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Bizarre Proposal to Increase the Number of Planets

 
 
oralloy
 
Reply Wed 16 Aug, 2006 05:38 am
Quote:
Nine Planets Become 12 with Controversial New Definition

Robert Roy Britt
Senior Science Writer
SPACE.com
Wed Aug 16, 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.

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, 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.



http://news.yahoo.com/s/space/nineplanetsbecome12withcontroversialnewdefinition&printer=1
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Wolf ODonnell
 
  1  
Reply Wed 16 Aug, 2006 06:38 am
Personally, I'd prefer it if the Pluto was dropped from the list of planets, instead of creating a new definition for something that's not quite a planet.
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 06:50 am
I had thought that Pluto was a "captured" comet.

Anyway, let's declare Jupiter and Saturn failed stars, and all of their satellites can be declared planets. We'll have lots and lots of the suckers.
0 Replies
 
stuh505
 
  1  
Reply Wed 16 Aug, 2006 07:34 am
Quote:
I had thought that Pluto was a "captured" comet.


There are a lot of objects with highly eccentric orbits around the distance of Pluto, we call them Kuiper belt objects and most of them we classify as comets. Pluto is hard to classify because it's orbit is much more eccentric than the other planets in our system, but still much less eccentric than the other KBO's. It's size is bigger than most KBO's, but we have now discovered bigger ones. Comets, by nature, are objects that "tried to escape " our solar system (instead of being accreted) but failed, so if you refer to a captured comet I assume you are talking about a comet from another star system that was captured by our system. This, I am sure, is not the case.

Quote:
Personally, I'd prefer it if the Pluto was dropped from the list of planets, instead of creating a new definition for something that's not quite a planet.


If it wasn't quite a planet, nobody would disagree with you -- but where are you getting YOUR definition of what exactly is a planet? It's all a very fuzzy business. The fact is that any distinctions at all about the objects in space is pretty arbitrary. In order to make sense of it all we choose certain criteria to make distinctions on; for instance, does the object orbit another object, what is it MOSTLY made out of, how was it created, does it undergo nuclear fusion...some distinctions are easy but when you are talking about a bunch of medium sized objects and we don't know EXACTLY how they all formed and they don't all fit neatly into very obvious classes, there will always be outliers.

I think that the distinction about the COM being outside the radius of either planet is a good way to distinguish between a binary planet and a planet moon pair. We have no problem with the nomenclature of binary stars so this would be consistent. If we find 2 planets A,B and A has mass of 10 and the other B has mass of 10.01, it is misleading to refer to A as a moon of B just because it is slightly less massive. The line has to be drawn somewhere and if their COM is outside the radius that is a pretty good measure.
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 07:47 am
Stuh, there was absolutely no reason for you to assume that i suggested that Pluto was a comet "captured" from another stellar system. I said nothing remotely resembling that. I simply pointed out that i had believed (based on something which i had read, and remember imperfectly), that Pluto was a former denizen of the Ort cloud which, due to it's size, had been "captured," and that its eccentric orbit was a degraded version of its former short-period orbit.

Have it any way you like, though, i'm not claiming any expertise here.
0 Replies
 
DrewDad
 
  1  
Reply Wed 16 Aug, 2006 08:10 am
So let's shoot a glob of water with enough velocity so that it no longer orbits Earth....

Sure, it'll freeze, but it'll be round, right?
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 08:34 am
I think we should hang onto all the water we've got.
0 Replies
 
jespah
 
  1  
Reply Wed 16 Aug, 2006 09:27 am
I say we can never have enough planets. Hell, let's make Venezuela a planet.

Seriously, though, the definitions are somewhat arbitrary after a while. I think we can all agree that stars are things that have or at least at one time had fusion going on, with various descendants such as black holes, etc. I'm not interested in getting into that. And a moon orbits whatever we're going to call a planet so Demos, for example, is a moon of Mars and not a planet (of the Sun). Comets are balls of gas, dust, ice and perhaps Velveeta that have exaggerrated elliptical orbits around a star. Smaller stuff is asteroids, debris and the occasional tool that an astronaut dropped.

Then it gets tricky, because the pieces out there that are in between all of this, and have elliptical orbits with one focus being a star, are apparently planets, but what do we do when these things are in a different elliptical plane (Pluto) or are smooshed in with a bunch of debris (Ceres)? And where's the line between planets and asteroids? Are planets big enough to be smooshed into spheres (or close to spheres as many are flattened a bit at the poles) by gravity? If that's the distinction (and it's not a bad one because at least it's measurable), then Ceres is indeed a planet and perhaps a few other asteroids are as well (I've forgotten if any others are big enough to have enough gravity for the smooshing process).
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 09:29 am
I had forgotten the crucial velveeta component of astrophysics. Thank you for reminding us all, Jespah.
0 Replies
 
DrewDad
 
  1  
Reply Wed 16 Aug, 2006 09:38 am
Setanta wrote:
I think we should hang onto all the water we've got.

I think you've taken the phrase "hold your water" a tad too seriously.
0 Replies
 
Francis
 
  1  
Reply Wed 16 Aug, 2006 09:38 am
That's the element I like the more in astrophysics, Jespah!
0 Replies
 
jespah
 
  1  
Reply Wed 16 Aug, 2006 09:41 am
Well, it seems more plausible than Nutella, which of course is a key element of nuclear fusion.

Oops, I've said too much.
0 Replies
 
Brandon9000
 
  1  
Reply Wed 16 Aug, 2006 09:53 am
Francis wrote:
That's the element I like the more in astrophysics, Jespah!

And this alleged sentence means.....?
0 Replies
 
Francis
 
  1  
Reply Wed 16 Aug, 2006 09:56 am
A long story about Velveeta, Brandon...
0 Replies
 
Noddy24
 
  1  
Reply Wed 16 Aug, 2006 12:49 pm
I like the idea that recent discoveries and current information makes the system outdated.
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 12:58 pm
Yes, a good point . . . the solar system is outmoded, and doesn't fit the contemporary paradigm . . . we need a different system . . .
0 Replies
 
stuh505
 
  1  
Reply Wed 16 Aug, 2006 02:16 pm
Setanta,

Sorry if I offended you, it was not my intention. I certainly do not claim to be an expert either, but I try to share what knowledge that I do have when I can. Your comment about "captured" was vague, so don't be surprised that I misunderstood.
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 02:18 pm
I simply meant that it was pulled into a less eccentric orbit, and one more nearly like a planetary orbit, by the grativational influence of the sun. I took not offense--no harm, no foul.
0 Replies
 
stuh505
 
  1  
Reply Wed 16 Aug, 2006 02:27 pm
Yeah, I got you. I vaguely remember hearing of this possibility as well. But this hypothesis isn't very satisfying either. Why would it's eccentricity be so much lower than the other Oort cloud comets, that are closer to 1? Or, maybe, it was just because it had a low eccentricity that it was susceptible to being downgraded into a lower orbit...
0 Replies
 
Setanta
 
  1  
Reply Wed 16 Aug, 2006 02:30 pm
Yes, that is a possible explanation. I don't recall the details of what i read that well, and it's been years ago. I believe the hypothesis was based upon the contention that its composition is that of objects in the Ort cloud, rather than characteristic of other planets. The article used the examples of Phobos and Deimos as examples of gravatational "captures," suggesting the the moons of Mars are "asteroids" which were trapped by its gravitational field because of eccentric obrits which brought them near the planet. The article suggested that Pluto was the same result on larger scales of distance.
0 Replies
 
 

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