That ain't no asteroid, bud.

[Lmoy]

Depth perception in a vacuum is more difficult too. A cleverly painted basketball could look like a planet from your spacecraft's windows. If we gave such a basketball a name-tag that said "Pluto", would people argue for its status as a planet?

 

[Notebook]

Its the only body named after a cartoon dog. For that alone, it should get reinstated. Have these astronomers no sense of humour?

N.

 

[RGClark]

"It has clouds" is a terrible reason to define something as a planet. Triton has clouds, but it isn't a planet. Titan's surface isn't visible because of how thick the cloud layer is, but nobody is arguing that it's a planet. Saying "Pluto looks like a planet so it is one" is unscientific and kind of insane.

Alan Stern is the leading expert on Pluto and the principle investigator (PI) for the New Horizons mission. There are several reasons why he suggests Pluto should be classified as a planet. I suspect he's being humorous here.

Bob Clark

 

[jedidia]

Its the only body named after a cartoon dog.

It is? I always thought it was named after the god of the underworld...

 

[Notebook]

No, Disney hired famous animator Clyde Tombaugh, and he created Pluto in 1932. I've seen the movies.

N.

 

[Urwumpe]

Its the only body named after a cartoon dog. For that alone, it should get reinstated. Have these astronomers no sense of humour?

N.

Eris is short for Ed Harris. Who played Gene Krantz in Apollo 13. or what did you think the name was chosen for?

 

[Notebook]

As much as I admire Ed Harris, fine actor that he is., who could forget him in Coma as patient number 2. I have.
However he doesn't come close to Pluto at his best...:https://www.youtube.com/watch?v=gl8fMiDCHYQ

N.

 

[RGClark]

As Star Trek navigator, I would never call Pluto a planet, but then, in TNG, even a Pluto with a much denser atmosphere would be considered to be an asteroid.

Dr. Alan Stern, as chief science officer on the starship would call it a planet.

Bob Clark

 

[Urwumpe]

Dr. Alan Stern, as chief science officer on the starship would call it a planet.

Bob Clark

The captain would sure like to beam him on the surface...

 

[TMac3000]

"It has clouds" is a terrible reason to define something as a planet..

I agree. By itself, that's a pretty bad reason.

But "It has clouds" combined with "It orbits the Sun" is quite convincing. That wouldn't demote any of the classical planets, and also would not promote anything in the Asteroid belt or Kuiper Belt (unless Ceres or Sedna could be shown to have atmospheres).

Of course, you can't require both, or Mercury would not be a planet. But both together should give an object the status of planet.

In other words: if it orbits the sun, it might be a planet (Ceres isn't). If it has an atmosphere, it might be a planet (Titan isn't). If it meets both, it is certainly a planet. (If Titan broke orbit with Saturn and started orbiting the sun, it would become a planet).

 

[Urwumpe]

But "It has clouds" combined with "It orbits the Sun" is quite convincing. That wouldn't demote any of the classical planets, and also would not promote anything in the Asteroid belt or Kuiper Belt (unless Ceres or Sedna could be shown to have atmospheres).

What about comets?

 

[Lmoy]

In other words: if it orbits the sun, it might be a planet (Ceres isn't). If it has an atmosphere, it might be a planet (Titan isn't). If it meets both, it is certainly a planet.

That definition appears to be strictly based in sentimentality. If there's any scientific logic behind it, you aren't explaining it well enough. Again I ask, why should clouds influence the definition at all? Titan isn't a planet because it doesn't function like a planet. In the path it takes around the sun, it comprises a minute fraction of the mass and directly controls almost nothing. Saturn is the dominant body here, affecting planetary/gravitational dynamics strongly enough to be comparable only to other planets. Saturn has clouds but it isn't a planet because of that, it's a planet because it is one of the gravitationally dominant bodies of the solar system, whereas Titan is not.

Like I said before, Pluto doesn't even come close to affecting other bodies the way a planet does. It is controlled by Neptune. Their orbital resonance is locked in by Neptune's influence on Pluto, not Pluto's influence on Neptune. Just as it would be ridiculous to call Triton or Titan planets, it's ridiculous to call Pluto a planet, as it just is not functionally a planet at all.

