Is Pluto Still a Planet? The Controversial Decision to Downsize the Solar System

Ceres was the first asteroid discovered, by Giuseppe Piazzi in 1801. At that time, there were a handful of planets known, all orbiting inside the orbit of Ceres. The discovery of more asteroids (mostly in the "belt" between Mars and Jupiter) eventually forced the classification of "planet" to be changed to "planet and asteroid". In the 1850s, Urbain Jean Le Verrier discovered the first object that would eventually be classified as a "planet" orbiting outside the orbit of Ceres (Neptune), and the classification of planet was changed to "planet, asteroid and comet". In the 1900s, Pluto was discovered, and it was the first object to eventually be
  • #36
" Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons. "

How odd. I would have thought that would be the LAST criteria to come into play. Forget about clearing its orbit, Pluto has captured Charon (a much more challenging feat). I would think this would actually strengthen its right to be in the club!
 
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  • #37
SpaceTiger said:
If you have any idea what you're talking about, please do explain how you think these thresholds are imaginary.
I know what he's talking about. Where's the confusion?

The boundaries between major planet and dwarf planet and KBO are weak. If we go looking for "planets" only, isn't that putting limitations on whether we find KBOs for example?

Or if we do studies, such as what is the average diameter of a planet? Well, that number has just changed in the last week. A study based on week definitions could be baised.

(This is pretty simplistic stance, I'm fairly confident that labels don't define the science done upon things. Nonetheless, this is jimmy's arg, not mine...)
 
  • #38
I'm curious how subjective the definition of planet is now. The terms used in the press seem a little vague, like "dominate it's neighbourhood". Is this vagueness in the technical version? What I'm really wondering is how open is this definition to arguments on whether or not to inculde some as yet to be discovered thing?
 
  • #39
shmoe said:
What I'm really wondering is how open is this definition to arguments on whether or not to inculde some as yet to be discovered thing?
Have no fear, no one is looking for as yet to be discovered things. As for the Earth, it will become a planet the minute we stop seeing meteors.
 
  • #40
DaveC426913 said:
" Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons. "

How odd. I would have thought that would be the LAST criteria to come into play. Forget about clearing its orbit, Pluto has captured Charon (a much more challenging feat). I would think this would actually strengthen its right to be in the club!
My understanding, and I'm sure ST will correct me if I'm wrong, is that part of the issue is that Charon may not just be a moon of Pluto, i.e., it doesn't orbit around Pluto, but instead, the two seem to share a common orbit sort of spinning around a central point between them. The best I can understand it, it seems like it's an issue of a primary vs secondary orbit. It first has an orbit shared with Charon, then the two together orbit the sun. Because of that, Pluto is doing something differently than the other planets with moons.

I still think that at this point, it's pretty much an issue of semantics. ST has mentioned that the more important question seems to be the origin of the "bodies" and their evolution. I would think that it's not terribly relevant whether you call it a planet or not at this point in time, as long as you don't let the name given to it bias your study of it in a particular direction. If/when sufficient evidence exists to say a certain set of "celestial bodies" formed in a particular way, and another set formed in a different way, then it seems it would be the better time to reevaluate naming systems to reflect such properties of the planets, and not just somewhat arbitrary designations. Then again, it's really not unlike the growing pains that biological classification systems go through, trying to determine what's the most important characteristics to use for grouping things. Ultimately, one would hope the criteria used are not just for taking objects already identified and sorting them out, but to have a way of comparing the characteristics of something newly identified with the classification rules of previously discovered objects, and then using that as a basis for where to begin study of the new object.
 
  • #41
DaveC426913 said:
I know what he's talking about. Where's the confusion?

The boundaries between major planet and dwarf planet and KBO are weak. If we go looking for "planets" only, isn't that putting limitations on whether we find KBOs for example?

No, and I don't see how this addresses the issue at all. The "thresholds" I'm referring to have nothing to do with the events of this past week, they are detection thresholds, as Astronuc already explained. There's nothing imaginary about them.
 
  • #42
This decision does have some anatagonists.

I'm not that bothered either way, OK it doesn't seem to have cleared it's orbit of the clutter, something we see in the "true planets" and is a twin article as has already been said, but this whole decision seems somewhat contraversial, so I thought this article may be of some interest.

http://news.bbc.co.uk/2/hi/science/nature/5283956.stm

A fierce backlash has begun against the decision by astronomers to strip Pluto of its status as a planet.

