Pluto the Planet :D

[Zeb.]

Does it have FREAKIN MOONS?

It's a planet

But what about Mercury and Venus? DO THEY HAVE FREAKIN MOONS???

As you can see, no amount of misguided argument will change the fact that it just doesn't fit into the "Planet" category. It's a dwarf planet, case closed.

[Sampa]

Pluto will ALWAYS be a planet in my book!

[NFUN]

Is there really going to be that much of an issue going forward if people call Pluto a planet instead of a dwarf planet? Hard to say, because people bicker constantly over such insignificant issues.

Is it okay to call a dwarf planet a planet? I don't see why not. "Dwarf planet" even has planet in the name, which implies it is a type of planet. If someone says, "Look at that car over there," I doubt anyone has ever responded with, "That's not a car, it's an SUV."

From my point of view, that analogy would be for gas giants vs ice giants vs terrestrial planets. I would contend that for dwarf planets, SUV would be replaced with truck, where one can call a truck a car if they wish, but they'd be modestly mistaken, and only correct if they called it an automobile.

[Albert VDS]

And a planet the size of Pluto or Ceres that has cleared its orbit would not be dwarf planet - and a planet the size of Earth or Jupiter that has not cleared its orbit would be dwarf planet?

It is mind boggling how many people misinterpret the 3rd criteria; "Clearing the neighborhood around its orbit".

It means that the object has removed, accreted or captured all other objects of comparable size in it's orbital zone.

In other words, a planet wouldn't be in the Kuiper or Asteroid Belt because it would have cleared it's orbital zone.

2 planets can still share an orbit as long as they aren't in each others orbital zone.

[peadar1987]

Dwarf planets are not planets, as per the IAU definition. They voted to designate Pluto a dwarf planet, and in the very next motion, voted against making dwarf planets a subset of planets. Pretty bizarre if you ask me.

[Superfluous J]

If someone says, "Look at that car over there," I doubt anyone has ever responded with, "That's not a car, it's an SUV."

Unless it's a Jeep. Jeep drivers for some reason refuse to think of their cars as cars, trucks, or even SUVs. They're Jeeps. Period. End of story.

[Dodgey]

Unless it's a Jeep. Jeep drivers for some reason refuse to think of their cars as cars, trucks, or even SUVs. They're Jeeps. Period. End of story.

I think a better example would be a comparison between a semi trailer, a standard cat and a child's ride on toy car. Although comparisons can be between them there is obviously one which does not belong.

I don't understand why people are calling for a more simple definition. The more simple the definition the more problems we have. For example if define a planet as a body with a raidus of more than 20'000km than what about a body with a raidus of 19'999km. Does that one kilometer really make a difference? Where do you draw the line. That's why we need more complex definitions not simpler.

[vger]

I think a better example would be a comparison between a semi trailer, a standard cat and a child's ride on toy car. Although comparisons can be between them there is obviously one which does not belong.

We have planets that have an atmosphere, and we have planets that are nothing but an atmosphere. I'd say we already have something pretty vague going on.

[Xannari Ferrows]

Don't you all know? That's where Amelia Earhart's plane is!

Also some other guy. Can't remember his name. I believe it was Fred? Fred someone, I don't know.

Edited July 17, 2015 by Xannari Ferrows

[lajoswinkler]

Wow, still beating the dead horse? Grow up, folks...

[Windspren]

standard cat

Where do I get one?!

[vger]

Wow, still beating the dead horse? Grow up, folks...

Technically, it's a Shetland Pony, not a Horse.

[Bill Phil]

Wow, still beating the dead horse? Grow up, folks...

This isn't a case of "growing up" or being immature. I think the IAU's definition is using external qualities relative to the body in question, whereas I believe that all means of determining how to classify what the object is should be based on internal qualities.

Internal meaning that they're physical properties it possesses. External properties are properties that aren't physical properties, such as where it is or the environment around it.

I believe eve that not only should Pluto be reclassified as a planet, but Ceres and other similar bodies should be classified as planets as well.

