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What does it mean?
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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.
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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 |
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"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 |
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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.
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"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 |
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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:
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.
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"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan |
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There has to be some apt mythological term for these "escort" planets.
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"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan |
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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.
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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.
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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. |
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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. |
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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.
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Here is a site with plenty of diagrams. |
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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:
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Why does not referring to Pluto as a planet somehow devalue the New Horizons mission? Pluto remains the same facinating object it has always been; it is still the largest KBO (If you consider the Scattered Disc separate) and it will doubless reveal a great deal about the early history of our Solar System, whatever word we decide to call it. My main problem with relying purely on internal physics in defining planets is that it ignores (and distorts) the overall structure of our solar system. The Kuiper Belt is a facinating structure in its own right, and the various objects within it are best seen, in my view, as components of a larger whole. To arbitrarily describe some (hundreds?) of those components as planets while ignoring the rest creates a lopsided view of our system, where nine planets exist between 0 and 40 AU, but 200 exist between 40 and 50 AU. Isn't it a bit misleading to say that they are planets, when in fact they are components of the Kuiper belt? After all, there aren't a lot of people campaigning to have all the rocks that make up Saturn's rings classified as moons. I also don't understand why Titan and Europa aren't considered planets, but then I'm having trouble understanding why Jupiter and Saturn aren't considered stars.
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There is a growing tendancy to think of Man as a rational, thinking being, which is absurd.- Marvin the Martian. It's gotten to the point where careful investigation is needed just to tell parody from reality. I think that means reality is broken.- Noclevername. |
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And I never claimed otherwise.
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There is a growing tendancy to think of Man as a rational, thinking being, which is absurd.- Marvin the Martian. It's gotten to the point where careful investigation is needed just to tell parody from reality. I think that means reality is broken.- Noclevername. |
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Sub-brown dwarfs are still considered stars, and their internal phyiscs aren't that different from those of Saturn and Jupiter.
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There is a growing tendancy to think of Man as a rational, thinking being, which is absurd.- Marvin the Martian. It's gotten to the point where careful investigation is needed just to tell parody from reality. I think that means reality is broken.- Noclevername. |
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That is a valid point, but it is not the issue here. Unfortunately, whenever you draw a line, there will be some object right on the edge of that line, challenging the validity of any such line. This is pretty inescapable, and will be true no matter what definition you choose. It is the fallacy of lines, but still they are necessary. We do the best we can. The issue is not where to draw the line, it is what the line should be based on. Physical (and astronomical) classifications should be based on the internal physics, so that you can try to extend knowledge across the class of objects. If sub-brown dwarfs were thought to have internal physics closer to Jupiter than the Sun, they would not be classified as stars (and perhaps they shouldn't be, that's another issue). It is felt that the fact that they have a significant nuclear energy source of some kind, and so have a structure that must readjust to reach equlibrium in a self-consistent way with that energy source, makes them more like a star than like Jupiter. At no point will you find the orbit of an object, or the effect it has on its surroundings, entering into the definition of a star, of a nebula, of a cluster, of a black hole, of an asteroid, of a dust particle, of an atom, of a universe. So what gives with planets?
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But all this demonstrates is that there is a group of astronomers who don't like the new definition. What a shock!Quote:
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I'm not talking about them.
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![]() I think if the original proposal had not also included the moon of Pluto, it probably would have passed. The barycenter thing is what the BA latched onto in his objection (the moon of Earth moving out to become a planet), whereas even a baseball/sun barycenter could be outside the sun if the baseball were thrown far enough away. |
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On this Site http://www.gps.caltech.edu/~mbrown/w...anplanets.html there is a list of all known objects in our solar system big enough to be round by by gravitation. (And a grafik of their orbits.) You can clearly see that even in this subset of KBOs Pluto is not the innermost. The most prominent KBO nearer then Pluto (39.53AE) would be Orcus (39.34AE) with 1100km diameter. And the nearest of the "planetlike" KBOs would be 2004TY364 (38.72AE) with 540km diameter (this is 0.81AE nearer then Pluto - more then the distance between Sun and Venus). |
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There is a growing tendancy to think of Man as a rational, thinking being, which is absurd.- Marvin the Martian. It's gotten to the point where careful investigation is needed just to tell parody from reality. I think that means reality is broken.- Noclevername. Last edited by parallaxicality; 03-October-2006 at 08:20 AM.. |
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