Pluto's Planet Status Up In The Air

(AP)  Nearly 2,500 astronomers from 75 countries were working Monday on a universal definition for what qualifies as a planet, and whether Pluto should keep its status.

For decades, most have defined our solar system as having nine planets, though some have questioned whether Pluto — smaller than Earth's moon — belonged. The discovery last year of an object larger and further away than Pluto has thrown cosmic definitions into chaos.

Scientists, gathered for the 12-day meeting of the International Astronomical Union in Prague, were considering whether to remove Pluto's designation as a planet, or to bring the new one, nicknamed Xena, into the fold, possibly along with dozens more.

"We of course need the definition of a planet first," said Pavel Suchan, one of the conference organizers.

Until now, there has been no definitive criteria, with most simply describing a planet as a large, round object that orbits the Sun. Scientists will work on establishing criteria for planet status — including the object's mass, orbit and distance from the Sun — and then whether Pluto and Xena meet the definition.

"So far it looks like a stalemate," Suchan said. "One half wants Pluto to remain a planet, the other half says Pluto is not worth being called a planet."

Depending on the results, to be announced at the end of the conference, the solar system could be expanded to include 23, 39 or even 53 planets. If the newly found Xena qualifies as a planet, some argue, so should several other bodies found in the outer reaches of the solar system. Other say, however, that if Xena is ruled out as a planet, Pluto should be as well.

A third group of scientists have suggested planets be classified into categories based on composition, similar to the way stars and galaxies are classified. Jupiter could be labeled a "gas giant planet," while Pluto and Xena could be "ice dwarf planets."

Astronomer Michael Brown, of the California Institute of Technology, announced the discovery of Xena in July 2005. Like Pluto, it is located in the Kuiper Belt, a disc-shaped zone beyond Neptune containing thousands of comets and planetary objects.

The Hubble Space Telescope measured the bright, rocky object at about 1,490 miles in diameter, roughly 70 miles larger than Pluto. It is 9 billion miles from the Sun, making it the furthest known object in the solar system.

The discovery stoked the planet debate, which had been simmering since Pluto was spotted in 1930.

For years, Pluto's inclusion in the solar system has been controversial. Astronomers thought it was the same size as Earth, but later found it was smaller than Earth's moon. Pluto is also odd in other ways: With its elongated orbit and funky orbital plane, it acts more like other Kuiper Belt objects than traditional planets.

The conference began Monday with discussions about galaxy evolution, star formation and so-called near Earth objects — such as asteroids — that could threaten the Earth.

"If an object with a diameter of at least 1 kilometer falls into the sea, then it would cause a disaster to the life on Earth," Suchan said. "After all, 65 million years ago, the dinosaurs became extinct most probably after an asteroid hit the earth."

[tommy6860]

Well, I disagree with the naysayers on classifying whether Pluto is a planet or not. Consider that as space discovery advances, so do the discoveries of other cosmic objects, whether they be planets or not. As we learn (more) about them, they will have to have some kind of classification, and now may be the time to begin classifying them.

Let's stop worrying about the history of what Pluto was deemed, and begin allowing what makes up these objects with with their own classification(s). We may not want this now for the reasons a few have already posted, but how does this serve the future education of those not yet born. We won't be around to worry about this quandary now, but deciding what classifies these objects now, have an effect on future generations and how they will understand these to be.

Change is good!

[learner11-2009]

If its out there,... and it has a atmosphere,..then it's a planet.

[mentat3]

As a public program assistant and public program supervisor at Lowell Observatory (where Pluto was discovered in 1930), I hear the question "Is Pluto really a planet?" every other hour. My counter to that is "Does it much matter?" It's really only a question of categorization. We only need to categorize to the extent that it is useful. Is it useful to de-categorize Pluto as a planet? Is it useful to include other objects such as Xena as planets?

To climb on my soap box a little, why hasn't this same issue arisen with the categorization of moons? What is a moon? Certainly Deimos and Phobos, the lopsided moons of Mars, are not like the Earth's moon, yet they fall under the same category. If we make such a big stink about whether or not Pluto belongs in the same category as other planets, why do we not spark debate over whether or not Callisto and S/2003 J12 belong in the same category?

If Pluto were discovered today, would it be considered a KBO? Yes. But it wasn't discovered today. It was discovered 76 years ago. This is why it currently holds planethood status while other objects such as Xena do not. Is that the way it should be? Does it matter?

Drew Baumgartel, Public Program Supervisor, Lowell Observatory

[mjpenterprises]

it seems that the more it changes the more it stays the same:2500 astronomers are going to decide for 6billions earth inhabitants as the old saying goes (if it ain't f..... don't fix it)if they are that bored then why don't they look into the seti conandruum ????????????

[yellowbean77]

Why can't we just leave well enough alone? Pluto has been considered a planet and part of our solar system for years, so why mess with it now?

You would think there would be more important things these scientists could be working on, such a real Mars mission. Or maybe on how to make our space flights safer. I may not be a college grad or even know that much about space, but it just seems silly to me. Children all over the world already think of Pluto as a planet and teachers have been teaching this for years. If these guys decide to change it, then we will have to spend money on updating text books that are otherwise still useful. Is it really worth it?

[capecodman]

having scientists gather to disscuss plantery evolution,and near earth collisions is a great thing that we need to know and be very aware of.

But to discuss, at this point in our life time with everything that is going on, as to wether Pluto can be classified as a planet or not is simply absurd. So the discovery of an "object" that is bigger then Pluto has thorwn everything into "chaos". Come on and give me a break, why does it have to come to this point now. You know how much sleep i'm going to be losing now.(sarcasam)

Look people it's been a planet, and will always be a planet. So lets just let this go and do more constructive things ok.

thank you.

Eric McCann

[jonathan1cas]

Beyond the classification of type of planet there is also the consideration of position and orbit.

Standard planets have near circular orbits in roughly the same plane.

Astroid belt planets have an orbit confined to a narrow region between Mars and Jupiter.

Kuiper Belt planets have eliptical orbits with orbital planes that are not neccessarily along the line of the standard planets and for the most of their orbits are beyond Neptune.

Only the media recognizes nine planets. IAU has for a long time recognized many more bodies.

Jonathan Cassidy, public observing manager, Hirsch Observatory, Rensselaer