Pluto defines a Planet as being a Planet!

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kheider

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<font color="yellow">>Are you are saying that a standard from 1,000 years of technically inferior science should override a modern day standard?</font><br /><br />I am sure Ron was referring to the fact that Mercury has been known as a Planet for thousands of years, were as Pluto has NOT even been known for 100 years. It just happens to be that modern science has shown that Mercury is the smallest planet (assuming of course that we do NOT call Pluto a planet).<br /><br /><font color="yellow">>I have thrown down the question (what differentiates a “Planet” from a “Dwarf Planet”) on the table and not one single satisfactory answer has arisen</font><br /><br />Your opinion. Some of us agree with the answers and agree they need some refinement.<br /><br /><font color="yellow">>I believe the IAU should have left Pluto as a planet </font>font color=orange>and not added any more planets to our solar system with the emphasis that the planet issue needs to be researched further.<br /><br />That's basically what they did! The IAU, as a group of professional astronomers, decided it was best to remove Pluto as one of the Planets and then do more research on what defines a Planet.<br /><br />-- Kevin Heider
 
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silylene old

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<font color="yellow">I am sure Ron was referring to the fact that Mercury has been known as a Planet for thousands of years, were as Pluto has NOT even been known for 100 years. </font><br /><br /><b>Umm, not.</b><br /><br />The Greeks thought the dim "star" they saw in the dawn and dusk skies circled the earth and was the messenger of the gods, riding a chariot.<br />The Romans thought the dim "star" they saw in the dawn and dusk skies circled the earth and was the god of travel and commerce.<br />The Germanics and Norse thought the dim "star" they saw in the dawn and dusk skies was Wotan, or Odin, the god of shamanistic magic and poetry.<br />The Mayans thought the dim "star" they saw in the dawn and dusk skies was the owl-skull god.<br />The Hindu thought the dim "star" they saw in the dawn and dusk skies was the ruler of numerology and vedic astrology.<br />The Medievalists thought the dim "star" they saw in the dawn and dusk skies circled the earth and was the symbol of duality and cleverness.<br /><br />You know, it wasn't until Newton that anyone got it somewhat right - that Mercury was an object that circled the sun (350 yrs ago).<br /><br />It wasn't known that mercury was spherical until phases were seen by Zupus in 1639 .<br /><br />Thousands of years? Not. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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kheider

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<font color="yellow">>Mercury has been known as a Planet for thousands of years, were as Pluto has NOT even been known for 100 years.</font><br /><br />Planets have been known as wanderers in the sky for thousands of years. Mercury has been observed moving amongst the stars since man first started looking up at the sky. Pluto has not!<br /><br />-- Kevin Heider
 
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silylene old

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<font color="yellow">Planets have been known as wanderers in the sky for thousands of years. Mercury has been observed moving amongst the stars since man first started looking up at the sky.</font><br /><br />At least your backtracking on your prior statement is getting somewhere now. "Wanderers" is correct: wandering gods, wandering skull-owls, and even a wandering horse drawn chariot. Anything but a spherical body of stone and metal orbiting around the sun according to the laws of gravitation! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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kheider

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<b>Planet</b>: One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to wander in the heavens above a fixed Earth and among fixed stars. The word “planet” comes from the Greek word for “wanderer".<br /><br />So, it is accurate to say, "Mercury has been known as a Planet for thousands of years, were as Pluto has NOT even been known for 100 years."<br /><br />-- Kevin Heider
 
