Nine Planets Become 12 with Controversial New Definition

[Matt-hurricanewatcher]

Nine Planets Become 12 with Controversial New Definition
By Robert Roy Britt
Senior Science Writer
posted: 16 August 2006
2:00 am ET


The tally of planets in our solar system would jump instantly to a dozen under a highly controversial new definition proposed by the International Astronomical Union (IAU).

Eventually there would be hundreds as more round objects are found beyond Neptune.

The proposal, which sources tell SPACE.com is gaining broad support, tries to plug a big gap in astronomy textbooks, which have never had a definition for the word "planet." It addresses discoveries of Pluto-sized worlds that have in recent years pitched astronomers into heated debates over terminology.

The asteroid Ceres, which is round, would be recast as a dwarf planet in the new scheme.
Pluto would remain a planet and its moon Charon would be reclassified as a planet. Both would be called "plutons," however, to distinguish them from the eight "classical" planets.
A far-out Pluto-sized object known as 2003 UB313 would also be called a pluton.
That would make Caltech researcher Mike Brown, who found 2003 UB313, formally the discoverer of the 12th planet. But he thinks it's a lousy idea.

"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.

Brown and other another expert said the proposal, to be put forth Wednesday at the IAU General Assembly meeting in Prague, is not logical. For example, Brown said, it does not make sense to consider Ceres and Charon planets and not call our Moon (which is bigger than both) a planet.

IAU members will vote on the proposal Thursday, Aug. 24. Its fate is far from clear.

Q&A on the Proposal / Gallery: The 12 "Planets" / Read the Draft Resolution

The definition

The definition, which basically says round objects orbiting stars will be called planets, is simple at first glance:

"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."

"Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor," said Richard Binzel, an MIT planetary scientist who was part of a seven-member IAU committee that hashed out the proposal. "Nature decides whether or not an object is a planet."

"I think they did the right thing," said Alan Stern, a planetary scientist at the Southwest Research Institute and leader of NASA's New Horizons robotic mission to Pluto. Stern expects a consensus to form around the proposal.

"They chose a nice economical definition that a lot of us wanted to see," Stern told SPACE.com. "A lot of the other definitions had big problems. This is the only one that doesn't have big problems."

“I feel that they have made the most rational and scientific choices; namely ones which are physically based and can be most readily verified by observations,” said Gibor Basri, an astronomy professor at the University of California, Berkeley. Basri made a similar proposal to the IAU in 2003, part of the long-running saga of failed attempts to define "planet."

Expect heated discussion

But the IAU draft resolution explaining the definition is more complex [Read the Draft Resolution], with caveats and suggestions and surprises that some astronomers think render the entire proposal unworkable.

In particular, this aspect was criticized: A pair of round objects that orbit around a point in space that is outside both objects—meaning the center of gravity (or barycenter) is between the two planets in space as with Pluto and Charon—would be called double planets. Alan Boss, a planet-formation theorist at the Carnegie Institution of Washington, called the deliniation arbitrary.

Brown said there will likely be other similar pairings discovered, and it's even possible a "triple planet" would be found given this definition.

In response to the criticism, Binzel said it was important to distinguish between planets and satellites. He noted that barycenters are used to define and describe double stars and so the concept should apply to planets, too.

"The planet and satellite definition must be universally applicable, to all solar systems, not just our own," Binzel said by email from Prague. "For example: Picture a pair of Jupiters discovered in another solar system. Would one of these Jupiters be a planet, and the other a satellite? The barycenter criterion means that a pair of Jupiters would be a double planet."

Other astronomers saw other problems.

"It looks to me like a definition that was written by a committee of lawyers, not a committee of scientists," Boss said. "I think these criteria are as arbitrary as any other you might come up with."

Asteroid Ceres, since it is round, would be considered a planet. Interestingly, Ceres was called a planet when first discovered in 1801, then reclassified. It is just 578 miles in diameter, compared to 1,430 for Pluto and 7,926 for Earth.

And if astronomers determine that asteroids Pallas, Vesta, and Hygeia are also round, "they will also have to be considered planets," said Owen Gingerich, an historian and astronomer emeritus at Harvard who led the committee. The IAU proposal suggests (but does not require) that these be called dwarf planets. Pluto could also be considered a dwarf, which the IAU recommends as an informal label.

So to recap: Pluto would be a planet and a pluton and also a dwarf.

Boss was bothered by the lack of definitiveness on this and other points.

Boss, along with Stern, was on an IAU committee of astronomers that failed to agree on a definition. After a year, the IAU disbanded that committee and formed the new one, which included the author Dava Sobel in an effort to bring new ideas to the process.

