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beskeptical
2009-Feb-24, 08:00 AM
Went to the most wonderful talk by Neil deGrasse Tyson tonight. Hilarious, absolutely hilarious. I love this guy. What a great presenter of astronomy and related topics. If you ever get the chance to hear the guy speak, go for it. You will not be disappointed.

But on to the topic, Pluto Is Not a Planet (http://www.planetary.org/explore/topics/topten/tyson_pluto_is_not.html). I have heard for years there was plenty of reasons Pluto was not a planet. So I'm not one of those folks who gave a rats behind. But right off the bat, just hearing we've IDed a gazillion other Kuiper Belt objects and I understood Pluto indeed is one of them and not a planet.

Tyson's talk was great. He understands what the difference is between facts that mean something and facts that don't.

novaderrik
2009-Feb-24, 10:03 AM
is he different in a live setting than he is on all those tv specials?
on tv, he comes across to me like he thinks he's talking to a bunch of 1st graders.

HypothesisTesting
2009-Feb-24, 04:39 PM
Went to the most wonderful talk by Neil deGrasse Tyson tonight. Hilarious, absolutely hilarious. I love this guy. What a great presenter of astronomy and related topics. If you ever get the chance to hear the guy speak, go for it. You will not be disappointed.

But on to the topic, Pluto Is Not a Planet (http://www.planetary.org/explore/topics/topten/tyson_pluto_is_not.html). I have heard for years there was plenty of reasons Pluto was not a planet. So I'm not one of those folks who gave a rats behind. But right off the bat, just hearing we've IDed a gazillion other Kuiper Belt objects and I understood Pluto indeed is one of them and not a planet.

Tyson's talk was great. He understands what the difference is between facts that mean something and facts that don't.

Exactly,

It is just a KBO. Obviously, when Clyde Tombaugh discovered Pluto in 1930 they were confused because they didn't know about the Kuiper belt objects. So they dreamed of it being a planet and made it into one.

I'm not sure I even agree with its current classification of dwarf planet because it is now mixed in with Ceres and others. I don't see the connection, Pluto is a KBO, Ceres is in asteroid belt. They should have just left Pluto as a KBO.

Amber Robot
2009-Feb-24, 05:31 PM
But right off the bat, just hearing we've IDed a gazillion other Kuiper Belt objects and I understood Pluto indeed is one of them and not a planet.

But see, that's the crux of the matter... it all depends on how you define the word "planet".

dgruss23
2009-Feb-24, 07:47 PM
I've felt for a long time that Pluto should not be considered a planet. I'm glad the IAU has attempted to clarify the definitions. I also think they need to re-evaluate how a "moon" is defined. IMO it is absurd to call every piece of space debris they find orbiting Jupiter and Saturn "moon".
How many new "moons" did they find when the Galileo probe reached Jupiter? All I know is that there were ~18 moons at one point and then it ballooned to over 60.

What will always make any classification system difficult is the boundary cases. If we say X criteria is needed to make something a planet, then there will likely be some object that has X+ or X- for that criteria just enough that someone will say "Well what about this object with X-?"

dgruss23
2009-Feb-24, 07:51 PM
But see, that's the crux of the matter... it all depends on how you define the word "planet".

In some ways I think defining planet is trickier than other classification systems. The sample size within our solar system was is so small to begin with that it doesn't take long before we find those borderline cases like Pluto.

I think that perhaps - and this is normally a bad idea when developing a classification system - we need a classification system for planet, moon, etc. that takes into account theories of solar system formation.

Jeff Root
2009-Feb-24, 08:57 PM
I don't see any need for a classification system.

I don't see any reason to change the meanining of the term "moon".
If you can identify and keep track of a body orbiting a planet, it is a
moon. So what if you can identify and track ten million of them?
They are still moons. Their numbers are irrelevant.

-- Jeff, in Minneapolis

Amber Robot
2009-Feb-24, 09:59 PM
I don't see any need for a classification system.

I don't see any reason to change the meanining of the term "moon".
If you can identify and keep track of a body orbiting a planet, it is a
moon. So what if you can identify and track ten million of them?
They are still moons. Their numbers are irrelevant.

-- Jeff, in Minneapolis

So you would say that Saturn's rings are all moons?

beskeptical
2009-Feb-24, 10:50 PM
is he different in a live setting than he is on all those tv specials?
on tv, he comes across to me like he thinks he's talking to a bunch of 1st graders.Funny, at first I thought you were talking about Pluto (the dog).

Tyson was a very engaging funny enthusiastic speaker/teacher. He does obviously enjoy teaching young children, and the talk was aimed at the lay person here.

But I know a fair amount of the science involved and I found what he had to say extremely interesting. I figured out why Pluto wasn't a planet in the first 5 minutes when Tyson described the discovery of other Kuiper Belt objects, same orbit, same composition. But it was especially interesting to learn the history of planetary discoveries and how Ceres had been named a planet at one time. No one cared when it was renamed an asteroid.

And Tyson also presented the information in a very critically thinking way. It doesn't matter what you name something, but rather does the name tell you anything useful. Grouping planets by other characteristics than the name, planet, provides much more relevant information. I just love hearing different ways of viewing the world.

beskeptical
2009-Feb-24, 10:54 PM
Exactly,

It is just a KBO. Obviously, when Clyde Tombaugh discovered Pluto in 1930 they were confused because they didn't know about the Kuiper belt objects. So they dreamed of it being a planet and made it into one.

I'm not sure I even agree with its current classification of dwarf planet because it is now mixed in with Ceres and others. I don't see the connection, Pluto is a KBO, Ceres is in asteroid belt. They should have just left Pluto as a KBO.
Tyson explained the history behind and the meaninglessness of the dwarf planet name. It's round (the size gravity makes a body round) and smaller than a planet and it is at the center of its group if it has moons (so as not to be an issue since a lot of moons are larger). :p That's it. Not a lot of useful category data.

KBOs OTOH, redefine the shape/nature of the solar system. Lot's of information in the name, KBO.

beskeptical
2009-Feb-24, 10:58 PM
But see, that's the crux of the matter... it all depends on how you define the word "planet".No, the crux is, it all depends on the usefulness of the label. :) That's what I learned last night.

beskeptical
2009-Feb-24, 11:02 PM
...
I think that perhaps - and this is normally a bad idea when developing a classification system - we need a classification system for planet, moon, etc. that takes into account theories of solar system formation.Bingo. The classification system is best if the categories mean something besides just arbitrary divisions on a continuum.

Round means a certain size gravity acts on. KBOs mean a certain orbit and a certain specific process when the solar system coalesced. Asteroid belt means the objects never cleared their orbiting field and became a planet. Gas giants and rocky planets formed with different processes and so on.

Amber Robot
2009-Feb-24, 11:55 PM
No, the crux is, it all depends on the usefulness of the label. :) That's what I learned last night.

Yes. I think Stephen Soter said it very well:



If Pluto is included as a planet, we have no physical basis for excluding Eris, dozens of other large spherical KBOs, and Ceres. The term "planet" would then lose any taxonomic utility. But an important function of scientific nomenclature is to reflect natural relationships, not to obscure them.
...
To be useful, a scientific definition should be derived from, and draw attention to, the basic principles.


http://arxiv.org/abs/astro-ph/0608359

Jeff Root
2009-Feb-25, 12:07 AM
I don't see any need for a classification system.

I don't see any reason to change the meanining of the term "moon".
If you can identify and keep track of a body orbiting a planet, it is a
moon. So what if you can identify and track ten million of them?
They are still moons. Their numbers are irrelevant.
So you would say that Saturn's rings are all moons?
Rings are not bodies-- they are collections of bodies.

Very few of the bodies making up Saturn's rings have been identified
and kept track of. When that does happen, those particular bodies
can be considered "moons".

-- Jeff, in Minneapolis

Jeff Root
2009-Feb-25, 12:24 AM
... it was especially interesting to learn the history of planetary
discoveries and how Ceres had been named a planet at one time.
No one cared when it was renamed an asteroid.
But then, Pluto has 14 times the mass of Ceres. In fact, Pluto
has three and a half times the combined mass of all the asteroids
in the main asteroid belt!

-- Jeff, in Minneapolis

Amber Robot
2009-Feb-25, 12:49 AM
Rings are not bodies-- they are collections of bodies.

Very few of the bodies making up Saturn's rings have been identified
and kept track of. When that does happen, those particular bodies
can be considered "moons".

