Goodbye, Pluto

[truth_andrew_ 0]

I strongly agree with Bernhard. Pluto? a Planet? seems more like an giant ice cube to me. The Weather Channel sympathizes with Pluto, then again the weather channel sucks at tracking hurricanes.

Andrew, formerly justanotherhiddennow

[Hummer bob 1 4]

Pluto will always be a planet in my eyes.

[BurroDiablo 222]

I was watching a program today on the formation of the Universe and the narrator kept going on about the EIGHT planets, going from Mercury to URANUS... honestly, what has Pluto done to be demoted? Must be boring at the science conventions to discuss that Pluto wasn't really a planet and in someway had to be booted off the scene. Sure, its a ball of rock and ice not much bigger than the moon, but after being classified as a planet for so long surely it deserves to stay that way?

To be honest... I don't even know why I care. Maybe its because iv'e been brought up being told for the last 21 years of my life (although this happened when I was 19) that Pluto was the Ninth planet. As with many others... Pluto will always be the ninth planet no matter what the freaking 'experts' say.

[Haljackey 17,302]

Well, we will find out for sure weather Pluto is a planet when the New Horizons spacecraft reaches the planet/moon/pluton/dwarf/whatever in 2015.  It was launched in 2006.  It will be the first spacecraft to ever visit the Plutoian system.

Originally posted by: Hummer bob 1 Pluto will always be a planet in my eyes.quote>

I couldn't agree with you more!

[panthersimcity4 162]

LEAVE PLUTO ALONE!!!1111111 *cries*

Sorry, it had to be said

[Duke87 1,070]

Originally posted by: El Burro I was watching a program today on the formation of the Universe and the narrator kept going on about the EIGHT planets, going from Mercury to URANUS... quote>

Yeah, um, Mercury to Uranus is only seven. Neptune is number eight.

honestly, what has Pluto done to be demoted?quote>

Pluto has done absolutely nothing except orbit the sun and spin on its axis. But it's not a matter of it doing something making it "deserving" of demotion. It's rather that new information previously unknown to us called its classification into question and thus it was reclassified.

Remember, back in the early-mid 19th century there was a "planet" Ceres. And then more and more things just like it were discovered in the same area, and it was realized that it wasn't quite so unique and thus it was demoted to being an "asteroid", like the thousands of others orbiting in the same region. Essentially the same thing happened with Pluto. It's now a Kuiper belt object, like the thousands of other hunks of rock just like it out there.

Things change with time as we learn new things. That's how science works. Look, before you were even born, we went from this:

to this:

to this:

to this:

to this:

to this:

to this:

And now, we're going to this:

but you want us to go to this instead:

Now tell me: What the hell kind of sense does that make?

Sure, its a ball of rock and ice not much bigger than the moon, but after being classified as a planet for so long surely it deserves to stay that way? quote>

How long it had a certain classification is irrelevant. So far as science is concerned, it isn't in any way "special" just because it was discovered first and it makes absolutely no sense to classify it as a planet but not all the other things just like it.

[fukuda 351]

I totally agree with Duke

quoting myself from another thread:

Often, when new discoveries are made, the classes and names are changed, like in this case. Not changing it is dogmatic.

There seem to be 3 types of big bodies revolving around the Sun, the inner rocky planets, the gaseous giant planets and the dwarf icy/rocky outer bodies. Pluto was believed to be unique, so his rank of planet was conserved. But when new discoveries were made, there was enough evidence that shown that there was a third group, so different to other 2 groups that its bodies more than probably have a different past and were formed in a different way. This new group of bodies was so big (tons of planetoid) and so different that they were classed apart to keep things simpler and more tidy, that's all.

It's the same story as the IUPAC (International Union for Pure and Applied Chemistry) changing the element and compound names, it's done objectively and keepig in mind that better and simpler organization was the final goal.quote>

anyway. planets don't deserve things, how we classify things has nothing to do with merits, it has everything to do with method

[Patricius Maximus 236]

The IAU definition is completely illogical. "Clearing the neighbourhood" is a subjective term that cannot be empirically observed, thereby giving special powers to the IAU. This is not scientific at all. Whether something is a planet or not is something that should be determined by observations of natural phonomena. Not some criteria created by the IAU.

