View Full Version : Pluto gets the boot

08-25-2006, 06:22 PM

Pluto booted off roster of planets

New definition also bars Ceres, Charon, Xena from lineup

Email this story | Print By Jim Erickson, Rocky Mountain News
August 25, 2006

Pluto was stripped of its planetary stripes Thursday, a celestial demotion that shocked and angered some planetary scientists, while pleasing those who have long viewed the iceball as an inconsequential chunk of cosmic debris.
At a meeting in Prague, several hundred members of the International Astronomical Union voted on a definition of planet that excludes Pluto. That decision drops the number of planets in our solar system from nine to eight.

Last week the IAU, the international arbiter of issues related to astronomical nomenclature, seemed poised to boost the number of planets circling the sun from nine to 12.

So Thursday's dramatic reversal stung Plutophiles like Boulder planetary scientist Alan Stern, who leads NASA's $700 million New Horizons mission to Pluto.

"It's going to be a laughingstock. It's going to be a mess for school kids. I don't think textbooks will even accept it," Stern said of the IAU resolution.

Stern said he predicts that the IAU will become known as the Irrelevant Astronomical Union.

"I'm writing a textbook for a big publisher, and we're not going to change it" to conform to the new definition, he said. "All we're going to do is have a little box with an article about how bad a definition this is."

The IAU resolution defines a planet as a celestial body that orbits the sun and is big enough that its self-gravity pulls it into a roughly spherical shape.

In addition, the object must have "cleared the neighborhood around its orbit" by sweeping up stray blocks of rock and ice.

Pluto doesn't meet the third requirement because it loops around the sun within the Kuiper Belt, a band of icy bodies beyond Neptune.

The new IAU definition establishes three categories of solar system objects.

The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Pluto becomes the prototype of new class of solar system object called a dwarf planet. They are roughly spherical objects that didn't manage to clear away nearby debris.

The remaining flotsam and jetsam - including most of the asteroids, all comets, and most Kuiper Belt Objects - will be known as Small Solar-System Bodies.

"My first reaction is relief," said University of Colorado planetary scientist Fran Bagenal. "Now we can move on and get on with life, not argue over what is really not the major issue it's been blown up to be."

At 9 a.m. Monday, Bagenal will begin teaching "Introduction to Planetary Science" to CU undergraduates.

She won't tell them that there are eight planets in the solar system. Or nine. Or 20.

"I'll say the IAU has this definition, which they've passed, and we'll talk about various ideas for defining planets," said Bagenal, a member of the New Horizons science team.

Last week at the Prague meeting, the IAU's executive committee unveiled its proposed definition to about 2,500 members from 75 nations.

Under that definition, Pluto would have remained among the elite, and three other objects would have gained planethood: Ceres, the largest asteroid; Charon, Pluto's largest moon; and 2003 UB313, the Kuiper Belt Object known as Xena.

But then the wrangling and lobbying and arm-twisting began.

Boulder planetary scientists Hal Levison and Bill Bottke, of the Southwest Research Institute, attended the Prague meeting but returned before Thursday's vote.

Levison was invited to help write a revised version of the resolution Aug. 18. He argued that Pluto should remain among the planets, but his suggestion was dismissed after he left town, he said.

Levison said he would have voted for the final version anyway.

"I think having a resolution to the issue is as important as getting it 100 percent right," he said Thursday.

Bottke supports the new three-tier solar system and lobbied for inclusion of the dwarf planets.

"Once you put Pluto in the dwarf-planet category, philosophically you've crossed the Rubicon. You've crossed the place where people didn't dare go before," he said.

"And now that we have this reorganization, I think it will be easier to think about the solar system and what it really means," he said. "It helps sort of clear the brush away so we can think clearly about these things."

But Stern sees problems ahead for the IAU definition.

Under the current wording, Earth does not qualify as a planet because it has not "cleared the neighborhood around its orbit," he said. Objects called near-Earth asteroids orbit the sun at roughly the same from our home star as Earth.

Caltech astronomer Michael Brown, the discoverer of Xena, said he supports the new definition, including the demotion of Pluto.

Xena has a diameter of 1,490 miles, plus or minus 60 miles. Pluto, discovered in 1930 by American astronomer Clyde Tombaugh, is 1,422 miles across - smaller than Earth's moon.

"Pluto would never be considered a planet if it were discovered today, and I think the fact that we've now found one Kuiper Belt Object bigger than Pluto underscores its shaky status," he said.

"I'm of course disappointed that Xena will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision," he said.

Meanwhile, the New Horizons spacecraft streaks toward a 2015 rendezvous with Pluto, moving at 43,500 mph.

If the IAU definition holds, the probe will explore a planet-less realm of icy mini-worlds.

"Pluto doesn't care," said Boulder planetary scientist Leslie Young, deputy project scientist for the New Horizons mission.

"It's all just names. It hardly bothers me at all," she said of the demotion.

"I am so thrilled that the spacecraft is on the way to Pluto, they could call Pluto a hedgehog and I'd still be a happy woman."

08-25-2006, 06:34 PM
lol...what's that gonna do for all the astrologists who use pluto to calculate some retrograde or some such? :D

08-25-2006, 06:37 PM
its still there, its just not a planet

08-25-2006, 06:42 PM
yea...but the planet-aspect of it is what they all use, i think. i gotta go check w/nancy regan's astrologist. hahaha.

08-25-2006, 06:48 PM
haha, they will have to use neptune now i guess, lol

08-25-2006, 07:23 PM
they already do. just that pluto added some extra dimension or something. lol.

09-01-2006, 04:59 PM
maybe pluto doesnt get the boot, http://news.yahoo.com/s/nm/20060901/sc_nm/space_pluto_dc