Would you classify an asteroid as something else if it's not on the asteroid belt? That's a similar type of thing with planets, although not quite exact.

[tater]

Science doesn't work by voting. Even so, the IAU cast the vote with a quorum of a tiny subset of members.

The new definition is arbitrary (as was the old). I'm fine with the rationale, but it's arbitrary. I'm a little more concerned with the lack of math in the definition, frankly. Define "cleared the neighborhood" for me mathematically. How small can a body be in the neighborhood, and bump a standing planet off the list? If a dwarf planet came swinging in, was perturbed into jupiter's orbit for some period of time, does Jupiter get bumped? Does the definition include a timeframe for possibly transient bodies?

Hydrostatic equilibrium? Ice will form a sphere with less mass than rock, why not set a mass? You could let liquid water out in a way that it would form a sphere, then freeze. If I put it between Uranus and Neptune, in a stable orbit, is it a planet?

I get that they don't want 1000 planets, and agree---but the definition should be mathematically precise.

[Kibble]

Internal meaning that they're physical properties it possesses.

Actually a good definition for (major) planet could be "has a differentiated interior, but is not doing nuclear fusion". Orbiting the Sun seems like a superfluous qualifier to me!

[vger]

Would you classify an asteroid as something else if it's not on the asteroid belt? That's a similar type of thing with planets, although not quite exact.

I'm siding with Pluto being a planet by the way, but it brings up an interesting point. Without the Dwarf Planet classification, how would you determine what is a planet vs. what is an asteroid? Is it simply a certain degree of roundness? If Phobos was Earth-sized and had its own orbit somewhere between Venus and Mercury, would it be a planet or an asteroid? Based on the technicals, we would be calling it an asteroid, but I'm pretty certain everybody would think that was ridiculous.

[Alshain]

Science doesn't work by voting. Even so, the IAU cast the vote with a quorum of a tiny subset of members.

The new definition is arbitrary (as was the old). I'm fine with the rationale, but it's arbitrary. I'm a little more concerned with the lack of math in the definition, frankly. Define "cleared the neighborhood" for me mathematically. How small can a body be in the neighborhood, and bump a standing planet off the list? If a dwarf planet came swinging in, was perturbed into jupiter's orbit for some period of time, does Jupiter get bumped? Does the definition include a timeframe for possibly transient bodies?

Hydrostatic equilibrium? Ice will form a sphere with less mass than rock, why not set a mass? You could let liquid water out in a way that it would form a sphere, then freeze. If I put it between Uranus and Neptune, in a stable orbit, is it a planet?

I get that they don't want 1000 planets, and agree---but the definition should be mathematically precise.

All definitions of this nature are arbitrary and none of them are mathematically precise. How can they be? This is the first time we've been close enough to get mathematical figures.

[tater]

What about trojans? How many objects does jupiter share its "neighborhood" with? Many thousands, right?

[Superfluous J]

What about trojans? How many objects does jupiter share its "neighborhood" with? Many thousands, right?

The difference is, the Trojans aren't there in spite of Jupiter, but because of it. I'm not saying the whole "clear the neighborhood" thing is a good idea, but that was already thought of and accounted for in the definition.

Everything in Jupiter's orbital "neighborhood" is either passing through once or a few times before it'll be gone (Comets and whatnot), or is there because it was so wrangled by Jupiter into that state. The same cannot be said of Pluto and the other billion KBOs.

[tater]

All definitions of this nature are arbitrary and none of them are mathematically precise. How can they be? This is the first time we've been close enough to get mathematical figures. Space has always been about observation, so it is appropriate that planets are defined by observations.

I said any such definition would be arbitrary. It's entirely possible to be mathematically precise, however, the definition is theoretical (precise), then applied to real bodies. They are talking about clearing orbital neighborhoods. They don't say how clear, the implication is a single intruding body would be disqualifying---if I can imply that, it starts looking like magical books that require interpretation, not science. Such a rule should not be as frankly random and subjective as it is. We should know that we have not mapped all the objects yet. At this point, it would be no more less arbitrary to make the definition a suggesting for attributing status, and vote case by case.

