So Pluto is a planet!?

[Canopus]

Why do people want Pluto being a planet so badly?

[Albert VDS]

The 2 reasons given so far are:

- Because that's what they learned in school and/or that what they are used to.

- Just because

As you can see very compelling reasons.

Edited October 6, 2014 by Albert VDS

[KerikBalm]

I don't understand it either.

As far as I can tell, its mostly anti-intellectualism.

How can it be people's favorite "planet".... all we have is a blur?

Why do they care about nomenclature...

It doesn't make sense to me.

[Fingal]

As far as I can tell, its mostly anti-intellectualism.

Hardly. Many people disagree with the classification of planet that's been given, myself amongst them. It seems more of an attempt to get a historical term to fit what we've learnt since the term was used than it is an attempt to provide a reasonable definition. I couldn't care less about Pluto but I don't understand why Mercury are Ganymede are given different definitions yet Mercury and Jupiter are considered the same. The "cleared out the orbit" requirement seems more about fitting it into a historical definition, which is a bizarre thing to do.

[Albert VDS]

It's not "Cleared out the orbit" it's "Clearing the neighbourhood around its orbit".

"Cleared out the orbit" means that the object is gravitationally dominant in it's orbit and cleared out the whole orbit. Which no planet has ever done.

"Clearing the neighbourhood around its orbit" means that the object is gravitationally dominant in it's place in it's orbit and cleared out it's neighbourhood.

[Fingal]

It's not "Cleared out the orbit" it's "Clearing the neighbourhood around its orbit".

"Cleared out the orbit" means that the object is gravitationally dominant in it's orbit and cleared out the whole orbit. Which no planet has ever done.

"Clearing the neighbourhood around its orbit" means that the object is gravitationally dominant in it's place in it's orbit and cleared out it's neighbourhood.

A minor point which doesn't remove the fact that this is an attempt to make a historical term somehow fit those bodies which were defined before we knew anything about them. It strikes me as pretty sloppy science.

[KerikBalm]

I don't understand why Mercury are Ganymede are given different definitions yet Mercury and Jupiter are considered the same. The "cleared out the orbit" requirement seems more about fitting it into a historical definition, which is a bizarre thing to do.

Mercury vs ganymede: obviously its about the "parent" body that they orbit.

Cleared the orbit: its why ceres doesn't count, its my the kuiper belt objects don't count.

It seems pretty clear to me.

If you want to group them into distinct groups, we can talk of gas giants, ice giants, terrestrial planets, etc...

[Fingal]

Mercury vs ganymede: obviously its about the "parent" body that they orbit.

Cleared the orbit: its why ceres doesn't count, its my the kuiper belt objects don't count.

It seems pretty clear to me.

If you want to group them into distinct groups, we can talk of gas giants, ice giants, terrestrial planets, etc...

It's clear to me too, it's just I don't understand why you'd do that unless you were trying to shoehorn reality into a historical definition of a cultural term that was made when we knew very little about the solar system.

[Albert VDS]

I have no clue what you mean, could you please clarify.

[Fingal]

I have no clue what you mean, could you please clarify.

What don't you understand?

[ZetaX]

I don't understand why Mercury are Ganymede are given different definitions yet Mercury and Jupiter are considered the same.

Ganymede is orbiting Jupiter instead of the sun. And Mercury and Jupiter are not considered the same, we have the distinction between terrestrial planets and gas giants (with sometimes ice giants added in).

[Albert VDS]

This part: "this is an attempt to make a historical term somehow fit those bodies which were defined before we knew anything about them".

[Fingal]

This part: "this is an attempt to make a historical term somehow fit those bodies which were defined before we knew anything about them".

Planet is a very old word that was given to things that were nothing more than points of light that moved against the background of stars. To try and find a retrospective scientific definition based on what we have since learnt about them that only includes those objects seems pointless and foolhardy.

[Fingal]

Ganymede is orbiting Jupiter instead of the sun. And Mercury and Jupiter are not considered the same, we have the distinction between terrestrial planets and gas giants (with sometimes ice giants added in).

Mercury and Jupiter are both considered planets, yet Ganymede is not. But Jupiter has very little in common with Mercury, other than an aspect relating to orbits that takes no account of their physical characteristics.

[m4v]

It's clear to me too, it's just I don't understand why you'd do that unless you were trying to shoehorn reality into a historical definition of a cultural term that was made when we knew very little about the solar system.

