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Fraser
2006-Aug-24, 03:10 PM
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.

Read the full blog entry (http://www.universetoday.com/2006/08/24/plutos-out-of-the-planet-club/)

Leafguy
2006-Aug-24, 05:45 PM
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.

Don Alexander
2006-Aug-24, 06:50 PM
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

joelm
2006-Aug-24, 09:28 PM
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."

trinitree88
2006-Aug-24, 10:31 PM
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"...
www.space.com/missionlaunches/050305_shuttle_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

gazelle1978
2006-Aug-24, 10:55 PM
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.

markg85
2006-Aug-24, 11:27 PM
and clear out their neighbourhood of orbital debris
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 :(

ArgoNavis
2006-Aug-24, 11:31 PM
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?)

Bojan
2006-Aug-24, 11:32 PM
o well.. now i can tear apart one of my posters since it`s no longer a planet :(

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

ArgoNavis
2006-Aug-24, 11:33 PM
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.

jkmccrann
2006-Aug-25, 12:18 AM
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"...
www.space.com/missionlaunches/050305_shuttle_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

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!

paladinsmeg
2006-Aug-25, 12:25 AM
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. :lol:

Ray Bingham
2006-Aug-25, 12:43 AM
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

CuddlySkyGazer
2006-Aug-25, 03:00 AM
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).

What_would_skywalker_do
2006-Aug-25, 03:05 AM
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."

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_djublonskopf/Flatearthsociety.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...

Leafguy
2006-Aug-25, 03:41 AM
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.

hhEb09'1
2006-Aug-25, 04:33 AM
Obviously Neptune has forced these bodies into these resonant orbits If that is obvious to you, could you explain it? I'd be very interested in hearing the explanation.

tulsi704
2006-Aug-25, 04:46 AM
What??? [COLOR="Navy"]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!!!!! :naughty: :evil: :mad: :think: [/COLOR:cry: Also, it would be interesting 2 know more about your decision. :think: :surprised :question:

paulie jay
2006-Aug-25, 06:14 AM
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.

sailom
2006-Aug-25, 06:43 AM
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

N5JYK
2006-Aug-25, 08:01 AM
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

;-)mab
2006-Aug-25, 08:09 AM
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.

dirty_g
2006-Aug-25, 09:47 AM
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.

CuddlySkyGazer
2006-Aug-25, 11:44 AM
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.

diatoms54
2006-Aug-25, 12:21 PM
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.

pghnative
2006-Aug-25, 12:45 PM
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.

paladinsmeg
2006-Aug-25, 01:24 PM
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.

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.

paladinsmeg
2006-Aug-25, 01:48 PM
According to BBC News Online (http://news.bbc.co.uk/2/hi/science/nature/5283956.stm):

There were 2,700 astronomers in Prague during that 10-day period. But only 10% of them voted this afternoon. Those who disagreed and were determined to block the other resolution showed up in larger numbers than those who felt 'oh well, this is just one of those things the IAU is working on'.

The above quote is from Owen Gingerich who
chaired the IAU's planet definition committee and helped draft an initial proposal raising the number of planets from nine to 12

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* :silenced:

joelm
2006-Aug-25, 03:59 PM
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?

Tigran
2006-Aug-25, 04:23 PM
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!)

dirty_g
2006-Aug-25, 04:23 PM
Seriously I think a vote that objects which are spereical and above a certain size should qualify as planets would be better than the one we have now. Why does a planet have to have an orbit? Planet by definition is "wanderer". I cant see why a planet has to hold an orbit. I'm pretty sure there are planets out there which have no star to call their own. What do you classify it as though? A supermassive asteroid?? I can not see the current definitions working well. I just think a planet should be over a certain size. Why do we always have to make things more difficult? Sometimes simpler is better. cheers.

Tigran
2006-Aug-25, 04:32 PM
Here is the link to those meeting, you can check what else is happening in the real astronomy world:

http://www.astronomy2006.com/symposia.php

Galaxy Evolution across the Hubble Time
http://astro.cas.cz/iaus235/

Near Earth Objects, our Celestial Neighbors: Opportunity and Risk
http://adams.dm.unipi.it/iaus236/

Triggered Star Formation in a Turbulent ISM
http://astro.cas.cz/iaus237/

"Black Holes - From Stars to Galaxies"
http://astro.cas.cz/iaus238/

Convection in Astrophysics
http://www.astro.keele.ac.uk/iaus239/

Jerry
2006-Aug-25, 07:27 PM
I Can't help but wonder how the vote would have gone if the ESA had a probe on the way to Pluto, or if Mike Brown were German or Danish. The definition is vague and in my opinion arbitratry: At what point is debris removed from an orbit?

A planet processing at the orbital distance of Pluto will take many more millenia to clean a path that a Mercury. Did Mercury become a planet long before Jupiter? What if Mars collides with a large asteroid and is thrown into a new orbit with a lot of debris. Does Mars cease to be a planet until the orbital path is cleaned up again?

The ancient definition of planet is better: Stars that wander.

edited to add:



The IAU claims to have 8,857 members worldwide. But when it comes to making important decisions - such as deciding what a planet is (or is not) only a very small fraction of that membership was allowed to participate. Only 428 members (less than 5% of IAU's global membership) were allowed to vote."

428 Cardinals, voting on how many angels can stand on the head of a pin.

Astromood
2006-Aug-25, 07:56 PM
I think the part about clearing out debris is aimed at asteroids. The asteroid belt has thousands of members, so does the Kuyper Belt. Neither will be cleared out any time soon if ever. It may also be aimed at extrasolar objects.

It is a little vague. But I agree Pluto is not a planet. If I had any say in the definition I would add that a planet should orbit in or near the plane of the ecliptic in a near-circular orbit. Or that it should have formed from the proto-planetary disk surrounding the young Sun. Kuyper Belt Objects don't orbit in the plane of the ecliptic, suggesting to me that they did not form from the proto-planetary disk but from the general cloud of dust and debris around the original solar nebula. Correct me if I'm wrong.

gazelle1978
2006-Aug-25, 10:19 PM
If a planet has to have a near circular orbit then that would mean alot of the exoplanets discovered are not planets. What do you call those?
Also it is difficult to determine how an exoplanet formed (proto-planetary disk).
I would have gone for a size definition myself. Ceres was already a "minor" planet, why not have a few more past neptune? Pluto goes in that scenario but it keeps things simple

CuddlySkyGazer
2006-Aug-26, 07:42 AM
If a planet has to have a near circular orbit ....
There's nothing in the new definition that says that a planet has to have a near circular orbit.

There are many possible definitions of planet you can come up with. People come up with different ones depending on what they consider to be the most important. It's just that of the people who actually got to vote on this, a majority considered the 'clearing the neighbourhood of its orbit' idea to be important. But they didn't ignore size - it's in there as well.

Dollhopf
2006-Aug-26, 11:56 AM
I Can't help but wonder how the vote would have gone if the ESA had a probe on the way to Pluto, or if Mike Brown were German or Danish.