It is not simple, granted. It's analogous to zoology (which is where astronomy was for a long time). Look at definitions of species, for example. Paleontological definitions, appearance, can they breed, will they breed, etc, etc.

I'm not a Pluto is a planet partisan, actually, it's pretty puny, and I'm fine with dwarf planet, but the new definition only gives the appearance of being objective when it is in fact subjective.

[Alshain]

What about trojans? How many objects does jupiter share its "neighborhood" with? Many thousands, right?

Jupiter Trojans are orbiting in Jupiter's Lagrange points, they can't really collide with Jupiter unless the Jupiter Trojans themselves collide and get ejected. In this case it's nearly impossible for Jupiter to clear it's orbit and that is not the intent of the definition.

[tater]

The difference is, the Trojans aren't there in spite of Jupiter, but because of it. I'm not saying the whole "clear the neighborhood" thing is a good idea, but that was already thought of and accounted for in the definition.

Everything in Jupiter's orbital "neighborhood" is either passing through once or a few times before it'll be gone (Comets and whatnot), or is there because it was so wrangled by Jupiter into that state. The same cannot be said of Pluto and the other billion KBOs.

The earth shares its orbit with thousands of asteroids. I read the definition, and I don;t see any mention of trojans, or in fact any co-orbital bodies, just "neighborhood."

Better to say µ must be >100 or something.

- - - Updated - - -

Jupiter Trojans are orbiting in Jupiter's Lagrange, they can't really collide with Jupiter unless the Jupiter Trojans themselves collide and get ejected. In this case it's nearly impossible for Jupiter to clear it's orbit.

They are in jupiter's neighborhood, are they not? They orbit the sun, right? What does the definition say? Nothing.

Like I said, imprecise.

Edited July 17, 2015 by tater

[Alshain]

They are in jupiter's neighborhood, are they not? What does the definition say? Heck, how does the definition treat moons?

Like I said, imprecise.

The definition of "neighborhood" is imprecise. I would say objects that never leave a lagrange point are not part of it's neighborhood. Like I said, it can't be defined mathematically unless you define every word of the definition mathematically and then you must define every word of those definitions mathematically ad infitum. I'll say it again, all definitions of this type are arbitrary and imprecise.

Edited July 17, 2015 by Alshain

[tater]

The definition of "neighborhood" is imprecise. I would say objects that never leave a lagrange point are not part of it's neighborhood. Like I said, it can't be defined mathematically unless you define every word of the definition mathematically and then you must define every word of those definitions mathematically ad infitum. I'll say it again, all definitions of this type are arbitrary and imprecise.

I might agree (actually, I do ), but the definition doesn't say squat about Lagrange points. Like I said, incredibly imprecise. Amazing it would occur to them to define something and not bother to, you know, define it. They should be explicit about hydrostatic equilibrium, as well. Define acceptable eccentricity, or just go with a mass, they can certainly pick a theoretical value for a mass that fulfills this. It;s also better because they can get the mass far easier than the shape observationally for faint objects.

[NFUN]

I might agree (actually, I do ), but the definition doesn't say squat about Lagrange points. Like I said, incredibly imprecise. Amazing it would occur to them to define something and not bother to, you know, define it. They should be explicit about hydrostatic equilibrium, as well. Define acceptable eccentricity, or just go with a mass, they can certainly pick a theoretical value for a mass that fulfills this. It;s also better because they can get the mass far easier than the shape observationally for faint objects.

There are ways to calculate the degree of which a body has cleared its neighborhood, such as the Stern-Levison parameter. It would be trivial for the IAU to choose a value to determine the cutoff point for being a planet or dwarf planet, or a range in which individual cases would be decided. In any case, the value between the most messy planet and cleanest dwarf planet differs by many orders of magnitude, regardless of what specific formula is used.

https://en.m.wikipedia.org/wiki/Clearing_the_neighbourhood