Pluto Demoted

[oDDity]

I was right, they have demoted pluto from the status of planet

http://www.space.com/scienceastronomy/0609...roidnumber.html

Pluto is not much smaller than Mercury, and its orbit at its closest to the sun actually brings it closer to the sun than Neptune. The I dont see a problem with Ceres being defined as a planet... The problem is there are a lot of objects in the Solar system (not to mention other star systems) that just don't easily fit into any simple categories. I personally like the definition of a planet as any object with sufficient mass to be roughly spherical. Obviously that would then include the moon and a large number of planetary satellites, but all of these definitons are arbitrary anyway, so we shouldn't get too hung up on what constitutes a planet and what doesn't (after all, they are just labels - they have no practical relevance at all).

 

Perhaps Mercury should also be demoted from its planetary status - after all it is smaller than some of the moons of Jupiter and Saturn.

Heh, time you eat your hat, you spent about 2 pages arguing with me on this one.

[Dram]

God, they were talking about this about a year ago, it's just that they wanted to wait. I am interested in the universe so I always like to check out this crap. Try Celestia educational version - VERY information-rich

[sparhawk]

Well. If Pluto is pissed off about it, it still takes some time until it stops orbiting sun once it knows about it.

[demagogue]

Well, science is science. No place for politics in a decision like this. (edit: I'm actually being ironic in saying this; I tend to think it's *mostly* a kind of politics and science is playing a supporting role at best.)

I suppose to be consistent we ought to stop kidding ourselves and similarly admit that Europe and Asia are (scientifically speaking, you know, since this is entirely a scientific question) one continent (Eurasia) and Australia merely the largest island.

 

 

 

As for my real opinion, I agree with a lot of the scientists from the recent conference that actually this isn't an important, or even very relevant, issue to science at all, since it is about nomenclature ... while most of the scientific debate is about the processes that create solar systems, which this decision will hardly effect. It's about the same way in which geology isn't about continents so much as plate techtonics, and whether you label some land masses as continents vs. islands, the theory doesn't care so much. Nomenclature is largely just for social uses or human-centered purposes, which is why it has to bend to both science (the facts on the ground) and a lilttle politics. But anyway, apparently this decision has been coming for a long time, scientists just feel more comfortable being a little consistent if they're going to claim authority based on reason, so it's no surprise ... and no one is really in a position to seriously disagree with them. So it goes.

Edited September 15, 2006 by demagogue

[Komag]

I've always thought that Pluto has no business being called a planet. It's not just "not much smaller than Mercury", rather it's a LOT smaller. It's mass is around 1/20 of Mercury, it's diameter is less than half, making the 2D surface area appearance less than 1/4 Mercury.

 

But more than that is it's location - way out there past all the gas giants, it's clearly just a large asteriod. You have the inner planets, small and rocky, then the gas giants, then this little puny twerp Pluto.

 

To top it off, it doesn't follow the plane of revolution of all the other planets, it's over 17% off! It's on it's own. Sorry Pluto, goodbye dude, you never should have been invited to the party, our bad.

 

I know my point of view isn't exactly scientific, but it's just based on my own personal "duh" factor.

[oDDity]

Like I was arguing with obscurus before, Pluto is nothing but one of thousands of Kuiper belt objects.

[obscurus]

Like I was arguing with obscurus before, Pluto is nothing but one of thousands of Kuiper belt objects.

 

 

This decision is unlikely to stand for long, because by the new definition the retards at the IAU have come up with, now technically, Earth, Mars, Jupiter, Saturn, Neptune are no longer planets because they have failed to "clear their neighbourhoods of other object". Venus rotates the wrong way to be a planet under the new definition. And the same goes for about 50+ extrasolar planets, becaue they don't happen to orbit around the Sun.

 

Of course it is all arbitrary semantics anyway, but the definition they have come up with for planets is the most inconsistent, unscientific rubbish I have ever heard.

 

This ruling by the IAU will almost certainly be overturned at the next meeting of the IAU, as most astronomers are more than a little bemused by it, and think the decision was very poor and based on emotion, not reason (they simply coundn't handle the idea of there being thousands of planets and having to come up with names for them).

 

Defining a planet in terms of its orbit, whether it has asteroids near it etc is just plain stupid. Really stupid.

