Last year we had 9 planets. Recently we were informed it would grow to 12. Now we've only got 8. The International Astronomical Union, currently meeting in Prague, voted on August 24, 2006 to demote Pluto down from planethood status. Now Pluto, Charon, Ceres and the newly discovered 2003 UB313 (aka Xena) will merely be known as "dwarf planets". Under the new definition, planets must orbit a star, be spherical in shape, and clear out their neighbourhood of orbital debris. Pluto has failed to fulfill the third requirement, so it's out of the planet club.

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A very strange verdict I think. I don't see wht Pluto isn't a planet. Its relatively speaking a matter of space. If Pluto has 1/10 the mass relative to another planet and has cleared out an orbit around it to the point where its 1/10 as clear as another planet, would that not make it a planet? Its pretty easy to evaluate for the other 8 planets, as they are easily observed, but it seems that they can't classify Pluto as a planet because they simply aren't sure what Pluto has cleared out of its orbit, simply because it's orbit covers so much area, and we probably haven't viewed enough of the sky to determine what degree of "clear" it is.

I also think it's a bit weird. Okay, Pluto crosses the orbit of Neptune, but you can also say it the other way around. So Neptune's no planet? Also, the orbits are in a 2:3 resonance, so the two bodies will never collide...

At least I hope this will now pave the way for naming 2003 UB 313!!!

Also, the question remains: If we discover something really big, say, larger than Mercury, out there, is that then a planet? This orbit-clearing thing is hard to prove, as has been noted by Leafguy.

Don Alexander

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David Alexander Kann
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With her vast retinue of Trojan asteroids, clearly Jupiter fails the planet definition. Though I am glad that since Earth is still listed as a planet, we no longer need to worry about those pesky "Near Earth Asteroids."

I like it. By their own hand....Earth is no longer a planet...also by the third criterion as Pluto. "clear out their neighborhood of orbital debris"...
http://www.space.com/missionlaunches...le_debris.html

We have ~ 9000 pieces of debris. shifty:

"www.space.com/missionlaunches/050305_shuttle_debris.html"
why does the forum edit my links?Pete

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This planet clearing idea wouldn't be very useful for classifying other systems, and may result in unintended results.

Young Systems may end up with no planets, though common sense would suggest otherwise. What about Tau Ceti?

You would think dwarf would be a size classification.

hmm... saturn has alot of debris arround it.. shouldn`t it be a "dwarf" planet than? so as all the other planets in our solar system..

this description of planets sucks!! and i think that as soon as close by planetary systems has been discovered with big planets and alot debris this description probly needs to be revised again...

o well.. now i can tear apart one of my posters since it`s no longer a planet

I don't understand (3).

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

Ok, this means that asteroids, TNO's, KBO's are all small solar system bodies.

But what about the exception? Specifically the term "satellites orbiting the Sun"? Should this read "satellites orbiting planets"? (which are Moons?)

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With this I would wait for the next meeting of IAU.....

Otherwise a sensible decision.

There really are only 8 planets.

If we lived on a planet orbiting elsewhere in the galaxy and were studying the solar system, we would really only consider the first 8 to be planets, the rest is debris.

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What a load of garbage! By their own hand, this definition has no effect on the status of the Earth - clearly these 9000 pieces of debris you talk about do not dominate the Earth and regulate the orbit the Earth enjoys - for a very simple reason, they're too small and insignificant to do that.

Rather, it is the other way around in this neck of the woods - the Earth effectively dominates this area of Space and the orbits of these Earth-crossing pieces of debris are highly effected by the perturbations of the Earth.

I would like to see you argue there is not a similar thing going on with regards to Neptune and the scores of Plutinos, including Pluto, that orbit in 2:3 resonance. Obviously Neptune has forced these bodies into these resonant orbits and is clearly the dominant object in that area of Space!

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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident." Arthur Schopenhauer - renowned 19th Century German philosopher.

According to the resolution, the wording specifically states:
"...that a “planet” is defined as a celestial body that (a) is in orbit around the Sun..."

The bold on the word "Sun" is my ephasis.

As far as I know the Sun (capital S) refers to Sol - our solar system's star.

So does this mean that there will be a different definition for planets outside of our solar system? Maybe one per solar system?

With all due respect to the IAU (and IMHO), I must say that while I admire their effort to try and more precisely define terms, but I think it has backfired and hasn't been thought out as well as it could have been.

So, when will we find out the definition for extra-solar planets? I'm sure *that* debate will cause controversy based on the wide variety of systems discovered so far...

Just my AUD$0.02.

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Greg
"I told my psychiatrist that everyone hates me. He said I was being ridiculous - everyone hasn't met me yet."
-- Rodney Dangerfield

I once heard that a camel was a horse deseigned by a committee. That is in reference to a group of people never being able to reach a reasonable decision. We now have another great example of what committees are actually unable to do. Reach a sensible decision.

Ray Bingham

Although the IAU hasn't precisely defined 'cleared the neighbourhood around its orbit' only those definitions that are consistent with Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune being planets can be valid. So, for example, 'cleared the neighbourhood around its orbit' does not mean that the Trojan points have to be empty.

