http://www.chicagotribune.com/news/nationw...nationworld-hed

 

By Jeremy Manier

Tribune staff reporter

Published August 16, 2006

 

 

Astronomers, hold on to your telescopes. The solar system has 12 planets, not nine.

 

That's the earth-shaking--and then some--conclusion of an influential international committee that on Wednesday will recommend a new definition of what qualifies as a planet.

 

The move is necessary, experts say, because of discoveries in the last decade that have revealed a glut of Pluto-size bodies beyond the orbit of Pluto--until now considered the farthest planet from the sun.

 

Those findings sparked an intense debate among planet-watchers: Should the new worlds be welcomed as planets, or was it a mistake to call tiny Pluto a planet in the first place?

 

Now there's an answer that just might satisfy Pluto boosters and Pluto-phobes alike.

 

A seven-member panel of astronomers, historians and one science writer gathered in Paris last month under the auspices of the International Astronomical Union to settle the question. After a sleepless night, they agreed on a simple yet revolutionary approach to the problem.

 

A planet, they decreed, is any star-orbiting object so large that its own gravity pulls in its rough edges, producing a near-perfect sphere.

 

That definition excludes some 200,000 small, odd-shaped rocks, comets and asteroids that wander around the sun.

 

It also means Pluto gets to remain a planet.

 

But the new definition also includes three other big space rocks, including one currently considered an asteroid and another long described as a moon of Pluto.

 

Also to be included is an icy body beyond Pluto, which would belong to a class of planets to be known as "plutons."

 

"In a day and a half of hammering it out, we came up with this unanimous recommendation," said Owen Gingerich, chairman of the IAU's "planet definition committee" and an emeritus historian of astronomy at Harvard University.

 

Because planet-seekers are finding new worlds beyond Pluto at a steady clip, the list of newly defined planets could grow well beyond 12--perhaps dozens more worlds await.

 

Astronomers from around the world are scheduled to vote on the new definition Aug. 24 at the IAU's meeting in Prague. It would constitute the first official recognition of new planets since Pluto's discovery in 1930.

 

Gingerich said Tuesday he already has received backing from 10 of the group's division chairmen. Although there's nothing binding about the vote, the IAU is considered the world's authoritative source on the naming of heavenly bodies.

 

The proposed planet definition got an endorsement Tuesday from an unlikely source: Neil deGrasse Tyson, director of the Hayden Planetarium in New York, who has argued that Pluto is not in the same class as the other eight "classical" planets. He said although there were other good definitions that would have left Pluto out, he supports the new proposal because it offers the first clear standard of planethood.

 

"What a planet is has never been defined, not since 2,500 years ago in ancient Greece," he said. "Provided this definition is unambiguous, I'll take it."

 

Tyson said the requirement of roundness gives a tidy standard. Objects typically do not have enough mass for gravity to pull them into spheres unless they are at least 500 miles across.

 

"By and large, these things are either round or not round--they're not sort of round," Tyson said.

 

Finding a solution to the "Pluto problem" has proven a surprisingly emotional task for the staid astronomical profession.

 

One of the most prominent volleys in the dispute came in 2000, when Tyson's planetarium banished Pluto from a display of the planets. One reason for the snub was that with a diameter of about 1,400 miles, Pluto is smaller than Earth's moon and is unlike the gas giants that dominate the rest of the outer solar system. Efforts to demote Pluto brought ire from a public that had grown attached to the miniscule yet plucky planet.

 

Some experts floated the idea that nothing smaller than Mercury should be called a planet. But that seemed arbitrary and no better than keeping Pluto's status solely out of sentiment.

 

Members of the IAU committee kept their deliberations and conclusion under close wraps over the last month. Richard Binzel, a committee member and asteroid specialist at the Massachusetts Institute of Technology, compared the decision to white smoke emerging from the Vatican upon selection of a new pope.

 

Binzel said that after a discouraging first day of deliberations, the members were surprised to find a definition that appealed to all of them.

 

"We want this definition to apply not only in our solar system, but in other solar systems as well," Binzel said.