Boss called their proposal "creative" and "detailed" but said it does not hang together as a cohesive argument.

"I'm sure this will engender a lot of heated discussion," Boss said by telephone prior to departing for the Czech Republic to cast his ballot. "This is what everyone will be talking about in the coffee shops of Prague for the next few days."

Tally would soar

Given all the nuances in the definition, a dozen other objects would be put on an IAU list of "candidate planets" which, upon further study, might bring the tally of planets in our solar system to 24.

Eventually the inventory of planets would soar.

Stern, the New Horizons mission leader, said there could be "hundreds and maybe a thousand" objects in our solar system that are at least as big as Pluto. That's fine with him. "This is what we do as scientists. You discover new things, you adapt to new facts."

Brown, the discoverer of the potential 12th planet, said the basic definition is fine, but "the resolution itself is a complete mess."

The resolution calls for a new IAU committee that would evaluate other candidate planets. Normally, that's a process that takes place in a scientific journal, Brown said. He called the notion of an IAU gatekeeper "bizarre" and "really a bad idea. The IAU should make a definition, then it's up to scientists to go about their business" of deciding what objects fit the definition.

Binzel defended the approach: "The IAU has existing committees that can do this—it is what the IAU
does. Someone has to officially bestow names, etc. It is just the way the system works." He added that quality papers published in science journals should and would continue to be part of the process of determining planet status.

Nobody can yet say how the vote will go.

"You're only left with a 'yes' or 'no' vote," Brown said. "And a 'yes' vote makes things ridiculous. A 'no' vote puts us back where we were."

Brown worries, however, that the vast majority of astronomers at the IAU meeting work in other fields, outside planetary science. "They are likely vote 'yes' because they're not familiar with the issue and, mostly, because they're sick of the topic," he said.

More to Explore
http://www.space.com/



What abunch of what! Just make Pluto the base line for planet. Everything which is smaller can be called a minor planet.

Planet should be at least the size of planet or around 1,400km sq. With it being a sphere. Also remember theres planets as big if not bigger then jupiter with not cirle path around its star. So that kills that planet is elongated. Heck alot of planets outside our solar system do that.

This needs to be good for all solar systems...

Also Pluto has 3 moons. The new planet is near 2,000km which is more big enough to be a planet. My friend there should only be 10 right now with my thinking and browns at least the last time I read. Make freaking Pluto the base line...If not what are you planet people going to base a base the buttom line off?

This is just my option!

[Matt-hurricanewatcher]

They could simply end all this by putting Pluto as the lower end.

http://www.spaceflightnow.com/news/n0608/16planets/

[Audrey2Katrina]

I know I'm old fashioned to begin with; but I think this is silly. If anything, a "planet" should be relegated to a substantially large body, very close to circular-round in shape, and within a few degrees of the ecliptic, and NOT possessing an extraordinarily eccentrinc orbit. This would end all this speculation that opens up a Pandora's box for potentially "thousands" of what some folks looking for their little chunk of immortality (Although who remembers the discoverer of Pluto?) becoming "new planets".

I mean the whole idea of making Charon a "planet" is ridiculous. Unless we're going to reclassify all of the large moons as planets, as it is by no means the largest moon in the solar system. There are the four Jovian moons--all larger, and Saturn's Titan, and of course, our own Moon... what will they call it? Planet Luna? Will we now have 2 classes of planets: single and multiple planetary systems (such as Saturn and its satellites, and Jupiter and its?) The whole proposal seems like making something ridiculously complex. If anything, they can declare Pluto a Kuiper body, (which it probably is in the first place) and continue to call those irregular shaped bodies, with "highly" eccentric orbits, as either asteroids, planetoids, plutons, whatever name some astronomer out to make a name for himself/herself wishes... but to make the MOON of Pluto--a small planet by any measure of the word, into a "planet" in and of itself.... well, it just seems absurd.

A2K

[Brent]

I mean the whole idea of making Charon a "planet" is ridiculous. Unless we're going to reclassify all of the large moons as planets, as it is by no means the largest moon in the solar system. There are the four Jovian moons--all larger, and Saturn's Titan, and of course, our own Moon... what will they call it? Planet Luna? Will we now have 2 classes of planets: single and multiple planetary systems (such as Saturn and its satellites, and Jupiter and its?) The whole proposal seems like making something ridiculously complex. If anything, they can declare Pluto a Kuiper body, (which it probably is in the first place) and continue to call those irregular shaped bodies, with "highly" eccentric orbits, as either asteroids, planetoids, plutons, whatever name some astronomer out to make a name for himself/herself wishes... but to make the MOON of Pluto--a small planet by any measure of the word, into a "planet" in and of itself.... well, it just seems absurd.