Also, the definition of planet given by the IAU is, as it says, only for the purpose of the Solar System, so technically has no application outside it (although it is likely it will be used by analogy).

Ah thank god, we can stop spending money on trying to find a way to save earth from texas size astroids.

obviously they didnt make the definitions vauge enough, just becuse there arent as many objects in the earths orbit, doesnt mean its completely clear of debre, im pretty sure i learned that it was 5 tons of stuff from space that falls to earth each day, or 50 tons, or something crazy like that. i think its more about astronomers wanting to be against the majority and the norm. really this isnt a time for a bunch of astronomers to start back with high school antics. I love the fact that we know there are coments and astroids and meteors that orbits around the sun, in the way of earth, all the apollo objects that orbit around the earth (if im correct on that name) yet, we consider our path "clear"...

why dont we just go back to saying that the earth is the center of the univer, and that the sun orbits around the earth. hell, why dont we all just join the flat earth society (http://www.alaska.net/~clund/e_djubl...rthsociety.htm) and the guys who say earth is a pentagon with a layer underneith the earth were green lizzard people and nazis live... (http://corridorofmadness.net/archives/000084.html)

and lets not all forget, the people who think that the internationl time line was created by the tv companys to make the earth round...(http://www.cca.org/woc/felfat/)

seriously, they've done a horrible thing by using the new "definitions" they make every planet nothing becuse there not all clear. i hope the resolution to change it is passed and the make pluto offically a planet again...

Jkmcrann, when you say that Neptune is the dominant force in that area of space. For an object such as Pluto with a 248 earth year orbit, which only crosses Neptune for something like 7 years I think it was. With such a small percentage, that can't possibly account for Pluto not being a dominant object. That still leaves 275ish years where Pluto is the dominant force in its orbit and should be called a planet.

The fact that it is also a definition solely based on our solar system alone has got to be the stupidest thing I have ever heard. If this scenario happens around another star, Pluto is for sure a planet. What is needed is a constant defined term for planet, not based on whether or not an object is the "dominant force" in a given orbit. Based on that theory, scientists will never be able to truly define a planet until we are physically able to map out space in the given region. They should have stuck with a mathematical category such as minimum 1000km in diameter and the ability to hold itself under its own gravity and isn't locked in gravity like a satellite.

If that is obvious to you, could you explain it? I'd be very interested in hearing the explanation.

[COLOR="Navy"]What??? In my opinion, Pluto should remain a planet!!!! Charon, Xena, and Ceres should be a dwarf planet... But, u guys are astronomers...you know muuuuch more than us. So, I guess you all are right.. But I'm still against this!!!!! [/COLOR Also, it would be interesting 2 know more about your decision.

In the spirit of Occam's razor I think that the decision is a victory for common sense. A KBO is a KBO is a KBO.

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In the spirit of the Occam's razor, the decision is nonsense.
We will need another definition once:
1. A new Kuiper Belt Object is found to be more massive than Mercury... without being the dominant object of its neighbourhood.
2. A new Kuiper Belt Object is found to be far less massive than Pluto... but does have a very stable orbit.

About semantics, it can't be said enough that the general public is a bit confused this morning. The dwarf planets are not "planets". However "dwarf stars" are stars just like dwarfs are people in our societies.
Welcome to the bright new world of 21st century astronomy.

www.sailom.blogspot.com

There seem to be several issues here, not the least of which is that the IAU seems to have made itself less relevant.

Scientific definitions should be reasonably sturdy, given the scientific method and all.

In reference to Beings looking at our solar system from the outside -- Perhaps they classify collections of mineral and gas based upon their greatest constituent instead of mass (hydrocarbon and water ice body). In that way, as we are want to do, the name can be modified by an additional word such as large (Large hydrocarbon and water ice body). Or perhaps they even give it a numeric value related to mass or constituents (400TeraUnits Hydrocarbon 20TeraUnits water ice body). They might have a gift for hyperbole so as to jazz up the names for objects they discover (big as Jack's nose Hydrocarbon water ice body). Simpler still, they might relate it to some objects they are familiar with that have proper names and modify those (88 Earth mass Hydrogen water ice body). It could get even more complicated from here...

Which is the point I'm attempting to make; We have developed so many ways to classify and name things in science. Is it really that hard to come up with a meaningful definition for a collection of matter? I could invent a solution that would reflect both the scientific and the political/historical/cultural significance of all the collections of matter floating in space. There are plenty more folks smarter than me who could do it even better. This isn't about science.

This "planet definition thing" has been, and I suspect will continue to be, a lesson in political science. There isn't much astronomy or planetary phisics going on at the IAU concerning this particular issue.

--these opinions are not reflective of my employer--

73 de N5JYK

i still think this decuision is the better one. with the other definition we would soon have an inflation of planets. using this definition all the planets (of our solar system) are visible in the sky (ok, Neptune..) and are quite differentiated from the debris and dwarf objects.
i would not bother if this definition has any effects on planets of other stars. basically i would refer to them as "extrasolar planets" and everything is ok.

