Why must they make things so difficult

I think that Pluto should remain designated a planet. It has been so since its discovery in 1930, so for 76 years we have thought that Pluto is a planet, so I think it should remain so. And in 2005 we have discovered an additional 2 moons circling Pluto for a total of 3.

SYDNEY, 16 August 2006: The Solar System may gain an extra three planets after today’s meeting of the International Astronomical Union (IAU) in Prague, upsetting text-books and science-classroom mnemonics world-wide.

With the advent of ever-more powerful telescopes, objects orbiting our Sun out beyond Pluto have been discovered. Some of these, Xena being the most famous example, are actually larger than Pluto and, its discoverers declare, should be considered as much of as planet as the others.

Other astronomers contest that these far distant objects are merely bits of rubble in an area of space filled with other bits of rubble, the Kuiper Belt.

The discoveries and the associated debate has thrown into question the definition of a ‘planet’ (see Cosmos, Issue 9 p 74) and at its general meeting this week, the governing body of such matters, the International Astronomical Union has sat down to nut out the problem.

The solution they propose is to describe all the objects as planets. Eight of them will be the ‘classical’ planets we have come to know and love. Ceres, an asteroid floating in the asteroid belt between Mars and Jupiter will become a planet. And a kind of sub-planet category known as 'plutons' will be invented for the remaining three planets. They will be Pluto, it's moon Charon and 2003-UB313, nick-named Xena. Xena's real name will be determined at a future date.

The part of "IAU Resolution 5 for GA-XXVI" that describes the planet definition, states: "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and ( is in orbit around a star, and is neither a star nor a satellite of a planet."

A recent poll of Cosmos Online readers found that a slim majority (28 per cent) preferred Pluto remaining a planet. Twenty per cent of respondents thought Pluto should be a Kuiper Belt Object, and 26 per cent wanted a new category for Pluto and the Kuiper Belt Objects. Some 25 per cent of readers playfully suggested that Pluto was a Disney dog.

Plutons are to be distinguished from classical planets in that their orbits around the Sun that take longer than 200 years to complete and their orbits are highly tilted with respect to the classical planets. Plutons also typically have orbits that are far from being perfectly circular.

The IAU said that all of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets.

Member of the Planet Definition Committee, Richard Binzel said, "Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor. Nature decides whether or not an object is a planet."

The draft “Planet Definition” resolution will be discussed and refined during the General Assembly and then it will be presented for voting on 24 August 2006.

An informal SPACE.com survey of astronomers who study planets in and out of our solar system found six in favor of the resolution and seven against. A separate private straw poll being conducted by the National Academies of Sciences has so far yielded an overwhelming "No" response, a source told SPACE.com.

'Terrible definition'

Clearly no consensus has emerged, however.

"I think it's a terrible definition," said David Charbonneau, a researcher at the Harvard-Smithsonian Center for Astrophysics who searches for and studies planets around other stars. Charbonneau joins two other astronomers close to the issue who sharply criticized the plan [see yesterday's story].

Charbonneau said the definition was motivated by a desire to determine whether Pluto and another object, 2003 UB313, are planets. But the IAU now says there are a dozen other objects that might be planets but need further study.

"It is ironic that we are left with more, not fewer objects for which we are uncertain of their 'planetary' status," Charbonneau told SPACE.com. "Perhaps astronomy will undergo a schism, with sects of astronomers proclaiming different numbers of planets."

"As representatives of an international community of planetary scientists, we urge that the resolution be approved," said the DPS statement, signed by chairman Richard French of Wellesley College.

In an email interview, French said he supports the defintion but realizes its shortcomings.

"My own personal definition would have been different from the final IAU resolution, but scientists have been stalemated for years by defending their own pet definitions," French said. "I understand the appeal of a simple declaration that Pluto is no longer a planet and that the solar system has only eight, but I also think there is value in the present definition that has applicability to planets around other stars as well."

The DPS has about 1,300 members, at least one-quarter of which are outside the United States. The statement does not represent the views of all members, said DPS Press Officer Sanjay Limaye. "There has been some feedback saying, 'I don't like it,'" he said.