This was the original definition proposed. It is more logical, and I personally use it:

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.quote>

According to this criterion, there would be anywhere from 20 to 60 planets. 

And the common argument that we cannot teach the names of hundreds of planets is groundless. The number of planets taught is entirely a curriculum issue, and they could only teach the ones perhaps bigger than Pluto at first.

Under this criteria, Ceres would be a planet, and Pluto-Charon would be considered a double planet. Also, Eris, Orcus, Ixion, and Make-make would be planets as well.

Not only would this be a better and more logical definition, it would also give astronomers more incentive to discover new objects, since they would be credited with the discovery of a planet instead of a plutoid, asteroid, or dwarf planet.

Lastly, the analogy between the asteroids and KBO's is not correct. Only Ceres (and possibly Vesta) meet the criteria to be planets under the above definition. The reason that all asteroids are not planets is because they are not all of them are spherical. Many KBO's are spherical, and as such, meet the criteria, unlike most asteroids. The KBO's that are not spherical are asteroids.

Now isn't that better than the 2006 definition? Astronomers can determine the status of their discoveries by themselves and then publish it, instead of deferring it to the IAU and their opinions.

[GMT 389]

Originally posted by: El Burro I was watching a program today on the formation of the Universe and the narrator kept going on about the EIGHT planets, going from Mercury to URANUS... quote>

must have been hell of an educated narrator...

from sun to god:

terrestrial:

mercury, venus, earth, mars, (ceres)

Jovians:

jupiter, saturn, uranus, neptune, (pluto, eris)

eight planets from mercury to uranus... well, either he counted ceres as a planet and forgot about neptune or he can't count at all

[fukuda 351]

The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and © has cleared the neighbourhood around its orbit.quote>

That's all, sounds objective to me

The complete resolution:

IAU Resolution: Definition of a "Planet" in the Solar System

Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

RESOLUTION 5A

The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

(1) A "planet" [1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and © has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], © has not cleared the neighbourhood around its orbit, and 

(d) is not a satellite.

(3) All other objects [3], except satellites, orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

IAU Resolution: Pluto

RESOLUTION 6A

The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

quote>

I don't see arguments about "teaching planets to children" anywhere, btw

[Muck308 55]

So Harry starts feeling around on all the trees., and then he says, "We on Pluto."

I said , Harry how can you tell?

From the bark you dummies... from the bark.

Hail President Screwb

[Patricius Maximus 236]

That's all, sounds objective to mequote>

Since "clearing the neighbourhood" cannot be observed empirically or objectively, it has to be deferred to the IAU. The IAU members will give their subjective opinions and it will be accepted by the astronomical community.

Sound objective to you? It doesn't to me. The definition I mentioned does not rely on the subjective opinions of people, only natural phonomena that can be observed objectively.

I don't see arguments about "teaching planets to children" anywhere, btwquote>

I did not state that the IAU definition had that in it. I stated that it was a common argument in favor of the IAU definition. Also, it was cited as a reason that some astronomers voted that way. Not very scientific of them, was it?

Also, the vote was held on the last day of the assembly, and only a small minority of actual IAU members voted on it. So, the entire IAU did not agree on it.

I still maintain my position that the 2006 IAU definition is illogical and not objective, and the definition I stated is more logical, objective, and scientific.

- Patricius Maximus

[fukuda 351]

Not only would this be a better and more logical definition, it would also give astronomers more incentive to discover new objects, since they would be credited with the discovery of a planet instead of a plutoid, asteroid, or dwarf planet.quote>

But, lol... "planet" and "dwarf planet" are at the same level in the tree diagram, discovering a body of any of the 2 categories is equal in acknowledgement. And there should be more important things in science than personal ego

Remember, Pluto is not being "demoted" is just being reclassified 

Originally posted by: Patricius Maximus

That's all, sounds objective to mequote>

Since "clearing the neighbourhood" cannot be observed empirically or objectively, it has to be deferred to the IAU. The IAU members will give their subjective opinions and it will be accepted by the astronomical community.quote>

Of course, the IAU represents the astronomical community. It was voted by the representatives, well-known astronomers that probably know this way better than us.