Your disappointment with the questionable decision to 'degrade' Pluto brings up the question whether words or definitions can influence reality:

Will the scientific data returned by the probe be influenced in any way by calling Pluto either a planet or a planetino? Will that definition cause any loss or gain of information in the antennas of the Deep Space Network?

:naughty: No, because nature is not altered by terms and definitions. But human behavior is, because the problem is a psychologic one. In his book 'The Strategy of Conflict' Thomas Schelling introduced so called 'focal points'. They are keys to 'tacit agreements'. A short time ago, Pluto was such a focal point, a kind of boundary stone. I guess that was tacitly important for the justification and the funding of 'New Horizons'. But that is all done. Meanwhile, the spaceship has left and no one will stop the enterprise because of the annoying outcome of discussions about definitions.

The scientific results of 'New Horizons' are not influenced, but one thing is also obvious. Namely, that propaganda influences the formulation of scientific goals.

Chuck
2006-Aug-26, 03:25 PM
http://www.worth1000.com/entries/261000/261276ChKG_w.jpg

interferometer
2006-Aug-26, 08:15 PM
I was quite happy with the first description of a planet being a round object due to its own gravity. (and not being a satelite or moon)

If they wanted to change that, why didn't they incorporated:
"being layerd" to distuingish between minor planet and dwarf planet
"having a (partial) magnetic field" between dwarf planet and planet
"radiates more energy then received" for planet and 'major' planet (limited by brown dwarfs).

This would also make it easy to define moons as being a "minor satelite planet" without to much fuzz thinking up new names.

Skygazer
2006-Aug-26, 11:03 PM
Ceres, discovered by Giuseppe Piazzi (1801), was thought to be a Planet.
The original search for a Planet (at 2.8 au) was pursued as a consequence of Bode's Rule.
Starting in the 1760's, 25 astronomers searched for a Planet at 2.8 au.
On January 24, 1801, Piazzi announced his discovery to fellow astronomers.

In February, 1801, Gauss determined Ceres had a semi-major axis of 2.77 au !!!

Giuseppe Piazzi initially thought Ceres was a comet then, after 24 recorded observations, lost it as it passed behind the Sun in early February, 1801. Gauss developed a method of orbit determination using 3 observations. In a few weeks, Gauss predicted the path of Ceres and published his results. On December 31, 1801, several astronomers independently confirmed the 'recovery' of Ceres using Gauss' orbit. Due to Bode's Rule (2.8 au), Ceres was called a Planet.

After the additional discoveries of Pallas(1802), Juno (1804) and Vesta (1807) no further 'Planets' were discovered for 38 years.
During those 38 years, these four (4) objects were counted among the Planets: each had its own planetary symbol.

Then, as more 'planets' were discovered (1845, Astraea), the idea of an Asteroid Belt between Mars and Jupiter took hold and Ceres, Pallas, Juno and Vesta became 'minor' Planets.

However, last week, the IAU (again) argued that Ceres was a Planet.
However, this IAU logic was actually an attempt to save Pluto's ranking as a Planet.
But, unlike Ceres, Pluto is not the largest member of the Kuiper Belt (at least Xena is larger).
As one consequence, Ceres, Pluto and Xena are now in the new IAU category called Dwarf Planet.

An Observation:
If you change ...
- 1801 to 1930
- Ceres to Pluto
- Piazzi to Tombaugh
- Asteroid Belt to Kuiper Belt
- The 44 year gap (1801 to 1845) for Ceres / AsteroidBelt ... to ... the 62 year gap (1930 to 1992) for Pluto / KuiperBelt

We can then step back from all the emotional arguments and now recognize two (2) extremely similar scenarios:
Ceres / AsteroidBelt
Pluto / KuiperBelt.


Some additional facts:
Pluto is 1,422 miles in diameter, i.e., 66% of our Moon's diameter.
Ceres, the largest Asteroid, is 578 miles in diameter.
Xena is 1,490 miles in diameter.

Unlike the eight (8) Planets ...
Ceres, Pluto and Xena are in orbits highly inclined to the Ecliptic and, for that reason alone, belong to Belt Structures, not the Planetary Category.
Additionally, Pluto crosses the orbit of Neptune, while none of the eight (8) Planets cross the orbit of another of the (8) Planets.

Chuck
2006-Aug-27, 01:20 AM
Pluto will now have to be renamed. Major Roman gods are reserved for planets.

interferometer
2006-Aug-27, 01:23 AM
I don't think any astronomer will (currently) doubt that Pluto is an KBO.
The question in this was .... does size matter, and what are the delimiters. Or, what definition makes an object an asteroïd or a planet etc.

The idea behind these redefinitions was at first to make an universal standard, but later on just a local standard. Just see it as an imperial or metric system.
(1Yard=3feet=36inch or 1meter=10dm=100cm)
(1asteroidbelt=bunch of asteroids=forced-named-big and mainly-small asteroids .. or
(1asteroidbelt=high density of objects=evenly distributed density around sun of objects)

Chuck
2006-Aug-27, 02:54 AM
Late breaking news: The Plutonian NAU has classified Jupiter, Saturn, Uranus, Neptune, and Pluto as planets. Everything inside the asteroid belt is now a Near Sun Object.

zephyr46
2006-Aug-27, 04:46 AM
There are so many attributes.

Geological activity could seperate Io and Triton from the catagory of moons.

I still get stuck on Comets, is a Coma an Atmosphere? If so, Centaurs are more interesting.

Having or posessing an Atmosphere can seperate several moons to the status of planets as well as.

I think Jupiter could be sitting on the edge of being a star, it emits more radiation than it receives, but neutron stars and black holes are smaller than jupiter, but no one would call either of them a planet, not even the ones that orbit stars.

I think asteroid belts are significant attributes of an enviroment around a star. Ceres is maybe best described as a Planetessimal in late accreation, if we have no objections to the accreation model of solar system creation.

With respect to creationists.

I think if you wish to stick to the historical label of Planet (wanderer) it should be visable to the naked eye or small telescope, if you want to keep Pluto.

I think Pluto is a great KBO because of Plutos inclination to the solar plane, and Mercury is a cheat of a Large asteroid lucky enough to be round and have an eliptical orbit with less inclination, and an atmosphere.

I am still curious about the dust cloud following in the Earths orbit, another interesting entity, as is the Zodiacal Dust.

raghunaram@yahoo.com
2006-Aug-27, 05:50 AM
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. :lol:


i feel the definition of Extra planet would have been more dominant in the minds of the Committe constituted by IAU to find planet Definition.

the defintion given by Working group on Extra Solar planet is important in the context what we are reading on the group. I dont like to make my view and reproduce the entire document please visit

http://www.ciw.edu/IAU/div3/wgesp/definition.html

for Definiton of Extrasolar planet.