A2K

I agree completely. I think it's stupid.

[Matt-hurricanewatcher]

Theres planets as big if not bigger then Jupiter in other solar systems having obrits that take it from 1 or 2 SOL to as far out as Saturn. So that means little. Also I think pluto should be the lower in...

[Aslkahuna]

The reason the Moon is not considered a planet is that the barycenter or the center of mass of the Earth-Moon system is about 1000 miles inside the Earth whilst the barycenter of the Pluto-Charon system is between the two objects and not within either. The largest moon in the Solar System, Jupiter's moon Ganymede is larger than Mercury but no one is going to claim it as a planet because it is clearly bound to Jupiter. If we had defined clearly what a Planet is years ago, we wouldn't be having this argument now.

Steve

[Matt-hurricanewatcher]

This is not stupid my friend. For one not all planets are going to be circleing a star...Heck we should not even make it something that is needed for soming to be a planet. We should also use Pluto as the smallest you can get....See to make a sphere you need gravity to form it into a sphere. I say 1,400km3 is the lower limite. Given the new world at 2000km3 planet status.

[Audrey2Katrina]

I completely disagree.. and still think it is stupid. What could be termed as potential "planets" is a vast quantity of what is known as "dark matter", I'm well familiar with that. To sit on the literal archaic derivation of the word "planet" as being "wanderer" would be as ludicrous as attempting to hold many words which we use today to their "original" root-word meanings. And why draw a line at 2000km^3 to define a planet? Why not a "spherical" body half that size? Why does it have to be a "sphere"-- what is so special about the shape being spherical defining a body as a planet? I'm strictly speaking/writing ad absurdum here; but in all honesty, with all this "new" way of looking at the word--who's to say in another century or so they won't want some of those "irregular" bodies that "orbit the sun" to become members of the club.

The reason the Moon is not considered a planet is that the barycenter or the center of mass of the Earth-Moon system is about 1000 miles inside the Earth whilst the barycenter of the Pluto-Charon system is between the two objects and not within either.

Yes, and that barycenter of the Earth-moon system is 3/4 out from the 'center' of the Earth (they are in mutual free-fall about each other, so IMO where the barycenter is is grasping at straws in drawing a clear definition of moon/satellite vs. double/multiple-planet system) ... and the moon is pushing further away from the Earth by approx. 4 cm/year... not much, but we're talking geological time here--so in other words what is a "moon" today, can become a "planet" with the passage of time simply because it moves the barycenter beyond the physical boundaries of the "larger" celestial body? Jupiter and Saturn are really huge gas giants, you don't even reach a "surface" of either without plunging quite a few thousand miles below that roiling atmosphere we see. The fact is that all this talk about "double-planets" (i.e: pluto and Charon--BTW what about the 2 "other" moons recently discovered orbiting around/near Pluto? Are they to become planets too?) is nothing new. "Planet-systems" have been thrown around as topics of discussion helter-skelter for years. I just think this is just a lot of sensationalistic nonsense by a few who want to just shake up the applecart. Hell, if you're going to draw such fine paramaters around what is, or isn't a planet by worrying exactly where it's barycenter might be as to its relationship with another body.. then you're really throwing the whole nomenclature in flux--at least geologically speaking. Are we now going to give the title of "planet" to each of the countless thousands upon thousands of asteroids in that belt? I mean their barycenters, while admittedly varying to a great degree, is undeniably moreso with the sun than any other body with very few, if any, exceptions--so I guess we have about 5 million planets!!! Or do we look ONLY for ones that are spherical in shape even though some more massive ones might not be as spherical? Or do we set parameters about a specific mass the object must be before calling it a planet? Seems a ludicrous system in contrast to all the other means of classifying in the worlds of science.

If we had defined clearly what a Planet is years ago, we wouldn't be having this argument now.

I whole-heartedly agree; it's just that I think someone out to make a few headlines is going to turn what could be a relatively easy method of nomenclature into an unnecessarily complex quagmire of what, when you really get to it, is little more than nit-picking at potentially thousands of mathematical computations that could be made with regard to these bodies.

I still say it's absurd--not that it'll do anything to keep those who just love to create novelty, headlines, and sensation (even when it's clearly not necessary) from doing just that.

A2K

[Terrell]

The IAU blew it, they should have made a definition where there are 8 planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Require that a object be large enough to be round and require that it not be a member of a "belt" of objects to be a planet. this would disqualify Pluto, Ceres, and 2003UB 313. Ceres as a member of the main Asteroid belt between Mars and Jupiter is disqualified, Pluto and 2003 UB 313 get disqualified as members of the Kuiper Belt beyond Neptune.

