So Pluto is a planet!?

[The Silent Majority]

Yeah, but I grew up with 105 elements, and protons, neutrons and electrons were elementary particles that couldn't be subdivided.

* Of course, some things won't change. Fifty years later, commercial fusion power is still forty years in the future.

Electrons are still elementary particles... (sorry, had to )

*I call it the "Fusion Constant."

OT: Why does it matter? as long as we send probes to it and learn more about it, I don't care what you call it.

[Superfluous J]

That's not a good analogy. Terra is the name of our planet... in Latin. Not sure about Sol, I thought it was the Latin name too.

That actually makes it a perfect analogy. Two latin names used in descriptors relating to what we today call "The Sun" and "The Earth," officially in scientific documents. Scientists do not refer to the Sun as "Sol." they refer to it as "The Sun" in the say way they'd refer to Cleveland, OH as "Cleveland, OH"

[ZetaX]

I'll go with the Star Trek method. If it looks like a planet on the viewscreen, it's a planet. Basically, if it has enough mass to reach hydrostatic equilibrium and doesn't produce nuclear fusion, it's a planet.

So the Moon, Ganymede and Titan are planets¿

[Kryten]

'Enough mass to reach hydrostatic equilibrium' is rather ambiguous. Vesta hasn't done it but has less mass than some moons that have, due to them having higher ice content.

[Sun]

Actually, Sun is not my IRL name.

[metaphor]

I, like most of us, grew up with Pluto being a planet, to have that changed is weird.

It's too bad there's no 180-year-olds alive today, who grew up with Ceres and a few others being planets. I bet they said the same thing when that changed.

Anyway, there's two conflicting ways to categorize a body: based on its orbital characteristics, or based on its physical characteristics. The current definition of "planet" is based on orbital characteristics, which have to do with the formation of celestial bodies (the bodies which grew first and fastest became larger and cleaned up their orbit).

I would propose another classification system based on their physical characteristics instead of orbital characteristics. Anything that's round and not a star would be called a "world" (or some other word that's not already taken...). An object being round basically means that it's large enough that it's differentiated on the interior. So we would have two classifications, one having to do with orbital characteristics and one having to do with physical characteristics. Pluto would be a world and also a dwarf planet, Earth would be a world and a planet, Titan would be a moon and a world, etc.

[Whirligig Girl]

I classify by the following objects (No specific order):

-Stars

-Major Terrestrial Planets (Rocky bodies that have cleared their orbit, a spherical*, and orbit a star)

-Gas Giant Planets (Large Gas Planets that have cleared their orbit, are spherical*, and orbit a star)

-Ice Giant Planets (Smaller Gas Planets with more ices that have cleared their orbit, are spherical*, and orbit a star)

-Dwarf Planets (Rocky or Icy bodies that orbit a star and are spherical*)

-Major Moon (Rocky [or potentially Icy] bodies that orbit any Planet, Asteroid, or even another moon; and are spherical*)

-Dwarf Moon (Rocky or Icy bodies that orbit any Planet, Asteroid, or other moon)

-Asteroid (Rocky bodies that are not spherical*)

-Kuiperoids (Icy bodies that are not spherical*, specifically found in the Kuiper belt)

-Plutoids (Icy Dwarf Planets, specifically found in the Kuiper belt)

-Comet (Icy Bodies in the Oort Cloud)

-Sednoids (Dwarf Planets outside of 3 times the distance to Neptune)

*Not actually Spherical. Bulges in the equator are fine, and Haumea is a dwarf planet despite being very oblate.

This technically doesn't conflict with the IAU definitions, it just clarifies more specifically what I'm talking about.

[m4v]

So an university in the US held a public vote about Pluto classification. How is the result relevant at all?

[ZetaX]

Well, definitions are just a consense. Thus theoretically, it is relevant. Practically, only the involved scientists will get a vote, and the problem itself is pretty uninteresting (define it whatever you want; it's not like it has any real implications).

[m4v]

"It held a debate  pro and con  and let the audience vote."

The way is worded makes me think that it wasn't scientists the ones voting, but just random people present in the debate. And really I don't expect any US citizen to stay unbiased in this subject.

Edited October 3, 2014 by m4v

[ZetaX]

We should hold a vote to decide if the moon is made of cheese.

[Camacha]

I posted this in the other topic, but it is relevant here too.

I feel it should be very simple. Objects that are rounded and circle a star are planets. Anything that circles a planet is a moon.

And yes, that means we get a boatload of planets all of a sudden, but the current definition seems totally arbitrary and vague. Dwarf planet? Clearing its neighbourhood? Really? So it is a planet, but not a planet? Of course, dwarf planet could still be a classification, but just to indicate a planet of small size or mass.

[lajoswinkler]

I think this whole butthurting nagging is really pathetic and annoying. Pluto was always an outcast and it shouldn't be called a planet in the first place. I always felt it didn't belong to the group.

There was a time when Ceres was considered being a planet. Does anyone nag about Ceres? No. Why? Probably because it wasn't discovered by an American. Yeah, sorry, but that's the core of the problem. Nationalism. Plain and simple. Boo-hoo.

Pluto is one of many similar bodies outside Neptune's orbit. There's a ton of them and we've just started discovering them. Who wants a solar system with 50 planets?

[Camacha]

Pluto is one of many similar bodies outside Neptune's orbit. There's a ton of them and we've just started discovering them. Who wants a solar system with 50 planets?

*Raises hand.

