New moon discovered at Pluto

[YellowSubmarine]

I'm just saying that you need to show these objects to the kids and focus on their physical characteristics as to why they are important, and it would make little difference if the 8 main planets are the “main planets” among many or the dwarf planets are “planetoids”. Neither is more confusing than the other.

 

[iguana_tonante]

You lost me here.

Physical characteristics, potential habitability, colour of the sky at sunset: you can focus on whatever you want during your lessons, but what you consider "important" (apparently, if you can write a science-fiction story set on them) doesn't mean anything to the actual definition of planet.

Personally, I feel that orbital characteristics are much more important than planetological features, but this is just because I'm much more interested in celestial mechanics than planetology.

 

[Pavonis]

... It's a Pluto exclusion clause.
We're going to treat planets out side the solar system in an accretion disk or kuiper belt differently? Where is the size definition here? How an you keep avoiding this issues of size?

It's not a "Pluto exclusion" clause. It's a new classification scheme to group objects based on their similarities, and objects in the Kuiper belt like Pluto are more similar to each other than to Earth or Mars.

As for the size definition, size is meaningless because composition determines mass and therefore gravity. Identically-sized balls of ice and iron are very different masses, so have different gravitational interactions.

I don't think there would be this much debate on the subject if they had just give a minimum size for a planet.

What minimum size would you prefer? A value that would just happen to include Pluto by size? How is that less arbitrary than the IAU's definition?

I'm just saying that you need to show these objects to the kids and focus on their physical characteristics as to why they are important, and it would make little difference if the 8 main planets are the “main planets” among many or the dwarf planets are “planetoids”. Neither is more confusing than the other.

Scientific definitions aren't crafted based on elementary school teaching requirements.

 

[Crazy Eddie]

The label is sound.

Not in astronomy it isn't, or celestial mechanics for that matter. Again, the reason for this is that a collection of free-floating objects large enough to form a "field" cannot remain stable for any amount of time; it will either drift apart, or clump together into a single object.

The only stable formations of that type are BELTS, where a series of objects roll into orbital trajectories to reduce collisions and render the system stable. The Trojan asteroids, for example, do not simply float there in space, but actually orbit the Jupiter-Sun libration point in a funky oscillating orbit shaped like a kidney bean; if you attempted to park an object near that point so that it was stationary with respect to Jupiter and the Sun, it would require constant thrust to hold it there against gravitational forces, and even then you'd have to constantly dodge other objects whirling about in a natural orbit.

To put that another way: the reason there's no such thing as an "asteroid field" is because gravitating bodies cannot be both stationary and close to each other at the same time. IF they're close enough to form a "field" then they'd can only stay that way if they're orbiting a common barrycenter, in which case they cease to be a field and become either a ring or a belt.

That makes no sense. Dominant merely means exerting a greater amount of control.

Right. In this case, greater than every other object in that orbital neighborhood combined. This is the reason that Ceres is considered to be a dwarf planet: even though it is considerably more massive than all the other asteroids, it only accounts for a third of the main belt's total mass. In order to be classified as a planet it would have to account for at least 50% of the belt's mass, but at that scale it would have to be at least twice as massive as it is now.

And for it's location Pluto and Ceres do indeed do.

But not for their ORBIT, which is the point.

 

[Crazy Eddie]

I'll say it again: they did it to avoid confusing school children.

This only makes matters worse then. All I can do is imagine the following conversation:

Johnnie: “Is Pluto a planet?”

Teacher: “It's a dwarf planet!”

Johnnie: “Cool!”

Two years later.

Johnnie: “My favourite planet is Pluto!”

Teacher: “Pluto is not a planet!”

Johnnie: “But you told me it is!”

Teacher: “No, I told you it is a dwarf planet!...”

Johnnie: “Isn't a dwarf planet a tiny planet?”

Teacher: “Yes.. No... Yes.. No... Um, yes... Um, no... Not really...”

Sort of a strawman you've introduced here, since most science teachers would (and do) answer that with a simple "yes." The GOOD ones will answer "Yes... but if you think about it, isn't a moon just a planet that orbits another planet?" and get a good classroom debate going.