Clearing the neighbourhood simply means that you pulled in or out all objects in your orbit and cleaned it, this is the case of all planets except  Pluto, and certainly not the case of Ceres

Sound objective to you? It doesn't to me. The definition I mentioned does not rely on the subjective opinions of people, only natural phonomena that can be observed objectively.quote>

Come on. It relies on your subjective opinion. An opinion relying on natural phenomena, like IAU's one.  Everything relies on subjective opinions, that's why there must be a method and also an organism to organize and put it all in its place.

 

I don't see arguments about "teaching planets to children" anywhere, btwquote>

I did not state that the IAU definition had that in it. I stated that it was a common argument in favor of the IAU definition. Also, it was cited as a reason that some astronomers voted that way. Not very scientific of them, was it?quote>

? Pragmatism and organization is also a part of science.

 

^ This total mess would be + or - all  bodies that could be called "planets" with the original definition, bodies with big differencies between them, that could be better described when put in new, separate categories.

Also, the vote was held on the last day of the assembly, and only a small minority of actual IAU members voted on it. So, the entire IAU did not agree on it.quote>

Ah, they didn't? If it was really the case, they would have asked for another vote.

I still maintain my position that the 2006 IAU definition is illogical and not objective, and the definition I stated is more logical, objective, and scientific.quote>

Ok, explain and expose carefully your scientific points to support that definition,  you're welcome

[Patricius Maximus 236]

I'll state my case in detail.

As I stated previously, a definition of any object in science should have criteria that are natural phonomena that can be observed empirically. The latest IAU definition lacks this, instead adding the subjective term "clearing the neighbourhood".

This marks a streak of geocentrism among the IAU, since the status of planet, which Earth has, would often be decided by a select group, thus making Earth part of a club with special status. It also shows blatant heliocentrism because the word "Sun" was used instead of "star".

The definition I mentioned in my last post is logical, and has it's criteria as natural phonomena that can be observed empirically, rather than decided by a select group of people. The argument that the IAU definition is objective is baseless. How can the opinions of a select group be objective?

Natural phonomena are undisputable because no one can deny that they exist.

Example. This object is spherical. No one can argue with that:



This object is not spherical. Again, this fact is undisputable:



Now, can you tell if any of these objects have "cleared the neighbourhood"?

I can't. This criterion cannot be observed empirically, and it is not a natural phonomenon. Therefore, it is not an objective criterion, and therefore is not scientific.

Which looks like a planet to you?

I know which one I'd pick.

Do these objects look like planets?



How about this one?



For the record, the first picture was Pluto, the second one was 433 Eros, the third one was three "dwarf planets", and the fourth was Eris.

Now the merit of the criterion comes into view. It cannot be observed objectively and without opinion, so it is not a good definition.

The criteria in the logical definition I stated can be observed objectively and without dispute.

You can observe objectively whether an object is orbiting a star or not.

You can observe objectively if an object is spherical or not.

You can observe objectively if an object is not a star.

You can observe objectively if an object is not the satellite of a planet.

You cannot observe objectively if an object has "cleared the neighbourhood" or not.

Pragmatism and Organization is part of Science, and categorization of objects is essential. That is why planets must be categorized also, but not on subjective criteria.

Some examples of planet categories are, Oceanic, Terrestrial, Gas Giant, and Ice Dwarf. These can have objective criteria just as a planet definition can.

Lastly, just because a certain body "represents" a group and decides something it does not mean that it is the correct decision. Just look at the US Congress or any other "represenative" body for evidence.

- Patricius Maximus

[confused04 14]

I'm just wondering, and I haven't taken the time to read through this thread so I may be repeating....

But...

With the added clarification of a planet having to "clear its neighborhood," would that make reclassify Earth in the far flung future when the barycentre of the Earth-Moon system is no lunger just under the Earth's surface due to the outward movement of the moon? What makes a double planet different from a "dwarf" planet that hasn't clear its neighborhood". I mean, based on that criteria listed above, I kinda find it hard to believe that Pluto would be called a dwarf planet and that Earth (which is slated to have more of a dance around the barycentre with the Moon in the future) would also fit the definition of "dwarf planet". It just seems that at some point, there must be an arbitrary point that size alone can be considered a planet.