Like I said, the current situations seems rather arbitrary, so let's include all the roundy floaty things and be done with it. It reflects the true nature of our solar system much more accurately too, as it is a lot less empty than those 9 big balls we generally take it to be.

[ZetaX]

Nationalism. Plain and simple. Boo-hoo.

I don't think it's really nationalism, it's probably plain old conservationism (or whatever the concept behind being conservative is called).

Maybe people also objected when Ceres was demoted, but much less due to the lack of fast communication like the internet.

[Camacha]

The debate about Pluto's status, of course, isn't just in the public but among some scientists. Some take issue with the definition agreed to by the IAU for a planet, they consider its third criteria "has cleared the neighborhood of its orbit" to be somewhat vague. What constitutes the "neighborhood of its orbit"? When is the orbit considered "cleared"? Some have even suggested that by the current definition Neptune is no longer a planet because it has never "cleared" Pluto, which crosses orbits with Neptune. Some may yet argue that Jupiter's orbit isn't clear because of the Trojan Asteroids, though this is easily countered by remembering that it is Jupiter's gravity that dominates these objects. Then there could be the argument that the Earth hasn't cleared its orbital neighborhood because there are Earth-crossing asteroids. Some also point out that the definition only holds for objects in our Solar System because the definition states that the object mud "orbit the Sun".

This is pretty much my whole issue with the situation as it stands. Clearing up a definition by making it more muddled is not how it should be done. The whole clearing the orbit thing is vague - not because some things just are in life, but because it is a lousy definition. There just is very little real reason to subdivide the planets that way, other than that it is inconvenient that we would otherwise suddenly deal with a lot of them.

I really do not mind whether Pluto is a planet or not, I do mind science not being able to make its mind up.

Edited October 3, 2014 by Camacha

[crubs]

Pluto just doesn't fit in with the rest of the planets. It's still a planet, it always was. Calling it a "dwarf planet" helps categorize solar objects better.

If you want to ditch the whole definition of what a planet is, then you'd better start counting Eris and Ceres as planets too.

Yeesh, I didn't realize pluto was that inclined. Did New Horizons even bother doing a plane change?

[Red Iron Crown]

Yeesh, I didn't realize pluto was that inclined. Did New Horizons even bother doing a plane change?

It did a gravity assist at Jupiter to direct it toward Pluto. Couldn't wait for it to be at the ascending or descending node, Pluto's orbital period is about 250 years and there's no timewarp.

[Camacha]

It did a gravity assist at Jupiter to direct it toward Pluto. Couldn't wait for it to be at the ascending or descending node, Pluto's orbital period is about 250 years and there's no timewarp.

Which means humans changed the plane of Jupiter ever so slightly, which is pretty cool.

[Red Iron Crown]

Which means humans changed the plane of Jupiter ever so slightly, which is pretty cool.

Shrank its orbit a tiny amount, too. We may want to keep quiet about this before environmental conservation types start protesting our careless altering of the planets' orbits.

[ZetaX]

Don't forget the tidal effects on jupiter, especially the clouds

[metaphor]

*Raises hand.

Like I said, the current situations seems rather arbitrary, so let's include all the roundy floaty things and be done with it. It reflects the true nature of our solar system much more accurately too, as it is a lot less empty than those 9 big balls we generally take it to be.

That's not at all as clear as the current definition of planet. There's lots of things that are right at the edge of being round, like Vesta for example.

The current definition is pretty clear-cut, at least with the objects we have discovered so far. There's the planets, which are the large, singular objects in roughly circular orbits without any chance of an orbit-altering encounter with another body; and there's the asteroids, KBOs, and comets, which are all part of families of similar objects orbiting in similar orbits (which are usually highly inclined and eccentric). The current classification says a lot about the history of those bodies, since all the planets formed on nice round orbits, and scattered everything else into inclined eccentric orbits.

- - - Updated - - -

Yeesh, I didn't realize pluto was that inclined. Did New Horizons even bother doing a plane change?

Not much of one, since Pluto is currently very close to its ascending node with respect to the ecliptic.

[Vanamonde]

Please, let's not get into casting aspersions on anyone's nationality.

[Camacha]

That's not at all as clear as the current definition of planet. There's lots of things that are right at the edge of being round, like Vesta for example.

That is not really an argument, as any definition is going to have objects right on the edge. The problem with the current definition is that the edge itself is vague, as TheShadow1138 has explained nicely. You might as well argue that some of our planets are not even planets any more.

The current definition is pretty clear-cut, at least with the objects we have discovered so far.

If you mean that the current definition seems concocted to maintain our understanding of how our solar system looks, then yes, you are right. There is little clear-cut about the third requirement otherwise - the other two are fine. Applying it outside our own and current solar system quickly leads to all sorts of definition related trouble.

Edited October 3, 2014 by Camacha

[lajoswinkler]

*Raises hand.

Like I said, the current situations seems rather arbitrary, so let's include all the roundy floaty things and be done with it. It reflects the true nature of our solar system much more accurately too, as it is a lot less empty than those 9 big balls we generally take it to be.

Every classification is arbitrary. Things in nature don't come with labels on them. People classify them.

The current classification's power is in the combination of its parts. It shows the history of planetary evolution. There are planets and there are larger lumps of crap scattered everywhere. It's pretty straightforward. Some of the lumps are large enough to have a hydrostatic equilibrium, big deal.

I said 50, and the probable number is waaaay more bigger. I wouldn't be surprised if there were thousands of such objects, not even counting in the stuff in Oort cloud.