 

A definition of an object should stand regardless of where the object is or what it is doing. A planet is a planet whether it is orbiting close to a star or drifting a trillion light years from any other object. It should be definable in terms of universal physical constants, hence, defining a planet as an object that becomes roughly spherical under the gravitation of its own mass is the best and least arbitrary definition.

 

Just as I am defined as a human being by my anatomical features, so should a planet be defined in terms of its physical features alone, and not those of things that may or may not be near it.

 

And there is no reason Pluto cannot be both a planet AND a Kupier belt object, just as Jupiter is both a planet AND a brown dwarf star, just as I am a human being and an Australian.

[oDDity]

It may be semantics, but the point in that last year the correct answer to the question 'how many planets are there in the solar system' was 9, but now it's '8'.

All names are semantics really, but you need them to distinguish one thing from another, so they're pretty useful.

[obscurus]

It may be semantics, but the point in that last year the correct answer to the question 'how many planets are there in the solar system' was 9, but now it's '8'.

All names are semantics really, but you need them to distinguish one thing from another, so they're pretty useful.

 

 

Yes, but now we have a semantic definition for planets that is utterly useless. I mean really, utterly, incomprehensibly useless. And by the new definition of what constitutes a planet, it is more like 2 or 3 planets now, as under the new definition, almost everything that anyone would consider to be a planet fails to meet the standard. Vague wishy-washy definitions like "clearing the neighbourhood of objects" have no place in science.

 

If a biologist tried to apply the same type of definition to a new species, they would be rightly ridiculed. A definition of a class of objects is useless if you cannot use the terms to define something in isolation. The new IAU nomenclature is equivalent to classing whales as fish becasue they live in the sea, and bats as birds because they fly. It would be better to simply class all big round things that don't emit more energy than they absorb as planets, then create subclasses from that in a hierarchy of terms, the way living organisms are classified.

 

Now, we have to come up with a new term to describe any object that is in nearly every way identical to say, Earth, but just doesn't happen to be orbiting the Sun, or is "too far away" or some such irrelevant nonesense.

 

What do you call an earth-like object orbiting another star now? Under the new IAU definition, it can't be a planet, simply as it is not orbiting the Sun. That is just retarded. Are you going to invent a whole new class of objects for every star system that has a planet-like object orbiting it? What do you call a planet not orbiting anything? This creates entirely unnecessary and unwieldy classification problems.

 

You can expect this definition to substantially change.

 

I would be quite happy if the IAU chose to refer to Mercury, Pluto, Charon, Xena et al as "Minor Solar Planets" and Venus, Earth, Jupiter, Saturn, Uranus and Neptune as "Major Solar Planets", since it allows you to have your small number of important solar bodies separate from the multitude of other planetoids without resorting to dodgy semantics and kludgy, unworkable definitions and classification systems.

 

Pluto is a planet by any sane definition. It might be a minor and fairly insignificant planet, and it can be both a planet and a Kupier belt object, but it is still big enough to form a round shape under its own gravity, and does not emit more radiation than it receives, so a planet it is AFAIAC.

[Darkness_Falls]

I agree that their new definition of a planet is left too wide open. They had a chance to make something very clear-cut and they failed. Don't get me wrong, I'm okay with Pluto being demoted. But I want it to be after the creation of a very absolute definition of a planet that is not open to interpretation and that does not rule out our planets or any others like them.

 

Well, science is science. No place for politics in a decision like this.

Politics, no; but semantics, yes. They really flubbed up the definition, imo.

 

Bottom line... I hope they have a slightly more detailed definition somewhere, because as it is read at http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html, I think that it might be flawed. What if there was an asteroid belt going through a Jupiter-like (or whatever) planet's orbit somewhere in the Universe. And what if there were numerous asteroids in that belt; and the belt stretched thousands or millions of light-years or some crazy thing. Each year that planet would end up going through the pathway of the belt; and each year it would hit new asteroids; but it would never clear it away. At least not for many many many years; or never. Are they saying it shouldn't be planet? Hmm...

 

Oops, nevermind. I see they say "In our solar system".

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, ( 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.