'Worst' decision

The definition would make a planet of the asteroid Ceres and also reclassify Pluto's moon Charon as a planet, on the logic that the center of gravity around which Charon and Pluto orbit is not inside Pluto but rather in the space between them. (Earth's Moon orbits our planet around a center of gravity that is inside Earth.)

Pluto and Charon would be called a double planet, and they'd also be termed "plutons" to distinguish them from the eight "classical" planets. Ceres would be termed a dwarf planet.

The definition entirely misses the key element of a solar system object, namely its role in the formation of the solar system," Charbonneau said. "There are eight fully formed planets. The other objects—Ceres, Pluto, Charon, [2003 UB313], and hundreds of thousands of others, are the fascinating byproducts of the formation of these eight planets."

David Jewitt, an astronomer at the University of Hawaii who searches for objects in the outer solar system, told SPACE.com that the proposal is "the worst kind of compromised committee report."

Jewitt has long avoided the whole debate over whether Pluto is a planet "because I think it is essentially bogus and scientifically it is a non-issue." He waded in reluctantly this week.

"Scientifically, whether Pluto is also a planet is a non-issue," Jewitt writes on his web site. "No scientific definition of planet-hood exists or is needed. Is that a boat or a ship? It doesn't matter if you are using it to float across the ocean. Scientists are interested in learning about the origin of the solar system, and setting up arbitrary definitions of planet-hood is of no help here."

Geoff Marcy, who has led the discovery of more planets around other stars than anyone, called the definition arbitrary.

"Pluto, its moon, and large asteroids cannot suddenly be deemed planets," Marcy said in an email interview. "How would we explain to students that one large asteroid is a planet but the next biggest one isn't?"

Astronomers made a mistake when they deemed Pluto a planet in the 1930's, Marcy and many other astronmoers say. "Scientists should show that they can admit mistakes and rectify them," he said.

'Just might work'

However, one mild endorsement came today from Brian Marsden, who heads the Minor Planet Center where asteroids, comets and other newfound solar system objects are catalogued.

Marsden was on an IAU committee of planetary scientists that tried for a year but failed to come up with a definition for the word "planet," which was never needed until recent discoveries of Pluto-sized worlds out beyond Neptune. The newly proposed defintion was crafted by a second IAU committee of seven astronomers and historians.

Marsden is a firm believer that there are eight planets, but the new proposal has him sounding more flexible than in the past.

In an email message from Prague, Marsden said the new definition is "intended to satisfy the eight-planet traditionalists (such as myself) and the 'plutocrats.'" He added that he's "not against" the idea of using roundness as a determining factor.

The IAU proposal will be voted on by IAU members Aug. 24.

"It all just might work," Marsden said.

In email interviews, several experts in planetary science share their views:

"The definition itself is not that important. There are lots of interesting bodies out there for us to study. We need to have a definition, though, because it makes it easier for people to understand what we mean."
—Amy Simon-Miller, NASA scientists and member of the DPS Committee that endorsed the IAU resolution

"I think most astronomers agree that there are eight planets, and (like myself) are not particularly passionate about either Pluto's status or the outcome of the 'debate.' It's clear, however, that removing Pluto from the list rouses strong emotions within the public (who ultimately pay the bills). So I would just retain the eight planets plus Pluto."
—Gregory Laughlin, University of California, Santa Cruz extrasolar planet researcher

"It [the definition] makes a lot of sense. There has to be a physically meaningful definition for a planet since we are finding lots of KBOs and planets around other stars. If you had an arbitrary cutoff at say Pluto or even Mercury, how would you justify it when looking for other bodies in the solar system or in other stellar systems?"
— Larry Lebofsky, senior research scientist at the Lunar and Planetary Laboratory

"My prejudice is to restrict the definition of planet and put Pluto and its large Kuiper Belt cousins in a different class...with a name to be determined (planetoid seems to serve well)."
—Jonathan Lunine, professor of planetary science and of physics at the Lunar and Planetary Lab