-- Jeff, in Minneapolis

So, if they will be moons once we can track them, why not call them moons now? One day we may have the technology to track them, and at that time, nothing about their nature will have changed.

Jeff Root
2009-Feb-25, 01:21 AM
Rings are not bodies-- they are collections of bodies.

Very few of the bodies making up Saturn's rings have been identified
and kept track of. When that does happen, those particular bodies
can be considered "moons".
So, if they will be moons once we can track them, why not call them
moons now? One day we may have the technology to track them,
and at that time, nothing about their nature will have changed.
That is fine.

-- Jeff, in Minneapolis

George
2009-Feb-25, 01:23 AM
Went to the most wonderful talk by Neil deGrasse Tyson tonight. Hilarious, absolutely hilarious. I love this guy. What a great presenter of astronomy and related topics. That is my impression as well.

His visits with comedians are quite a treat. Here he is discussing Pluto on the Jon Stewart Show (http://www.thedailyshow.com/video/index.jhtml?videoId=216998&title=neil-degrasse-tyson).

beskeptical
2009-Feb-25, 02:05 AM
But then, Pluto has 14 times the mass of Ceres. In fact, Pluto
has three and a half times the combined mass of all the asteroids
in the main asteroid belt!

-- Jeff, in MinneapolisSo your point is Pluto should be a planet and all the other Kuiper Belt objects not planets because they are smaller?

timb
2009-Feb-25, 02:09 AM
Bingo. The classification system is best if the categories mean something besides just arbitrary divisions on a continuum.


Quite. That's one reason many astronomers dislike the planet/BD distinction that the IAU has drawn: is the mass under or over 13 MJ? In their view giant planets, brown dwarfs and stars probably form by different processes, and it happens that the mass range of brown dwarfs overlaps with that of the largest planets and the smallest stars.


Round means a certain size gravity acts on. KBOs mean a certain orbit and a certain specific process when the solar system coalesced. Asteroid belt means the objects never cleared their orbiting field and became a planet. Gas giants and rocky planets formed with different processes and so on.

I look forward to the IAU defining a terrestrial planet as one with a mass of less than 10 ME :rolleyes: With exoplanets part of the problem is that mass is one of the few things we generally have an estimate for, so there is tendency to want to hang everything on mass. It's a bit like trying to classify Earth's living things according to only their mass.

In fairness to the IAU, it's appropriate that the definition evolve. Because our understanding of planetary formation is limited it is to be expected that the current definitions are only provisional and objects are going to be reclassified.

Jeff Root
2009-Feb-25, 07:13 AM
But then, Pluto has 14 times the mass of Ceres. In fact, Pluto
has three and a half times the combined mass of all the asteroids
in the main asteroid belt!
So your point is Pluto should be a planet and all the other Kuiper
Belt objects not planets because they are smaller?
No, I didn't say anything about other Kuiper Belt objects. I just
said that Pluto is enormous compared to any asteroid in the main
asteroid belt.

-- Jeff, in Minneapolis

beskeptical
2009-Feb-25, 11:50 AM
Did you have a point then?

Jeff Root
2009-Feb-25, 12:18 PM
Not that I know of.

-- Jeff, in Minneapolis

Starfury
2009-Mar-01, 09:16 PM
I applauded Dr. Tyson for his decision to remove Pluto from the planetary display at the Hayden Planetarium. I saw a program about Pluto's status on the Science Channel, and they had a sound bite from a grade schooler who said "I think Pluto should be a planet, it has lots of interesting geographical features."

My reaction was "How do you know what Pluto's geographical features are?? Not even the Hubble can take a clear picture of it. Son, if you know what Pluto's geographical features are, there are scores of planetary scientists who want to talk to you."

:lol:

beskeptical
2009-Mar-02, 01:10 AM
Well, just wait a few years... (http://www.nasa.gov/mission_pages/newhorizons/news/nh_jupiter_oct09.html)


New Horizons passed Jupiter on Feb. 28, [2007] riding the planet’s gravity to boost its speed and shave three years off its trip to Pluto.

Neverfly
2009-Mar-02, 03:01 AM
Did you have a point then?

I caught the point.

Our classification system is invented and reality doesn't conform to it-not will it ever.

If Saturn has Moons and one of those moons is a nameless speck of dust that no one has seen- who cares? We still know that a bunch of stuff is floating out there.
So we draw lines - then folks argue about where those lines are.

Pluto falls between our carefully drawn lines.
It doesn't really match a KBO very well either.

I say that we just end the problem by classifying Pluto as a Pluto and just saying that the Solar System contains only one.
We have such and such many planets, such and such many moons, such and such many asteroids, Such and such many KBO's, One Star and One Pluto.

Neverfly
2009-Mar-02, 03:08 AM
I can Picture a Kid in Astronomy Class now...

"What's that?"
"That's Venus. It's a Planet. It orbits the Sun. It has a massive greenhouse effect that makes it the hottest planet in the system."
"What's that?"
"That's Earth. That's also a planet. It orbits the Sun too, and it's where we live."
"What's that?"
"That's a Comet. That one is named Halley's, it orbits in a long elliptical orbit that is close to the Sun a short time and very far away the rest of the time."
"What's that?"
"That's a pluto. Our Solar System has only one of those, but there may be many solar systems and Moon systems that have one similar to it. Ours is called Pluto. It orbits the Sun and causes arguments on Earth."

Amber Robot
2009-Mar-02, 03:10 AM
"That's a pluto. Our Solar System has only one of those, but there may be many solar systems and Moon systems that have one similar to it. Ours is called Pluto. It orbits the Sun and causes arguments on Earth."

An astronomy teacher who would say this isn't very good.

beskeptical
2009-Mar-03, 12:34 AM
...
Pluto falls between our carefully drawn lines.
It doesn't really match a KBO very well either.....That's not what Tyson said. What are you basing that statement on?

beskeptical
2009-Mar-03, 12:36 AM
...
"That's a pluto. Our Solar System has only one of those, but there may be many solar systems and Moon systems that have one similar to it. Ours is called Pluto. It orbits the Sun and causes arguments on Earth."No, our solar system has thousands of KBOs. That was the problem. If you continue to categorize Pluto as a planet, what do you call all the other newly discovered KBOs?


Kuiper Belt Objects (http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong)
More than 1,000 KBOs have been identified since 1992.One is even bigger than Pluto. It was called Xena but now has the official name, Eris. (http://web.gps.caltech.edu/~mbrown/planetlila/)

beskeptical
2009-Mar-03, 12:48 AM
Here are 2 more sources worth looking at.

Kuiper Belt Object Homepage (http://www.ifa.hawaii.edu/faculty/jewitt/kb.html)

Wiki on KBOs (http://en.wikipedia.org/wiki/Kuiper_belt)

Bearded One
2009-Mar-03, 12:48 AM
No, our solar system has thousands of KBOs. That was the problem. If you continue to categorize Pluto as a planet, what do you call all the other newly discovered KBOs?I'm for calling them planets if they are big enough. The current system limits us to 8 planets... forever. Even bodies around other stars can't be called simply "planets". Why is having more than 8 planets a bad thing?

Neverfly
2009-Mar-03, 12:50 AM
No, our solar system has thousands of KBOs. That was the problem. If you continue to categorize Pluto as a planet, what do you call all the other newly discovered KBOs?


Kuiper Belt Objects (http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong)One is even bigger than Pluto. It was called Xena but now has the official name, Eris. (http://web.gps.caltech.edu/~mbrown/planetlila/)

You seem to have totally missed the joke...

HypothesisTesting
2009-Mar-03, 03:48 PM
Tyson explained the history behind and the meaninglessness of the dwarf planet name. It's round (the size gravity makes a body round) and smaller than a planet and it is at the center of its group if it has moons (so as not to be an issue since a lot of moons are larger). :p That's it. Not a lot of useful category data.

KBOs OTOH, redefine the shape/nature of the solar system. Lot's of information in the name, KBO.

It would be best if they had a scientific classification system based on the history of the solar system, how certain groups of objects formed.

This would group all KBOs into a group defined by their history as comets and thus they have similar props. to each other. These would include Pluto, Eris.

This would group the Oort cloud objects, probably including Sedna.

The asteroid belt group would have a certain history.

This could be repeated for all the objects, because they are in groups of similar histories.

