Chatroom
 

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Bad Astronomy and Universe Today Forum > Space and Astronomy > Astronomy
Register FAQ Members List Calendar Mark Forums Read

   

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #331 (permalink)  
Old 27-September-2006, 02:52 PM
baric's Avatar
baric baric is offline
Senior Member
 
Join Date: May 2005
Location: Texas
Posts: 472
Default

Quote:
Originally Posted by hhEb09'1 View Post
It seems to me that you both are talking past each other. Isn't it just a question of what is meant by "significant" or "cleared out"? Of course, Neptune has not cleared out Pluto, but Pluto is nowhere near Neptune. Of course, Pluto is insignificant with respect to Neptune, but I would consider Pluto to be signficant.
"cleared out" does not mean "created a surrounding vacuum"

Neptune has definitely "cleared out" Pluto, whose orbit is completely controlled by Neptune -- much like a moon orbiting a planet.
__________________
"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan
Reply With Quote
  #332 (permalink)  
Old 27-September-2006, 03:10 PM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 8,224
Default

Quote:
Originally Posted by baric View Post
"cleared out" does not mean "created a surrounding vacuum"
What does it mean?
Quote:
Neptune has definitely "cleared out" Pluto, whose orbit is completely controlled by Neptune -- much like a moon orbiting a planet.
We've discussed this before. Pluto and the plutinos do not appear to have been sheparded into place, but rather are the remnants of the previous population after Neptune has cleared out the rest.
Reply With Quote
  #333 (permalink)  
Old 27-September-2006, 03:55 PM
Kullat Nunu's Avatar
Kullat Nunu Kullat Nunu is offline
Senior Member
 
Join Date: Sep 2003
Location: Earth
Posts: 2,742
Default

Not only Pluto is insignificant in size compared to Neptune, but Pluto's orbit is under Neptune's dominance (in 2:3 orbital resonance). In addition, being a member of the Kuiper Belt, Pluto does not control its neighborhood, i.e. hasn't "cleared its neighborhood".

That of course does not mean that Pluto itself is insignificant, no way. It is a very intriguing object, however not a planet.
__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman
Reply With Quote
  #334 (permalink)  
Old 27-September-2006, 04:17 PM
peteshimmon peteshimmon is offline
Senior Member
 
Join Date: Jul 2003
Location: uk
Posts: 1,646
Default

Clearing happens very slowly out there! It was a stitch-up!
Reply With Quote
  #335 (permalink)  
Old 27-September-2006, 04:54 PM
kheider's Avatar
kheider kheider is offline
Member
 
Join Date: Aug 2006
Location: Sacramento, CA
Posts: 38
Talking Pluto was a Planet when it was 14,500km in diameter!

Quote:
Originally Posted by baric View Post
"cleared out" does not mean "created a surrounding vacuum"
Quote:
Originally Posted by hhEb09'1 View Post
What does it mean? Pluto and the plutinos do not appear to have been sheparded into place, but rather are the remnants of the previous population after Neptune has cleared out the rest.

"and (c) dominates the neighborhood around its orbit clearing it of comparable objects."


Rather Pluto, Orcus, Ixion, and Huya where born or forced into their orbit, they never come close to Neptune because of the 3:2 resonance period. Pluto gets closer to Uranus than Neptune.


Pluto was announced in the New York Times on March 14th, 1930, in an article titled: "Ninth Planet Discovered on Edge of Solar System; First Found in 84 Years" No. 26,347. The article starts: "The Sphere, Possibly Larger than Jupiter, Meets Predictions." Lowell Observatory thought they had found Planet X (6.6x more massive than Earth, 8,000+ miles in diameter)

In 1959 a lot of astronomers still thought Pluto was 14,500km (8,700 miles) in diameter. That was back when Pluto was truly considered a Planet! We now know that Pluto is 1/500 Earth's mass and only 2300km in diameter.

(click here to see Pluto starting to shrink in 1959)
Source: Planets 'Other Worlds of Our Solar System' Golden Library of Knowledge (1959)

-- Kevin Heider
Reply With Quote
  #336 (permalink)  
Old 27-September-2006, 11:44 PM
Murff's Avatar
Murff Murff is offline
Member
 
Join Date: Jun 2006
Location: North Dakota
Posts: 53
Default

Lets say, for example, that there were still alot of objects in Neptune's orbit. Under the new definition, would it not be a planet?

This definition seems to mean at some point, a planet like Neptune, Mars, etc would look the same as they do now but not be considered a planet because there is too much "debris" in it's orbit. In 400 years, if Pluto's orbit were cleared (not that this is realistic) would it be promoted to Planet status again?

I do not think this was as scientifically thought out as some of you seem to think. But that is just my opinion.