[Komag]

We call things whatever we WANT to call them. Our language is simply what we say, and that's that. Tradition, semantics, politics, all of those are valid things that affect our language. If you only want cold hard science to rule the day then life would be pretty drab.

 

For instance, if we simply took a big poll and voted on what we should call planets, that is just as legitimate and valid as some strong and consistent scientific definition. It's not stupid, it's humanity.

[Vadrosaul]

Now if we could only reach one of these planets/planetoids/celestial objects, not just the one circling Earth 400K clicks away

[obscurus]

I agree that their new definition of a planet is left too wide open.

 

Quite the contrary, they made a definition that was far too narrow, and even then, one of the criteria for planethood is so vague and poorly defined that you can fudge anything in or out on a whim. It has nothing to do with science.

 

Bottom line... I hope they have a slightly more detailed definition somewhere, because as it is read at http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html, I think that it might be flawed. What if there was an asteroid belt going through a Jupiter-like (or whatever) planet's orbit somewhere in the Universe. And what if there were numerous asteroids in that belt; and the belt stretched thousands or millions of light-years or some crazy thing. Each year that planet would end up going through the pathway of the belt; and each year it would hit new asteroids; but it would never clear it away. At least not for many many many years; or never. Are they saying it shouldn't be planet? Hmm...

 

 

This is exactly what is happening - most of the planets (especially Jupiter and Mars) routinely cross the orbits of a range of objects, and pretty much every planet crosses the orbit of some other body at some point or another. So by the very definition set by the IAU, you can scrub Earth, Mars, Jupiter, Saturn, Uranus, and probably Neptune off the list, because the criteria for planethood are now so vague and open to interpretation that you can fudge all kinds of things to justify some object not being a planet.

 

A definition of planethood should have nothing to do with how close it is to a star, what angle it orbits it at or anything else that cannot be observed in isoloation.

 

Suppose some object passing through the Solar system ripped Mars out of its current orbit into a new orbit in the Kupier belt, and at a wildly different angle to the orbit of the other planets. Would you then say it isn't a planet, because it no longer sits in some arbitrary orbit?

 

A hierarchical classification system similar to the one used to classify living things is appropriate, even if it means that the number of known planets in the Solar system shoots up to twenty million. A classification system based purely on an emotional dislike of Pluto and other large objects in the Kupier Belt is grossly inappropriate and has no place in serious scientific discussion.

 

I should point out that the vote was very close, and had more Astronomers bothered to participate (most Astronomers regard the IAU as a bunch of largely irrelevant wankers, so they don't often participate unfortunately), the definition I am endorsing would have gotten up (it looked like it would for a while), and you would have had to add another 3 planets at minimum (not counting the 50+ known extrasolar planets that have now been demoted to who knows what).

 

 

From the IAU website:

"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 (c ) has cleared the neighbourhood around its orbit."

 

a - What about objects orbiting stars other than the Sun? After all, there are over 50 (and counting) things that used to be called planets orbiting other stars. Now we have to come up with a new classification for them as well. Stupid, stupid, stupid. Does not exclude Pluto, however.

b - I agree with this one, this is the only part they got right, and it certainly does not exclude Pluto.

c - WTF? This excludes just about everything, including the Earth as being a planet - by this criterion, only Mercury makes it in. But it is so arbitrary and vague - you could take this to mean just about anything.

 

From the IAU website:

"(1) A "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, and (c ) 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 , (c ) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

 

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

 

This is a needlessly complicated definition. They should have used a nested, hierarchical classification system, that used simple terminology for each class. The above classification system is contrived soley for the purpose of excluding Pluto and other objects, and serves no other purpose. It is useless for any other practical purpose.

 

They didn't define satellite very well either - a planet is still a satellite of a star, and this bizarre scheme puts a lot of objects into a wierd classification limbo.

 

This would not happen if they used a hierarchical classification system, where an object can fit into several categories at once.

Edited September 13, 2006 by obscurus

[obscurus]

We call things whatever we WANT to call them. Our language is simply what we say, and that's that. Tradition, semantics, politics, all of those are valid things that affect our language. If you only want cold hard science to rule the day then life would be pretty drab.

 

For instance, if we simply took a big poll and voted on what we should call planets, that is just as legitimate and valid as some strong and consistent scientific definition. It's not stupid, it's humanity.