On Thursday, experts approved a definition of a planet that demoted Pluto to a lesser category of object.

But the lead scientist on Nasa's robotic mission to Pluto has lambasted the ruling, calling it "embarrassing".

And the chair of the committee set up to oversee agreement on a definition implied that the vote had effectively been "hijacked".

I have nothing but ridicule for this decision
Alan Stern, Southwest Research Institute

The new solar system
The vote took place at the International Astronomical Union's (IAU) 10-day General Assembly in Prague. The IAU has been the official naming body for astronomy since 1919.

Only 424 astronomers who remained in Prague for the last day of the meeting took part.

An initial proposal by the IAU to add three new planets to the Solar System - the asteroid Ceres, Pluto's moon Charon and the distant world known as 2003 UB313 - met with considerable opposition at the meeting. Days of heated debate followed during which four separate proposals were tabled.

Eventually, the scientists adopted historic guidelines that see Pluto relegated to a secondary category of "dwarf planets".
 
  • #43
The part about Stern's objection that I liked the best was the obvious fact that Neptune hadn't cleared its path either. Pluto is in there.
 
  • #44
jimmysnyder said:
The part about Stern's objection that I liked the best was the obvious fact that Neptune hadn't cleared its path either. Pluto is in there.
Wrong.
Pluto's nodes (the points at which the orbit crosses the ecliptic) are both situated outside Neptune’s orbit and are separated by a distance of 6.4 AU (that is, over six times the distance of the Earth from the Sun).
http://en.wikipedia.org/wiki/Pluto#Distance_from_Neptune
 
  • #45
I thought Pluto was supposed to drop inside Neptune's orbit at some point, but that Wikipedia article makes it look completely outside Neptune's orbit.

I went back to a 30+ yr old (when I used it) textbook (1966) and it mentions that "Pluto's perihelion is 35 million miles within Neptune's orbit." Pluto's orbital plane is also inclined to the ecliptic by 17°10'. Back then, Pluto was anticipated because of perturbations in orbits of Neptune and also Uranus, and it was then thought that it has a mass ~0.80 of earth. :rolleyes:

So we now know that Pluto and Charon have been perturbing the orbits of Nepture and Uranus. But Pluto's mass is (0.0021 Earths) according to Wikipedia article.

Then there is - http://www.daviddarling.info/encyclopedia/P/Pluto.html

But
Pluto's orbit is often described as 'crossing' that of Neptune. In fact, Pluto's nodes (the points at which the orbit crosses the ecliptic) are both situated outside Neptune’s orbit and are separated by a distance of 6.4 AU (that is, over six times the distance of the Earth from the Sun). Furthermore, due to the orbital resonance between them, Pluto executes 2 full cycles while Neptune makes 3; this means that when Neptune reaches the 'closest' point on the orbit, Pluto remains far behind and when Pluto in turn reaches that point, Neptune is far (over 50°) ahead. During the following orbit of Pluto, Neptune is half an orbit away. Consequently, Pluto never gets closer than 30 AU to Neptune at this point in its orbit.
http://en.wikipedia.org/wiki/Pluto in section cited by EL.

Interesting times we live in. :-p

And I still want to know - what happens to Rupert? And what about the Grebulons? :biggrin:
 
  • #46
EL said:
Wrong.
I don't get it. Neptune is in Pluto's path, but Pluto is not in Neptune's?
 
  • #47
I think it is a pretty stupid decision, and won't make a difference in the study of planets.

The definition of an 'atom', if we were so skeptical, would be such that the current conventional 'atom'. i.e. the one with the electrons, protons and neutrons, wouldn't be called a atom if by definition. But since we have been constantly using it for a long time, I think it would be most unwise to change it to something else.
 
  • #48
jimmysnyder said:
I don't get it. Neptune is in Pluto's path, but Pluto is not in Neptune's?

No, their paths never cross each other.
Pluto's orbit is tilted compared to Neptune's so at the points you would think they'd cross each other just by naively projecting them onto the same plane, they are actually above/below each other.
 