Earth (in the future)

-will be a sufficient mass to be spherical...

-orbits only the sun

-technically will not have cleared its neighborhood (Moon being 1/6 the mass of the Earth and being far enough away that the common center of mass lies between the two).

Would this not make Earth suddenly a double dwarf planet system as there is no size or mass limit to the definition?

Mercury

-sufficient mass to be spherical

-orbits only the sun

- has nothing to clear and defaults to planet status

The mere happenstance of not having enough objects in the neighborhood shouldn't default planets that are marginally larger than Pluto.

Something seems amiss about the definition. I really don't care anymore what they call Pluto. I'm more excited by exoplanets and moons these days anyway.

[Duke87 1,070]

Um, you can too observe empirically and and objectively whether or not an object has cleared its neighborhood. Not by looking at the object, but rather by looking around it. Simply put:

Is there anything similar to it orbiting nearby it?

Planets either orbit a star alone or have everything else nearby orbiting them. With the asteroid and kuiper belts, this is not the case. You have a bunch of objects all orbiting the sun in the same region, not just one.

How is that not an objective difference?

[krbe 193]

It might resemble Nazi terminology, but Alan Stern, who himself is opposed to the reclassification of Pluto and has noted that several planets haven't entirely cleared their neighbourhoods came up with another definition in 2000, which is perhaps closer to reality:

Hence, we define an

[Patricius Maximus 236]

Um, you can too observe empirically and and objectively whether or not an object has cleared its neighborhood. Not by looking at the object, but rather by looking around it. Simply put:

Is there anything similar to it orbiting nearby it?quote>

How do you objectively define "nearby" and "neighbourhood" with natural phonomena?

You cannot. So, my statement is correct.

No, it doesn't, it shows that the IAU wanted a definition for our own solar system. If I'm right they're currently considering how to classify objects in other solar systems.quote>

It does. Since the IAU is going to apply one definition to our solar system, and another to others, that shows heliocentrism. Other solar systems are not different than our own in terms of planets and characteristics of them. Why should they be classified differently?

[krbe 193]

Not different? So all of them contains different types of planets, Kuiper Belts, astroids, dwarf planets, plutoides, etc.? Would a double star solar system's objects necessarily share characteristica with our solar system?

[Patricius Maximus 236]

I am saying that they are made out of the same materials, and have the same physical laws governing them.

There should be different classes of planets for different types, such as Hot Jupiters. There should be one scheme for classfiying planets both in our Solar System and in others. There could be a Hot Jupiter class in a classification scheme; it's just that we don't have any in our system.

That's what I meant. I did not mean that every star system is a clone of ours.

[fukuda 351]

This marks a streak of geocentrism among the IAUquote>

Not again, use words wisely, please. "Geocentrism" and "Heliocentrism" have nothing to do with this.

The argument that the IAU definition is objective is baseless. How can the opinions of a select group be objective?quote>

I lost the argumentation here, why they can't be objective? And why the opinions of an individual are more objective?

Natural phonomena are undisputable because no one can deny that they exist.quote>

Like interstellar plasma, I guess.

You can observe objectively if an object is not a star.quote>

Actually not, there's quite an argument to differentiate between huge jupiters and brown dwarfs.

Some examples of planet categories are, Oceanic, Terrestrial, Gas Giant, and Ice Dwarf. These can have objective criteria just as a planet definition can.quote>

Really? At wich % of water coverage of a planet it becomes an oceanic planet? It's subjective, too, you can say at 90% or at 95% or even at 98%, the number you choose has nothing to do with reality, it's just to put a limit inbetween them.

With the added clarification of a planet having to "clear its neighborhood," would that make reclassify Earth in the far flung future when the barycentre of the Earth-Moon system is no lunger just under the Earth's surface due to the outward movement of the moon?quote>

Don't worry, it's not going to happen anytime soon. there won't be humans to reclassify it anyway.

