Pluto is was and always will be a planet

Ziggurat said:
No. You can classify the largest body in the co-orbiting group as the planet and the smaller ones as moons.
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Unless of course it is a binary where the difference in size between the two is not statistically significant (meaning they have a mass ratio extremely close to 1; something > .9, maybe > .8, should be close enough).*

Then they should both be considered planets if they otherwise classify. Anything less and one is a moon IMO. (Some scientists have actually proposed that smaller mass ratio systems should be considered double planets. Those scientists are smelly & dumb and, most importantly, wrong. :))

But from what we know about the formation and evolution of solar systems they (mass ratios near 1) should be extremely rare. So improbable in fact that the term Double Planet is not even officially recognized by the IAU.

Nothing in our solar system comes even close. The closest is Pluto–Charon with a mass ratio of .11 or so (Earth-Moon being like .011, and the gas giants and there moons being like .00011). Nothing in any solar system we discover should come even close to it.

But because of the size of the universe, we should assume they do exist.**




*Not to be confused with merely being a binary system where the bodies orbit a point clearly outside of either body (their barycenter).


**A neat statistical side effect of the unfathomable size of the universe. There are some extremely low probability things that it should be basically impossible for us to find in any random solar system, or even galaxy. But yet because of the insane size of the universe, they are somewhere. (And, unfortunately, guess what is very likely one of those things? Intelligent sentient life.)
 
I actually wouldn't mind a simpler definition of planet that includes large moons, like the Moon, and rogue planets that don't orbit a star. Basically just a simple definition that's based on the object itself and isn't related to it's movement or environment.
 
Roboramma said:
I actually wouldn't mind a simpler definition of planet that includes large moons, like the Moon, and rogue planets that don't orbit a star. Basically just a simple definition that's based on the object itself and isn't related to it's movement or environment.
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Planet: Spherical, orbits a star. Rogue planet: Would be a planet, but no star. Moon: Orbits a planet.

If the bizarre criteria of "easy for school children to remember them all" (a criteria we don't apply to literally anything else - stars, mountains, rivers, fish, countries, states, presidents, wars, etc), then... Planet: One of the original nine so named in the Solar system. Good luck remembering all the millions of non-planet "planets" out there, chump schoolteachers!

Seriously, Belz... What's with this 'think of the schoolchildren' crap? Is there anything that would convince you to renounce it as a terrible criteria?
 
There were 7 original planets, and the sun and moon were members.

Then Yoko came along.
 
theprestige said:
Seriously, Belz... What's with this 'think of the schoolchildren' crap? Is there anything that would convince you to renounce it as a terrible criteria?
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I don't know. Is there anything that would convince you to renounce your strawman?

Hell, even Ziggurat brought it up. The point is that when we create a definition for something, it's either to reflect usage or, in the case of technical things, to serve specific purposes. So what's the purpose of the term "planet"? Well, for one it serves to help astronomers and astrophysicists distinguish them from other stuff and work with them in their theories, calculations and observations, and for another it helps us plebs learn about them, including our kids who have to learn them at school. And about the second, well if you want kids to learn the planets, which sounds like a good idea, you'll have a hard time getting that done if there are 6891 planets in the solar system.
 
It's a shame that the real scientists got involved in this. Science fiction types had this sorted years ago.

Any body large enough to pull itself into a spheroid was a planetary body, unless it was so large that fusion had begun, in which case it's a star.

Planetary bodies that orbit stars are planets.

Planetary bodies that orbit planets are planetary moons.

Planetary bodies that share a barycenter orbit outside the other planetary body's surface are double planets.

Planetary bodies that travel freely, not orbiting other bodies are rogue planets.

Doc Smith, through Star Trek, we agreed on these things.
 
Feet to the fire even lumping Mercury/Venus/Earth/Mars and Jupiter/Saturn/Uranus/Neptune into the same category feels weird to me.

I'm perfectly okay with the statement "As of this moment the major bodies of the solar system other than the Sun are 4 rocky planets, 4 gas giant planets, and 5 dwarf planets and those numbers and categories could change as our knowledge of the solar system increases."
 
This is The End said:
Nothing in our solar system comes even close. The closest is Pluto–Charon with a mass ratio of .11 or so (Earth-Moon being like .011, and the gas giants and there moons being like .00011). Nothing in any solar system we discover should come even close to it.
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True for all the planets, dwarf planets, and moons so far discovered in the Solar System, but not true for "one" (or should that be two ?) of the largest of the Jupiter trojan asteroids, 617 Patroclus. This was discovered in 1906, and in 2001 was observed to consist of two almost equally sized bodies, each about 100 km in diameter, orbiting around their common centre of mass in a roughly circular orbit 680 km apart.
 
The word 'planet' is Ancient Greek, meaning 'wanderer' - and was originally applied to differentiate the few moving lights in the sky from all the other 'fixed stars' which, over normal human time scales, remain in fixed positions relative to each other.