Because they wanted to reserve the word planet for the most significant bodies of the solar system, they did it so we have less than a dozen of planets instead of hundreds or thousands of planets that nobody but nerds like us will care.

[KerikBalm]

Exactly, the definition of a planet is mainly orbit based.

Orbits a body that is a star

Orbit is gravitationally dominated by the candidate planet

The last criteria is almost meaningless when observing the above criteria... I doubt you'd find a body that was able to gravitationally dominate its orbit without having enough mass to be in hydrostatic equilibrium.

As I pointed out earlier (in this thread? in that other thread on definitions for planets?), we could also use inclination to the invariable plane to arrive at the same set of planets.

The orbital characteristics seem to be most distinct.

Not just how much mass it has, what its atmosphere is, etc.

FYI, ganymede and Mercury aren't all that similar... sure, they are both solid, but one is denser than the other, and the composition of Ganymede is quite different from Mercury, since most of Ganymede's mass would be lost to space if it orbited as close to the sun as mercury does.

[Fingal]

Because they wanted to reserve the word planet for the most significant bodies of the solar system, they did it so we have less than a dozen of planets instead of hundreds or thousands of planets that nobody but nerds like us will care.

But why would they do that? I can't understand the point of it.

[N_las]

But why would they do that? I can't understand the point of it.

We could start with the idea, that there a different groups of objects in the solar system, without naming them. But after a while it would be clear that names are in order to help discussing ideas.

We could just name the groups "tzultierts", "polkuhnst" and "qwertys". But it would be way easier to rely on names that are already historically used for objects in the sky. The group of objects that were historically called "planets" has the biggest overlap with the group of 8 main objects in our solar system. So we call them planets.

If we would use the term "planet" for every round rock that is out there, it would have nothing to do anymore with the historical use of the term.

And also this:

http://scienceblogs.de/astrodicticum-simplex/files/2014/10/plutoceres.jpg

[LLlAMnYP]

For one thing, because the gravitational influence of all the stuff except the planets (and the Sun) is negligible. The 8 planets (and the Sun) are the objects that dominate the orbital mechanics of our solar system. Everything else is just debris.

[LLlAMnYP]

And also this:

http://scienceblogs.de/astrodicticum-simplex/files/2014/10/plutoceres.jpg

Thank you, good Sir, this has just made my day.

[benkh]

We could start with the idea, that there a different groups of objects in the solar system, without naming them. But after a while it would be clear that names are in order to help discussing ideas.

We could just name the groups "tzultierts", "polkuhnst" and "qwertys". But it would be way easier to rely on names that are already historically used for objects in the sky. The group of objects that were historically called "planets" has the biggest overlap with the group of 8 main objects in our solar system. So we call them planets.

If we would use the term "planet" for every round rock that is out there, it would have nothing to do anymore with the historical use of the term.

And also this:

http://scienceblogs.de/astrodicticum-simplex/files/2014/10/plutoceres.jpg

Oh I love Florian F.

[Fingal]

We could start with the idea, that there a different groups of objects in the solar system, without naming them. But after a while it would be clear that names are in order to help discussing ideas.

We could just name the groups "tzultierts", "polkuhnst" and "qwertys". But it would be way easier to rely on names that are already historically used for objects in the sky. The group of objects that were historically called "planets" has the biggest overlap with the group of 8 main objects in our solar system. So we call them planets.

If we would use the term "planet" for every round rock that is out there, it would have nothing to do anymore with the historical use of the term.

So do you agree the IAU's definition of a planet was just an exercise in shoehorning in a definition that fits a group of objects?

Incidentally, other scientific disciplines aren't exactly embracing the definition. Certainly geologists and geophysicists don't feel compelled to pay the slightest bit of attention to it.

And also this:

http://scienceblogs.de/astrodicticum-simplex/files/2014/10/plutoceres.jpg

What do you mean by that? Are you calling me and the geophysical word a "whiney little ....." just because we think the IAU are in error with their definition?

[Fingal]

For one thing, because the gravitational influence of all the stuff except the planets (and the Sun) is negligible. The 8 planets (and the Sun) are the objects that dominate the orbital mechanics of our solar system. Everything else is just debris.

Do you include Mercury in that?

[Sylandro]

Viva la Pluto, mother****ers.

Best Stardroid and best planet. And you can have my word for that, kiddies.

[m4v]

... just because we think the IAU are in error with their definition?

ITT, random people on the Internet think that they know better than the professionals that invest their lives in the study of the solar system.