How do you objectively define "nearby" and "neighbourhood" with natural phonomena?

You cannot. So, my statement is correct.quote>

Uh, yes we can. It's neighborhood is defined as the zone (usually disc-like) where any other object than the planet is driven by its gravity "field" and sees its trajectory modified by it. Look at the asteroid belt, you see its disc-like shape? It's because its stuck inbetween Jupiter's and Mars's neigborhood zones.

When bodies catch another body into its gravity zone and force it to orbit them, it becomes a satellite and the neighboring zone is cleane again as they both reach equilibrium.

Since the IAU is going to apply one definition to our solar system, and another to others, that shows heliocentrism.quote>

Sorry, but I don't see the relationship between believing that the Sun is the center of the universe and calling bodies in other systems with different names...

Other solar systems are not different than our own in terms of planets and characteristics of them.quote>

It's just faith or that we already know everything about the universe?

I am saying that they are made out of the same materials, and have the same physical laws governing them.quote>

Err the first assumption is a bit risky to take yet, as far as we know, there could be at least 2 types of terrestrial planets, silica-based (like Earth) and carbon-based. And tons more of possibilities open when looking about gaseous planets. Only better light collectors (telescopes) to do more accurate stectrometry will tell.

[Duke87 1,070]

Originally posted by: Patricius Maximus

Um, you can too observe empirically and and objectively whether or not an object has cleared its neighborhood. Not by looking at the object, but rather by looking around it. Simply put:

Is there anything similar to it orbiting nearby it?quote>

How do you objectively define "nearby" and "neighbourhood" with natural phonomena?

You cannot. So, my statement is correct.quote>

Okay, let me rephrase that:

Do you heave a single object in orbit or a group of objects collectively in orbit?

You're not going to deny that there is a clear and obvious difference between this:

and this:

are you?

They are clearly two different situations. It would be silly to classify them as the same thing.

[crayzzgoalee 0]

My Very Eldery Mother Just Served Us Nine ...

[Duke87 1,070]

Science doesn't care whether or not the old mnemonic still works.

Also, isn't it "my very educated mother"?

[Patricius Maximus 236]

You are oversimplifing the Kuiper Belt. While I do not deny that there is a difference between the two pictures you just mentioned, the two pictures mentioned oversimplify the matter.

For instance, we have a body eligible in the Asteroid belt for planet status (or dwarf planet status). This object is Ceres. You haven't grumbled about that object being a member of the Main Belt. But you have expressed disapproval over many more objects in the Kuiper Belt. Where is the rationality in that?

Also, in your second diagram, not all of the KBO's are like the irregular asteroids. They are spherical objects. I find no scientific rationale that would disqualify these objects from being planets.

The objects mentioned are not in the same orbit. They have their own orbits around the Sun.

And you have not defined how large the group of objects has to be. Under your definition of "clearing the neighbourhood", many more objects, including Earth, Jupiter, and Neptune would be classed as "dwarf planets".

This only supports what I said about the objectivity of the term "clearing the neighbourhood". Since you cannot observe it objectively, it has to be deferred to the IAU, which is not objective.

A definition of a planet must depend on physically observable natural phonomena intrinsic to the planet. Is a star turned into a "dwarf star" because there are more around it? Is a galaxy turned into a "dwarf galaxy" when it's in a close cluster?

We accept large numbers of stars, galaxies, and black holes, but there is some kind of blockage in some people's minds to having large numbers of planets; probably because Earth is a planet, and people want to be in a special planet club with a limited number of members. Is this Science? I don't think so.

For furthur reading, click here to go to the New Horizons web site and read the team's and Alan Stern's take on the definition.

- Patricius Maximus

[krbe 193]

He's linking to a piece from the Space Review; where he's telling us " it is becoming clear that Pluto was the advance harbinger of a populous new region of the solar system lying beyond the giant planets." He also tells us that he suspect these new discoveries, in addition to Pluto and Neptune's moon Triton to be formed from impacts between fomerly large objects orbiting the sun (and he also points to the tilt of Uranus and Neptune). Further, he points to the vast differences between the outer and inner region. Wether you call them planets or not, they're diffrent.