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vonster

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<blockquote><font class="small">In reply to:</font><hr /><p>I agree with your entire post, except for item 5:<br /><br />"5) A planet is at least as big as Pluto. This is arbitrary, cultural, historical and controversial. A dividing line has to be made somewhere."<p><hr /></p></p></blockquote><br /><br />I also agree that syline's definition seems to cover everything but this final point <br /><br />... which is an important one and the key to the whole inability to find a consensus.<br /><br />What nobody seems to want to admit is that -- with some issues --- "arbitrary" dividing lines DO need to be drawn because we are dealing with 'analog' rather than 'digital' information:<br /><br />A body circling a star can vary in both a) Size -- b) Mass and -- c) Orbital Status (to name three most impt criterion) along a continuous scale ...<br /><br />Where all three scales are combining in different relationships. So it is very difficult if not impossible to avoid arbitrary cutoffs ... particularly if there is any chance that the definition will be broad enough to cover undiscovered extrasolar objects and configurations <br /><br />The social status of Pluto as being a "loved little planet" only confused the real issue. Which I think is what I just stated.<br /><br />Take sylines definition and modify it this way:<br /><br />5) A planet is at least as big as Pluto<br /><br />6) A <b> planetoid</b> is at least as big as Ceres, and up to the size of Pluto<br /><br />IF there is resistance to this because of the potential for discovery of more Kupier belt type objects in the future, THEN we can modify it this way:<br /><br />5) A planet is at least as big as Mercury<br /><br />6) A planetoid is at least as big as Ceres, and up to the size of Mercury<br /><br />This puts all those objects in Planetoid class (much more appropriate and obvious nomenclature than "dwarf planet) and keeps it manageable.<br /><br />SO (full definition):<br /><br />1) A planet circles a star or stars. If it does circle another
 
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Philotas

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What we need is a scientific definition; not just a definition that looks good on the paper. We don't any dwarf planets nor planetoids, they're just messing up everything. If a space object is big enough to differentiate(sp?), it's a planet. And this happens when the object is round! And what do you think of when you hear the word planet? A round world. This definition satisfies both the human mind and science. It's a bargain. ;) <div class="Discussion_UserSignature"> </div>
 
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jakethesnake

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I said:<br /><br />“I have thrown down the question (what differentiates a “Planet” from a “Dwarf Planet”) on the table and not one single satisfactory answer has arisen”<br /><br />You said:<br /><br />“Your opinion. Some of us agree with the answers and agree they need some refinement.”<br /><br />My opinion is base to a larger extent because of answers such as this.<br /><br />So I ask the question again and refine it so it makes scientific sense and the cutoff is reasonably clear:<br /><br />What differentiates a “Planet” from a “Dwarf Planet”?<br /><br />------------------------------------------------------------------------------------------------------------<br />If you don’t know don’t add to the confusion! <br /><br />If you don’t know leave it alone until you do! <br /><br />If you don’t know admit it! <br /><br />If you don’t know don’t cost everyone a lot of money pretending you do!<br />------------------------------------------------------------------------------------------------------------<br /> <div class="Discussion_UserSignature"> <strong></strong> </div>
 
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vonster

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<blockquote><font class="small">In reply to:</font><hr /><p>What we need is a scientific definition; not just a definition that looks good on the paper. [edit] ...<br /><br />If a space object is big enough to differentiate(sp?), it's a planet.<p><hr /></p></p></blockquote><br /><br />Your point is taken -- however -- this again goes back to the primary issue that --- in the case of planetary classification:<br /><br />The information required for classification requires 3 main criterion (Size - Mass - Orbital Status) at the very least .. possibly more.<br /><br />And defining information for these criterion are:<br /><br /> "analog" (along a continuous scale) <br /><br />as opposed to <br /><br />"digital" (along a scale with discreet, easily managed and predictable steps)<br /><br />AND<br /><br />All 3 of these criterion combine in -- what looks like at this point -- an astronomically (pun intented) large number of combinations.<br /><br />This makes any system as simple as the one you are proposing far too unmanagable for purposes of real life human needs: <br /><br />Reference, education, scientific notation, focus of scientific research, textbook manufacturers, memorization by schoolkids ... etc ..<br /><br />So arbitrary limits need to be set -- that meet real human needs.<br /><br />Why is meeting real human needs (as stated above) not "scientific"?<br /><br />How can classification and human scientific knowledge progress without categorizing phenomena into easily managed units?<br /><br />This is where the whole process is getting hung up. <br /><br />Again: the modification I added to silylenes definition (see above) accomplishes this.<br /><br />If not, why not?<br /><br />.<br /><br /><br /><br /><br />
 