"The whole debate, with Pluto as the pivot point, seems a bit silly to me, to make such a big deal of it. If planets are round, then there are a whole lot more than 12 of them."
—Laurance Doyle, SETI Institute extrasolar planet researcher

"The astronomers who oppose the resolution on pure or ostensibly pure science grounds find the criterion that makes Charon a planet —the center of mass is outside the body of the more massive partner—most objectionable. I also think that this criterion is new to them and they might fine it less objectionable after it gets to be a familiar rule."
—Stephen Maran, retired NASA astronomer and author of " Astronomy for Dummies"

Population classification. This definition requires a little more explanation and a little more understanding of the solar system, but, in the end, leads to the most satisfactory definition of "planet". Just like the solar system very naturally divides itself between round objects and non-round objects, it also very naturally divides itself between solitary individuals and members of large populations. The best known example of a large population is the asteroid belt. We call it a population because one region of space contains objects with a continuous range of sizes from one moderately large object (Ceres) to a handful of slightly smaller objects (Vesta, Pallas, Hermione) to a huge number of extremely small objects (rocks, dust particles). The solitary individuals are much different. In their region of space there is only them (Earth, say) and then a collection of much much smaller objects (the near-earth asteroids), with no continuous population in between. A single example helps to dramatize the difference between a continuous population and a solitary individual. Ceres, the largest asteroid, has a diameter of 900 km. The next largest asteroid, Pallas, has a diameter of 520 km. After that is Vesta at 500 km, and Hygiea at 430 km, and the list continues on down. The jump in size between asteroids is never more than a factor of two. In contrast, the earth has a diameter of about 12,000 km, while the largest other object in the earth's vicinity, the asteroid Ganymed, has a diameter of about 41 km, a factor of 300!

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune all count as solitary individuals by this definition. Pluto and Quaoar do not. Pluto is clearly a member of the Kuiper belt population, as can be seen from the fact that there are objects in the same vicinity slightly smaller than Pluto (Quaoar, 2004 DW, Varuna), and then even a larger number slightly smaller than that, and then on down.

What about Sedna? Sedna is currently the only object known in its orbital vicinity, but we strongly suspect that there will be many others found out there with time. We thus feel it is more reasonable to classify Sedna as a member of a large population (the inner Oort cloud of objects) rather than a solitary object. This classification saves us from having to go back and reclassify Sedna in a decade when we find more objects!

Since there is a clear scientific distinction between solitary individuals and members of large populations it is instructive to come up with words to describe these objects. The large populations can each be described by the particular population (asteroid belt, Kuiper belt, inner Oort cloud, Oort cloud). What about the solitary individuals? Isn't the best word to describe them "planet"?

Let's examine this definition in more details. First, it is certainly scientifically motivated and well-founded. But so was the "gravisphere" definition above. Is there any historical basis for saying that a planet is a solitary individual that is not a member of a large population? Yes! As mentioned earlier, historically Ceres and the first few asteroids were initially classified as planets. Only when it became known that there were many many asteroids in similar orbits was it decided that they should no longer be classified as planets. Historically, there is a clear distinction between planets and populations. Any definition which fails to make this distrinction is in strong trouble on historical grounds. This simple look at history shows that Pluto is completely analogous to Ceres. Pluto was initially thought to be a solitary individual. Over time we found more objects in the vicinity and realized instead that it is a member of a large population. Historically, then, Pluto, too, should no longer be considered a planet.

We are thus left with a final concept of the word planet. Every object in the solar system quite naturally can be classified as either a solitary individual or a member of a large population. The individuals are planets. The populations are not. This definition fits the historical desire to distinguish between asteroids and planets, and this definition fits all of the requirements of scientific motivation.

Even this definition is not perfect. People will always be able to imagine (and perhaps even find) pathological scenarios in which the above classification scheme fails. In contrast, the first three definitions are much more rigorous and will never need refining. We don't find this aspect of the first definitions an advantage, however. As we learn more about our solar system our language -- both popular and scientific -- should change to fit our knowledge. We think that our proposed classification scheme will suffice for everything that is found in our solar system, but we would like nothing better than to find some object which defies everything that we currently think we know and forces us to completely rethink fundamental questions like "what is a planet."