I don't think that Pluto's size or it's inclined elliptical orbit should be problems for it's status, the only problem is it's location in the Kuiper belt and it's similiarity to the other KBO's that make it a member. Those things are what should disqualify Pluto as a planet.

Ceres was originally thought to be a Planet when it was first discovered between Mars and Jupiter, then came Pallas, Vesta, and Juno, and many others, Astronomers realized those things couldn't all be planets.

The new definition will result in there being thousands of "planets" in our solar system. Pluto is a Kuiper Belt Object, it's past time to reclassify it as such.

Pluto is currently known to have 3 moons Charon, Nix, and Hydra

[Matt-hurricanewatcher]

Then what will be the buttom for the size of whats needed to be a planet? How about worlds around a draft star/white draft? Pluto fits planet all the way around it doe's not matter at all if its obriting a star why because theres likely planets drifting out in space.

The reason I went a lower limit is to not allow small objects to be planets but minor planets. I feel that Pluto should stay for a good reason. Kuiper belt really should not matter a whole lot if you look at that all planets at least in theory started out in a disk of rocks and dust. Which come together by gravity to form the planets. A world half the size of Pluto answering A to K quasiton would likely not have the gravity needed to make a perfect or near perfect sphere. If not Pluto then Mercury is the next on the hot oven. I feel that pluto has earned it...There is so many weird things we are find its amazing...So setting something that can go along with more then just our own solar system is a good idea. Disagree if you went.

[Matt-hurricanewatcher]

Also theres no way the moon is a planet. Why because it go around earth. While Pluto and its "moon" moves around a barycenter which is between them. Making it a two planet system.

[Matt-hurricanewatcher]

Charon should be a minor planet because of its size...The moons that where just discovered should be moons because they go around Pluto. But yes that world which is bigger then pluto should be the 10th planet. I think its possible we could find a few more larger then pluto but not that many more.

[kevin]

The changes make sense, and I am happy about them. Hopefully the draft will be approved.

[Terrell]

As we continue to search the Kuiper belt how many more objects larger than Pluto will we find? 10, 100, 1000, more? If we call ALL of them Planets the solar system planets we're going to have LOTS of planets.

We found the first KBO in 1930 when Clyde W. Tombaugh found Pluto, during his search for Planet X at the Lowell Observatory near Flagstaff Arizona it just wasn't known at the time that he found a KBO and not a Planet. Because Charon, discovered by James Christy at the Naval Observatory in 1978 is Pluto's moon, it didn't call into question Pluto's status as a planet, but it did allow us to determine just how small Pluto really was (we originally believed that Pluto was much larger that it is but over time it's estimated size had shrunk). A big blow was the discovery of 1992 QB 1 in 1992 by Jewitt and Luu, this showed that Pluto wasn't alone, in orbit beyond Neptune. 2003 UB 313 just forced the issue being bigger than Pluto.

Discoveries thus far
TNOs and similar bodies
cis-Neptunian objects
centaurs
Neptune Trojans
trans-Neptunian objects (TNOs)
Kuiper belt objects (KBOs)
cubewanos (classical KBOs)
plutinos (2:3 resonant KBOs)
twotinos (1:2 resonant KBOs)
scattered disc objects (SDOs)
Oort cloud objects (OCOs)
Over 800 Kuiper belt objects (KBOs) (a subset of trans-Neptunian objects (TNOs)) have been discovered in the belt, almost all of them since 1992. Among the largest are Pluto and Charon, but since the year 2000 other large objects that approached their size were identified. 50000 Quaoar, discovered in 2002, which is a KBO, is half the size of Pluto and is larger than the largest asteroid, 1 Ceres. 2005 FY9 and 2003 EL61 "Santa", both announced on 29 July 2005, are larger still. Other objects, such as 28978 Ixion (discovered in 2001) and 20000 Varuna (discovered in 2000) while smaller than Quaoar, are nonetheless quite sizable. Sedna, a small red planetoid with a diameter roughly half-way between Pluto and Quaoar, was first sighted on November 14th 2003. The exact classification of these objects is unclear, since they are probably fairly different from the asteroids of the asteroid belt. The largest recent discovery is 2003 UB313, nicknamed Xena. It has led scientists to question the definition of the term Planet, as it is larger than Pluto and has already been called a tenth planet by some sources [1].

Neptune's moon Triton is commonly thought to be a captured KBO.

http://en.wikipedia.org/wiki/Kuiper_belt

With many of those things being larger than Ceres, which is also a sphere, those KBOs would also be planets under the IAU's new definition. This is not practical as planets will ultimately number into the thousands in this system alone! The science is in, Pluto is not like the 8 planets, and this definition has been made to hold on to it for largely sentimental reasons.