And like you said yourself, the definition falls apart as soon as you look at Mercury, requiring you to make an exception (which defeats the point of a definition), or you drop the "clouds" requirement and just make it anything that orbits the sun, and we know that that won't work either.

 

[TMac3000]

What about comets?

A coma is not the same as an atmosphere: it is not gravitationally bound to the comet.

---------- Post added at 11:17 AM ---------- Previous post was at 11:03 AM ----------

Again I ask, why should clouds influence the definition at all?

As I said, by itself it doesn't. But when a gravitationally bound atmosphere is combined with a solar orbit, in my opinion the rest of the requirements should be waived and the object should be considered a planet. Mercury is a planet because, while it does not have an atmosphere, it meets the IAU requirements that excluded Pluto.

Titan isn't a planet because it doesn't function like a planet.

No...Titan isn't a planet because it orbits Saturn, not the sun.

In the path it takes around the sun, it comprises a minute fraction of the mass and directly controls almost nothing. Saturn is the dominant body here, affecting planetary/gravitational dynamics strongly enough to be comparable only to other planets.

I don't see why any of those things should be a factor.

Like I said before, Pluto doesn't even come close to affecting other bodies the way a planet does. It is controlled by Neptune. Their orbital resonance is locked in by Neptune's influence on Pluto, not Pluto's influence on Neptune. Just as it would be ridiculous to call Triton or Titan planets, it's ridiculous to call Pluto a planet, as it just is not functionally a planet at all.

I would be a smart-aleck here to accuse you of suggesting that Pluto orbits Neptune. We all know better than that, and I don't think you are saying that. But...what exactly are you saying with that?

And like you said yourself, the definition falls apart as soon as you look at Mercury

Umm...no. While I mentioned that anything that meets both of those conditions (orbit the sun and have an atmosphere) should definitely be called a planet, I did not say that a body that is missing one or the other should not be called a planet. Hence, my assertion is, first of all, not a definition, and secondly, does not exclude Mercury.

Now, I say my assertion is not a definition because 1), it is not an AND gate, otherwise it would exclude Mercury, and 2) it is not an OR gate, otherwise it would include Ceres and Vesta. It is merely an exception to the IAU requirements.

 

[Urwumpe]

A coma is not the same as an atmosphere: it is not gravitationally bound to the comet.

And the atmosphere of Pluto is really different? Its only 0.3 Pa surface pressure and it is constantly blown away by the weak solar wind.

 

[TMac3000]

And the atmosphere of Pluto is really different? Its only 0.3 Pa surface pressure and it is constantly blown away by the weak solar wind.

True--but it's still gravitationally bound while it's there, and it is replenished by the planet itself. That makes it different from the pseudo-atmosphere of Mercury, which is nothing more than a veil of solar wind.

 

[Urwumpe]

True--but it's still gravitationally bound while it's there, and it is replenished by the planet itself. That makes it different from the pseudo-atmosphere of Mercury, which is nothing more than a veil of solar wind.

Well, what about that then:

http://news.nationalgeographic.com/...eris-dwarf-planets-occultation-space-science/

In some years Pluto might be like Eris and have no atmosphere at all because it is too cold.

 

[TMac3000]

Then it would be suitable to demote Pluto from planet. Until then I see no reason not to keep it.

 

[Urwumpe]

Then it would be suitable to demote Pluto from planet. Until then I see no reason not to keep it.

So, you mean it should be a "perihelion-only-planet"?

 

[TMac3000]

Hmmm...no. Now that is a good point there

Look, I'm not emotional or sentimental about this. I just think that, while it's silly for people to complain about Pluto being demoted, it's equally silly to heap ridicule on anyone who might have a difference of opinion with the IAU and have some reasoned arguments to back it up, and lump them in with moon-hoaxers and 9/11 truthers. I'm not saying that you did that--you certainly haven't--but still...

 

[martins]

The whole planet/no planet dilemma seems to stem from the human compulsion to categorize. At heart we all appear to be autists who get uncomfortable whenever we discover continuous transitions in formerly neatly separate species.

Given that the planet yes/no separation is necessarily arbitrary and therefore meaningless, why not allow a subjective component, giving up generality in favour of individual freedom:

"A body is a planet if you feel it should be"