The only teachers who will stumble over that issue are the ones who don't know what the fuck they're talking about and probably shouldn't be teaching science to begin with.

It's confusing.

Only if you take the extra effort to MAKE it confusing. But that's been true of science since at least the bronze age.

My classmates used to complain for far smaller discrepancies, and some of them simply couldn't get their head around them.

And that proves what, exactly? My classmates used to complain about having to do homework on Fridays.

The confusion with respect to the number of objects in the Solar system has a single simple solution – create a detailed map of the Solar system and show it to the kids.

How detailed should it be? Should it show only the main eight planets plus the asteroid belt? Should it show the eight planets plus Ceres and the four Plutoids? Should it show all eight planets, plus their moons, plus the centaurs, plus the long period comets, plus the four Plutioids, plus the dozen or so dwarf planet candidates?

Children, like conservatives, do not react well to subtlety. All of us learned the BASIC categories first and were introduced to the subcategories and exceptions later, in high school and college. Most people stop learning after that, and apply those grammar school labels to what we read in the papers; it is for THEM that the labels were changed, to keep things simple and un-subtle. For everyone else, the difference between a planet and a dwarf planet is a discernible difference that exists among various OTHER categories: Trans-Neptunian Objects, Classical Kuiper Belt Objects, Non-Classical Kuiper Belt Objects, Dwarf Planet Candidates, etc etc (i.e. objects in space that can belong to MULTIPLE categories and may or mat not ALSO be dwarf planets).

IOW: "Dwarf planet" is a general label that stupid people apply to a class of objects they don't have the time or patience to learn more about. The label applies because those objects--including Pluto--are unlike OTHER planets in a way that is meaningful to scientists, but general enough that you don't have to have a degree to understand why.

You can't really spare the kids from teaching them about those numerous objects

Correct. But at now you can put those various objects into a separate chapter called "Dwarf planets" and create another map that focusses on them specifically.

I'm just saying that you need to show these objects to the kids and focus on their physical characteristics as to why they are important...

Why ARE they important, exactly? And for which grade level?

I mean, if I were teaching a high school science class I would focus on Europa, Ceres and 64-Cybele, objects which are strongly believed to be largely composed of water and are significant in the debate about the origins of water--and therefore life--on Earth. The focus would be considerably different for lower grades, who may or may not know what an "asteroid" even is.

 

[Saquist]

The label is sound.

Not in astronomy it isn't, or celestial mechanics for that matter. Again, the reason for this is that a collection of free-floating objects large enough to form a "field" cannot remain stable for any amount of time; it will either drift apart, or clump together into a single object.

That's not true. It is accepted in astronomy and is no more stable than an asteroid belt. Stability isn't part of the qualification of the term. I have friends at the Brazos Bend Observatory (which I've volunteered for) that accept asteroid field or asteroid belt. They'll tell you it's the same thing. No one is that particular.

The only stable formations of that type are BELTS, where a series of objects roll into orbital trajectories to reduce collisions and render the system stable.

That's not true. The Asteroid belt is far from stable thus the constant watch because of perturbation by Jupiter or collisions by the observers. I've been told that their orbits are only reliable for about a year and then they are check again to make sure they don't became NEO's.

Right. In this case, greater than every other object in that orbital neighborhood combined. This is the reason that Ceres is considered to be a dwarf planet: even though it is considerably more massive than all the other asteroids, it only accounts for a third of the main belt's total mass. In order to be classified as a planet it would have to account for at least 50% of the belt's mass, but at that scale it would have to be at least twice as massive as it is now.

That's so arbitrary.
I can see why they didn't do this previously.

It's not a "Pluto exclusion" clause. It's a new classification scheme to group objects based on their similarities, and objects in the Kuiper belt like Pluto are more similar to each other than to Earth or Mars.

...so planets would be big asteroids then. At what point is an asteroid no longere an asteroid but a planet. There has to be a way to determine.