Of course, this won't happen. The history is too strongly implanted in scientists' memories so they can't let go of that "planet" designation even it's an asteroid like Ceres, still they cling to "dwarf planet" , etc. In 2006, the IAU was correct to demote Pluto, but then they did not follow through correctly and invented that "dwarf planet" nonsense.What is a planet originally, a
"wanderer" which included the obvious zodiac belt objects.

beskeptical
2009-Mar-03, 11:10 PM
I'm for calling them planets if they are big enough. The current system limits us to 8 planets... forever. Even bodies around other stars can't be called simply "planets". Why is having more than 8 planets a bad thing?It isn't but if you start adding every rock and asteroid, every KBO and so on, you just end up with a meaningless name, planet. Might as well call them all orbiting thingies.

beskeptical
2009-Mar-03, 11:11 PM
You seem to have totally missed the joke...I'm still missing it. Care to fill me in?

beskeptical
2009-Mar-03, 11:14 PM
....

Of course, this won't happen. The history is too strongly implanted in scientists' memories so they can't let go of that "planet" designation even it's an asteroid like Ceres, still they cling to "dwarf planet" , etc. In 2006, the IAU was correct to demote Pluto, but then they did not follow through correctly and invented that "dwarf planet" nonsense.What is a planet originally, a
"wanderer" which included the obvious zodiac belt objects.Your time frame is too short. It will happen. It has happened in the past.

I was not aware before hearing Tyson's talk but apparently the Moon and the Sun were in the original list of planets. And the first asteroid was a planet then it wasn't.

Jeff Root
2009-Mar-05, 07:56 AM
Piazzi's initial estimate of the size of Ceres was far too large. He
thought it was larger than Earth. After the discovery of Pallas, William
Herschel determined that the new bodies are very small compared to
the other planets, but severely underestimated the diameter of Ceres
as only a quarter of what we now measure. He proposed that these
bodies should be called "asteroids" rather than planets, and the term
has become standard in English. Other terms used synonymously
include planetoid and minor planet.
We can wonder if Herschel would have made up a new term if he had
thought Ceres was the size of Pluto.

-- Jeff, in Minneapolis

Jeff Root
2009-Mar-05, 08:13 AM
...if you start adding every rock and asteroid, every KBO and so on,
you just end up with a meaningless name, planet. Might as well call
them all orbiting thingies.
The term "planet" sounds better than "orbiting thingy", and
distinguishes natural bodies orbiting a star from things put into
orbit by humans.

I would argue that any body smaller than a star but large enough
to be seen from a distance may be reasonably termed a "planet".
If it orbits another planet, of course, it would also be a "moon".

The smaller bodies of the Solar System are generically termed
"minor planets".

-- Jeff, in Minneapolis

beskeptical
2009-Mar-06, 10:45 AM
The term "planet" sounds better than "orbiting thingy", and
distinguishes natural bodies orbiting a star from things put into
orbit by humans.

I would argue that any body smaller than a star but large enough
to be seen from a distance may be reasonably termed a "planet".
If it orbits another planet, of course, it would also be a "moon".

The smaller bodies of the Solar System are generically termed
"minor planets".

-- Jeff, in MinneapolisSo then, are comets and asteroids also planets, minor or otherwise?

Disinfo Agent
2009-Mar-06, 04:34 PM
I think that perhaps - and this is normally a bad idea when developing a classification system - we need a classification system for planet, moon, etc. that takes into account theories of solar system formation.Taking the formation into acount is a good idea in a classification system. It's what they do in biology with living beings, and in a sense also what Mendeleev did in chemsitry with his periodic table. I would even go so far as to say that a classification system based on formation is the ideal system of classification.

The problem is, I think, that at this moment in time there is still a great deal we don't know about the formation of the planets and other stellar bodies.

Jeff Root
2009-Mar-06, 06:01 PM
The term "planet" sounds better than "orbiting thingy", and
distinguishes natural bodies orbiting a star from things put into
orbit by humans.

I would argue that any body smaller than a star but large enough
to be seen from a distance may be reasonably termed a "planet".
If it orbits another planet, of course, it would also be a "moon".

The smaller bodies of the Solar System are generically termed
"minor planets".
So then, are comets and asteroids also planets, minor or otherwise?
That is a direct inference from what I said, yes.

-- Jeff, in Minneapolis

beskeptical
2009-Mar-07, 08:41 AM
That is a direct inference from what I said, yes.

-- Jeff, in MinneapolisIt makes the name, planet, mean very little. A planet orbits a sun. If it is tiny, we call it a dwarf planet.

That's a heck of a lot of planets (http://en.wikipedia.org/wiki/File:InnerSolarSystem-en.png) in our solar system then.

Jeff Root
2009-Mar-07, 09:10 AM
It makes the name, planet, mean very little.
It does??? Please explain.



A planet orbits a sun. If it is tiny, we call it a dwarf planet.
Is that your interpretation of what we have currently, your
interpretation of my terminology, your own preference, or
something else?



That's a heck of a lot of planets (http://en.wikipedia.org/wiki/File:InnerSolarSystem-en.png) in our solar system then.
Yes.

-- Jeff, in Minneapolis

beskeptical
2009-Mar-07, 09:25 AM
I'm not getting very far in this discussion so here's what Tyson had to say (http://www.haydenplanetarium.org/tyson/read/articles/plutosrequiem) and perhaps it will better explain why the name, planet, is not very informative if it refers to anything that orbits a sun.
... The word planet seems to hold an irrational sway over our hearts and minds. That level of fascination made sense in the days before telescopes could observe details in planetary atmospheres; before space probes had explored Mars and bulldozed into a comet; before we understood the history of asteroid and comet collisions that links celestial bodies large and small. But today, the rote exercise of planet-counting rings hollow, and stands in the way of appreciating the full richness of our cosmic environment.

Suppose other properties are what matter to you. Interested in cyclones? You might lump together the thick, dynamic atmospheres of Earth and Jupiter. Interested in the chemistry of life? Icy moons like Jupiter's Europa and Saturn's Enceladus may be the best extraterrestrial places to find liquid water, a crucial ingredient for biology. Or suppose instead you care about ring systems, or magnetic fields, or size, or mass, or composition, or proximity to the Sun, or formation history. And the discovery of planets around other stars has exposed entire new categories like "hot Jupiters"—giant, gassy worlds heated to near-incandescence by their astonishing proximity to their suns.

These classifications say much more about an object's identity than whether its self-gravity made it round, or whether it is the only one of its kind in the neighborhood. Why not rethink the solar system as multiple, overlapping families of objects? Then, the way you organize the properties is up to you. The fuss over Pluto doesn't have to play out as a death in the neighborhood. It could mark instead the birth of a whole new way of thinking about or cosmic backyard.

There's a lot more to read in the article and in the many other things Tyson has written for that web site.

Jeff Root
2009-Mar-07, 10:21 AM
Does that text support what you said in your previous post? It doesn't
appear to answer either of my questions. I was really hoping to learn
what you meant by "It makes the name, planet, mean very little."



perhaps it will better explain why the name, planet, is not very
informative if it refers to anything that orbits a sun.
Not really. Can you put it in your own words?

-- Jeff, in Minneapolis

pumpkinpie
2009-Mar-07, 06:54 PM
Thanks for the link and quote, beskeptical. That's the point I try to make when I am teaching about the solar system, although Tyson states it much more eloquently. We make up names, definitions, and categories.....but it doesn't change what things *are.* They will be what they are no matter if we know they exist or not!

Jeff, to me that's what beskeptical means. We have to get more specific than "planet" to know the true nature of an object. Both Jupiter and Earth are planets. By going on the IAU definition, all we know is they orbit the Sun, are round, and have cleared their orbits. Even adding the words "terrestrial" or "rocky" and "gas giant" gives much more information, but we have to be even more specific than that to understand their similarities and differences. That's what science is about....comparing and contrasting, not just naming. (This last point is not directed right at you Jeff but a general statement from me.)

Jeff Root
2009-Mar-07, 07:49 PM
That's the point I try to make when I am teaching about the solar
system, although Tyson states it much more eloquently. We make
up names, definitions, and categories.....but it doesn't change what
things *are.* They will be what they are no matter if we know
they exist or not!

Jeff, to me that's what beskeptical means. We have to get more
specific than "planet" to know the true nature of an object.
What you say in those two paragraphs (which I quoted in part)
appear to contradict, rather than support each other. The first
says that specific names don't matter, while the second says that
specific names are critical to knowing a thing.