A modification of Brown’s definition can link it explicitly to the dynamics of planet formation: A planet is a body that has swept up or scattered most of the mass from its orbital zone in the accretion disk around a central star or substar. In this paper I propose an observational criterion to quantify this definition.

The end product of secondary disk accretion is a small number of relatively large bodies (planets) in either non-intersecting or resonant orbits, which prevent collisions between them. Asteroids and comets, including KBOs [Kuiper Belt Objects], differ from planets in that they can collide with each other and with planets.

As previously stated, the upper mass limit for a giant planet has to be below the limiting mass for thermonuclear fusion of deuterium (WGESP 2005). The lower mass limit for a giant planet is often assumed without much deliberation, but could be stated as: ‘An object is a giant planet if it is able to keep its atmosphere, composed mainly from the solar-composition gas of the parent body, against the surrounding vacuum.’

In the absence of the well-quantifiable physical property which would distinguish a rock (minor planet) from a (terrestrial) planet, we propose to apply the planethood criterion valid for giant planets also to the terrestrials. Previous similar concepts required a body to have an atmosphere. This was unsatisfactory because this requirement excluded atmosphereless planets (e.g. Mercury), and had a difficulty in setting the limit between an ‘atmosphere’ and a ‘vacuum’.

We argue that an object should not be called a planet if it is not capable to retain its envelope (volatiles) when connected to vacuum (i.e. to an empty space, as opposed to the
proto-planetary nebula gas cloud). We do not require an atmosphere, just the capability to retain it.

It is amazing we never had a definition for a planet in the first place...

"A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and ( b ) is in orbit around a star, and is neither a star nor a satellite of a planet."

In other words, if it's round(ish) and circles a star, it's a planet.

This really messes up that remembering thing:

My
Very
Eager
Mother
Just
Served
Us
Nine
Pizzas



:bye: pluto

tomorrow morning 60,000 people who opposed the plan with set fire to the building where the astronomers had their conference. They will overthrow the astronomers, and the government, and will force pluto back into planethood. . . teachers will implode.

So there aren't any Plutons?

So it has finally shrunken to 8...No plutons.

Hello, new to the board. I too read the news this morning that Pluto is no longer being
Anyway, this news today kind of contradicts the new released about a week ago that Astronomers planed on boosting our solar system to 12 planets. They also propose keeping Pluto in the club. Guess not!

Plus, Last year, the astronomers classified a 10th planet, called Quauar. They forgot to mention that today.

At least we don't have a planet Xena with a moon Gabriel.

Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.

Stern, in charge of the robotic probe on its way to Pluto, said the language of the resolution is flawed. It requires that a planet "has cleared the neighborhood around its orbit." But Earth, Mars, Jupiter and Neptune all have asteroids as neighbors.

"It's patently clear that Earth's zone is not cleared," Stern told SPACE.com. "Jupiter has 50,000 trojan asteroids," which orbit in lockstep with the planet.

Stern called it "absurd" that only 424 astronomers were allowed to vote, out of some 10,000 professional astronomers around the globe.

"It won't stand," he said. "It's a farce."

Stern said astronomers are already circulating a petition that would try to overturn the IAU decision.

Owen Gingerich, historian and astronomer emeritus at Harvard who led the committee that proposed the initial definition, called the new definition "confusing and unfortunate" and said he was "not at all pleased" with the language about clearing the neighborhood.

Gingerich also did not like the term "dwarf" planet.

"I thought that it made a curious linguistic contradiction," Gingerich said in a telephone interview from Boston (where he could not vote). "A dwarf planet is not a planet. I thought that was very awkward."

Gingerich added: "In the future one would hope the IAU could do electronic balloting."

Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight.

After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930. The new definition of what is — and isn't — a planet fills a centuries-old black hole for scientists who have labored since Copernicus without one.

I still wish they'd take into account the historical significance of Pluto having been considered a planet for such a long time. Let it be an honorary planet or something.

Besides, in another hundred years they'll change it again.

Um, Pluto hasn't been a planet for a while now.