They need to define a size, period. If we find a Jupiter size planet orbiting a different star, and find out it is surrounded by a large asteroid field, what will we call it? We will call it a planet without even a second thought.
__________________
I'm a professional, please don't try this at home...
Reply With Quote
  #337 (permalink)  
Old 28-September-2006, 12:33 AM
greenfeather's Avatar
greenfeather greenfeather is offline
Senior Member
 
Join Date: Jul 2006
Location: Valley Forge PA
Posts: 598
Default

Quote:
Originally Posted by Swift View Post
For those of you who would like to keep Pluto as a non-minor planet, you now can have t-shirts and bumperstickers, to identify your fellow travelers.
LINKY
(And no, this is not a statement of my position on this, nor a commercial)
Pluto T-shirts?? I'm way more excited about Europa than Pluto. Why can't I have a Europa t-shirt? Europa can beat Pluto anytime, and I bet it's larger, too!!!
__________________
"I am happy to report that once again the universe is doing just great, thank you, purring with perfection, ever-changing same as always. Light is still cruising along at 186,000 miles per second, and the expanding universe shows no signs of contracting. At this rate, it won't be long before they'll have to let the photon belt out another notch."
Swami Beyondananda's 2007 State of the Universe address
Reply With Quote
  #338 (permalink)  
Old 28-September-2006, 01:38 AM
Macro Mouse's Avatar
Macro Mouse Macro Mouse is offline
Member
 
Join Date: Jan 2004
Location: United States
Posts: 85
Default

Quote:
Originally Posted by Murff View Post
Lets say, for example, that there were still alot of objects in Neptune's orbit. Under the new definition, would it not be a planet?
In an evolved stellar system such as ours, that scenario is highly improbable...Neptune's gravity would clear out or dominate any significant objects. The only type of system where you'll see a gas giant that hasn't cleared its orbit will be in a protoplanetary disk...but then IMO we're dealing with protoplanets/planetoids, not true planets.

Quote:
This definition seems to mean at some point, a planet like Neptune, Mars, etc would look the same as they do now but not be considered a planet because there is too much "debris" in it's orbit. In 400 years, if Pluto's orbit were cleared (not that this is realistic) would it be promoted to Planet status again?
Yeah a planet and planetoid could easily look the same. So what do Titan and Io look like?

If Pluto's orbit was cleared in 400 years it would be promoted, but again... you'll only find objects in the process of clearing their orbits in young, evolving stellar systems.

Quote:
They need to define a size, period. If we find a Jupiter size planet orbiting a different star, and find out it is surrounded by a large asteroid field, what will we call it? We will call it a planet without even a second thought.
A planet, since I don't think even a large asteroid belt will come close to rivaling the mass of the giant planet.

I used to favor calling everything gravitationally-round and not a star a planet with different sub-classes. In fact, I still think this type of scheme will be the most efficient at some point in the future...but a big flaw in this idea is that nobody is going to accept or call a moon a "secondary planet." The public actually understands the concept of moons, so there's no reason to change that and make things (in the public's eye) confusing. I should note I think a moon should still be round...non-spherical satellites can be called moonlets.

So since we're already accepting a certain class of spheroids as non-planets based on orbit...we might as well eliminate objects with another significant orbital trait: shared/non-dominance. For these objects (including objects in a young stellar system) I prefer planetoid instead of dwarf planet simply because it's not an oxymoron. So our solar system contain planets, planetoids, and moons...plus asteroids, comets, moonlets, and debris. Still plenty of sub-categories from there based on physical traits or location relative to the Sun.
__________________
This space is for rent.
Reply With Quote
  #339 (permalink)  
Old 28-September-2006, 01:51 PM
baric's Avatar
baric baric is offline
Senior Member
 
Join Date: May 2005
Location: Texas
Posts: 472
Default

Quote:
Originally Posted by Murff View Post
Lets say, for example, that there were still alot of objects in Neptune's orbit. Under the new definition, would it not be a planet?
It depends on the mass and orbital properties of those bodies. There are BILLIONS of objects in Saturn's orbit, but Saturn is still a planet because it completely dominates those billions of bodies.

Quote:
This definition seems to mean at some point, a planet like Neptune, Mars, etc would look the same as they do now but not be considered a planet because there is too much "debris" in it's orbit. In 400 years, if Pluto's orbit were cleared (not that this is realistic) would it be promoted to Planet status again?

I do not think this was as scientifically thought out as some of you seem to think. But that is just my opinion.
I do not think that your opinion is as scientifically thought out as you seem to think. To honestly think that there would be any difference between Pluto's orbit now and in 400 years is absurd. Pluto was formed and settled into its orbit billions of years ago. Planets are not bouncing around the solar system as if it were a pinball machine.

Quote:
They need to define a size, period.
No, not "period". "Period" is used when you want to establish your opinion without discussion. That is not going to happen on an internet forum!

