Is Pluto Still a Planet?

[slugcountry]

http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html

"PRAGUE, Czech Republic (AP) -- Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight."

...

 

[moose]

I think I will just wait about ten years before trying to look up what the planets in our solar system are.

 

[Chi Meson]

Dang it! I just bought stock in Charon!

 

[scott1]

There going to change it...Everone likes pluto...

 

[Blahness]

Let's riot until they ban changing the number of planets.Anyone? *Grabs picket*

^Also: "They're". Pluto(capitalized).

</EnglishOCD>

 

[scott1]

Yeah let's ban the astromers against Pluto!

Who's ready for Planet Killer Champions!

 

[marlon]

It always makes me laugh to see how much people actually care about some stupid sphere. They actually organised a big conference on this in Prague, i believe, just to define "what is a planet" ?

Talkin' about your udder waiste of money.

marlon

 

[EL]

Won't this have some inpact on Astrology?

 

[Jimmy Snyder]

In my opinion, this decision was unwise. Does it serve any scientific purpose?

 

[marlon]

Won't this have some inpact on Astrology?

marlon

 

[EL]

In my opinion, this decision was unwise. Does it serve any scientific purpose?

If Pluto would have remained a planet, at least three more objects in our solar system should also qualify as planets. And in a near future we would probably find hundreds of more such "mini-planets" outside Pluto, and in that case I'd feel quite sorry for the children having to learn all the names in school...

 

[Astronuc]

. . . They actually organised a big conference on this in Prague, i believe, just to define "what is a planet" ?

The meeting in Prague is the 26th General Assembly of the International Astronomical Union (IAU) or UAI in French.

http://www.astronomy2006.com/

http://www.iau.org/IAU_MEETINGS.110.0.html - a number of meetings in Prague coincident with the GA.

 

[SpaceTiger]

In my opinion, this decision was unwise. Does it serve any scientific purpose?

Classification schemes serve as phenomenological guides that aid in the study of the formation and subsequent evolution of some set of objects. Optimally, the different categories would reflect not only differences in present appearance and behavior, but also physical history. In this case, Pluto's origins and evolution may have more in common with that of other Kuiper Belt objects than of the official eight planets.

One might ask, does a study of Kuiper Belt objects include Pluto? Does a simulation of evolution of planetary orbits include it? Ultimately, the answers to these questions will depend on the study in question. Scientists can choose to conduct their studies in any way they see fit (perhaps ignoring the official classification scheme), but it's usually convenient to have some kind of consistency.

Personally, I don't think it's earth-shattering and am amused that people get so worked about it, but I do think it's important to have a definition (even if somewhat vague). In this respect, any decision made by the IAU would be a step forward.

 

[Astronuc]

Won't this have some inpact on Astrology?

Yeah, they just retroactively invalidated all previous horoscopes.

 

[Gagan A]

One page less in science textbooks and one more in history textbooks.

 

[EL]

Yeah, they just retroactively invalidated all previous horoscopes.

Ah, so now we know why they never worked before!
Guess the new Astrology will be much more successful...

 

[Jimmy Snyder]

One might ask, does a study of Kuiper Belt objects include Pluto?

If there is a definition for Kuiper Belt objects and Pluto meets the definition, then Yes. If it doesn't meet the definition, then No. If there is no definition, the the IAU should have made one. What has this got to do with the issue at hand?

 

[SpaceTiger]

If there is a definition for Kuiper Belt objects and Pluto meets the definition, then Yes. If it doesn't meet the definition, then No. If there is no definition, the the IAU should have made one. What has this got to do with the issue at hand?

As I said, the origins and evolution of Kuiper Belt objects are likely different from that of planets. Putting it in both categories may not make sense, depending on what one wishes the classification to reflect.

 

[Jimmy Snyder]

Classification schemes serve as phenomenological guides that aid in the study of the formation and subsequent evolution of some set of objects. Optimally, the different categories would reflect not only differences in present appearance and behavior, but also physical history.

But this is not what the IAU did. They classed together Pluto and Ceres. The reason Pluto was kicked out of the limousine had to do with its orbit, not its history. If they needed a word for "Planet, but not Pluto", I think they should have made one up.

There are attempts being made to find planets revolving about other stars. Are these attempts now to be relabeled, or are we not interested in extra-solar Kuiper Belt objects?

 

[SpaceTiger]

But this is not what the IAU did. They classed together Pluto and Ceres. The reason Pluto was kicked out of the limousine had to do with its orbit, not its history.

Here's a quote from the article:

Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

In other words, Pluto is part of a "belt", so it has not cleared the region around its orbit (a facet of its history/evolution) and is not to be classified as a planet.

There are attempts being made to find planets revolving about other stars. Are these attempts now to be relabeled, or are we not interested in extra-solar Kuiper Belt objects?

Everything found (or being looked for) so far would probably fall into the definition of a planet, not a Kuiper Belt object or asteroid.

 

[Jimmy Snyder]

Everything found (or being looked for) so far would fall into the definition of a planet, not a Kuiper Belt object or asteroid.

Then here's to finding things that are not being looked for. Anyway, I'm off the case. It turns out that Pluto's fate is similar to that of Ceres.