Exact opposites!



Both Jupiter and Earth are planets. By going on the IAU definition, all
we know is they orbit the Sun, are round, and have cleared their orbits.
Bowling balls, for example.



Even adding the words "terrestrial" or "rocky" and "gas giant" gives
much more information,
Does it? How much more information would you estimate? I'm not
versed in information theory, and I don't expect that you are, either.
The idea that adding a word "gives much more information" is very
interesting, and I want to know more about it.



but we have to be even more specific than that to understand
their similarities and differences.
I wouldn't expect any amount of specificity in naming things to
provide any understanding at all. Understanding comes from
experience with things, not specific, detailed names for them.



That's what science is about....comparing and contrasting, not
just naming.
Okay, I think you are saying the same thing as me. But are you
saying that specific names are essential to understanding, or are
you saying that a planet by any other name would look as sweet?

Exact opposites, and I can't tell which position you're arguing for.
You argue for one position in one sentence, and the opposite in
the next sentence.

-- Jeff, in Minneapolis

beskeptical
2009-Mar-08, 03:43 AM
What Tyson said in his talk was, go ahead and call Pluto anything you want. It just isn't very useful to call it a planet.

It's a lot more useful to identify Pluto as belonging to the group of objects it belongs to, that is, the KBOs.

It's more useful to identify Mercury, Venus, Mars and Earth as rocky planets, than to call them planets and lump them together with objects belonging to non-rocky planet groups of objects.

The asteroids are a group that almost got the name, planets, until it became more useful to identify them as the group, asteroids.

Jupiter, Saturn, Uranus and Neptune are more accurately called gas giants than simply planets because it is more specific.

The name, planet, was applied to the Moon and the Sun. What do you think about calling the Moon and Sun planets today? You'd probably say, but they aren't planets because..... At one time, they were considered planets. Now we find it more useful to group them differently because they belong to different groups of objects. The name, planet, would be even less useful if it included everything in the sky beyond the atmosphere.

Jeff Root
2009-Mar-08, 01:32 PM
What Tyson said in his talk was, go ahead and call Pluto anything
you want. It just isn't very useful to call it a planet.

It's a lot more useful to identify Pluto as belonging to the group of
objects it belongs to, that is, the KBOs.
Based only on your précis here, it appears that Tyson is avoiding
taking a side as to whether to continue calling Pluto a "planet".
Obviously it is useful to identify Pluto as a KBO. But I disagree
with him if he really is saying that it isn't useful to call it a planet.

However, I read the article, and agree with what he says there.
I particularly agree with what he says about counting. That has
been a pet peeve of mine for a long time.

He does not say that it isn't useful to call Pluto a planet.



It's more useful to identify Mercury, Venus, Mars and Earth as
rocky planets, than to call them planets and lump them together
with objects belonging to non-rocky planet groups of objects.
Is it? I don't think so.

Certainly it is useful to note that Mercury, Venus, Mars, and Earth
all lack certain characteristics common to Jupiter, Saturn, Uranus,
and Neptune -- in particular, deep atmospheres consisting largely
of hydrogen.

But it is also useful to identify them as planets, which is what you
did when you called them "rocky planets" instead of "rocky things".

I expect that when you said "non-rocky planet groups of objects",
you had the gas giant planets in mind. I want to point out that
each of those planets probably contain more rock than do all the
terrestrial planets combined. Certainly Jupiter and Saturn do.

About 25 years ago I started writing a movie/planetarium show
on exploration and development of the smaller bodies of the Solar
System. Maybe someday I'll finish it. It begins:


[Presenter outdoors on a sunny day]

The ground beneath our feet is the surface of an immense ball of
rock and metal, which we call "the Earth".

[Dolly back from presenter to show the entire planet]

There are many such chunks of dense matter in our Solar System.
Those which are about the size of Earth, or larger, we call "planets".

[views of the planets]

Between the planets is Space. Lots and lots and lots of Space.
But it isn't empty Space. There are other chunks of dense matter
in our Solar System, smaller than planets. First of all, there are
the moons...

[views of Luna, followed by the Galilean moons of Jupiter]
Just to let you know that I've been thinking about this stuff
at least as long as Neil deGrasse Tyson has. And I'm a bit
astonished to see in his article on "Pluto’s Requiem" the phrase
"chunks of rock and metal" -- exactly the words I used, arranged
only slightly differently.



The asteroids are a group that almost got the name, planets, until
it became more useful to identify them as the group, asteroids.

Jupiter, Saturn, Uranus and Neptune are more accurately called
gas giants than simply planets because it is more specific.
No, that is not more accurate. The Hindenburg was a gas giant.
The Eagle Nebula is a gas giant. Neither of those are planets.

Calling Jupiter, Saturn, Uranus, and Neptune "gas giant planets" is
more specific and more detailed than simply calling them "planets",
but it isn't more accurate. Sometimes you want more specificity
and more detail; sometimes you want more generality and less
detail. It depends on the situation.

You don't need to change the definition of "planet" in order to add
the words "gas giant" to get more specificity when you want more.



The name, planet, was applied to the Moon and the Sun. What do
you think about calling the Moon and Sun planets today? You'd
probably say, but they aren't planets because..... At one time,
they were considered planets. Now we find it more useful to group
them differently because they belong to different groups of objects.
The Moon and Sun are still considered planets in astrology.

As viewed from within the Solar System, the Moon and Sun are
planets. However, since the Sun is a star, and has a unique place
in the Solar System, more than 700 times the mass of everything
else in the Solar System combined, it makes sense to classify it
as "not a planet". The Moon, on the other hand, fits my idea of
what a planet is quite well. I sometimes refer to the Moon as a
"world". I have no good reason not to refer to it as a "planet".



The name, planet, would be even less useful if it included
everything in the sky beyond the atmosphere.
I don't see why the name (or, more accurately, word or term)
"planet" would become less useful if its meaning became more
inclusive. Do you think that the more inclusive a word, the less
useful it is? Is the word "insect" less useful than "lepidoptera"
and "hymenoptera"? Is "lepidoptera" less useful than "butterfly"
and "moth"? Is "hymenoptera" less useful than "ant", "bee", and
"wasp"?

-- Jeff, in Minneapolis

EDG
2009-Mar-08, 10:15 PM
It does??? Please explain.

The original definition of planet was "wanderer", because the bright dots in the sky as seen from Earth wandered around as time progressed. So yes, technically it does it means very little.

Jeff Root
2009-Mar-08, 11:17 PM
The original definition of planet was "wanderer", because the
bright dots in the sky as seen from Earth wandered around as time
progressed. So yes, technically it does it means very little.
That is a non sequitur.

You appear to assume that the meaning of any English word
derived from Greek is limited to a literal translation of the Greek
word. You appear to assume that "wanderer" means very little.
And you appear to assume that meaning of a word is not added
to by learning about the thing that the word references.

Think about your use of the word "technically".

Think about where meaning comes from, and what it is.

-- Jeff, in Minneapolis

beskeptical
2009-Mar-10, 11:40 AM
....He does not say that it isn't useful to call Pluto a planet.Actually, he did, several times in the talk. You seem to have an issue with it. What use is it to you to call Pluto a planet?

Tyson's point was the title, planet, was irrelevant when it comes to Pluto. It offers no meaning, no information. But you seem to be invested in Pluto being a planet. And I can't quite understand why you care.



....But it is also useful to identify them as planets, which is what you did when you called them "rocky planets" instead of "rocky things".I have no issue calling both groups, planets. If you want to consider Pluto a planet, then you must consider all the KBOs planets.




....Just to let you know that I've been thinking about this stuff at least as long as Neil deGrasse Tyson has. And I'm a bit astonished to see in his article on "Pluto’s Requiem" the phrase "chunks of rock and metal" -- exactly the words I used, arranged only slightly differently.Well if that is what they are made of, I'm not sure what is surprising about that. If you are this interested, you should read Tyson's book, The Pluto Files. (http://books.google.com/books?id=ogOZSop6EIcC&dq=tyson+pluto+files&printsec=frontcover&source=bl&ots=DuLw8ecQHW&sig=UJdcIggh3dXioaHWs1fvH1zCOag&hl=en&ei=B1G2ScqyLZqqtQOv45D6CA&sa=X&oi=book_result&resnum=1&ct=result) It's an easy read.