N.Sri Raghuandan Kumar
General Secretary
Planetary Society, India
9347511132
www.ournewplanets.com

drjgokhale
2006-Aug-27, 12:04 PM
This new developement has disturbed a lot of people partly because of the language, i.e., the word dwarf in the definition dwarf planet. It sounds like an undeserved kick to Pluto.

Why not change it to "petite planet" instead, and people would feel happier, I think. Make it that anything smaller than Mercury is in that category if it is planet-like in other ways.

In addtion call the Pluto-Charon system a petite planet couple, since the centre of gravity is not in Pluto or Charon.

I don't see the problem about Pluto having a different orbit, in that it is closer for twenty out of 248 or so years. Makes it interesting. There might be more interesting stuff out there, too. (Read Nemesis by Asimov and think of Jupiter and compare it to his brown dwarf/planet Megas.)

There might indeed be large planets beyond Kuiper belt in our own system and it does seem a bit too much to have forty planets for sake of fairness to everything round Pluto-size, but beauty of language (petite instead of dwarf) should do the assauging and it is important even in science not to ignore the beauty whether of facts or language.

cress
2006-Aug-27, 01:33 PM
In a way, the "clearing its orbit" phrase is a little unfortunate, many people (some astronomers included) are taking it as the dynamicists 'hijacking' the definition. For me, this is nonsense; the final definition is based on both physical and dynamical properties. That's how good science is done: based on all the available evidence, not only the convenient bits.

Moreover, "clearing its orbit" is a rather unassuming phrase. This is not only telling you about a body's current dynamics, it's telling you about its formation history. So really we have a three-part definition: physical properties, dynamical properties, and formation process. The eight planets utterly dominate the region of space they reside in, not just now but during their formation. They've all swept up the surrounding material and control nearby orbits. Pluto does not have this property - it's 'merely' yet another object in the Kuiper Belt, and the surrounding bodies' total mass is comparable/greater than Pluto's. Same goes for Ceres.

This is telling us that Pluto has formed differently to the planets, or at least that it never made it to the final stages of the formation process. And if it formed differently, and it behaves differently, then it's a different class of object. End of story.

It's a shame they couldn't have extended the definition to extrasolar planets, but it's taken the IAU a decade just to work up the courage to find suitable nomenclature for our solar system (and there were plenty of members who wanted to delay it till the next meeting, something I don't doubt one or two of them could have kept up indefinitely). The biggest issue for me was the name "dwarf planet", which sounds suspiciously like a cop-out to sway the last few members into voting for it, by keeping the word "planet" in the title for historical reasons. Planetoids or Tombaugh objects or, well, anything would've been better. As long as it isn't confusing people - as dwarf planet has been - then a name is a name is a name.

Oh, and as for the New Horizons mission - that's some real shortsightedness coming from NASA, which is a shame. They've gone from studying the smallest, most distant and insignificant planet to the nearest, most important, prototypical object for a whole new class of bodies. If anything that makes the mission more important, not less; practically everything we know about dwarf planets will come from it. It's not as if Pluto itself has been changed any.

hhEb09'1
2006-Aug-27, 01:41 PM
This is telling us that Pluto has formed differently to the planets, or at least that it never made it to the final stages of the formation process. And if it formed differently, and it behaves differently, then it's a different class of object. End of story.Not quite. Looking back on Alan Stern's work (thanks to a now-banned poster), it seems that he was calculating the ability of an object to clear its orbit, and came up with a characteristic time frame for that to happen. Objects farther out would take a lot longer to do so. So it may just be that the inner objects are done (maybe!), and the outer objects haven't finished yet.

So, they may be forming similarly, and behaving similarly.

cress
2006-Aug-27, 02:05 PM
That's perfectly true, the longer dynamical times make formation much a much longer process further out. But then either it hasn't finished, and it probably never will before our Sun becomes a white dwarf; or else Neptune has gained dominance over those objects (via the 3:2 resonance) and will prevent Pluto ever getting substantially bigger by accreting that belt. Either way, it's not going to satisfy the definition anytime in the next few billion years. As far as human experience cuts it, formation is finished. The rest is just tidying up.

This essentially makes a natural cut-off for how far out you can form planets. Anything farther out will have to have been scattered there, or migrated outwards (as Neptune and Uranus apparently did, by interaction with the planetesimal disc).

hhEb09'1
2006-Aug-27, 02:13 PM
or else Neptune has gained dominance over those objects (via the 3:2 resonance) and will prevent Pluto ever getting substantially bigger by accreting that belt.How does that resonance prevent it? wouldn't it more or less shepard them all into the same vicinity? Seems like it would increase the chances.

And, then there's the question, if Pluto hits on Xena, whose name goes to the child? :)

cress
2006-Aug-27, 02:51 PM
How does that resonance prevent it? wouldn't it more or less shepard them all into the same vicinity? Seems like it would increase the chances.
I haven't studied this properly, but I would assume the resonance is holding everything stable and in place. If they're holding in orbits that are too similar it takes an age for them to meet, because they're travelling with the same period and never 'catch up' to each other (like Jupiter's Trojans)... or at least, the Lyapunov time would be so huge as to make it a ridiculously long formation time again.

Look at it this way: there are objects in the 3:2, and objects in several other resonances with Neptune too. The bodies sharing that resonance with Pluto are still there. If Pluto was going to speed the process up we should have seen signs of it after 5 billion years.

paladinsmeg
2006-Aug-27, 03:59 PM
i feel the definition of Extra planet would have been more dominant in the minds of the Committe constituted by IAU to find planet Definition.

the defintion given by Working group on Extra Solar planet is important in the context what we are reading on the group. I dont like to make my view and reproduce the entire document please visit

http://www.ciw.edu/IAU/div3/wgesp/definition.html

Thanks for the info, Raghuandan. I really should have done a little homework regarding the IAU and extrasolar planets before posting, so thanks for enlightening me.

The fact that it is relatively easy to make observations in our solar system, and so much harder to make observations in other systems would, I imagine, make it much harder to figure out if a newly discovered low mass object around another star is a planet or not, since we only have a few parameters of the object (such as mass estimates and radial velocities) and a lot less parameters such as composition, atmosphere, (debris) "cleaned out orbits", etc to work with.

Given these difficulties (and the level of uncertainty about the specifics of extrasolar 'planets' so far) I see now that limiting this vote to our solar system makes sense.

hhEb09'1
2006-Aug-27, 04:03 PM
Look at it this way: there are objects in the 3:2, and objects in several other resonances with Neptune too. The bodies sharing that resonance with Pluto are still there. If Pluto was going to speed the process up we should have seen signs of it after 5 billion years.Like Charon? :)

One of the things brought out in the discussion of the BA's blog about the moon moving away from earth due to tidal friction, is that the process is limited by the angular momentum. Once total tidal lock occurs, the process reverses due to solar tidal effects, and the moon spirals into the earth. That takes a long time of course, too long to even get to tidal lock in the case of the earth and moon, but in the case of Pluto the tidal lock has already occurred, so solar system tidal effects are probably causing its moon to get closer to Pluto.

