Out Beyond Pluto, Astronomers Find Something New

WASHINGTON (Reuters) - It's the biggest thing found orbiting the sun since astronomers discovered Pluto in 1930, but please do not call it 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, who first detected the object on June 4. His findings were presented on Monday 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 a billion miles 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 harbors 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 percent 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 percent, 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.

Scientists have long suspected that big, planet-shaped objects like Quaoar would be found in the Kuiper Belt; this is by far the largest they have discovered.

Brown said Quaoar's presence some 4 billion miles 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.

Pluto's no planet.

The fact that it has another piece of matter revolving around its gravitational pull doesn't make it a planet.

If Kate Moss was hovering in Space outside the distance of Pluto, she could have a very fattening keylme pie revolving around her but she'd still be moving around the Sun and I wouldn't call her a planet.

She's not a planet. She's a STAR, yes ...

Pluto is midget wrestling. Interesting, but nobody at NASA is aiming any missions that direction.

Planet needs to have a singular influence in size, interest and solar system fun ... ness ... to warrant our care.

The outer gas giants annoy us enough. OK Neptune ... you are a coagulation of ammonia and sulferous and nitrous oxide .... We're not going to make a movie about you housing a tribe of beautiful women wearing swimsuit uniforms and sporting perfectly cone shaped breasts.

Orbits the sun, is big and round.

You are confusing a "planet" with Louie Anderson.

Unless that planet has an alcoholic father too ...

Well, "big and round and orbits the sun" used to work, before the discovery of the Kuiper belt. Now, though, it turns out that there's a huge number of objects that are in the Kuiper belt. So far, Pluto (and it's companion, Charon) is the largest Kuiper belt found, and it a lot more reflective than most. And it was discovered back in the '30's. The day that a Kuiper belt object that's larger than Pluto is discovered, the astronomers will have to decide whether to declare it a 10th planet, or to downgrade Pluto.

"It is quite difficult to argue that Pluto isn't a planet when Pluto has it's own moon Charon ..."

There are asteroids that have smaller asteroids orbiting them, but that doesn't make them (major) planets.

And you can argue that Charon isn't a satellite of Pluto. Turns out that the center of Charon's orbit is outside Pluto's surface: in other words, both Pluto and Charon orbit each other around a common point that's between them. So Pluto and Charon are more like a binary planet than planet and satellite.

Also: there's only one moon in the solar system, and that's the Moon. All other bodies orbiting planets are satellites, whether they are natural or artificial.

"Interesting, but nobody at NASA is aiming any missions that direction."

That will likely change. Funding for this is proceeding, after having been cancelled once and then brought back to life.

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