People like Pluto, but Pluto isn't really a planet, it's a KBO and should be classified as such. That doesn't mean that Pluto is any less interesting as a celestial body, or that we shouldn't explore it and learn as much as we can about it, it just means that there are 8 known planets in the Solar System, not 9 and not 12 either.

[Audrey2Katrina]

People like Pluto, but Pluto isn't really a planet, it's a KBO and should be classified as such. That doesn't mean that Pluto is any less interesting as a celestial body, or that we shouldn't explore it and learn as much as we can about it, it just means that there are 8 known planets in the Solar System, not 9 and not 12 either.

I agree with you 100%. The proposed new method of classification is destined for chaos or failure--or both.

theres likely planets drifting out in space.

Ahhh, but you see, therein lay the rub--the very definition of a "planet". By yours, no doubt there are--by others...not so.

Also theres no way the moon is a planet. Why because it go around earth. While Pluto and its "moon" moves around a barycenter which is between them. Making it a two planet system.

As pointed out earlier, there is also a barycenter between the Earth and the Moon, we are creating a semantic quagmire here, simply because that "barycenter" happens to be roughly 3/4 OUT from the center of the planet Earth--but make no mistake, they do have a mutuality orbit. Additionally, as pointed out earlier, the orbit of the former is moving slowly but consistently further and further away. Does this imply that at X-distance it will attain "planet" status?

A world half the size of Pluto answering A to K quasiton would likely not have the gravity needed to make a perfect or near perfect sphere.

Really? How large is Ceres in relation to Pluto? I believe it's diameter is about 950 or so Km, while that of Pluto is over 2200 Km, which makes Ceres substantially smaller than "half the size of Pluto". And yet it's up for "planet" status. I have always taught my students that while it is classical understanding that we have nine "known" planets, that the ninth is, in all likelihood, the first of the Kuiper bodies. Had the organization approached it from this angle, there would be far less disagreement and room for disputation, IMO. I think Terrell is spot on in that this creates the potential for a "solar system" with hundreds, if not thousands of "planets"... and as far as "minor planets" such as suggested for Charon--this is more semantic maneuvering. What next. "Tiny Planets?" "Teeny Planets?" "Teeny-tiny Planets?" "Itsy-Bitsy Planets" "Itsy Bitsy-Teeny Tiny Planets?" (Brings to mind an old song doesn't it? "Planetesimals?" Again, I stress that this is NOT said to deride or poke fun at any individual--but to illustrate what I perceive as the absurdity this reclassification could be opening up. I respect the opinions of those who "welcome" the change, and even those who encourage it--it's just that I strongly disagree with it.

Makes no logical sense to me whatsoever.

A2K

[Matt-hurricanewatcher]

What would you say if they found a world as big as Mercury out there? Or maybe as big as Mars. This makes no sense.

[Terrell]

What next. "Tiny Planets?" "Teeny Planets?" "Teeny-tiny Planets?" "Itsy-Bitsy Planets" "Itsy Bitsy-Teeny Tiny Planets?" (Brings to mind an old song doesn't it?

Yeah, with yellow polka dots. But since only Earth (Gaia, Tellus), Venus, and Ceres are female I don't know about the bikinis.

[Terrell]

What would you say if they found a world as big as Mercury out there? Or maybe as big as Mars. This makes no sense.

If it's in the Kuiper belt, and made of ice and rock, like the other KBOs, then it's a Kuiper belt object, just like the other ones, if it's in the Oort Cloud and it's made like the other Oort cloud objects then it's an Oort cloud object. For it to be a planet it cannot be in either of those 2 zones.

[Matt-hurricanewatcher]

So any way if its in the kuiper belt it can be a gas giant in be called a Kuiper belt object? What I stated that Pluto should be the lower limit seems to be the much better system for all solar systems. There even planets that are going to be in space with out going around the sun. I don't understand where your going. If its a planet I don't care if theres a million planets.

[Terrell]

So any way if its in the kuiper belt it can be a gas giant in be called a Kuiper belt object? What I stated that Pluto should be the lower limit seems to be the much better system for all solar systems. There even planets that are going to be in space with out going around the sun. I don't understand where your going. If its a planet I don't care if theres a million planets.

If it's a gas giant it's not made of the same stuff as the KBOs, not to mention if it were a gas giant (in the Kuiper Belt) we would have already found it. As I said before, if it's in the Kuiper belt, and is made of rock and ice, like the other Kuiper Belt Objects, then it's a Kuiper Belt Object.