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Philotas

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<blockquote><font class="small">In reply to:</font><hr /><p><br />This makes any system as simple as the one you are proposing far too unmanagable for purposes of real life human needs: <br /><br />Reference, education, scientific notation, focus of scientific research, textbook manufacturers, memorization by schoolkids ... etc .. <p><hr /></p></p></blockquote><br /><br />Not sure what your point is<br /><br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Why is meeting real human needs (as stated above) not "scientific"? <br /><br />How can classification and human scientific knowledge progress without categorizing phenomena into easily managed units? <br /><p><hr /></p></p></blockquote><br /><br />It can't get much easier than by just having 3 criteria. The easiest would be just 2 criteria:<br /><br />*It's has enough to maintain spherical shape<br />*It does not have more mass than 13X that of Jupiter; then it is a fusor<br /><br />With newly discovered objects, size estimates are little precise. Setting an arbitrary limit wouldn't make this part easier, and it wouldn't be possible for a teacher to give a pupil a scientific reason why this limit was created in the first place.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Again: the modification I added to silylenes definition (see above) accomplishes this. <br /><br />If not, why not? <p><hr /></p></p></blockquote><br /> <br />It doesn't because it's too complicated. We do not really need any complicated definitions, as the definition for a planet is for public use. Whether Pluto is a planet or not is completely irrelevant for what scientific priority it should have. <div class="Discussion_UserSignature"> </div>
 
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kheider

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<font color="yellow">>With newly discovered objects, size estimates are little precise. Setting an arbitrary limit wouldn't make this part easier.</font><br /><br />Definitely. Back in 1886 (source: 1886 Recreations In Astronomy/Henry White Warren), they thought Mars inner moon Phobos was only 7.5 miles in diameter. Now we know it is 17x12 miles in diameter. They also thought Jupiter was only 213x the mass of the Earth, instead of 317x.<br /><br />-- Kevin Heider
 
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vonster

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<blockquote><font class="small">In reply to:</font><hr /><p><br /> This makes any system as simple as the one you are proposing far too unmanagable for purposes of real life human needs:<br /><br /> Reference, education, scientific notation, focus of scientific research, textbook manufacturers, memorization by schoolkids ... etc ..<br /><br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Not sure what your point is<p><hr /></p></p></blockquote><p><hr /></p></p></blockquote><br /><br /><br />I'll explain it another way then. What is the difference between:<br /><br />- a dust devil<br /><br />- a tropical storm<br /><br />- a tornado, and<br /><br />- a hurricane<br /><br /><br />All are circular wind patterns created by convection currents and other factors in the atmosphere.<br /><br />But we dont call all of them "hurricanes". There are reasons for that.<br /><br />Where do we draw the dividing lines? For the most part, its somewhat arbitrary. Yes you can quibble about the details ....<br /><br />But why do we give them all different names for the most part? We choose a size and an intensity and method of generation and we give it a name<br /><br />Why? To make understanding these phenomena manageable for all the reasons I gave above.<br /><br />Its not complicated at all. Its common sense. Yet imo this is precisely where this is getting all hung up.<br /><br /><br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Again: the modification I added to silylenes definition (see above) accomplishes this.<br /><br /> If not, why not?<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>It doesn't because it's too complicated. We do not really need any complicated definitions, as the definition for a planet is for public use.<p><hr /></p></p></blockquote><br /><br />No -- as I said, its not complicated at all.<br /><br />On the contrary: it becomes infinitely more complex to manage what is what, and study these things without enough dividing points to break it d</p></blockquote>
 
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wonky

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Saying that Pluto is a planet just because it's a "Beloved little planet," that's nothing more than an illusion.<br /><br />We now know that it is in no way unique.
 