I suppose the BA could have made the point that at some time in the future, the Pluto/Charon barycenter might be inside Pluto. :)

ASTROBLEME
2006-Aug-27, 04:57 PM
Pluto will now have to be renamed. Major Roman gods are reserved for planets.

Great observation Chuck!

My concern for this new definition is for public support and funding of research into the future. Taxpayers and/or elected officials may very well decide that too much money and effort is being spent arguing about matters that they have already accepted as fact. What happens when research budgets are cut as limited resources are directed elsewhere? A private sector solution could be found in the International Astronomical Union selling naming rights!

01101001
2006-Aug-27, 05:26 PM
Pluto will now have to be renamed. Major Roman gods are reserved for planets.
Like Ceres (http://en.wikipedia.org/wiki/1_Ceres), Vesta (http://en.wikipedia.org/wiki/4_Vesta), Minerva (http://en.wikipedia.org/wiki/93_Minerva), Apollo (http://en.wikipedia.org/wiki/1862_Apollo) and Juno (http://en.wikipedia.org/wiki/3_Juno)?

hrizzo
2006-Aug-27, 05:28 PM
It is interesting to note that Alan Stern, the same A.S. that today fights the IAU decision, proposed almost the same notion six years ago:

http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf

Maybe, the reason for that change of mind lies not in science, but in his present position at NASA.

ASTROBLEME
2006-Aug-27, 06:15 PM
Like Ceres (http://en.wikipedia.org/wiki/1_Ceres), Vesta (http://en.wikipedia.org/wiki/4_Vesta), Minerva (http://en.wikipedia.org/wiki/93_Minerva), Apollo (http://en.wikipedia.org/wiki/1862_Apollo) and Juno (http://en.wikipedia.org/wiki/3_Juno)?

The tradition holds that all PLANETS (except Earth) carry names from Roman or Greek mythology. Names from Gods and one Goddess (Venus) was used for these major objects. This nomenclature obviously needs to be corrected for these minor objects;

Ceres: Goddess of agriculture
Vesta: Goddess of fire
Minerva: Goddess of wisdom
Apollo: God of light and the Goddesses choir leader
Juno: Queen of Olympian Gods

Certainly the IAU can find lesser mythological characters to use for these…

cress
2006-Aug-27, 07:09 PM
Look at it this way: there are objects in the 3:2, and objects in several other resonances with Neptune too. The bodies sharing that resonance with Pluto are still there. If Pluto was going to speed the process up we should have seen signs of it after 5 billion years.Like Charon? :)
Heh, no, not Charon. One major collision does not a planet make (see also: binary asteroids). That those two are tidally locked at all tells you how long they've been like that. I merely meant that the 3:2, and nearby resonances, are very heavily populated; if Pluto was meant to be sweeping that stuff up, why is it still there? We have to conclude it's not going to happen any time soon.

hhEb09'1
2006-Aug-27, 08:12 PM
It is interesting to note that Alan Stern, the same A.S. that today fights the IAU decision, proposed almost the same notion six years ago:

http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf

Maybe, the reason for that change of mind lies not in science, but in his present position at NASA.It appears that you are accusing him of some sort of hypocrisy. That's a pretty serious charge, so I took the time to read that paper. Nothing in it supports your charge, that I can find. In fact, the opposite: "it is our belief that planethood should be a genetic attribute of object class, rather than location, present circumstance, state, or exterior attributes." He describes a criteria very similar to the original proposal to the IAU.

Further, in classifying sub-types of planets, he has a table that lists the Earth in the Dwarf Planet column.

What did you mean?

Heh, no, not Charon. One major collision does not a planet make (see also: binary asteroids).You asked for signs--as if there were none. There are actually three, right?
That those two are tidally locked at all tells you how long they've been like that. I merely meant that the 3:2, and nearby resonances, are very heavily populated; if Pluto was meant to be sweeping that stuff up, why is it still there? We have to conclude it's not going to happen any time soon.Conclude based upon what?

cress
2006-Aug-27, 08:44 PM
You asked for signs--as if there were none. There are actually three, right?
No, this was what I was mentioning in passing without meaning to go into depth upon, but just because there's been a big collision (Nix and Hydra may result from other collisions, the same one, or be captured randomly passing KBOs) doesn't mean the process is going any faster. It just means there's been a collision. (To get something that massive there will have been many, but probably not so violent.) This collision happened a long time ago (evidenced by tidal locking), and there's no evidence of more recent - dare I even say ongoing - activity. The point is, all the other (smaller) stuff is still there.


Conclude based upon what?
Based upon the system having extremely long dynamical timescales and being without any sort of perturbing body. All that other material is not going to vanish any time soon.

hhEb09'1
2006-Aug-27, 09:11 PM
No, this was what I was mentioning in passing without meaning to go into depth upon, but just because there's been a big collision (Nix and Hydra may result from other collisions, the same one, or be captured randomly passing KBOs) doesn't mean the process is going any faster. It just means there's been a collision. (To get something that massive there will have been many, but probably not so violent.) This collision happened a long time ago (evidenced by tidal locking), and there's no evidence of more recent - dare I even say ongoing - activity. The point is, all the other (smaller) stuff is still there.Going any faster than what?

It's an ongoing process--and Pluto's small moons are certainly evidence of it.

If they are not, what sort of evidence would you be looking for?

cress
2006-Aug-27, 09:46 PM
Going any faster than what?
It was a turn of phrase, I'm sorry if it read as literal. I only meant that one collision, a long time ago, does not imply an accretion rate fast enough to 'finish' (ie sweep up much of the debris) accretion any time soon.


It's an ongoing process--and Pluto's small moons are certainly evidence of it.

If they are not, what sort of evidence would you be looking for?
It's an ongoing process in the sense that the Solar System still isn't 'finished', as above - Shoemaker-Levy 9 being a wonderful example - but as I said before, all that's left is either so slow as to be static from a human perspective, or 'tidying up' (such as S-L 9). The major activity is over (not that they'll be thinking that shortly before the Big One hits the Earth, but you know what I mean!). Nix and Hydra certainly aren't evidence of anything big happening; as far as I understand it (which isn't much, I add) their near-resonances seem to imply they were there before Charon migrated out to it's present location. At any rate there's no reason to assume they were captured recently.

(I hope we haven't got crossed wires here... ongoing physical activity, and ongoing observational activity.)

From a formation perspective, evidence would be large scale accretion. Globally, the last such event would be the Late Heavy Bombardment, but if we're just looking at the Kuiper Belt, then I'd want evidence of 'recent' repeated collisions with Pluto (or Neptune; or maybe among the belt itself) from KBOs. (This may be inferred from an anomalously heavy band of dust around their orbits, for example.) Instead we have an essentially static population quietly minding its own business. There seems to be some mild leakage from the resonant populations, but nothing to get excited about, sadly (except for the astronomers studying those populations, of course!).