  • #49
Moonbear said:
My understanding, and I'm sure ST will correct me if I'm wrong, is that part of the issue is that Charon may not just be a moon of Pluto, i.e., it doesn't orbit around Pluto, but instead, the two seem to share a common orbit sort of spinning around a central point between them. The best I can understand it, it seems like it's an issue of a primary vs secondary orbit. It first has an orbit shared with Charon, then the two together orbit the sun. Because of that, Pluto is doing something differently than the other planets with moons.
Phase I of the downsizing of the Solar System is complete. Can we now start Phase II by eliminating Jupiter as a planetary satellite of the Sun? :devil:
 
  • #50
BobG said:
Can we now start Phase II by eliminating Jupiter as a planetary satellite of the Sun? :devil:

I don't think we should remove Jupiter as a planet. It's very massive, so removing it might perturb the Earth orbit in an undesirable way.
 
  • #51
Rach3 said:
I don't think we should remove Jupiter as a planet. It's very massive, so removing it might perturb the Earth orbit in an undesirable way.
Good hint.
 
  • #52
BobG said:
Phase I of the downsizing of the Solar System is complete. Can we now start Phase II by eliminating Jupiter as a planetary satellite of the Sun? :devil:
Bored and looking for something to do? Or, are you just up to no good?

Rach3 said:
I don't think we should remove Jupiter as a planet. It's very massive, so removing it might perturb the Earth orbit in an undesirable way.
Well that seems to be the motivation behind BobG's plan. I suspect he has been secretly using computers at work to analyze the impact of the eliminating Jupiter from the Solar System, and then using them to work out the logistics for his plan. Hmmmm.
 
  • #53
Astronuc said:
Bored and looking for something to do? Or, are you just up to no good?

Well that seems to be the motivation behind BobG's plan. I suspect he has been secretly using computers at work to analyze the impact of the eliminating Jupiter from the Solar System, and then using them to work out the logistics for his plan. Hmmmm.
Over 24 hours and it didn't dawn on anyone that the center of mass of the Sun-Jupiter system is outside the surface of the Sun? :eek:
 
  • #54
BobG said:
Over 24 hours and it didn't dawn on anyone that the center of mass of the Sun-Jupiter system is outside the surface of the Sun? :eek:
No it isn't.
 
  • #55
and nyaa nyaa nya nya nya, as well.
the whole pluto problem seems to really bring out the pissiness in people
 
  • #56
Since it's the only "planet" discovered by an american?:rolleyes:
 
  • #57
EL said:
Since it's the only "planet" discovered by an american?:rolleyes:
I don't think that's it, as long as we still own all of them it doesn't really matter if we discovered them or not.
 
  • #58
tribdog said:
I don't think that's it, as long as we still own all of them it doesn't really matter if we discovered them or not.
That's true!...wait...do you own them all?
 
  • #59
all of them except for Uranus. Just because no one should really own Uranus, at least not ALL the time. Everyonce in a while is okay, but you got to be careful. Like a time share.
 
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  • #60
But Uranus is big enough to be called a planet though?
 
  • #61
mine's not, don't know about yours
 
  • #62
You know Myanus is not a planet...
 
  • #63
It's a black hole.
 
  • #64
Since if you're trapped you won't get out...?
 
  • #65
DaveC426913 said:
It's a black hole.
:smile: :smile:
 
  • #67
Are we being just a bit geocentric about the Solar System?

http://www.unitedmedia.com/comics/jumpstart/archive/jumpstart-20070107.html

Such bad puns can't be ignored. :smile:
 
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  • #68
"Plutoed" chosen 2006 word of the year

http://www.mercurynews.com/mld/mercurynews/news/local/states/california/northern_california/16405925.htm"

"Plutoed" was chosen 2006 Word of the Year by the American Dialect Society at its annual meeting on Friday.

To "pluto" is "to demote or devalue someone or something" much like what happened to the former planet last year when the General Assembly of the International Astronomical Union decided Pluto didn't meet its definition of a planet.​
 
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  • #69
D H said:
http://www.mercurynews.com/mld/mercurynews/news/local/states/california/northern_california/16405925.htm"

"Plutoed" was chosen 2006 Word of the Year by the American Dialect Society at its annual meeting on Friday.

To "pluto" is "to demote or devalue someone or something" much like what happened to the former planet last year when the General Assembly of the International Astronomical Union decided Pluto didn't meet its definition of a planet.​

That has such a nice ring to it, it really adds to the list of possible phrases:

"This is the hardest thing a manager has to do..."

"We've decided to use you as our on-call busboy." (How my first ever real job ended).

"You remember what happened to Pluto? When you think about it, that wasn't so bad, and now that you mention it..."
:smile:
 
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  • #70
So I guess that probe flying in space somewhere showing 9 planets is obsolete...
 

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