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kmarinas86

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<font color="yellow">Frankly it's not the discovery of new scientific facts, like pulsars or black holes but the arbitrary redefining of something, which has no real physical basis, except they will now draw the line *here* instead of *there*.</font><br /><br />AMEN!
 
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jakethesnake

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The IAU is an international organization that has a very important job of coordinating astronomical information world wide. The IAU’s has the responsibility of disseminating information globally by breaking down language barriers through common definitions to enable data to be interpreted by all. Also the IAU has another important function in which it has failed miserably and that is to set concrete understandable definitions that enables the educational process for the public and future teachers, astronomers, astrophysicists and scientist as a whole to be educated.<br /><br />FACTS:<br /><br />1. The IAU’s definition of a “Planet” is exclusive to our solar system only and the IAU acknowledged this.<br /><br />2. The IAU has also admitted that that their definition of a “Planet” is an “Arbitrary” classification to divvy up the data studies and sorting process.<br /><br />3. The IAU had established two comities over the last three year to try and iron out a definition of what a “Planet” is. The first comity could not come to an agreement after two years of squabbling. The second comity came to an agreement which added three new planets to our solar system. Then finally the IAU’s definition of a “Planet” happened in a matter of days and came down to a less than unanimous vote because nothing could be agreed upon.<br /><br />In light of what I have unarguably just outlined several facts surface without debate. <br /><br /><br />The IAU has basically admitted that does not have a firm knowledge as to what a “Planet" is by the disagreement within its own establishment and it’s clear inability to come up with a definition over the last three years. Also by limiting its definition to our own solar system the IAU has shown that they have little confidence and/or enough knowledge to clearly define what a “Planet” is so they chose a definition to soot their own purposes.<br /> <div class="Discussion_UserSignature"> <strong></strong> </div>
 
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Philotas

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Took me long to get back to this thread...anyway:<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>I'll explain it another way then. What is the difference between: <br /><br />- a dust devil <br /><br />- a tropical storm <br /><br />- a tornado, and <br /><br />- a hurricane <br /><br /><br />All are circular wind patterns created by convection currents and other factors in the atmosphere. <br /><br />But we dont call all of them "hurricanes". There are reasons for that. <br /><br />Where do we draw the dividing lines? For the most part, its somewhat arbitrary. Yes you can quibble about the details .... <br /><br />But why do we give them all different names for the most part? We choose a size and an intensity and method of generation and we give it a name <br /><br />Why? To make understanding these phenomena manageable for all the reasons I gave above. <br /><br />Its not complicated at all. Its common sense. Yet imo this is precisely where this is getting all hung up.<p><hr /></p></p></blockquote><br /><br />Mhm. Take a look at this:<br /><br />Mercury and an as of yet undiscovered KBO or some icy object from another solar system are equally big in mass and size.<br /><br />By your definitions based on size, these two completely different objects would both be classified as the same. <br />This is only confusing the understanding of planets. If you want sub-classifcations, go for composition.<br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p> No -- as I said, its not complicated at all. <br /><br />On the contrary: it becomes infinitely more complex to manage what is what, and study these things without enough dividing points to break it down. <br /><br />Small Stelllar Body (SSB), Planetoid, Planet, Brown Dwarf --- its makes much more sense to just slot the objects into categories that allow us to identify them. <br /><br />Otherwise, lets just go back to calling all wind patterns "Hurricanes" <br /><br />and let everybody just work out exactly what it is we are tal</p></blockquote> <div class="Discussion_UserSignature"> </div>
 
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kheider

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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!<br /><br />(click here to see Pluto starting to shrink in 1959)<br /><br />Source:<br />Planets<br />Other Worlds of Our Solar System<br />Golden Library of Knowledge (1959)<br /><br />-- Kevin Heider
 
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wonky

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When I was a kid in the 80's, I had a book called "Our Universe." I think it was put out by National Geographic?<br />In any case, even back then, in the Pluto chapter they talked about reclassifying it as an asteroid!
 
