’s planetary status. “There are nostalgic forces that are operating that prefer to call it a planet,” he said. “If Pluto were discovered today, there are very few people, other than the person who discovered it, who would want to call it a planet.”
Brown said, however, that even if it is not a planet, Pluto is “an incredibly interesting body” that deserves to be studied.
Quaoar is named after the creation force of the Tongva tribe, the original inhabitants of the Los Angeles basin where Caltech is located. It can be detected just northwest of the constellation, Scorpio.