 

The three new planets encompassed by the group's definition would be the asteroid Ceres, Pluto's moon, Charon, and an object beyond Pluto called 2003 UB313, nicknamed Xena.

 

For Ceres, it would be a belated promotion. By far the largest asteroid at 580 miles across, Ceres actually was called a planet when discovered in 1801. But further findings of asteroids between the orbits of Mars and Jupiter led astronomers to class it with those smaller objects. A study last year of Hubble Space Telescope images proved that Ceres is round, placing it within the new definition.

 

Charon is called Pluto's moon, but it was included in the new planet definition because many astronomers believe the two worlds comprise a "double planet" system. Pluto and Charon orbit each other, and their common center of gravity lies outside of Pluto, unlike any other planet-moon system.

 

The existence of Xena was announced last year by Mike Brown, an astronomer at the California Institute of Technology, who also served on the IAU committee. Hubble images have shown the object is at least as big as Pluto. Brown and other experts believe there may be dozens of such worlds in an area called the Kuiper Belt.

 

That doesn't mean schoolchildren need to ditch reliable old mnemonics for the planets' names and order--such as My Very Earnest Mother Just Served Us Nine Pizzas. Gingerich said although our definition of a planet may expand, the solar system still is dominated by the eight largest planets.

 

"I'd suggest [students] focus on the classical eight planets, plus this category of plutons," Gingerich said.

 

Tyson believes the great planetary debate has distracted from teaching about the origins of the solar system. But that wasn't the reaction of most Adler Planetarium visitors Tuesday.

 

Linda Marquardt, who strolled the halls with her husband and teenage son, said she found the expansive new definition inspiring.

 

"It makes it more interesting to me that there's more stuff out there to discover."

 

What is a planet and a pluton?

 

INTERNATIONAL ASTRONOMICAL UNION (IAU) DEFINITION

 

Planets

 

Under the proposed definition, two conditions must be satisfied for an object to be called a "planet."

 

1. Must be in orbit around a star, while not being itself a star.

 

2. Must be massive enough for its own gravity to pull it into a nearly spherical shape.

 

PLANET CATEGORY

 

A pluton is a new category of planet now being defined by the IAU. To be a pluton, a body:

 

1. Must satisfy the technical definition of planet.

 

2. Resides in orbit around the sun that takes longer than 200 years to complete (i.e., orbits beyond Neptune).

 

3. Typically has an orbit that is highly tilted with respect to the classical planets and is far from being perfectly circular.

 

NON-IAU DESCRIPTIVE DEFINITIONS

 

Classical planet

 

The eight largest planets, discovered by sky watchers and astronomers starting from the beginning of human history until the year A.D. 1900. Example: Venus

 

Dwarf planet

 

Generally used to describe any planet that is smaller than Mercury.

 

Ceres would be an example.

 

Source: International Astronomical Union (IAU)

 

Chicago Tribune

I seem to remember hearing about this (or something similar) a few years back. But then they couldn't agree on whether they should be planets or not so they were not made planets.

I seem to remember hearing about this (or something similar) a few years back. But then they couldn't agree on whether they should be planets or not so they were not made planets.

 

Yeah, I remember the big deal when the found the "10th planet" and they were fighting over exactly what it was back then. That's why the new definition is really interesting, plus the fact that it contains two more bodies that the general public didn't even know were being considered.

So how do add the new planets to this sentence to remember them?

 

My Very Excellent Mother Just Served Us Nine Pizzas

Edited August 16, 200619 yr by mreye

Ceres, Pluto's moon, Charon, and an object beyond Pluto called 2003 UB313

 

So, for those that follow this closer than I, why would Charon be added as a planet but a moon like Ganymede didn't make the cut?

So, for those that follow this closer than I, why would Charon be added as a planet but a moon like Ganymede didn't make the cut?

 

From the sounds of the definition, either it isn't big enough or round enough. I don't know anything about that particular moon, so I don't know specifically.

That's what confused me. Ganymede is the biggest moon in our known Solar System, it is one of Galileo's Jupiter moon findings.

 

You could be right about the round part though. Jupiters fast rotation could be distorting Ganymede enough to not be considered.

That's what confused me. Ganymede is the biggest moon in our known Solar System, it is one of Galileo's Jupiter moon findings.