 

Sure you are correct insofar as we can arbitrarily call anything by any name we like.

 

But you are wrong about it not being stupid. It is stupid because the definition is unclear and vague. If they had come up with a consistent, logically tenable system for classifying stellar objects that happened to change Pluto's object class, I would be fine with that. As a biologist, I'm used to the classification of organisms changing as the need for further distinciton is required, or more information makes old classification schemes unworkable.

 

And that is the other reason why the IAU's decision is stupid. It is unworkable. It creates a situation where it is extremely difficult to know what someone is talking about when they say "planet", and it will take an inordinately long time to work out whether an object meets criterion C of the scheme, since it is unclear about what it means, and it is difficult to assess how many objects are in the neighbourhood of another object, and what you define as the "neighbourhood" of a planet or otherwise. And it makes it difficult for astronomers to classify extrasolar objects, because the IAU in its typically narrowminded way failed to consider objects beyond the orbit of Sol.

 

A classification sheme isn't just for the purpose of having fancy names to muse over. It is a functional system for communicating useful information, and analysing the world. Scientific terminology needs to be much more rigorously thought out than just any old twit arbitrarily naming things as they please.

[Komag]

If they went with your better definition, how round would be round enough? "That lump is too big, it's not a planet!" "Yes it is, a speroid doesn't have to be perfectly sperical you idiot!" Where to draw the line?

[obscurus]

If they went with your better definition, how round would be round enough? "That lump is too big, it's not a planet!" "Yes it is, a speroid doesn't have to be perfectly sperical you idiot!" Where to draw the line?

 

 

They did go with my definition (see criterion b ), they just tacked a lot of useless fluff onto it that just about rendered the final definition worthless. I would simply scrap a ) and c ) of the IAU definition.

 

But you are correct, there is a bit of arbitrariness here. Saturn is substantially out of round - you could arguably say it isn't round enough to be a planet. So you would have to take a somewhat arbitrary ratio of the polar radius and the equatorial radius as your definition of "round", taking into acount the rotational velocity of the planet, as this will distort the "roundness" - if Saturn were to stop spinning on its axis (and had no rings or satellites), it would become perfectly round. You can't avoid being arbitrary here, but you can minimise the degree by avoiding vague, poorly thought out classification systems.

 

Regardless, the criterion of roundness is far less arbitrary and far more scientifically based than the other two that were tacked on. a ) is no good because an objects orbit should be irrelevant to its clasification, and at the very least "Sun" should be changed to "Star" in order to include other planetary systems, c ) is no good because it is too vague and poorly defined.

Edited September 13, 2006 by obscurus

[Darkness_Falls]

Obscurus wrote: Quite the contrary, they made a definition that was far too narrow, and even then, one of the criteria for planethood is so vague and poorly defined that you can fudge anything in or out on a whim. It has nothing to do with science.

I think we're agreeing actually. I say they left it too wide open (for interpretation), and you agree that things can be fudged. So we agree.

 

You're right, this whole thing about it needs to be around "the Sun" is rediculous. A planet shouldn't be restricted to our solar system. There should be exact criteria set forth what is necessary to qualify and quantify a near-spherical object as being a planet anywhere in the universe. There are several ways it could've been made clearer

 

Komag wrote: We call things whatever we WANT to call them. Our language is simply what we say, and that's that. Tradition, semantics, politics, all of those are valid things that affect our language.

We do call things what we want them, but I think most dictionaries aim to provide absolute definitions to leave little room for interpretation. As does science. What use is it to try to explain to someone what a "rock" is, only to find some people interpret a rock as a plastic ball, while others define it as a styrofoam sphere? The purpose of definitions is to try to get everyone on the same page. Not to play a game of semantics every time you talk to someone. Tradition playing a part in science could maybe be construed as religious-like. If science creates a definition for a planet that leaves no room for interpretation and it is accepted, and Pluto is no longer classified as a planet, then Pluto should be disqualified as a planet. The tradition of how I was taught in 3rd grade that Pluto is a planet should have no bearing on whether or not Pluto should always be considered a planet. (PS: I still feel their new definition of a planet bites.)

 

If you only want cold hard science to rule the day then life would be pretty drab.