Can I take a step back here? All I originally said was that the new definition implicitly includes/excludes bodies based on their formation history. Apart from the odd, widely-spaced impact event, the eight planets' accretion is over because they ate (almost) everything. Pluto's formation may or may not be 'over', but if it isn't it's so slow that it isn't going to finish before the inner planets are destroyed. From our point of view, therefore, Pluto can never satisfy the third condition. Maybe some alien civilisation will come along one day and find ~5 planets in orbit around a white dwarf, but it isn't happening for us, I'm afraid.

Leafguy
2006-Aug-28, 07:17 AM
Very interesting points Cress,
I completely agree with your points, minus the fact about Pluto never being able to satisfy the third condition.

I think the bottom line is about our point of view is that we probably will never know if Pluto will fill the third condition. We simply haven't had the technology available to document it, as well as Im sure we aren't to worried about it either. Pluto could very well have satisfied the condition already if it has had a stable orbit for a long period of time, say in the realm of a billion years.

shrub
2006-Aug-28, 09:55 AM
Well it seems that the pedantic folk at IAU have been so absorbed with being technically correct about Pluto's place in the universe, in fact so much so, that they failed to notice a second, gigantic sun lurking within our own solar system!!!

Well I'm no expert, but if you examine the ‘image’ of the planets that IAU have provided - you can clearly see all of the planets are lit by a much brighter light source coming from the top right corner. Worrying this is…

cress
2006-Aug-28, 10:58 AM
Pluto could very well have satisfied the condition already if it has had a stable orbit for a long period of time, say in the realm of a billion years.
Oh, I agree that it may one day make the grade, but I have my doubts as to whether the human race will still be around to see it. But be careful not to confuse "cleared" with "stable" - to the best of my knowledge, that 3:2 resonance is exceptionally stable, and Pluto may well have been there since shortly after the LHB ended. I understand what the IAU was trying to do, it's just a shame they mucked up the language so spectacularly. I guess they were in a rush to get something passed, even if the wording wasn't quite right, so they had something to work with and build upon. Hopefully a working group can tighten it up in future (when they get round to defining ES planets, maybe).



Well I'm no expert, but if you examine the ‘image’ of the planets that IAU have provided - you can clearly see all of the planets are lit by a much brighter light source coming from the top right corner. Worrying this is…
Ha ha, that is worrying. However this is nothing compared to the BBC's revolutionary discovery that Pluto's orbit is an "oblong"! (The link to the video story was here (http://news.bbc.co.uk/1/hi/sci/tech/5282440.stm) (top right) but the clip no longer seems to be working for me.) Now that would revolutionise planetary science, and celestial mechanics, and gravitation, and...

mlibanio
2006-Aug-28, 01:30 PM
Hey does anyone remember the LEVY asteroids that hit Jupiter? Talk clearing your neighbourhood, IT SWALLOWED THEM!! Pluto lives in a region dominated by asteroids, meteors and assorted debris, so the likelyhood of Pluto being smashed to smithereens by a KBO all these centuries is far more likely than any hitting the so-called BIGGER planets. It just goes to prove in my view that the mere fact it is there means it is capable, of "clearing the neighbourhood." PS. Mercury has no moon, is so close to the sun, anybody outside our solar system would likely never see it, and any asteroid that would make it that deep into our solar system is likely to miss mercury by a long shot. PLUTO IS A PLANET AND THAT IS MY OPINION!

hhEb09'1
2006-Aug-28, 02:46 PM
Well I'm no expert, but if you examine the ‘image’ of the planets that IAU have provided - you can clearly see all of the planets are lit by a much brighter light source coming from the top right corner. Worrying this is…Do you have a link?
PS. Mercury has no moon, is so close to the sun, anybody outside our solar system would likely never see it, and any asteroid that would make it that deep into our solar system is likely to miss mercury by a long shot.Ever hear of Caloris (http://antwrp.gsfc.nasa.gov/apod/ap960120.html)? :)

jkmccrann
2006-Aug-28, 03:07 PM
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?

I don't quite understand exactly what you are getting at here.

You propose that the definition be accepted by all, but then make a populist appeal that Pluto should still be referred to as a Planet (which seems a direct contradiction of what you just said - doesn't that mean that you should also, by your logic, be referring to Ceres, Vesta, Juno & Pallas as planets as well? - They were once called planets, so I expect to see you campaigning for them to be called as such - because apparently once an object is classified as a planet - even the progress of science should not be enough to alter a previous designation.)

Just a question, have you ever heard of Copernicus? And have you ever been to the `End of the Earth?'

Then, to top it all off - you compare the IAU Congress to the voting system used in American Idol! Huh? Are you aware that members of the IAU are professionally qualified astronomers - they aren't just regular joes who walked in off the street to judge a beauty contest - if anyone is qualified to deliberate on planetary nomenclature - it is the IAU. When it comes to American Idol - its all about whoever manages to get a better PR machine rolling

I utterly fail to see the comparison you're making there, particularly your equivalence of the IAU with the average voter of American Idol. Were I a member of the IAU I'd imagine I'd be quite insulted to be dismissed in such a manner.

jkmccrann
2006-Aug-28, 03:14 PM
If that is obvious to you, could you explain it? I'd be very interested in hearing the explanation.

Having read through this thread, I see that cress has answered many of your queries regarding the IAU's decision.

However, I am happy to point you in the direction of the wikipedia article on orbital dominance.

Orbital Dominance (http://en.wikipedia.org/wiki/Orbital_resonance)

Obviously - as it explains, bodies in orbital dominance are in that state because of the gravitational influence they're exerting over each other. In the case of Neptune and the Plutinos, the gravitational pull of Neptune far exceeds that of the Plutinos - which is the basis for the claim that I made that `Neptune has forced these bodies into resonant orbits' - as opposed to the other way around

Which, in my book - points strongly to the fact that it is the dominant object in that area of Space.

hhEb09'1
2006-Aug-28, 03:35 PM
Having read through this thread, I see that cress has answered many of your queries regarding the IAU's decision.I didn't make any queries about the IAU's decision in this thread. My questions were directed to comments made by others.
which is the basis for the claim that I made that `Neptune has forced these bodies into resonant orbits' - as opposed to the other way aroundThat webpage mentions "Other (much more numerous) Neptune-crossing bodies that were not in resonance were ejected from that region by strong perturbations due to Neptune." It does not say that Neptune forced the remaining bodies into resonant orbits. There is a difference.

mlibanio
2006-Aug-28, 05:00 PM
And I still maintain that the definition is pointless of bodies capable of clearing a path being a planet. If mercury is incapable of moving mini to large meteors or other debris causing so much pitting, then clearly it too is not a planet, or is it a planet just because it is so close to Sol. Oh and Neptune not being able to get Triton into a proper orbit I suppose means that it too is not a planet by their definition, but it is because its big and blue, and that it is more attractive than a grey spec in the sky like Pluto! And can somebody explain how a tiny body like that can hold onto 3 moons in a stable orbit? Interesting I say.

mlibanio
2006-Aug-28, 05:18 PM
I submit a new defnition:
A planet is defined as:
A body of mass capable of maintaining a stable orbit (Score 1 for Pluto)
A body with sufficient mass to have a gravitational force capable of repelling and attracting other bodies (By its continued existence Score 2, Score 3 for Charon, Score 4 for Nix, Score 5 for Hydra
A body in orbit around its sun, unaffected by other bodies in orbit (Score 6 for Pluto)
I concede the last point may be debated because of Neptune, but it seems Pluto has maintained this orbit for quite some time. Further other planets have issues too, but again because they are big means they are planets. See size does matter, its always the guy thats smaller that gets made fun of.