As for the size definition, size is meaningless because composition determines mass and therefore gravity. Identically-sized balls of ice and iron are very different masses, so have different gravitational interactions.

Then the term drawf planet should be thrown out. It's automatically a misnomer. There should be asteroids and then planets. Planets can be defined as the original dominating Stellar accretions from solar system formation defined by it's solar orbit inclination to solar zero

What minimum size would you prefer? A value that would just happen to include Pluto by size? How is that less arbitrary than the IAU's definition?

But they're the ones that chose an arbitary method instead of a reasoning. They chose to call it drawf and that name is based on size.

If they excluded Mercury based on the idea that it was a escaped moon from Neptune using it's extreme inclination and eccentricity that would make more sense thus it didn't form from the stellar accretion disk in seculsion but rather as part of another system. Then we could rightly call it a plutoid kuiper object because of it's location. But the location doesn't make it a plutoid it's orbit determines that non planet label.

There seems to be a distinct difference betwen formed moons and the Ceres and Eris type bodies....They are round but still irregular for the most part.

I just find it odd that they made the definition because of the possibility of finding more object's the size of ERIS but don't include a size determination in the definition....very baffling.

 

[Pavonis]

Mercury?

You're stuck on the term "dwarf", Saquist, like it is an insult. It is descriptive. There are dwarf stars and dwarf galaxies, and they're called that because they're smaller than the usual.

 

[YellowSubmarine]

There are dwarf stars and dwarf galaxies, and they're called that because they're smaller than the usual.

I do not think the comparison is completely fair – dwarf galaxies are usually smaller, less massive or at least less densely populated than non-dwarf galaxies. The is more or less true about dwarf stars when compared to giant stars and the dwarf stars would be less bright. In both cases, you can simply observe the object and tell that it is a dwarf one, and a non-dwarf one stands out in comparison next to it.

On the other hand, let's compare these:

On the left you have a planet, on the right you have a dwarf planet orbiting at 500 AU (hey, the cloud cycle is fuelled by nuclear fusion reactors!).

It's not necessarily a bad thing, but it's not unfair to complain that “dwarf” is a misnomer, and the objects you compare it to do not have this particular problem.

 

[Pavonis]

How would it be a misnomer in your example? If Earth were out in the Kuiper belt, I don't know if it would clear the orbit or not. But why label objects based on hypotheticals?

 

[YellowSubmarine]

The word “dwarf” usually refers to intrinsic characteristics (like in lemurs, stars and galaxies), in this case it refers to an extrinsic one, and so it violates the rule of least astonishment. I do not see it much of an issue given that “planet” in itself describes an extrinsic characteristic, but it's still a valid complaint.

 

[Pavonis]

Relative size is an extrinsic property, and dwarf is used in the same context for planets as for stars and galaxies. So far, the dwarf planets are smaller than the major planets. But size isn't the important property here.

If an Earth-sized body were found in the Kuiper belt, unless it cleared the entire orbit, it would be a dwarf planet. Why? Because it would be a dwarf relative to the size/mass required to clear the orbit.

By the way, 500 AU is at least 10 times further out than the Kuiper belt.

 

[Saquist]

THAT just makes no sense at all.
A planet the size of Earth in the Kuiper belt would still be a Dward planet. I'm concinced they have no idea what their doing.

 

[Pavonis]

You're welcome to join the community of active professional astronomers and become a member of the IAU. It's not as though the votes on the definitions were unanimous. You'd find some agreement with your position.

Personally, I think your definitions are more arbitrary and less rational than the current IAU definition.

 

[iguana_tonante]

I have friends at the Brazos Bend Observatory (which I've volunteered for) that accept asteroid field or asteroid belt. They'll tell you it's the same thing. (...)

Well, I cannot possibly refute your second-hand recount of things you might have heard one day talking with people tangentially involved in astronomic stuff, instead of, well, people who actually work as astronomers and the entire fucking International Astronomic Union. But I'm sure your friends at a second-rate kids' observatory know better than them.