I think you're confusing science with hospitals... Without science, you would have no clue how to make airplanes fly; computers wouldn't be here; the Earth would still be the center of the Universe, and flat; your car would only work if it was pushed down a hill; and you'd be reading this message by candlelight via a hand-written page I sent off to you a couple months ago. I'm not saying science should rule the day. But in terms of defining a planet, I think it's maybe best to use scientific observations and extrapolating the best definition based on those observations, rather than having George Bush and Putin deciding in a summit meeting how to define planets (political), or having the general population define it based on what they were taught in grade school (tradition).

[oDDity]

I would be quite happy if the IAU chose to refer to Mercury, Pluto, Charon, Xena et al as "Minor Solar Planets" and Venus, Earth, Jupiter, Saturn, Uranus and Neptune as "Major Solar Planets", since it allows you to have your small number of important solar bodies separate from the multitude of other planetoids without resorting to dodgy semantics and kludgy, unworkable definitions and classification systems

 

That would suit me as well. As long as there's e clear distinction between real planets and tiny balls of ice that just happen to be orbiting the same star.

Not really up to us though, any more than deciding that blue is called blue and not red. Some one else decided, and we just go with the flow.

 

Aside from that, I just don't think aball of ice should ever be called a planet, no matter how round it is or what it's orbiting.

One good way to define it would be if it has, or used to have a core above a certain temerature - like all the real planets did. This excludes any ball of ice for obvious reasons.

[Dram]

Jupiter is both a planet AND a brown dwarf star

 

No it's not. Our sun is a third generation star, which means it formed from a nebula of a previous, second generation star. When the nebula started re-collapsing due to gravity, it forms a small star at the centre which slowly gets more and more material and grows in size and temperature. As material spirals in it forms a large disc around the sun, which has several rings of different types of material. Our Earth was on the closer rings which contained more iron and rock and thus is solid, Jupiter formed in a gaseous ring and thus is gaseous. It was never a star, nor can it be defined as one. You can't make a pear into an apple, you might be able to cut it and make it look like one, but it'll never BE an apple.

[oDDity]

He's right, only objects 12 times as massive as Jupiter are called brown dwarfs.

[obscurus]

No it's not. Our sun is a third generation star, which means it formed from a nebula of a previous, second generation star. When the nebula started re-collapsing due to gravity, it forms a small star at the centre which slowly gets more and more material and grows in size and temperature. As material spirals in it forms a large disc around the sun, which has several rings of different types of material. Our Earth was on the closer rings which contained more iron and rock and thus is solid, Jupiter formed in a gaseous ring and thus is gaseous. It was never a star, nor can it be defined as one. You can't make a pear into an apple, you might be able to cut it and make it look like one, but it'll never BE an apple.

 

 

That depends on your definition, and there are a few floating around. Many astronomers would classify Jupiter as a Brown Dwarf for the simple reason that it emits more energy than it receives form the Sun.

 

And many models of Solar System formation predict that the Earth was once more like a gas giant, having a much thicker atmosphere than it did now.

 

However, recent discoveries of extrasolar planets have put most of the more popular theories of planetary formation in the garbage bin.

 

oDDity:

That would suit me as well. As long as there's e clear distinction between real planets and tiny balls of ice that just happen to be orbiting the same star.

Not really up to us though, any more than deciding that blue is called blue and not red. Some one else decided, and we just go with the flow.

 

Aside from that, I just don't think aball of ice should ever be called a planet, no matter how round it is or what it's orbiting.

One good way to define it would be if it has, or used to have a core above a certain temerature - like all the real planets did. This excludes any ball of ice for obvious reasons.

 

The material an object is made of is irrelevant to wether or not you classify it as a planet. That is an entirely arbitrary and pointless distinction. It makes no difference if it is made of ice, granite, methane, peanut butter or brie.

 

And again, it should make no difference what the object is orbiting, or if it is orbiting anything at all - that is irrelevant. Earth would remain a planet if it were flung far into interstellar space, it would be a planet if it was composed entirely of water ice.

 

Defining a planet by the temperature it has, or especially used to have is a monumentally stupid idea. Temperature is irrelevant.