Cedna and all the other large KBO's could hardly claim a stable orbit being buried so deeply in the Kuiper Belt. Their surfaces must make Mercury's look like a freshly paved parking lot in comparison.

cress
2006-Aug-28, 05:58 PM
That webpage mentions "Other (much more numerous) Neptune-crossing bodies that were not in resonance were ejected from that region by strong perturbations due to Neptune." It does not say that Neptune forced the remaining bodies into resonant orbits. There is a difference.
Maybe I can help. The picture most astronomers accept now is as follows: The four giants formed much closer to the sun than we see today. Beyond Neptune was a huge planetesimal disc, where nothing particularly massive had been able to form (presumably due to the longer dynamical times). Neptune interacted with this disc, scattering it's contents inwards and migrating outwards itself (by ang mom conservation). Most of the contents were thrown to the rest of the developing planets (causing the LHB) but a few were caught in resonance as Neptune moved outwards - particularly in the 2:1 and 3:2.

It's a beautifully simple idea, and it seems to explain almost everything we see today. Morbidelli, Tsiganis, Levison and Gomes wrapped it all up pretty neatly in three Nature letters in the same edition, if anyone wants to search further.

Their work largely follows from this paper by Malhotra (http://arxiv.org/pdf/astro-ph/9504036) (unfortunately scanned back-to-front), while this one of Gomes, Morbidelli and Levison (http://www.obs-nice.fr/morby/papers/migration.pdf) explains the migration itself, and has plenty of references to, well, everything. The numerical simulations themselves are highly convincing.

Basically, Neptune went outwards, utterly disrupted/formed the Kuiper Belt, and caught a bit of it and Pluto in the process. Poor Pluto never had a chance. Note also this model would mean all the currently defined planets originated within about 18-20 AU of the Sun, making a further distinction between them and the larger TNOs. It seems there really were two different processes at work.

hhEb09'1
2006-Aug-28, 07:50 PM
Maybe I can help.Thanks for the effort, but it doesn't really answer the question (http://www.bautforum.com/showpost.php?p=811552&postcount=17). Elsewhere, I think, this point has come up--if Neptune were forcing bodies into those resonances (rather than ejecting them away) wouldn't the gradual accumulation strengthen rather than weaken Pluto's ability to accrete more mass? jkmccrann had said that it was obvious that Neptune was doing that (forcing, I mean).

cress
2006-Aug-28, 08:11 PM
I believe it does answer the question, but not in the way you expected. 'Forcing' is a dangerous word, I never used it. Neptune migrated outwards sufficiently slowly that any bodies that happened to fall into resonance were caught there - as it moved outwards, the resonance moved slowly outwards too, sweeping everything up like a broom. You'd see this thin band of resonant bodies slowly drifting outwards. Pluto was caught along with everything else.

Maybe if Neptune hadn't moved outwards, the dominant bodies there would have made another planet (be it Pluto or something else). But it did, so they didn't.

hhEb09'1
2006-Aug-28, 08:20 PM
I believe it does answer the question, but not in the way you expected. 'Forcing' is a dangerous word, I never used it. Yes, but it was used in the post that I questioned.

If you think it does answer the question, then actually it was the answer that I expected. :)

cress
2006-Aug-28, 08:24 PM
I love a happy ending.:cry:

kheider
2006-Aug-28, 08:25 PM
Can somebody explain how a tiny body like Pluto can hold onto 3 moons in a stable orbit? Interesting I say.

Pluto is roughly 10x more massive than Charon, so keeping it in a stable orbit is easy.

We even live in a solar system where Spheroids orbit Asteroids (http://www.nineplanets.org/ida.html)!

lrh_geh
2006-Aug-28, 09:00 PM
Maybe it would help to remember how Pluto was discovered. Its gravity effects on other planets were large enough for its existence to be inferred. As I recall, Tombaugh deduced roughly where it could be found, and eventually found it by telescope.

Thus, perhaps the definition of a planet should be modified to state that a planet must be massive enough for its gravitational effects on other planets to be detected. By that definition, the traditional nine planets would remain planets, but Ceres and UB313 would not qualify.

pghnative
2006-Aug-28, 09:25 PM
Maybe it would help to remember how Pluto was discovered. Its gravity effects on other planets were large enough for its existence to be inferred. Except that Pluto's gravity is not large enough to noticibly affect the eight planets. Finding Pluto where they were looking was pure chance. See here (http://www.nineplanets.org/pluto.html) (from the out-datedly named "nineplanets.org").


Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.

Mike Johnson
2006-Aug-29, 06:25 AM
I appreciate the comments on this board about what happened at the IAU General Assembly in Prague. My biggest misgiving is that the general public seems to think that Prague was only about Pluto--which was really one of the most irrelevant things on the agenda.

I guess, I am a little bit old school. I did my dissertation on Titan and just about every researcher then called Titan a planet. In my book, there are at least 36 planets in the solar systems--objects circling the sun with sufficient mass to overcome internal resistance and form near spherical bodies. Some may dominate their orbital area and some may circle other planets.

Fundamentally, we need to ask why we need a definition of a planet. Scientists establish definitions as a means of studying things. My problem with the definition out of Prague is that it is irrelevant to the scientific community (and that would have been true with the orginal draft of Resolution 5 as well). The basic problem is that any definition that includes both the gas giants and the rocky planets (regardless of whether it also includes KBOs or Ceres) is useless for studies--the properties of each are so different that grouping them into a single category doesn't make sense.

So, why propose and approve a resolution with such a useless definition? The answer, I think, had more to do with creating an answer for public consumption. The public only cared about a list of planets and wanted the scientists to certify such a list--especially now that a KBO is very likely to be larger than Pluto. The result is a useless definition that provides eight classical planets one on side and initially 3 dwarf planets (growing rapidly in the future) primarily so that the public can be satisfied. The public might have been satisfied with 12 planets, but would not have been satisfied with an open ended definition that would grow rapidly as KBOs are verified as meeting the original proposed definition. But, to not be open ended, the scientists had to come up with a definition that removed Pluto from the list for the public or rather put it in a secondary category. Of course, Pluto has been called "the accidental planet" for decades now.

Personally, if I were running the IAU, I never would have agreed to certify a definition. There is nothing wrong with Pluto being a planet and a KBO.