....Calling Jupiter, Saturn, Uranus, and Neptune "gas giant planets" is more specific ..Sounds fine to me.



....The Moon and Sun are still considered planets in astrology.Not something I care about.


...I don't see why the name (or, more accurately, word or term) "planet" would become less useful if its meaning became more inclusive. Do you think that the more inclusive a word, the less useful it is?
-- Jeff, in MinneapolisLike I said, include all the KBOs as planets and your including Pluto as a planet at least makes sense. It's less useful however because the KBOs as a group are in a different orbit, formed differently, and are likely made of their own class of materials. Just as most people consider the asteroid belt as a planet that never formed, the KBOs are different than the other 8 planets.

beskeptical
2009-Mar-10, 11:42 AM
That is a non sequitur.

You appear to assume that the meaning of any English word
derived from Greek is limited to a literal translation of the Greek
word. You appear to assume that "wanderer" means very little.
And you appear to assume that meaning of a word is not added
to by learning about the thing that the word references.

Think about your use of the word "technically".

Think about where meaning comes from, and what it is.

-- Jeff, in MinneapolisThe point Tyson made about the name, wanderer, was that it meant something at the time. Now that we have a clearer picture, there is no need to keep the label, wanderer.

dgruss23
2009-Mar-10, 07:52 PM
Taking the formation into acount is a good idea in a classification system. It's what they do in biology with living beings, and in a sense also what Mendeleev did in chemsitry with his periodic table. I would even go so far as to say that a classification system based on formation is the ideal system of classification.

The problem is, I think, that at this moment in time there is still a great deal we don't know about the formation of the planets and other stellar bodies.

I disagree with this for this reason: Many classification systems come about before we know very much about the objects we are classifying. An empirical classification system can help to organize our thoughts and see patterns that may lead to new theoretical developments.

For example, Hubble avoided constructing his galaxy classification scheme based upon theories of galaxy evolution. His classification scheme was developed on empirical grounds alone.

The stellar spectral classification scheme is another system that was based upon empirical criteria - not theoretical criteria.

Mendeleev's periodic table was based upon empirical criteria as well - atomic masses, observed chemical behavior.

So in general I disagree. I think that the best option is to develop a purely empirical classification scheme. Then, if sufficient knowledge accumulates, the scheme can be revised to take into account theoretical developments.

Disinfo Agent
2009-Mar-10, 08:31 PM
I don't really disagree with you. My point was simply that often a classification system will start out as purely empirical, but eventually develop into an "evolutionary" system as the subject matter becomes better understood. And this development, while not immediatly attainable, is often desirable to scientists.

Still, even from an empirical point of view, Pluto seems to be in a different league than the rest of the (terrestrial, traditional) planets.

pumpkinpie
2009-Mar-11, 05:48 PM
I teach this topic a lot in a planetarium....sometimes to six or more classes daily. So I have a lot of time to think about what to say and try different ways of saying it to make it the most clear. This is what makes the most sense to me:

I show a map of the solar system, characterizing the different types of objects. Rocky planets, asteroid belt, gas giant planets, Kuipber belt, Oort cloud. I have visuals of all of them. (It's a scaling software, sort of like powers of ten.) It's so easy to show the Kuiper Belt and how Pluto's orbit fits in with it, and to say that Pluto is a KBO. (I can do the same with showing the orbit of Ceres.) But most students know that Pluto is a dwarf planet, so I have to go in to exactly what that means. I'd rather not go into that detail because I have other things to move on to.

It would be so much easier to say it's a KBO, and nothing more. I wish the whole "dwarf planet" category would go away. Well, maybe not go away, but not have it be the primary designation. Pluto is a KBO. It's one of the few known that HAPPENS to be round, so we also call it a dwarf planet. Do we differentiate between round and non-round moons? Not that I know of. (Correct me if I'm wrong.) So that shouldn't be the most important thing about Pluto.

I know many people here disagree, and we can and HAVE argued until we're blue in the face. Since I'm not a scientist, but an astronomy educator, I defer to the IAU. I try to describe as best I can WHY things are called as they are, and I may not agree with the decisions they have made. But I should not teach something that's my "opinion."

dgruss23
2009-Mar-13, 06:45 PM
I don't really disagree with you. My point was simply that often a classification system will start out as purely empirical, but eventually develop into an "evolutionary" system as the subject matter becomes better understood. And this development, while not immediatly attainable, is often desirable to scientists.

Still, even from an empirical point of view, Pluto seems to be in a different league than the rest of the (terrestrial, traditional) planets.

Don't misunderstand - I agree that Pluto is different and should be classified as something other than a planet. I also think many of the tiny "moon's" need to be classified as something different than the Earth's Moon and the major moons of the gas giants.

My comment was just about classification systems being empirical vs. theory based.

Lord Jubjub
2009-Mar-14, 10:20 PM
I think an empirical classification is important to start with because it allows for everything to be classified even if its correct theoretical placement in is contention.

I see nothing wrong with calling Ceres a rocky dwarf planet and Pluto an icy dwarf planet. The difficult line to draw would be between dwarf and non-dwarf planets. Because there is no known body occupying that space at the moment, I feel that dwarf planet is a valid category. When we find a body that lies in that gap, then we can re-open the discussion.

loglo
2009-Mar-15, 12:35 AM
Balls! They should all be called balls, apart from life bearing bodies. Rock balls, ice balls, gas balls, small/large. Oblate/Irregular. No mess and no fuss.

This would make the planet mnemonic very simple indeed! And if you want something to be called a planet, well quit moaning and just start a colony there!

SpaceCowboy
2009-Mar-15, 01:53 AM
I think that Illinois actually ruled that Pluto is a planet! LOL

beskeptical
2009-Mar-16, 02:23 AM
I teach this topic a lot in a planetarium....sometimes to six or more classes daily. So I have a lot of time to think about what to say and try different ways of saying it to make it the most clear. This is what makes the most sense to me:

I show a map of the solar system, characterizing the different types of objects. Rocky planets, asteroid belt, gas giant planets, Kuipber belt, Oort cloud. I have visuals of all of them. (It's a scaling software, sort of like powers of ten.) It's so easy to show the Kuiper Belt and how Pluto's orbit fits in with it, and to say that Pluto is a KBO. (I can do the same with showing the orbit of Ceres.) But most students know that Pluto is a dwarf planet, so I have to go in to exactly what that means. I'd rather not go into that detail because I have other things to move on to.

It would be so much easier to say it's a KBO, and nothing more. I wish the whole "dwarf planet" category would go away. Well, maybe not go away, but not have it be the primary designation. Pluto is a KBO. It's one of the few known that HAPPENS to be round, so we also call it a dwarf planet. Do we differentiate between round and non-round moons? Not that I know of. (Correct me if I'm wrong.) So that shouldn't be the most important thing about Pluto.

I know many people here disagree, and we can and HAVE argued until we're blue in the face. Since I'm not a scientist, but an astronomy educator, I defer to the IAU. I try to describe as best I can WHY things are called as they are, and I may not agree with the decisions they have made. But I should not teach something that's my "opinion."I highly recommend Tyson's book, the Pluto Files, if you teach astronomy. It won't take you much time to read and I think you'll be glad you heard what he had to say. The man is a gifted educator.

beskeptical
2009-Mar-16, 03:05 AM
I think that Illinois actually ruled that Pluto is a planet! LOLThe BA's blog discussed the Illinois legislation, Illinois plutocrats are frakkin’ goofy (http://blogs.discovermagazine.com/badastronomy/2009/03/05/illinois-plutocrats/).

