BREAKING NEWS - IAU Vote

As for 'verbal manipulation', there hasn't been any. There was never a definition of a planet before now.

Up to now any discovery was decided on its own merit without any definition. For example Ceres was once a planet, but after more asteroids (SSSB's ) were discovered its status was downgraded and the term asteroid was coined.

The discovery of Xena and Sedna in recent years would have merited a similar individual discussion. But it was decided a few years back that a definition to work with should be devised before any discussion on their status took place.

So we have 5a:

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

(1) A planet1 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) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

1c is the critical point. I assume that its meant to implicitly exclude satellites. However according to the media reports it is this aspect that rules pluto out as a planet, since it impinges on neptunes orbit. If thats the case it can logically be argued that Neptune, by implication, has not cleared the neighbourhood around its orbit either.

Resolution 6b

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

Is therefore needed to create the fudge to exclude Pluto.

Rejecting 5B and 6B are sensible. Though I'd have preferred 6 to be rejected altogether. I don't think it ads anything.

Its easy enough to come up with nit-picking points regarding 5A. Though in our solar system I can see why its written the way it is. The IAU wanted to come up with a defintion that would have 8 planets.

So the IAU conference passes us by and we are left a little worse off than we were. The oppertunity to pass a definition based on physics was passed over in favour of a definition that preserves a classical view of the solar system. In doing so they have produced a rule that is usless for extra solar planetary descriptions; and give our poor understanding of planetary system formation may even not be useful for our solar system in the coming years.

To be honest I dont care whether Pluto is called a planet or not. Once we are consistent. One of the initial drafts simply required that a planet orbit the sun and has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape. Sure it would have given us lots of planets!, but at least its scientific and free from historic prejudice and scentimental classical views. Unfortunately the sentimental view persisted and we have a fudge of a definition to preserve it.

Pluto lasted 76 years as a planet which is longer than I think this definition will last. As our understanding of planetary systems improves with better scans of our own system as well as better data coming from extra solar planets I think there will be a push to open this pandoras box again to create a unified scientific definition.

The world must really think astronomers are just cataloguers of space at this stage. For once being a cosmologist seems a sensibile thing!

Cheers,
~Al

the cosmologists have it easy. they wait until the astronomers discover something and then say "i told you so, i've just come up with the same idea myself on the back of an envelope" . we have yet to see one of them come up with a definition .

Eamonn, sorry, Al

I'm sure this will come out in the wash on Sunday but I see 5A as based on nothing but science. I don't see any non-science in there?

The argument around clearing its 'neigbourhood' is interesting though I uderstood that 5A is the clincher for Pluto not being a planet and being a Dwarf Planet. I guess that Neptune has cleared its own neighborhood but Pluto has not. The fact their orbits cross is, I assume, a non-issue. Their orbits cross, but the two objects do not (there's be a helluva bang if they did).

6A simply sets up a new category (name to be determined) and recognises Pluto as the prototype for that category. I don't see it as a fudge.

So, now we have the stage set for Sunday, I'm going to keep my arguments close to my chest in the interests of a Kenny-Ahern shoot-out for the delectation of IFAS members (or should that be affiliates?)

Dave

As for 'verbal manipulation', there hasn't been any. There was never a definition of a planet before now.

Up to now any discovery was decided on its own merit without any definition. For example Ceres was once a planet, but after more asteroids (SSSB's ) were discovered its status was downgraded and the term asteroid was coined.

The discovery of Xena and Sedna in recent years would have merited a similar individual discussion. But it was decided a few years back that a definition to work with should be devised before any discussion on their status took place.

Sorry Al, missed the point. Are you saying that there is/has been verbal manipulation of an 'unwritten' definition? Or are you agreeing that there wasn't a definition before now and therefore there could not have been verbal manipulation...

There most certainly was a "definition" of a planet before now...going back to when the ancient Greeks mentioned the "wanderers" among the stars.
If a group of geologists decide to give their own definition of a mountain that does not mean that "mountain" never previously had a "definition".

Every language on Earth has a different name for the Earth.

It is unimportant what people CALL things:

" A rose by any other name would smell as sweet"
Poet: Shakespeare.

There were no Shakespeares among that lot.
"An asteroid by any other name would smell as sweet".
Poet: pmgisme.

Sorry Al, missed the point. Are you saying that there is/has been verbal manipulation of an 'unwritten' definition? Or are you agreeing that there wasn't a definition before now and therefore there could not have been verbal manipulation...

Agreeing with you about there not being a definition before; was just putting osme context on it. I understand that thay may come as a shock

I do think that the definition was written after a decision was made rather that starting from first principles with the physics. But like I've said many times before on this subject, a rose by any other name is still a rose. Pluto, Xena, Ceres etc. are not going to suddenly change orbit and go to another star just because the IAU changed their names!

At least the conference is over and they decided something!