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<span style='color:purple'><span style='font-size:14pt;line-height:100%'><span style='font-family:Impact'>;-)mab</span></span></span>

I think it's long been known Pluto didnt really qualify as a planet due to it being a large Kuiper belt object. Still I think the way it has been demoted is a strage one. As people have said though if something the size of earth was found floating in the kuiper belt then most people would actually call it a planet. It wouldnt exactly be a dwarf planet would it. I think the definitions of a planet are a bit too simple and many arguments could arise from this. Why could a planet not just be classified as a spherical object over a certain size? It would be a very easy definition to understand and I also belive less arguments would arise.

It might be an easy definition to understand, but I have my doubts it would produce less arguments! Where would you draw the line - and on what basis? And astronomers don't like arbitrary definitions - they want some basis on physical properties or phenomena, no matter how vague in practice.

The original IAU definition was one that the planetary geologists would like - as it was basically based on the properties of the object itself. However, dynamicists - astronomers who study the motion and gravitational effects of celestial objects - apparently didn't like it, so they stuck in the cleared the neighbourhood criterion.

I'm just glad that the meeting took place in Europe where a perfectly common-sensical decision was taken. If the meeting had taken place in the USA, Pluto would have remained a planet.....reason? It was only designated a planet in the first place to make America feel on a par with Herschel and the lads. As we all know the Yanks had discovered Jack Nothing, planetary speaking, up to the point where good 'ole Clyde turned up.

Supposedly when the proposed definition was read out to be voted on, an astronomer asked whether Neptune qualified as a planet since it had not "cleared" Plute from it's orbital zone. The answer was that Footnote 1 clearly specified that Mercury, Venus,..., Neptune were all planets.

Someone then suggested that they simply ignore the proposed definition, and instead simply vote on the footnote.

mab- I fully agree that the previous proposal could have openned a can of worms (planets!) and left poor school children having to memorise potentially hundreds or thousands of planet names (not to mention the IAU having to scratch their heads to come up with the names!).

But it is very unscientific to define the term "planet" only in relation to OUR solar system. What makes our system so special (well, apart from the fact we're in it)?

One of the main principles upheld by physics/cosmology for a long time has been the "equivalence principle" which states that there is no "special" reference point in the Universe and that the laws of physics are constant from any vantage point you take. Surely this must mean that a planet is a planet no matter if it is in our solar system or any other. Currently we do not have two definitions for a star - our one and all others?

One day we will get a probe to the Alpha Centauri system and I for one don't want the IAU to have to come up with a seperate definition just for that system- or worse, adjust the current definition to take into account what we find when we inspect it close up.

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Greg
"I told my psychiatrist that everyone hates me. He said I was being ridiculous - everyone hasn't met me yet."
-- Rodney Dangerfield

According to BBC News Online (http://news.bbc.co.uk/2/hi/science/nature/5283956.stm):
The above quote is from Owen Gingerich who I won't repeat the rest of the article, go and have a read yourself, but it puts a whole new spin on things if the above revelation is true.

If true, this ruling looks even less important as before, since it was only voted on by "10%" of the attendees. Not exactly a good sample size.

This whole farce I think is quite humourous to the general public who mostly likely just shrug and laugh at those 'silly scientists' that they can't make their minds up of such a 'simple' definition as a planet.

It's more disturbing to me that this vote was the most important thing that IAU has done in a long time (from the public's point of view), due to the amount of press any decision would generate. In a time when science is under attack from all sides, this whole debacle only serves to fuel the pseudo-scientists, astrologers and the like: 'science can't even define the term planet!'.

I think we have not heard the last of this debate and it would not surprise me to hear at the next IAU meeting that this issue is raised yet again...

*steps off soapbox*

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Greg
"I told my psychiatrist that everyone hates me. He said I was being ridiculous - everyone hasn't met me yet."
-- Rodney Dangerfield

I propose that the definition be accepted by all -- let the astronomers have their 15 minutes of fame -- but allow Pluto to retain its title of planet the way an ex-mayor is forever referred to as "your honor" or an ex-president(even if impeached) is always refered to as Mr President.

This let's everyone and all the history books save a little face, does due honor to the astrnomers and teachers that went before, and allows children to sleep well not thinking that "science" is something utterly arbitary that is voted on like American Idol.

All in favor? So how do we make this happen?

Interesting debate ...

First of all I agree with the point that media makes lot's of buzz from this irrelevant matter, but hey they are there for that kind of things isn't it?
The article in BBC news forgot to mention:

* that there is a committee at IAU and that committee which has right to put a proposal of such kind. Those members of "Planet Committee" are well respected members of astronomical community.

* that only 10% of participant of IAU meeting in Prague are actually IAU members. Which means only they can vote on such kind of matters. To become an IAU member you should prove yourself worthed and it's not only like you pay your memberships.

So the other 90% of astronomers who attend the meeting in Prague are actually attending one or a few minisymposia which are organised along with the IAU general assembly meeting. For many of that participants the general assembly meeting is not only irrelevant, but also boring!

Don't think that all astronomers there can't sleep from that decision or are eager to challenge that. People are attending many very important minisymposia where the actual science is presented (and full stop!)

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