So, using the original meaning of the word, it was quite correct to include the Sun and the Moon in with what we now consider to be planets.
 
ceptimus said:
The word 'planet' is Ancient Greek, meaning 'wanderer' - and was originally applied to differentiate the few moving lights in the sky from all the other 'fixed stars' which, over normal human time scales, remain in fixed positions relative to each other.

So, using the original meaning of the word, it was quite correct to include the Sun and the Moon in with what we now consider to be planets.
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Yeah but by the same token that'd include asteroids and specs of dust.
 
Not really - because the ancients didn't have telescopes, so they could only see naked-eye objects.
 
Belz... said:
I don't know. Is there anything that would convince you to renounce your strawman?
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You're right. I'm sorry.

So. I definitely used some uncalled-for hyperbole, but this:

Belz... said:
if you want kids to learn the planets, which sounds like a good idea, you'll have a hard time getting that done if there are 6891 planets in the solar system.
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Is not a straw man. And there's a few things to say about it.

One thing to say is, "sounds like a good idea" is an argument from feelings, which elsewhere in the thread you seem to oppose.

Another thing: Do we want kids to learn the planets? One thing your argument does for me is cause me to question the basic premise. So what if kids don't learn the planets right away?It's not like the planets are going anywhere. It's not like anyone needs to know their names and numbers to get through life. My sister made it all the way to high school thinking the sun and the moon were the same size, which is very silly but also entirely inconsequential.

It's also special pleading. We want kids to learn countries and presidents and mountains and rivers and stars, but we don't dumb down the definitions of these things to make it easier on their child brains.

"Planets are spherical under their own gravity - you'll learn more about that next year, Johnny - and orbit a star. There are seven planets in our sky that were visible to the naked eye, and named by the ancients. There are two more planets that were found by telescopes in the past couple hundred years. Since then, we have found a handful more planets in our solar system, as well as additional planets orbiting other stars. Here's a list of books in the library that you can read, if you're interested in learning more about all these planets."

"Mountains are numerous. Here's a few of local or historical interest to get your brain juices flowing. Here's some books in the library you can check out if you're interested in learning more about mountains."

"This country has had 45 presidents, with more to come. You don't have to memorize all of them, but refer to the poster on the back wall of the classroom if you'd like to try. Meanwhile, here's a few that have special historical significance, and here's a list of library books..."

Etc.

The way I see it, teaching children about the planets is not terribly important after all, and having a large number of planets in the catalog is no real impediment to such teaching if you decide you'd like to do that.
 
Belz... said:
IWell, for one it serves to help astronomers and astrophysicists distinguish them from other stuff and work with them in their theories, calculations and observations
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Does it really, though? Is that an argument that Tyson has actually put forth - that it's easier for him to do planetology if he doesn't have to think of Pluto as a planet? As JoeMorgue implies, it seems like he'd still be stuck on Mars and Jupiter both being "planets", not trying to wrap his head around Pluto.
 
theprestige said:
Planet: Spherical, orbits a star. Rogue planet: Would be a planet, but no star. Moon: Orbits a planet.
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Sure, that works. I just think there's something more elegant about the idea that anything like the earth would be a planet, no matter where it ends up.

"Like the earth" of course doesn't mean identical to the earth, and we can go back and forth about how different from the earth something can be without wanting to have a different category.

Maybe "like the earth" shouldn't even be the criterion. That's just what I found when I thought about what a planet is to me and why I would want one thing or another included in that definition. Someone could present an argument for a better way of thinking about what planets are and I might be swayed by it.

If the earth's orbit was perturbed to the point where it was expelled from the solar system I think I'd still consider it a planet, and similarly if it somehow ended up orbiting Jupiter.
 
theprestige said:
One thing to say is, "sounds like a good idea" is an argument from feelings, which elsewhere in the thread you seem to oppose.
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Ok, call it a reasonable thing to do, since knowing about the universe is part of teaching children about the world around us. The result is the same: sounds like a good idea to me.

Another thing: Do we want kids to learn the planets?
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Yes, because if you throw general topics at them early on, not only will that equip them with all sorts of knowledge that may come in handy, and allow them to understand things from at least a basic perspective, but it also will open doors to them, and potentially interest them in a future career.

It's also special pleading. We want kids to learn countries and presidents and mountains and rivers and stars, but we don't dumb down the definitions of these things to make it easier on their child brains.
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No but you exclude streams from the rivers category, don't you?

Why? You're stating these rules like they're fundamental principles or immutable laws.
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I don't understand your objection. I was responding to ceptimus' post about keeping the original definition of planet. If we keep it, then it would apply to what we know now of our solar system. Otherwise we have to alter the definition to excluse the other "wanderers" we've discovered and we're right back to square one.

Does it really, though?
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I think so. All professions have categories of this or that so you can classify them to simplify language and operations. Why do you think it would be different here?
 
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