California passed earlier legislation (http://www.spaceref.com/news/viewsr.html?pid=21982), with reasons that are good for a ROTFLOL episode.
...WHEREAS, The mean-spirited International Astronomical Union decided on August 24, 2006, to disrespect Pluto by stripping Pluto of its planetary status and reclassifying it as a lowly dwarf planet; and

...WHEREAS, Pluto, named after the Roman God of the underworld and affectionately sharing the name of California's most famous animated dog, has a special connection to California history and culture; and

WHEREAS, Downgrading Pluto's status will cause psychological harm to some Californians who question their place in the universe and worry about the instability of universal constants; and

WHEREAS, The deletion of Pluto as a planet renders millions of text books, museum displays, and children's refrigerator art projects obsolete, and represents a substantial unfunded mandate that must be paid by dwindling Proposition 98 education funds, thereby harming California's children and widening its budget deficits; and

WHEREAS, The deletion of Pluto as a planet is a hasty, ill-considered scientific heresy similar to questioning the Copernican theory, drawing maps of a round world, and proving the existence of the time and space continuum; and


But the last 2 reasons make one wonder if the legislation wasn't intended to be sarcastic.
WHEREAS, The downgrading of Pluto reduces the number of planets available for legislative leaders to hide redistricting legislation and other inconvenient political reform measures; and

WHEREAS, The California Legislature, in the closing days of the 2005-06 session, has been considering few matters important to the future of California, and the status of Pluto takes precedence and is worthy of this body's immediate attention; now, therefore, be it

New Mexico's legislation is a more mundane version except it highlights their ignorance while touting their state as a center of astronomical education.

beskeptical
2009-Mar-17, 03:14 AM
Apparently Yahoo is feeling the twitter.

As Science Evolves, So Does Pluto (http://news.yahoo.com/s/space/20090316/sc_space/asscienceevolvessodoespluto)

A.DIM
2009-Mar-17, 12:37 PM
Hi Beskeptical.

I just finished that article on space.com.
The debate is far from over and a few things concern me:

"Tuesday evening's conversation revealed how uncertainty can breed politics in science — but also how scientists deal with an evolving understanding of the universe."

"The whole debacle has painted a new picture of how planetary scientists operate."

"I think this has been one of the more disappointing episodes for science with regard to the IAU," Stern said. "Now school kids see science as voting, and that's not the best way to do science."

"After all, the panelists suggested, it's perhaps more important to love the scientific process rather than the scientific facts."

This last quote actually, is close to my stance personally, but I point to the others as my youngest children and I have had these debates about pluto. My son, 10 says it's not a planet while my daughter, 8, says leave him alone until we know more.

I'm rather like Tyson, why the need just yet for "planetary" classification schemes? We know too little about the system we're exploring!

:)

beskeptical
2009-Mar-21, 09:03 AM
You can now hear Tyson's talk online!

Speakers' Forum: Neil deGrasse Tyson: The Pluto Files (http://www.kuow.org/program.php?id=17148)
In 2000, astrophysicist Neil deGrasse Tyson headed a $200 million reconstruction project at New York's Hayden Planetarium. His exhibit on the solar system included a subtle, crucial change based on some new thinking: There were only eight planets. The ninth, Pluto, was reassigned as one of the "icy bodies" orbiting beyond Neptune. The New York Times reported the change and letters poured in. Five years later, the International Astronomical Union made it official. The IAU voted on a new definition for planets, and Pluto was out.

In this lecture at Seattle's Town Hall on February 23, 2009, Neil deGrasse Tyson tells the story of the strong reaction to Pluto's demotion to "dwarf planet" status. Much of it was directed at him personally by angry third graders. Tyson appeared as part of the Seattle Science Lectures sponsored by the Pacific Science Center and Elliott Bay Book Company.


This was an interesting comment piece:
PLUTOIDS, RUTOIDS, SCHMUTOIDS (http://www.ifa.hawaii.edu/faculty/jewitt/kb/plutoids.html)

It references the IAU page, News Release - IAU0804: Plutoid chosen as name for Solar System objects like Pluto (http://www.iau.org/public_press/news/release/iau0804/)

Noclevername
2009-Mar-25, 02:26 AM
Technically, everything in a planetary orbit is a planet. But counting dust particles is annoying and inconvenient for us, so we cop out and say "oh, this one's not a planet, that one's not a planet" and come up with rationalizations and excuses to make it seem so. Kuiper Belt Objects, asteroids, comets, we're embarassed by our country relatives and so pretend they're not part of the family. But gravity and orbital mechanics are thicker than blood.

C'mon, let poor Pluto come to the family picnic! I'll even let Eris fill a plate if she promises not to cause any trouble.

pumpkinpie
2009-Mar-25, 01:00 PM
Technically, everything in a planetary orbit is a planet. But counting dust particles is annoying and inconvenient for us, so we cop out and say "oh, this one's not a planet, that one's not a planet" and come up with rationalizations and excuses to make it seem so. Kuiper Belt Objects, asteroids, comets, we're embarassed by our country relatives and so pretend they're not part of the family. But gravity and orbital mechanics are thicker than blood.

C'mon, let poor Pluto come to the family picnic! I'll even let Eris fill a plate if she promises not to cause any trouble.
Can you give a source to that claim? I'm not challenging you, I just want to see where that statement came from.

Noclevername
2009-Mar-30, 09:55 PM
Can you give a source to that claim? I'm not challenging you, I just want to see where that statement came from.

From the definitions of "planetary orbit" and "wanderer", from logic, and from me. I take all the blame and/or credit, as per the Humpty Dumpty school of subjective linguistics-- that when I use a word, it means what I want it to. ;)

pumpkinpie
2009-Mar-30, 10:25 PM
From the definitions of "planetary orbit" and "wanderer", from logic, and from me. I take all the blame and/or credit, as per the Humpty Dumpty school of subjective linguistics-- that when I use a word, it means what I want it to. ;)

That's good enough of a reason for me! :lol:

tracer
2009-Mar-31, 02:58 PM
His visits with comedians are quite a treat. Here he is discussing Pluto on the Jon Stewart Show (http://www.thedailyshow.com/video/index.jhtml?videoId=216998&title=neil-degrasse-tyson).

My favorite moment there came the next day, when Jon Stewart was doing a fake "recap" of what they'd discussed on the show:

"I was like, 'Red dwarf stars in their planetary nebulae phase are comparable in mass to our sun!' and Neil was all, 'You're an idiot!' "

(And of course he was an idiot -- no red dwarf star has yet lived long enough to reach its planetary nebula phase! ;) )

laurele
2009-Apr-01, 05:35 AM
I show a map of the solar system, characterizing the different types of objects. Rocky planets, asteroid belt, gas giant planets, Kuipber belt, Oort cloud. I have visuals of all of them. (It's a scaling software, sort of like powers of ten.) It's so easy to show the Kuiper Belt and how Pluto's orbit fits in with it, and to say that Pluto is a KBO. (I can do the same with showing the orbit of Ceres.) But most students know that Pluto is a dwarf planet, so I have to go in to exactly what that means. I'd rather not go into that detail because I have other things to move on to.

It would be so much easier to say it's a KBO, and nothing more. I wish the whole "dwarf planet" category would go away. Well, maybe not go away, but not have it be the primary designation. Pluto is a KBO. It's one of the few known that HAPPENS to be round, so we also call it a dwarf planet. Do we differentiate between round and non-round moons? Not that I know of. (Correct me if I'm wrong.) So that shouldn't be the most important thing about Pluto.

I know many people here disagree, and we can and HAVE argued until we're blue in the face. Since I'm not a scientist, but an astronomy educator, I defer to the IAU. I try to describe as best I can WHY things are called as they are, and I may not agree with the decisions they have made. But I should not teach something that's my "opinion."

Wow, I've been away way too long. FYI, I was not banned, just busy with other stuff.

What makes the IAU decision anything other than just one more opinion? We all know how few people voted on it, the flawed process they used, and the rejection of their definition by hundreds of professional astronomers. Why defer to anyone instead of explaining that there is an ongoing debate and how and why you reach your conclusions as well as how others reach differing ones?

Not all KBOs are created equal. Roundness is not just a random feature. It is proof that an object is large enough to be rounded by its own gravity, a state known as hydrostatic equilibrium. This is a characteristic of planets and not of shapeless rocks, asteroids and KBOs. Pluto, Haumea, Makemake and Eris are BOTH planets and KBOs. Why is the idea of them having a dual classification such a problem?

Ceres is spherical and therefore a planet as well. Comparing public reaction to its demotion in the 19th century to objections over Pluto's demotion is comparing apples and oranges. Information traveled much more slowly 150 years ago. How many people even knew about Ceres' discovery, let alone its demotion? The fact that Ceres is round was not known until well into the late 20th century, so its demotion is understandable but ends up having been wrong.

Even Tyson is moving away from the "Pluto is not a planet" stand to one that it might be too early in the field of planetary science for us to be making these definitions. He moderated the Isaac Asimov Memorial Debate on March 10 at the American Museum of Natural History, and I was fortunate enough to attend this event. All six astronomers on the panel, even the dynamicists, stated clearly that they do not like the IAU definition nor do they find it useful. The dynamicists' main objection is to the wording requiring objects to "clear their orbits." They also expressed reservations about the rushed process the IAU used in Prague. From the discussion, it was clear that this debate is very much ongoing and that more data from observation of Pluto, Ceres, Kuiper Belt Objects and other solar systems is needed to make any definitive classification system.