The primary impact of this decision, I think, is that textbooks in the future will likely only include the eight classical planets, although they might conceivably have a section on dwarf planets. It won't effect research at all.

Leafguy
2006-Aug-29, 08:20 AM
Mike,
I like the fact you point out that there could be 36 potential bodies that could be considered planets. I think with reference to Cress' points about the planets moving outwards (specifically the gas giants), that there very well could have been a large number of planets earlier in the life of the solar system. Specifically, it can be noted by the composition of Jupiter's Galilean moons, as well as a Titan and a few other moons. Most of these were likely planets at one time or another probably quite close to the sun before being sucked up by the larger Jovian planets.

jkmccrann
2006-Aug-29, 10:20 AM
Mike,
I like the fact you point out that there could be 36 potential bodies that could be considered planets. I think with reference to Cress' points about the planets moving outwards (specifically the gas giants), that there very well could have been a large number of planets earlier in the life of the solar system. Specifically, it can be noted by the composition of Jupiter's Galilean moons, as well as a Titan and a few other moons. Most of these were likely planets at one time or another probably quite close to the sun before being sucked up by the larger Jovian planets.

I believe the definition of the IAU covers what you say here - in the sense that under the current definition - those large number of planets you refer to in the earlier life of the solar system - were not in fact fully-fledged planets because self-evidently they did not clear their neighbourhood of debris - they were in fact cleared themselves!

So, there is a definite difference between these putative objects of the early solar system that no longer exist - and the planets we recognise today.



I appreciate the comments on this board about what happened at the IAU General Assembly in Prague. My biggest misgiving is that the general public seems to think that Prague was only about Pluto--which was really one of the most irrelevant things on the agenda.


Not quite sure how you can come to this conclusion. Evidently, the issue of planethood was the issue that connected the general public at large to the goings on at the IAU Congress in Prague. If it is such an irrelevant issue how can it engage the public at large to such an extent?

Are you aware that much of the funding of various astronomical pursuits comes from either the public purse (for NASA, ESA for instance), or perhaps the purse of prestigious Universities. If astronomers and the IAU alienate the people who foot the bills - the government for instance, then should they be surprised in future that their funding is cut - and that that telescope for studying extra-solar planetary systems in detail is never launched - because the public don't think these guys deserve the public subsidies flowing their way.

If you treat the public flippantly, expect to be treated flippantly in response.

The public can well turn around and say, why should we direct money to these guys if they treat the most broadly interesting subjects they're dealing with so dismissively - the very things that engage the public at large and help to attract future young scientists and engineers to the profession!

I have no doubt that there was a lot of worthwhile science under review and discussion in Prague - that no doubt to those in the fields in question was indeed a lot more interesting than trying to define a planet - but so what? In your post, although you dismiss the public fascination with the discussion of what a planet is - you provide no example to back up your claim by mentioning anything else that was actually under discussion!

I would just repeat, I don't for a minute doubt that there were a lot of interesting discussions under way in Prague, the new information relating to dark matter is indeed something that comes to mind immediately, but I find it quite offensive for you to dismiss the whole planetary discussion as really one of the most irrelevant things on the agenda!

I may disagree with Alan Stern on what he's said about the IAU decision, but his opposition does make sense - will you accept that were Pluto just merely a KBO discovered in the mid 1990s that it would be extremely unlikely that authorisation - and funding - for the New Horizons mission would ever have been granted?

As well as dismissing the discssion of the term planet, are you equally ready to dismiss the New Horizons mission and anything it discovers as irrelevant? The 2 are intricately linked in the mind of the public and, flowing from that, in the minds of the congressman and managers who sit in judgment of these funding decisions.

Given the lack of interest in sending manned probes to explore the Kuiper Belt, besides Pluto - and even the difficulties in achieving funding for the New Horizons mission itself as it was, and the difficulties for instance in finding funding to explore the Asteroid Belt with the Dawn mission - which is to bodies much closer and more accesible than your average KBO, I'm more than a little amazed that you would so easily dismiss the public by contending that they were only concentrating on one of the most irrelevant things on the agenda!

jkmccrann
2006-Aug-29, 11:05 AM
Thanks for the effort, but it doesn't really answer the question (http://www.bautforum.com/showpost.php?p=811552&postcount=17). Elsewhere, I think, this point has come up--if Neptune were forcing bodies into those resonances (rather than ejecting them away) wouldn't the gradual accumulation strengthen rather than weaken Pluto's ability to accrete more mass? jkmccrann had said that it was obvious that Neptune was doing that (forcing, I mean).

Ok, I will concede that maybe saying that the objects in 2:3 resonance with Neptune were forced into those orbits is the wrong terminology to be using.

However, reading what Cress has said, and what others have said about planetary migration - and in particular the outward planetary migration of Neptune, I believe that it is fair to say these objects in 2:3 resonance have been coralled into those orbits by Neptune.

If Neptune had not migrated out towards these objects - then it is unlikely that these objects would all be in the orbits they currently are. It has been the outward migration of Neptune that has caused this resonance to occur, not the inward migration of the Plutinos, or indeed the outward migration of the Plutinos - it is correct so say that the resonance has been created because of the actions of Neptune - its outward planetary migration.

So, I guess to say Neptune forced these bodies into resonance may be inaccurate - because many of the bodies in that region were apparently ejected from the Solar System or sent on parabolic or hyperbolic orbits - and were not coralled, but Neptune has created the resonance of the Plutinos by its own movement - its outward planetary migration.

Distribution of the Plutinos (153 as of February 2006)
Plutino Distribution (http://en.wikipedia.org/wiki/Image:TheKuiperBelt_60AU_Plutinos_distribution.svg )

hhEb09'1, do you find what I've said here - as well as what cress and others have added, as an adequate representation of what has happened/is happening out there - and also as an adequate explanation of what I was attempting to say earlier?

:)

hhEb09'1
2006-Aug-29, 01:40 PM
Ok, I will concede that maybe saying that the objects in 2:3 resonance with Neptune were forced into those orbits is the wrong terminology to be using.

However, reading what Cress has said, and what others have said about planetary migration - and in particular the outward planetary migration of Neptune, I believe that it is fair to say these objects in 2:3 resonance have been coralled into those orbits by Neptune.I was fine with the terminology (although I like "corralled" too, kinda like Neptune herding dogies :) ), I was just wondering why you said the effect was obvious. As near as I can tell from the responses, rather than forcing or corralling, the process has been more one of attrition. There are planetary gravitational influences (obviously? :) ), but it sounds like the orbits that are there now were more or less pre-existing, rather than created by Neptune. Objects that weren't in resonance were ejected. That's an oversimplification, but the whole reason I started down this path was I was interested in the details of a mechanism that allowed Neptune to "corral" other objects. I guess there is no such known mechanism, other than something like Jupiter's Trojan points.

cress
2006-Aug-29, 02:38 PM
Watch video number 4 I put in the orbital clearing thread. I hope that will give you both a good picture of what was going on.