The classification of Ceres has changed more than once. At the time of its discovery it was considered a planet, but upon the realization that it represented the first of a class of many similar bodies, it was reclassified as an asteroid for over 150 years.

http://en.wikipedia.org/wiki/1_Ceres

By the way, SpaceTiger, it seems that the sturdy classification scheme you desire did not come about:

It is not yet clear whether dwarf planet status is, like planet status, a sole defining category, or whether dwarf planets also retain their previous minor body classifications such as "asteroid."

Or Kuiper Belt object.

 

[SpaceTiger]

Then here's to finding things that are not being looked for.

They're not being looked for because we're not capable of detecting them. With the possible exception of pulsar planets (which are so strange that I'd question classifying any of them alongside our own planets), any orbiting body our instruments can see would clear its orbit on a very short timescale.

By the way, SpaceTiger, it seems that the sturdy classification scheme you desire did not come about:

I'm in partial agreement on this point, but I still think this is a step forward. Previously, the planets were defined based on our history rather than theirs, an unpleasant state of affairs for a scientific classification scheme.

 

[Jimmy Snyder]

They're not being looked for because we're not capable of detecting them.

And here's to detecting things you didn't think you could.

 

[SpaceTiger]

And here's to detecting things you didn't think you could.

So you're saying we should spend money to look for things that are way below our detection threshold?

 

[Moonbear]

One page less in science textbooks and one more in history textbooks.

One of my friends has been talking on and on about this this week. I guess he's been following it in the news or something. My reaction was more, "It's still there, right? It hasn't suddenly disappeared or gone zooming out of its orbit, right? Then it's just an issue of semantics."

I wonder if the textbook writers are backing this change? It would mean all the schools would need to update the textbooks to remain current.

I suspect the kids would like it if the list got too long. Once it gets to that point, it's no longer something the schools think is worth memorizing, and instead, they put a sentence in like, "There are now over # known planets." And then teachers awe the class by telling them something like, "Would you believe that back in the 20th Century, they thought there were only 9 planets?!" That's when the kids all giggle and are shocked that people used to be that ignorant.

 

[Jimmy Snyder]

So you're saying we should spend money to look for things that are way below our detection threshold?

Here's to imaginary thresholds. And fantastic bargains.

I'm the one paying for this stuff. If the IAU was worried about how I would react to this change, they didn't say. I'll let it pass this time, but they should by no means take me for granted.

 

[Astronuc]

imaginary thresholds.

They are not imaginary, but limitations on what optics and electronics can do. We've just been building better and better systems, e.g. Keck, Hubble, etc. As we obtain systems with greater capability, we discover 'new' things, i.e. new to us, but they've always been there. And occasionally, new discoveries cause us to re-evaluate and perhaps change our understanding and views of the universe.

 

[Jimmy Snyder]

They are not imaginary, but limitations on what optics and electronics can do.

Of course. Real thresholds are real and imaginary ones are imaginary. We need to recognize both of them.

 

[DaveC426913]

Everybody's talking about how this is going to force a change in the textbooks.

Actually, in the long run, nothing could be further from the truth. It means, after this, textbooks will likely never have to change again.

The downgrading of Pluto also serves to define all future objects in the Solar System as non-planets. If we hadn't made this definition once and for all, we'd have to rewrite the textbooks every time we discovered a new pluto-sized object in the outer Solar System.

 

[DaveC426913]

Of course. Real thresholds are real and imaginary ones are imaginary. We need to recognize both of them.

We do, the technology doesn't.

A scope does not have instructions like "show me all planets around that star, BUT ignore dwarf planets".

It's not like these definitions will affect the data-gathering aspect of astronomy.

 

[DaveC426913]

A question:

What is it exactly in the new definition of planets that has disqualified Pluto?

 

[Ivan Seeking]

Planets don't have long noses.

 

[DaveC426913]

My confusion around the downgrading of Pluto is this:

It is disqualified becasue it has not cleared its neighborhood, correct? i.e. Neptune is still in its neighborhood.


So, why is Neptune not disqualified too? It has not cleared its neighborhood of Pluto.

 

[Ivan Seeking]

Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.

http://news.nationalgeographic.com/news/2006/08/060824-pluto-planet.html

 

[SpaceTiger]

Here's to imaginary thresholds. And fantastic bargains.

If you have any idea what you're talking about, please do explain how you think these thresholds are imaginary.

 

[DaveC426913]

" 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!

 

[DaveC426913]

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...)

 

[shmoe]

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?

 

[Jimmy Snyder]

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.

 

[Moonbear]

" 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.

 

[SpaceTiger]

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.

 

[Schrodinger's Dog]

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".

 

[Jimmy Snyder]

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.

 

[EL]

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

 

[Astronuc]

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.

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.

And I still want to know - what happens to Rupert? And what about the Grebulons?

 

[Jimmy Snyder]

Wrong.

I don't get it. Neptune is in Pluto's path, but Pluto is not in Neptune's?

 

[Bladibla]

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.

 

[EL]

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.

 

[BobG]

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?

 

[Rach3]

Can we now start Phase II by eliminating Jupiter as a planetary satellite of the Sun?

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.