Quote:
If we find a Jupiter size planet orbiting a different star, and find out it is surrounded by a large asteroid field, what will we call it? We will call it a planet without even a second thought.
OK, let's be clear about something. If there is a Jupiter-size planet surrounded by a large asteroid field, then we are surely witnessing the result of some catastrophic and recent event. The very reason that you DON'T see Jupiter-size planets in asteroid fields is because their immense gravity either ejects or absorbs any asteroids in their immediate vicinity rather quickly.
__________________
"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan
Reply With Quote
  #340 (permalink)  
Old 28-September-2006, 01:58 PM
baric's Avatar
baric baric is offline
Senior Member
 
Join Date: May 2005
Location: Texas
Posts: 472
Default

Quote:
Originally Posted by Macro Mouse View Post
So since we're already accepting a certain class of spheroids as non-planets based on orbit...we might as well eliminate objects with another significant orbital trait: shared/non-dominance. For these objects (including objects in a young stellar system) I prefer planetoid instead of dwarf planet simply because it's not an oxymoron. So our solar system contain planets, planetoids, and moons...plus asteroids, comets, moonlets, and debris. Still plenty of sub-categories from there based on physical traits or location relative to the Sun.
I agree that dwarf planets is an awkward and misleading name because it implies that the distinction is based on size rather than orbital properties. However, I think planetoid has the same problem. We have 3 known types of shared/non-dominant orbits: moons, trojans, and the unnamed category of resonant bodies like Pluto.

There has to be some apt mythological term for these "escort" planets.
__________________
"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan
Reply With Quote
  #341 (permalink)  
Old 28-September-2006, 11:42 PM
Murff's Avatar
Murff Murff is offline
Member
 
Join Date: Jun 2006
Location: North Dakota
Posts: 53
Default

Quick question: Percentage wise, what is the amount of KBO's closer to the sun than Pluto vs. the amount of KBO's farther out than Pluto?

Everything I have seen so far on my search shows Pluto, then the Kuiper Belt, not Pluto in the Kuiper Belt.

If you have a good sight that shows what I am asking, please Linky it.

Thank you for the help.
__________________
I'm a professional, please don't try this at home...
Reply With Quote
  #342 (permalink)  
Old 28-September-2006, 11:47 PM
Murff's Avatar
Murff Murff is offline
Member
 
Join Date: Jun 2006
Location: North Dakota
Posts: 53
Default

Quote:
To honestly think that there would be any difference between Pluto's orbit now and in 400 years is absurd.
That is why I stated "(not that this is realistic)". I am not really concerned about Pluto itself, more about how the definition will hold up to other objects that will be discovered in the near future. Let's say we find a planet the size of Mercury in our asteriod field ( I know it is not possible in our solar system, but it is not impossible to see elsewhere, I just use ours for the sake of clarity), how would we classify it?


Quote:
No, not "period". "Period" is used when you want to establish your opinion without discussion. That is not going to happen on an internet forum!
I meant "Period" as in to use nothing else but size to considered to determine planet status, not as in "Period, end of discussion". I wouldn't be on a board asking so many questions if I didn't expect different answers.



Quote:
OK, let's be clear about something. If there is a Jupiter-size planet surrounded by a large asteroid field, then we are surely witnessing the result of some catastrophic and recent event. The very reason that you DON'T see Jupiter-size planets in asteroid fields is because their immense gravity either ejects or absorbs any asteroids in their immediate vicinity rather quickly.

Considering all the different things scientist discover each year, I don't think a "what if" scenario for discussion is very absurd in relation to what the IAU has set forth as requirements to be a planet.
__________________
I'm a professional, please don't try this at home...

Last edited by Murff; 29-September-2006 at 01:07 AM. Reason: Clarity....I hope.
Reply With Quote
  #343 (permalink)  
Old 29-September-2006, 04:16 PM
CuddlySkyGazer CuddlySkyGazer is offline
Member
 
Join Date: Aug 2006
Location: London
Posts: 91
Default

Quote:
Originally Posted by Murff View Post
Let's say we find a planet the size of Mercury in our asteriod field ( I know it is not possible in our solar system, but it is not impossible to see elsewhere, I just use ours for the sake of clarity), how would we classify it?
I'm assuming you're talking about an object the size of Mercury orbiting another star within an asteroid belt around that star?

If so, then under the IAU's current definition in relation to extrasolar planets, it would be a planet.

Under the IAU's definition of planet in our solar system, it would be a dwarf planet.
Reply With Quote
  #344 (permalink)  
Old 01-October-2006, 12:42 AM
Ken G's Avatar
Ken G Ken G is offline
Senior Member
 
Join Date: Oct 2005
Posts: 10,541
Default

Quote:
Originally Posted by CuddlySkyGazer View Post
If so, then under the IAU's current definition in relation to extrasolar planets, it would be a planet.