I still prefer 'swept' but 'coralled' is good too.:lol:

TheThorn
2006-Aug-29, 10:55 PM
I think that definition works well. Check out this figure:

http://www.spaceobs.com/perso/textes/solarsystem2.gif

(The entire article it is contained in is worth a read at:
http://www.spaceobs.com/perso/textes/planetsandasteroids.htm )

There's an obvious gap in mass and orbital inclination (eccentricity too for that matter, but it's not shown in the figure) between one group of objects and the other group of objects. The reason for the gap is that they are fundamentally different - they formed differently. The one group is the 8 planets, the other group is (call it what you want - minor planets?). There are no objects even near the line. (BTW, our understnading 40 years ago would have put Pluto on the other side of the line. We were wrong.)

The division between "dwarf planets" and "small solar system bodies" (talk about awkward terms) seems arbitrary and forced. I guess it's there to make some Pluto fans a little less unhappy. But there is no gap between an almost-but-not-quite-round small body and a close-enough-to-round-to-count dwarf planet. There will be objects right on the line.

The gap between planets and minor planets (if you let me use that term) is even more obvious if you divide these objects into two classes based on composition - terrestrial (rocky) and gas (or ice - composed mostly of volatiles). In the terrestrial group, from Earth at the heavy end to Mercury at the light end, there's just over one order of magnitude difference in mass (with Venus and Mars in between, so no gaps), then there's a gap of over 2 orders of magnitude to Ceres, followed by a continuum of sizes with no gaps down to a grain of sand. In the gas group we find exactly the same situation: from Jupiter to Uranus there's just over one order of magnitude range in masses (with Saturn and Neptune in between so no gaps), followed by a gap of over three orders of magnitude down to UB313, then a continuum of sizes with no gaps down at least to small comets, probably to particles of frost.

Those gaps mean something. The objects are different in some way.

So is it important to get the definition right? Well, it can affect the way these objects are viewed and ultimately direct our understanding of them. What if biologists decided 1000 years ago that everything in the ocean over 1000 kg was called a whale, and everything under 1000 kg was called a fish? Would that have helped our understanding? Getting the definition right should be the first step, not the last.

So I think a definition that honours the gaps that nature is showing us is probably the best one we can come up with. The fact that they did it without saying "everything over 10^23 kg is a planet and everything under is not" is even better - they found a way to draw that line without being arbitrary about it.

A lot of the discussion here is on what is meant by "clearing its orbit". That's going to be easy to sort out. In fact, it's already obvious to me, but I'm not a lawyer.

Mike Johnson
2006-Aug-30, 04:45 PM
Pluto will now have to be renamed. Major Roman gods are reserved for planets.

Why?

Ceres, Juno, and Vesta were also major Roman dieties and when these were downgraded to minor planet/asteroid status, they didn't lose their names. They were every bit as important godesses as Venus was. For that matter, so was Minerva--the name of asteroid number 93, named long after the original four were downgraded to asteroids. Apollo (ok, Greek, but adopted wholesale by the Romans) and Vulcan are also asteroids. Diana is a satellite of Saturn and another major Roman diety--counterpart of Artemis.

Also, Uranus wasn't a Roman diety, but a Greek diety. The Roman counterpart was Coelus.

Earth wasn't a Roman diety either, but goes back to old English and Indo-European. Originally earth meant "land" as opposed to "sea" and not the planet. Terra and Tellus were Roman counterparts and Gaea was the Greek counterpart. Terra and Gaea are still used as synonyms for Earth.

Pluto was never the brother of Jupiter (and thus the real counterpart of Hades, brother to Zeus). Orcus was the Roman brother of Jupiter and god of the underworld, and thus the real counterpart of Hades. Orcus is the name of a large KBO with similar orbit elements to Pluto. At some point, the Romans identified Pluto and Orcus as being the same, but their Greek counterparts never were so identified.

The third most important Roman diety (after Jupiter and Mars) was Quiranus and to date nothing has been named after him.

Pluto was named as much in honor of Percival Lowell (PLuto) as anything else. It was Lowell who predicted its existence because the computed orbital elements of Uranus were then not fully explained by Neptune and thus, Lowell initiated a major search for Planet IX to explain Uranus' orbit. Clyde Tombaugh was a volunteer at the Lowell Observatory when he discovered Pluto. It was the Lowell Observatory that promulgated the discovery of Planet IX. Lowell dabbled in a lot of things--e.g., canals on Mars, initial estimates of the structure of Jupiter and Saturn. He was wrong on almost everything, but he advanced astronomy more than almost anybody else in his day. I think Pluto is a fitting tribute to the man.

hhEb09'1
2006-Aug-30, 04:54 PM
Clyde Tombaugh was a volunteer at the Lowell Observatory when he discovered Pluto. I didn't think he was, I thought he was on the payroll. Online references, that I've googled, say he was hired at the start of his job.

Mike Johnson
2006-Aug-30, 05:30 PM
I didn't think he was, I thought he was on the payroll. Online references, that I've googled, say he was hired at the start of his job.

Thanks, I thought he was too, but recently was corrected that he was a volunteer not an employee. Either way, he was part of a large Lowell Observatory effort to find Planet IX. He wasn't off doing research on his own. Being an employee makes more sense for me, given that he moved to Flagstaff to be part of the effort.

peteshimmon
2006-Sep-02, 12:58 PM
Remember Tombaugh went on to search the rest of
the ecliptic to +&- 20 degrees declination (I
think) using the same method that found the
ninth planet. His negative result still has
relevance today notwithstanding the finding of
other bodies recently. But the history since his
work has been of pressure to make science more
"teamwork" and play down individual success.
So many veritable eminences made just silly
utterances neglecting Pluto!

TwAgIssmuDe
2006-Sep-08, 10:55 AM
Atleast now everybody can move on with their lives, and worry less about pluto. Its out of the planet club, somehow we all new this was going to happen, it was just the matter of when. Bye pluto, but in my heart you will always be a planet like the other eight...sigh!!

CharlesBell
2006-Sep-08, 06:14 PM
Yesterday the Minor Planet Center posted an Editorial

http://cfa-www.harvard.edu/mpec/K06/K06R19.html

which gives specifics on (1) Ceres, Pluto and 2003 UB313.

Whether we like it or not, the IAU has ruled.
It reminds me quite a lot about bad bosses and bad days at work. We have to let it go or you may end up on depression medicine like me.

I took some images of the planet Pluto recently before the ruling:

http://www.quantumhyperspace.com/imagefiles/Pluto-08122006-0452UT.jpg

http://www.quantumhyperspace.com/imagefiles/Pluto-08192006-0419UT.jpg

http://www.quantumhyperspace.com/imagefiles/Pluto-08202006-0427UT.jpg

I'm going to keep on calling it a planet and leave off that dwarf word and go about my business. That's for the "bean counters"!! to fuss about. I don't think it has added anything scientific to the world.