 

 

Again, you are proposing a ridiculously complex and baseless definition of planets purely to satisfy your strange and inexplicable dislike of small icy objects - did you choke on an ice cube or something as a child?

Edited September 13, 2006 by obscurus

[Dram]

And many models of Solar System formation predict that the Earth was once more like a gas giant, having a much thicker atmosphere than it did now.

 

Do you know any links to one of these theories? I'd like to read it, I'm genuinely interested

 

The only theories I've heard (more or less the most accepted ones) was that Earth was always rocky and that a long time ago it collided with Orpheus (a planet bit bigger then our moon) which completely destroyed Orphues and severly damaged Earth. This collision left some parts of Orphues on Earth and some parts of both in a ring around Earth which reformed into the moon. If Earth had been a gas giant this could not have happened, so there's a conflict. Of course, the planet collision theory is not confirmed, nor can it be, but it is the most possible and most likely.

[demagogue]

My favorite (fringe) theory is that some massive body passed through the solar system and in the course ripped off a chunk off of Earth, which fell back to become the moon, the rest of it becoming Pangea.

 

(it also apparently obliterated the planet after Mars (making the asteroid belt), and it ripped off chunks off other planets making their moons, as well, and by looking at the rotational differences of different moons, the guy actually plotted the trajectory and rough planet arrangement, allowing him to date it ... convienently to 65 million years ago, his version of the extinction of dinosaurs, which carries the necessary implication of dino fossils on the moon , and the beginning of Pangea's break-up, as well as weird stuff like out-of-place boulders, what we now usually attribute to glaciers).

 

I don't think it is credible, certainly the dating part (the idea of the gravity of another body pulling off the moon I don't know, but I've never heard it anywhere else, which probably means no one takes it seriously), but I really liked the guy's enthusiasm in putting facts together and seeing how far he could go. It's sort of like recreational psudo-science, trying to figure out where his reasoning works and where it might go astray. Even if a theory is wrong, people may disagree *why* it's wrong, and that itself can be interesting.

Edited September 14, 2006 by demagogue

[obscurus]

Do you know any links to one of these theories? I'd like to read it, I'm genuinely interested

 

The only theories I've heard (more or less the most accepted ones) was that Earth was always rocky and that a long time ago it collided with Orpheus (a planet bit bigger then our moon) which completely destroyed Orphues and severly damaged Earth. This collision left some parts of Orphues on Earth and some parts of both in a ring around Earth which reformed into the moon. If Earth had been a gas giant this could not have happened, so there's a conflict. Of course, the planet collision theory is not confirmed, nor can it be, but it is the most possible and most likely.

 

 

I remember reading it in an article apearing in New Scientist a few years ago. The idea was that the thick atmosphere was quickly stripped off by the solar wind (which would have been much stronger then than it is now) very early in the Earth's history, and Earth was struck by Orpheus later. Supposedly there is some physical evidence to back this up in the concentrations of hydrogen found in rocks, and the fact that Earth still has a strong magnetic field also supports this theory, as strong magnetic fields are expected as a result of rocks being crushed into a superfluid metallic state by tremendous pressure and spinning around, but it has been a while since I read it. I shouldn't have said many theories, as I know of only one for sure. Whoops

 

I think the idea has been somewhat discredited by the discovery of numerous extrasolar Gas Giants orbiting very close to stars. None of the accretion models do a very good job of explaining the characteristics exhibited by these big planets in other systems, so there is plenty of room for any and all solar system formation models to be wrong.

 

 

The fact that Venus has a very slow retrograde orbit indicates that it either collided (or nearly collided) with something very big in the past, or it itself was flung from a very different location and captured into a new orbit by the Sun - it is a big presumption to think it formed where it is now (and this is really the case with all planets). Either way, planets move around, and for all we know, half of the planets in our solar system could have formed in another star system, and were later captured by the Sun.

 

But then this is why orbital patterns should never be used as a criterion for classifying stellar objects, as planets, stars, asteroids etc get flung around so often that you can really only guess at what hapened - there is too much going on to model, and the physics is too complicated for even present day super-computers to handle. The orbit of an object should be completely disregarded as a criterion when deciding whether something is a planet. IMO.

Edited September 14, 2006 by obscurus

[Dram]

That's pretty interesting

 

If you find any more links about this then please post them