THAT just makes no sense at all.
A planet the size of Earth in the Kuiper belt would still be a Dward planet. I'm concinced they have no idea what their doing.

lol wut? Today's lesson: don't write about astronomy when you are drunk.

 

[Crazy Eddie]

The label is sound.

Not in astronomy it isn't, or celestial mechanics for that matter. Again, the reason for this is that a collection of free-floating objects large enough to form a "field" cannot remain stable for any amount of time; it will either drift apart, or clump together into a single object.

That's not true. It is accepted in astronomy and is no more stable than an asteroid belt. Stability isn't part of the qualification of the term.

Never said it was. I said that the lack of stability is the reason why asteroid fields CANNOT EXIST for any amount of time. It would be the same as if you started talking about a "reactionless space drive." The concept is linguistically sound, and is even mentioned in scientific circles, but it's not a real thing that has ever been known to exist, or is even postulated to exist in the future.

That's not true. The Asteroid belt is far from stable

Stable enough that the belt will not dissipate before the destruction of the solar system, which in ASTRONOMICAL terms makes it a stable formation. An asteroid field, so defined, can only exist for a period of a few months at most, and then can only form in the first place from the breakup of another object (i.e. a collision between two asteroids that shatters both of them).

I've been told that their orbits are only reliable for about a year and then they are check again to make sure they don't became NEO's.

You've been lied to.

That's so arbitrary.

Science usually is.

...so planets would be big asteroids then. At what point is an asteroid no longere an asteroid but a planet.

When it is large enough to pull itself into a sphere.

Then the term drawf planet should be thrown out. It's automatically a misnomer. There should be asteroids and then planets. Planets can be defined as the original dominating Stellar accretions from solar system formation defined by it's solar orbit inclination to solar zero

First of all, the planets weren't the ORIGINAL dominating stellar accretions, but the FINAL ones. Second of all, NONE of the planets have a zero inclination, all of them are slightly inclined above or below solar zero.

But they're the ones that chose an arbitary method instead of a reasoning. They chose to call it drawf and that name is based on size.

Actually, it is based on MASS. That is to say, a dwarf planet is a planet that has NOT cleared its neighborhood of other massive objects. Again, Earth would be a dwarf planet if it shared an orbit with Venus and Mars.

I just find it odd that they made the definition because of the possibility of finding more object's the size of ERIS but don't include a size determination in the definition....very baffling.

Because it isn't about size, it's about MASS. A ten ton object that shares its orbit with two dozen one-ton objects is NOT the dominant body in that orbit. It doesn't matter if that object is the size of a house or the size of a mouse, if it's the size of a box or the size of a fox. If it doesn't have the majority mass, then it is a dwarf planet.

 

[Crazy Eddie]

It's not necessarily a bad thing, but it's not unfair to complain that “dwarf” is a misnomer, and the objects you compare it to do not have this particular problem.

In this case dwarf is NOT a misnomer, since these are indeed spherical (i.e. planetary) bodies that are not dominant in their orbital neighborhoods. It's a fairly rigid and testable definition that allows for non-arbitrary classification of new objects, even if the definition ITSELF was arrived at arbitrarily.

FYI: the Sun is a yellow dwarf star. That isn't a misnomer either.

 

[YellowSubmarine]

Yellow dwarf star is certainly a misnomer, the Sun is white, not yellow.

 

[Maurice]

Yellow dwarf star is certainly a misnomer, the Sun is white, not yellow.

Is it's spectral class A? Nope, it's G, so it's yellow.

 

[YellowSubmarine]

Some less luminous G type stars might be yellowish, but the Sun is most definitely white. The white colour that humans perceive was determined by the light from Sun in the first place. I'm almost certain that any alien race perceives their own star as white actually.

 

[iguana_tonante]

Some less luminous G type stars might be yellowish, but the Sun is most definitely white. The white colour that humans perceive was determined by the light from Sun in the first place. I'm almost certain that any alien race perceives their own star as white actually.

Sunlight looks an extremely bright yellow to me, not white. Actually, I've never heard anyone saying that they perceived sunlight as white.