What is wrong with establishing dwarf planets as a subcategory of small planets that are planets due to being in hydrostatic equilibrium but are of the dwarf subcategory because they do not gravitationally dominate their orbits? Similarly, what is wrong with calling round moons, whose composition is essentially that of planets, secondary planets, as was done in the 19th century?

I cannot understand the claim that having too many planets or too many types of planets makes the term useless. We have billions of stars divided into subcategories via the HR diagram, and no one has a problem acknowledging that while they are all very different from one another, they all fall under the broad category of star. It's only a matter of time before exoplanet discoveries will put the total planet count we know into the thousands, hundreds of thousands, and then millions.

A good book that presents the other side of this debate is "Is Pluto A Planet?" by Dr. David Weintraub. Anyone interested in this should at least read materials representing both sides (yes, I have read Tyson's book; I even spoke to him personally, and no shoes or tomatoes were thrown! :) ) before making up their minds.

Also FYI, the person who lobbied the Illinois legislature for the resolution supporting Pluto's planet status attended the Great Planet Debate last year and is a good friend of mine--and of Dr. Alan Stern, who expressed his unqualified support for the gesture.

Jeff Root
2009-Apr-01, 09:22 AM
laurele,

I generally agree with most of what you say, but, curiously, I like the bit
about a planet "clearing its orbit" and think the bit about a planet being
spherical due to its own gravity is arbitrary and trivial, so I dislike it.

My understanding is that dust particles in a protoplanetary disk will stick
together due to electrostatic forces. When a clump of dust happens to
avoid getting knocked to pieces by collisions with other clumps, it can
grow massive enough to collect more dust and gas around it just by its
own gravity. When that happens, it clears the path of its orbit. Very
similar to the rings of Saturn. I made an illustration of it for this page:
Meteoroids vs Asteroids (http://www.freemars.org/jeff/meteor/)

-- Jeff, in Minneapolis

grant hutchison
2009-Apr-01, 11:23 AM
"I think this has been one of the more disappointing episodes for science with regard to the IAU," Stern said. "Now school kids see science as voting, and that's not the best way to do science."
Also FYI, the person who lobbied the Illinois legislature for the resolution supporting Pluto's planet status attended the Great Planet Debate last year and is a good friend of mine--and of Dr. Alan Stern, who expressed his unqualified support for the gesture.I'm struck by the incongruity of this juxtaposition.
Stern seems to be unhappy for science to be done by the votes of actual scientists, but happy for science to be done by politicians legislating in response to lobbyists.

Grant Hutchison

laurele
2009-Apr-01, 04:19 PM
I'm struck by the incongruity of this juxtaposition.
Stern seems to be unhappy for science to be done by the votes of actual scientists, but happy for science to be done by politicians legislating in response to lobbyists.

Grant Hutchison

Stern understands that the Illinois vote is a symbolic gesture that makes no attempt to impose this view on anyone--unlike the IAU vote, in which participants attempt to dictate to the whole world what is and isn't a planet and what to teach in schools. I won't presume to speak for Stern, but my guess is he is happy to see people refusing to blindly accept the IAU decision. It's not that he wants science to be done by politicians; it's that he wants it to be a process that evolves organically through the accumulation and interpretation of data rather than by an organization's decree.

Also, the "lobbyist" in question is not some high-paid firm but an individual who lives in Clyde Tombaugh's birthplace, Streator, Illinois, and has, like me, spent a lot of time learning about this issue and advocating Pluto's reinstatement.

grant hutchison
2009-Apr-01, 04:44 PM
Stern understands that the Illinois vote is a symbolic gesture that makes no attempt to impose this view on anyone--unlike the IAU vote, in which participants attempt to dictate to the whole world what is and isn't a planet and what to teach in schools.The IAU was formed in order "to promote and safeguard the science of astronomy in all its aspects through international cooperation". The Illinois government was formed in order to make laws for other people to obey.
Symbolic gestures do require a little care, since they may end up symbolizing different things to different people.

Grant Hutchison

laurele
2009-Apr-01, 04:46 PM
laurele,

I generally agree with most of what you say, but, curiously, I like the bit
about a planet "clearing its orbit" and think the bit about a planet being
spherical due to its own gravity is arbitrary and trivial, so I dislike it.

My understanding is that dust particles in a protoplanetary disk will stick
together due to electrostatic forces. When a clump of dust happens to
avoid getting knocked to pieces by collisions with other clumps, it can
grow massive enough to collect more dust and gas around it just by its
own gravity. When that happens, it clears the path of its orbit. Very
similar to the rings of Saturn. I made an illustration of it for this page:
Meteoroids vs Asteroids (http://www.freemars.org/jeff/meteor/)

-- Jeff, in Minneapolis

The problem with the concept of "clearing its orbit" is its vaguenes. None of the planets in our solar system has fully cleared its orbital field of asteroids. Neptune has not cleared its orbit of Pluto. If applied literally, this term could lead to us having no planets in our solar system! That is why the term "gravitationally dominant" is better. That means the planet is the "big guy" or dominant object in its orbital path, and it acts on the orbits of the smaller objects rather than being acted upon by anything else.

The early period when the solar system was being formed was very violent, with multiple planetesimals, which had coalesced from the protoplanetary disk, impacting one another constantly. Most of these planetestimals were destroyed in these impacts. Those that were not destroyed grew larger by accumulating gas and dust. However, there is a difference between accretion, in which objects are held together by chemical bonds, and hydrostatic equilibrium, which is a crucial threshold. When planetesimals reached a certain mass and size, gravity took over and pulled them into a spherical shape. Many though not all objects that reached this threshold became geologically differentiated with core, mantle, and crust--all characteristic of planets and not of asteroids.

The rings of Saturn are made of tiny particles that never came together to form a planet, likely due to the gravitational influence of Saturn--the same reason why most of the asteroid belt never coalesced into a large planet.

I disagree that the criterion of being spherical due to its own gravity is arbitrary or trivial. For more on this, see this article and podcast in Sky and Telescope by Dr. David Grinspoon: http://www.skyandtelescope.com/skytel/beyondthepage/38235059.html and this one by Dr. Stern: http://www.sciencenews.org/index/generic/activity/view/id/38770/title/Debates_over_definition_of_planet_continue_and_ins pire

laurele
2009-Apr-01, 04:52 PM
The IAU was formed in order "to promote and safeguard the science of astronomy in all its aspects through international cooperation". The Illinois government was formed in order to make laws for other people to obey.
Symbolic gestures do require a little care, since they may end up symbolizing different things to different people.

Grant Hutchison

"Promoting and safeguarding the science of astronomy" does not include dictating one view in an ongoing debate and imposing it on the world by claiming that the IAU is "the authority" on such matters. It does not include marginalizing significant numbers within the planetary science community who view the issue differently. In fact, at the Isaac Asimov Memorial Debate, Dr. Mark Sykes commented that the IAU is NOT the only professional organization that deals with planetary classification. The American Geophysical Union and the European Geophysical Union are all still discussing the "what is a planet" issue. If this many planetary scientists still believe more debate is needed, what makes the IAU the "central authority" on this as opposed to these other groups? Stern notes that no one ever voted on relativity or gravity. Over time, scientists came to consensus on these because they were proven correct. People seem to be in a hurry for a "decision" but sometimes, what is really needed is time for the discussion to evolve organically, even if that takes decades. By precluding this process and pronouncing a decree, the IAU is failing in its mission to "promote and safeguard the science of astronomy."

grant hutchison
2009-Apr-01, 05:16 PM
"Promoting and safeguarding the science of astronomy" does not include dictating one view in an ongoing debate and imposing it on the world by claiming that the IAU is "the authority" on such matters.I simply remark that endorsing a "symbolic gesture" by a state legislature is a good way to undermine one's claim to the moral high ground vis-à-vis the IAU. A law-making body has now been urged to pronounce on an issue it is not qualified to pronounce on.

Presumably I'm not the only person who is now struggling to supress a smile while recalling the small difficulty the pot had with the kettle.