 

You could be right about the round part though. Jupiters fast rotation could be distorting Ganymede enough to not be considered.

 

After a google search about the moon, I think this is the killer part.

 

1. Must be in orbit around a star, while not being itself a star.

 

Charon technically doesn't orbit around Pluto, as much as they orbit around each other, as I understand it.

 

Charon has been a part of the controversy over Pluto's status as a planet. Under the latest proposal, which will be decided on August 24, 2006, the International Astronomical Union may classify Charon as a pluton, officially making Charon a planet. Under this proposal, Charon would be considered a binary planet with Pluto since the two orbit each other around a center of mass that is outside either body.[4] Those who have argued against Pluto as a planet consider the two as the first discovered trans-Neptunian objects.

 

That would be my best guess, but that is an awesome question to have answered.

 

Yeah I just found this while searching google news

 

Charon, 2003 UB313

 

Pluto's moon, Charon, with a 1,200-kilometer diameter, will qualify as a planet and a pluton under the guidelines because it meets the mass and size criteria, and orbits around a point in space between Pluto and itself, rather than around a location under the surface of Pluto, according to documents posted on the union's Web site. The pair would constitute a ``double planet.''

 

http://www.bloomberg.com/apps/news?pid=206...mp;refer=europe

One observer claims at least 53 "planets" with new definition

 

"It's flattering to be considered discoverer of the 12th planet," Brown said in a telephone interview. He applauded the committee's efforts but said the overall proposal is "a complete mess." By his count, the definition means there are already 53 known planets in our solar system, with countless more to be discovered.

Yea, cause all those asteroids are now 'planets' if they're big enough.

What they need to do is devide the planets into "native" and "captured/irregular". Under the current understanding of planetary development, TRUE (or "native") planets form on the same orbital plan as the rotation of the sun and have a fairly circular orbit. All the others are either captured plants or massive bodys that were nocked off orbit.

 

In my optinion, the 8 inner plannets are "native" while all these other crazy orbit ones are not.

Xena.

 

heh.

In my optinion, the 8 inner plannets are "native" while all these other crazy orbit ones are not.

 

Agree. I would just consider planets such as Pluto, X, etc as Kuiper Belt objects and be done with it for now. Otherwise they will spend alot more time finding new "planets".

Yea, cause all those asteroids are now 'planets' if they're big enough.

Actually, based on this standard, I don't think it covers any of the "asteroids' between Mars and Jupiter other than Ceres. Most of the ones he'd be talking about are KBO's/other Trans-Neptunian objects like Xena, Pluto, etc.

 

What they need to do is devide the planets into "native" and "captured/irregular". Under the current understanding of planetary development, TRUE (or "native") planets form on the same orbital plan as the rotation of the sun and have a fairly circular orbit. All the others are either captured plants or massive bodys that were nocked off orbit.

 

In my optinion, the 8 inner plannets are "native" while all these other crazy orbit ones are not.

So where does that leave Ceres? It fits all of your criteria. Furthermore, what happens in other solar systems wehre we discover Jupiter-sized planets on highly eccentric orbits (something which has already happened repeatedly?)

Pluto/Charon = Minneapolis/St. Paul

 

Cold and boring.

Yea, cause all those asteroids are now 'planets' if they're big enough.

Just another example of the soft bigotry of low expectations.

Pluto/Charon = Minneapolis/St. Paul

 

Cold and boring.

Boo.

 

MSP > NYC

Pluto/Charon = Minneapolis/St. Paul

 

Cold and boring.

 

I guess that makes Michigan City like UB 313... confusing in name and in the middle of nowhere

I guess that makes Michigan City like UB 313... confusing in name and in the middle of nowhere

So you're saying that Michigan City is bigger than Minneapolis/St. Paul?

This might not be settled after all... Pluto may still get demoted

This might not be settled after all... Pluto may still get demoted

WOO HOOO!!! THere's still a chance!

Pluto for life!

I'm gonna be really pissed at those planetary scientists if they try to steal our word "Pluton." That's a large igneous body moving up through the crust, no matter what those bastages say it is.