Besides, as I've said before, he's had his own take on this before, classifying them in

[fukuda 351]

I would have er.. chosen an author a bit more neutral than Alan Stern, who has personal interests in Pluto, to make a point.

[Patricius Maximus 236]

I pointed it out because I thought it was interesting article to read. I did not say that he was neutral, or supported my statements.

There is also Michael Brown, discoverer of Eris. You could argue he has a personal interest, but he supports the IAU definiton.

I thought that I'd point out the New Horizons probject's arguments about the definition, since they'd now be sending a probe to a "dwarf planet".

I was not trying to make a point when I linked to the article.

[Duke87 1,070]

Originally posted by: Patricius Maximus

For instance, we have a body eligible in the Asteroid belt for planet status (or dwarf planet status). This object is Ceres. You haven't grumbled about that object being a member of the Main Belt. But you have expressed disapproval over many more objects in the Kuiper Belt. Where is the rationality in that? quote>

In case you didn't notice, I did mention the story of how Ceres used to be considered a planet earlier.

And I fail to see where this inconsistency of approval is. Ceres is an asteroid. Pluto and those other such things out there are KBOs. Where is the inconsistency?

Also, in your second diagram, not all of the KBO's are like the irregular asteroids. They are spherical objects. I find no scientific rationale that would disqualify these objects from being planets. quote>

Ceres is round too, you know.

The objects mentioned are not in the same orbit. They have their own orbits around the Sun.quote>

Two objects naturally having the exact same orbit would be a highly improbable occurrence, certainly.

But it's not that they don't have their own orbits, it's that their orbits greatly overlap and come into proximity with the orbits of other similar objects.

And you have not defined how large the group of objects has to be. Under your definition of "clearing the neighbourhood", many more objects, including Earth, Jupiter, and Neptune would be classed as "dwarf planets".quote>

How exactly would Earth and Neptune end up in that group? I can see where you're coming from with Jupiter due to the Trojan Asteroids, but bear in mind that that's hardly the same thing as being a belt of objects instead of a planet since:

1) The Trojans don't stretch all the way around the sun. They're just two small clusters.

2) They never get very close to Jupiter at all since they orbit well in front of and behind it.

3) Jupiter is so much bigger than them.

The difference may be hard to define objectively based on something that isn't arbitrary, but nevertheless there is a clear difference.

And then we have this idea of having "uberplanets" and "unterplanets". Well, um, how exactly is that any different from having "planets" and "dwarf planets"? That is exactly what we have, after all. And in any case, this definition even has objects of the two belts eligible for the latter classification. Sure, it's round like a planet, but it's too small to be a planet. And the name given to it describes it as just that: a "small planet" (except we use the word "dwarf" instead of "small").

You could even make the argument that under the current definition, Pluto and all those other such things are planets. I mean, their classification has the word "planet" in the name!

---

Okay, let's try this. What do you people think of this classification hierarchy?

Planet: an object orbiting a star which is in hydrostatic equilibrium.

Dwarf Planet: a planet with a radius less than or equal to 2000 km

              ¤In our star system: Ceres, Pluto, Makemake, Eris

Midsize Planet: a planet with a radius greater than 2000 km and less than 20000 km

              ¤In our star system: Mercury, Venus, Earth, Mars

Giant Planet: a planet with a radius greater than or equal to 20000 km

              ¤In our star system: Jupiter, Saturn, Uranus, Neptune

That sound fair enough?

[fukuda 351]

How exactly would Earth and Neptune end up in that group? I can see where you're coming from with Jupiter due to the Trojan Asteroids, but bear in mind that that's hardly the same thing as being a belt of objects instead of a planet since:

1) The Trojans don't stretch all the way around the sun. They're just two small clusters.

2) They never get very close to Jupiter at all since they orbit well in front of and behind it.

3) Jupiter is so much bigger than them.

quote>

Well, the thing is that Trojans are in the Lagrange Points, so they are already in equilibrium with Jupiter, they are not orbiting around him, but Jupiter captured them

For a longer, yet simple, explanation go here:

http://www.physics.montana.edu/faculty/cornish/lagrange.html