Grant Hutchison

laurele
2009-Apr-01, 06:11 PM
I simply remark that endorsing a "symbolic gesture" by a state legislature is a good way to undermine one's claim to the moral high ground vis-à-vis the IAU. A law-making body has now been urged to pronounce on an issue it is not qualified to pronounce on.

Presumably I'm not the only person who is now struggling to supress a smile while recalling the small difficulty the pot had with the kettle.

Grant Hutchison

While the Illinois legislature is a law-making body, at every level of government, there is a distinction between laws, which must go through a very specific process to be adopted, and resolutions, which have no force in law. This resolution is no different than those adopted routinely honoring various ethnic heritages, awareness weeks/months for certain diseases, etc. While it may have generated some laughs, the positive side is it also got people thinking about astronomy.

Jeff Root
2009-Apr-01, 06:20 PM
The problem with the concept of "clearing its orbit" is its vaguenes.
I don't have a problem with vagueness.



None of the planets in our solar system has fully cleared its orbital
field of asteroids.
Are asteroids known to be in the same orbit as Mercury or Venus?
Are any of Jupiter's Trojan asteroids known to have been in that
orbit since the Solar System formed? Or is it possible that they
all arrived there within the last billion years?

Why would an orbit need to be "fully" cleared? When a plowing
contractor comes to clear the parking lot of snow, are they "fully"
clearing the lot even if I can still see snow on it? Where did you
get the word "fully" from, anyhow? A straw man?



Neptune has not cleared its orbit of Pluto.
They are not in the same orbit. As far as I can tell, both Neptune's
and Pluto's orbits are very clear. I don't know how they got that
way, but they currently appear to be very clear.



If applied literally, this term could lead to us having no planets in
our solar system!
I think that's what the term "strawman argument" is about.



That is why the term "gravitationally dominant" is better.
Equally as vague as "cleared the orbit". I'll grant that it has a
whopping advantage of actually being knowable. We can see
whether a body is gravitationally dominant in its orbit, while we
can't see whether that same body ever cleared its orbit in its
multibillion-year hiistory.



That means the planet is the "big guy" or dominant object in its
orbital path, and it acts on the orbits of the smaller objects rather
than being acted upon by anything else.
Well, now, it's a two-way path, of course. Everything affects
everything else, and everything is affected by everything else.
But there probably is some way of defining dominance so that
the idea works, yeah.



The early period when the solar system was being formed was very
violent, with multiple planetesimals, which had coalesced from the
protoplanetary disk, impacting one another constantly. Most of these
planetestimals were destroyed in these impacts. Those that were not
destroyed grew larger by accumulating gas and dust. However, there
is a difference between accretion, in which objects are held together
by chemical bonds, and hydrostatic equilibrium, which is a crucial
threshold.
Hydrostatic equilibrium is not a threshold of anything, much less a
crucial threshold. Nothing is significantly different about a body
which is just over the line compared to one which is just under the
line. The line is completely arbitrary. Every body which holds on
to material by gravity approaches a spherical shape, and every solid
body deviates some from hydrostatic equilibrium. It is a continuum,
with spheres at one end and not-spheres at the other. Everything
is in between the extremes.



When planetesimals reached a certain mass and size, gravity took
over and pulled them into a spherical shape.
Not really. When they were a quarter the certain mass you have
in mind, even then, gravity was pulling them into a spherical shape.
When they are four times the mass you have in mind, gravity will
still not have completed the job. Earth has mountains.

But! But! The mountains were built after the Earth was formed!

Yes, but the asteroids in planet-crossing orbits got there after the
planets formed! Same thing!



Many though not all objects that reached this threshold ...
It is not a threshold. Assuming we agreed on a measure of
sphericity to serve as the dividing line-- There is no fundamental
difference between a body above that line from a body below it.



... became geologically differentiated with core, mantle, and
crust--all characteristic of planets and not of asteroids.
Many of the meteorites I've seen and handled came from bodies
which were geologically differentiated. Did they come from planets?
From spherical asteroids? Inquiring minds want to know!

Anyhow, you jumped over a significant threshold: Between a body
which has too little mass to attract and hold on to matter by its
gravity, and one which has enough mass. That threshold is not
the same as the arbitrary dividing line between round and not round.

It is probably just as arbitrary, but it isn't the same line, and it is
a very important threshold. It is the point at which a body starts
clearing its orbit, adding mass to itself by gravity alone, collecting
gases (not just dust), and getting moons.



The rings of Saturn are made of tiny particles that never came
together to form a planet, likely due to the gravitational influence
of Saturn--
I think there is a fairly strong concensus that the rings are much
younger than the planet. Or was that last year?



the same reason why most of the asteroid belt never coalesced
into a large planet.
That analogy doesn't quite work. Did you mean "the gravitational
influence of Saturn's moons"? Jupiter's gravitational influence
is generally blamed with the failure of the asteroids of the main belt
to collect together. I have some doubt about it, but have no
evidence against the idea.



I disagree that the criterion of being spherical due to its own gravity
is arbitrary or trivial.
The sphericity of course depends very much on the material the
body is composed of, and the question of how close to spherical
should be considered spherical can only be answered arbitrarily.
As arbitrarily as any other measure of planethood.

-- Jeff, in Minneapolis

Tucson_Tim
2009-Apr-08, 07:13 PM
I'm actually glad that Pluto is no longer a planet. Now I can say I've seen all the planets (at least those in our solar system). It's been bugging me for years that I've never been able to see Pluto with my scope.

Celestial Mechanic
2009-Apr-08, 07:26 PM
[Snip!]

I disagree that the criterion of being spherical due to its own gravity is arbitrary or trivial.
The sphericity of course depends very much on the material the
body is composed of, and the question of how close to spherical
should be considered spherical can only be answered arbitrarily.
As arbitrarily as any other measure of planethood.
{Emphasis mine}
I agree. Any measure of planethood is likely to be arbitrary, so the best way to have the least amount of arbitrariness is to keep the number of arbitrary measures small. That is why I favor a two clause definition of planethood:

1. It orbits its star and not some other body; and
2. Its mass is greater than 10-8 solar masses, or 2x1022 kg in SI units.

No folderol about shape or clearing orbits, just two simple tests anyone can understand. Think about this: if the Earth's moon really was formed in a collision with a Mars-sized body, for how long was the Earth not a planet until it became spherical enough again and had cleared most of the debris of the collision from its orbit? :think:

Disinfo Agent
2009-Apr-08, 07:32 PM
I'm actually glad that Pluto is no longer a planet. Now I can say I've seen all the planets (at least those in our solar system). It's been bugging me for years that I've never been able to see Pluto with my scope.Now, there's a nice, objective criterion of planethood we can all agree on!

Tucson_Tim
2009-Apr-08, 07:38 PM
Oh no! I'm in the cross-hairs of the DA. :eek: Serpentine! Serpentine!

HenrikOlsen
2009-Apr-16, 03:31 PM
No, our solar system has thousands of KBOs. That was the problem. If you continue to categorize Pluto as a planet, what do you call all the other newly discovered KBOs?

Kuiper Belt Objects (http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong)One is even bigger than Pluto. It was called Xena but now has the official name, Eris. (http://web.gps.caltech.edu/~mbrown/planetlila/)

You seem to have totally missed the joke...

I'm still missing it. Care to fill me in?
Eris was probably named, at least partially, for the goddess of discord because it would be an argument for both sides in the debate about the planethood of Pluto.

Noble Ox
2009-Apr-17, 07:30 PM
I can't understand all the fuss really. Pluto is not a planet - never was. Its a political situation where the US of A wants to have someone who discovered a planet. But the europeans did it all first. End of story

Amber Robot
2009-Apr-17, 07:38 PM
Pluto is not a planet - never was.

Doesn't that depend on how you define "planet"?

Noble Ox
2009-Apr-17, 07:42 PM
There are zillions of chunks of ice/rock/dirt out there. Why should pluto be special other than by the nationality of its discoverer.
Pluto doesn't even have its own orbit.

Amber Robot
2009-Apr-17, 07:59 PM
Pluto doesn't even have its own orbit.

I don't know what that means. Are you saying that other objects cross its orbit? Because all kinds of orbits cross other orbits.

It is clear that you have in your head a definition for the word "planet". Care to tell us what it is?

CJSF
2009-Apr-17, 09:22 PM
Its a political situation where the US of A wants to have someone who discovered a planet.

What evidence do you have that this is true?

CJSF