Under the IAU's definition of planet in our solar system, it would be a dwarf planet.
And this underscores the silliness of the situation. Basically, we have a different definition in our own solar system simply because people wanted to keep the number of "planets" down to a small number when in our own solar system. That's it, that's the whole reason, and a poor reason at that. It would be like defining stars in the normal way in other galaxies, but only stars with solar systems like ours should count as stars in our own galaxy-- so as to avoid having too many stars in our own back yard! The definition of planet should just be based on the internal physics of the object, and that pretty much comes down to size. Who cares how many end up being in our solar system, that's not our concern. If we're going to have "dwarf planets", then it already means we have subclasses of planets, so why not also "major planets", and "satellite planets"? Then you can keep the "major planets" down to 8, that's fine. That would certainly seem like the rational thing to me, it would not devalue investigations like New Horizons, it would extend seamlessly to other star systems, and it would be fully in keeping with the way other objects are classified in astronomy. I am at a loss why there's any other alternative that makes sense.
Reply With Quote
  #345 (permalink)  
Old 01-October-2006, 02:48 AM
Eckelston Eckelston is offline
Senior Member
 
Join Date: Dec 2005
Posts: 248
Default

Quote:
Originally Posted by Murff View Post
Quick question: Percentage wise, what is the amount of KBO's closer to the sun than Pluto vs. the amount of KBO's farther out than Pluto?

Everything I have seen so far on my search shows Pluto, then the Kuiper Belt, not Pluto in the Kuiper Belt.

If you have a good sight that shows what I am asking, please Linky it.

Thank you for the help.
There are very few objects that orbit outside Neptune's and inside Pluto's orbit. However a large chunk of the Kuiper belt's population (about 15-20%, over 200 known objects) share their orbit with Pluto. More precisely they have a semi-major axis very close to Pluto's.

Here is a site with plenty of diagrams.
Reply With Quote
  #346 (permalink)  
Old 01-October-2006, 01:02 PM
CuddlySkyGazer CuddlySkyGazer is offline
Member
 
Join Date: Aug 2006
Location: London
Posts: 91
Default

Quote:
Originally Posted by Ken G View Post
Basically, we have a different definition in our own solar system simply because people wanted to keep the number of "planets" down to a small number when in our own solar system. That's it, that's the whole reason, and a poor reason at that.
No. The reason why the definition was restricted to our solar system was to avoid arguments like whether all planets must orbit stars etc. It was just a simpler problem. The IAU now has a committee looking at extending the definition to extrasolar planets.

The current definition relating to extrasolar planets is incomplete (because there was strong disagreement), and was designed as a working definition to tide things over until a more formal definition could be agreed to. It's not surprising there was some contradiction between it and the new definition.

The reason why the 'clearing the neighbourhood of its orbit' was inserted was because the orbital dynamicists and other people interested in the formation of solar systems (as opposed to the planetary astronomers who are primarily interested in the objects themselves) argue that there is a fundamental, demonstrable difference based on this concept of orbital dominance between the 'big 8' and the rest. I think they would agree that the actual wording leaves a little to be desired (but they only had a few days to come up with it), and I wouldn't be surprised if this wasn't tidied up in the future.

Quote:
The definition of planet should just be based on the internal physics of the object, and that pretty much comes down to size.
An arguable point of view, but not one everyone shares. Ganymede is bigger than Mercury in dimension, but not in mass, but even if it were very few astronomers would accept it as a planet, because it is orbiting Jupiter and not the Sun - a criteria based on where it is.

Quote:
If we're going to have "dwarf planets", then it already means we have subclasses of planets....
No, it doesn't. Unless you're going to argue that a minor planet (like Eros) is a type of planet? Or the Pennsylvania Dutch are Dutchmen living in Pennsylvania? Or a golden parachute is a type of parachute? 'Dwarf' in 'dwarf planet' is not an adjective. 'Dwarf planet' is a compound noun.

Quote:
I am at a loss why there's any other alternative that makes sense.
Perhaps this says something about you? You're at liberty to argue what you wish, but just because other people disagree with you doesn't make them irrational.
Reply With Quote
  #347 (permalink)  
Old 01-October-2006, 03:50 PM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 8,224
Default

Quote:
Originally Posted by CuddlySkyGazer View Post
The reason why the 'clearing the neighbourhood of its orbit' was inserted was because the orbital dynamicists and other people interested in the formation of solar systems (as opposed to the planetary astronomers who are primarily interested in the objects themselves) argue that there is a fundamental, demonstrable difference based on this concept of orbital dominance between the 'big 8' and the rest. I think they would agree that the actual wording leaves a little to be desired (but they only had a few days to come up with it), and I wouldn't be surprised if this wasn't tidied up in the future.
But there are apparently orbital dynamicists who disagree strongly with that concept. So the argument continues on all fronts, not just between planetary astronomers and orbital dynamicists.
Reply With Quote