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
  • #1
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."

... :rofl:
 
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  • #2
I think I will just wait about ten years before trying to look up what the planets in our solar system are.
 
  • #3
Dang it! I just bought stock in Charon!
 
  • #4
There going to change it...Everone likes pluto...
 
  • #5
Let's riot until they ban changing the number of planets.Anyone? *Grabs picket*

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

</EnglishOCD>
 
  • #6
Yeah let's ban the astromers against Pluto!

Who's ready for Planet Killer Champions!
 
  • #7
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
 
  • #8
Won't this have some inpact on Astrology?
 
  • #9
In my opinion, this decision was unwise. Does it serve any scientific purpose?
 
  • #10
EL said:
Won't this have some inpact on Astrology?
:rofl: :rofl: :rofl:

marlon
 
  • #11
jimmysnyder said:
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...
 
  • #12
marlon said:
. . . 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.
 
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  • #13
jimmysnyder said:
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.
 
  • #14
EL said:
Won't this have some inpact on Astrology?
Yeah, they just retroactively invalidated all previous horoscopes. :rofl:
 
  • #15
One page less in science textbooks and one more in history textbooks. :wink:
 
  • #16
Astronuc said:
Yeah, they just retroactively invalidated all previous horoscopes. :rofl:
Ah, so now we know why they never worked before!
Guess the new Astrology will be much more successful...
 
  • #17
SpaceTiger said:
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?
 
  • #18
jimmysnyder said:
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.
 
  • #19
SpaceTiger said:
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?
 
  • #20
jimmysnyder said:
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.
 
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  • #21
SpaceTiger said:
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.

wikipedia said:
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:


wikipedia said:
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.
 
  • #22
jimmysnyder said:
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.
 
  • #23
SpaceTiger said:
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.
 
  • #24
jimmysnyder said:
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?
 
  • #25
Gagan A said:
One page less in science textbooks and one more in history textbooks. :wink:
:rofl:

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. :rofl:

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. :biggrin:
 
  • #26
SpaceTiger said:
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.
 
  • #27
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.
 
  • #28
Astronuc said:
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.
 
  • #29
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.
 
  • #30
jimmysnyder said:
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.
 
  • #31
A question:

What is it exactly in the new definition of planets that has disqualified Pluto?
 
  • #32
Planets don't have long noses.
 
  • #33
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.
 
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  • #34
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
 
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  • #35
jimmysnyder said:
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.
 

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