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MeteorWayne

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Glad you brought that up. I may have that book somewhere in my archives. Let you know if I find it. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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kheider

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<font color="yellow">There is not a single credible reason for redefining planet at this time. </font><br /><br />Yes there is. The IAU had to come up with a definition of a Planet because of all the other TNOs (a group for which Pluto belongs to) being discovered. Since one object (Eris) was discovered to be bigger than Pluto they could infer that other objects would also be bigger than Pluto. The IAU either had to keep Pluto as a Planet and let many other non-dominant obects be included as Planets OR they had to remove Pluto as a Planet. Keeping Pluto as an exception to the rule would be unscientific.<br /><br />Planet: One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to wander in the heavens above a fixed Earth and among fixed stars. The word “planet” comes from the Greek word for “wanderer". <br /><br />Mercury (which modern science has shown to be the smallest planet) has been known as a Planet for thousands of years, were as Pluto has NOT even been known for 100 years.<br /><br />Once it became apparent that Pluto was much smaller than Mercury, and not the 14,500km Super Earth they originally thought, Pluto's status as a Planet was on borrowed time.<br /><br />-- Kevin Heider
 
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wonky

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MeteorWayne, here's the book I'm talking about.<br />http://www.amazon.com/National-Geographic-Picture-Atlas-Universe/dp/079222731X<br />Note all the reviews are 5 stars, from people who remember the book from childhood memories.<br />I literally wore this book out as a kid. It fell apart. At that point I was in high school and my parents bought me the new edition, which included the Voyager photos from Uranus (not sure about Neptune.) It's still up in my parents' attick. Next time I go back home I'll pick it up!
 
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Philotas

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<blockquote><font class="small">In reply to:</font><hr /><p>Composition is NOT a primary characteristic, or necessary characteristic of a planet. It's size and orbit of a star are, essentially. <p><hr /></p></p></blockquote><br /><br />Yes, but for the different classes of planets it's pointless to define after mere size.<br /> <div class="Discussion_UserSignature"> </div>
 
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Philotas

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<blockquote><font class="small">In reply to:</font><hr /><p>Yes asteroids do differ a lot from each other. Many are rocky masses, composed mostly of silica rich and other related rocky compounds very similar or identical to those found on the crust of the inner planets and our Moon. <br /><br />Another group is metal/rocky and the last is almost pure metals, nickel/iron at least 90% plus or more. There are the chondritic asteroids consisting of masses of small to larger spheres of calcium aluminate silicates, some water, clays, etc. There are the carbonaceous asteroids which consist of masses of graphite, carbon, water, some admixtures of ammonia, etc<p><hr /></p></p></blockquote><br /><br />As I said. They 'all' belong to a gorup/class of asteroids; they aren't so interesting in their own right.<br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>And lastly it's been found that some if not many asteroids are the burnt out remnants of comets, witt a very low mass, occ. less than that of water consisting of rocky substances, methane, water, etc. And a coating of a dusty rocky material, the residue of the volatiles after they were removed by considerable solar heating. <br /><br /><br />So asteroids too, are a very diverse group of minor planets. Just like the major planets like mercury, mars, jupiter and Pluto all differ in composition. But as in the case of asteroids, the compositional differences among then do not have much to do with being a major or minor planet. Orbit and size are the two keys.<p><hr /></p></p></blockquote><br /><br />Asteroids aren't so different from each other as planets are/can be.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Try picking up a astronomy and/or scientific text before just spouting off on the subject, people. The internet is information rich when one is careful. You might actually learn something and then your posts would have the credibility of learning, rather than their current appearance of being unscientific, un</p></blockquote> <div class="Discussion_UserSignature"> </div>
 
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rhm3

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I've thought about this issue some more and have come up with a scheme that (I think) comprises all views on the issue and retains significant scientific merit. I got the idea of the classifications from a Stern & Levison (2000) paper.<br /><br /><br />UNIVERSAL PLANET CLASSIFICATION SCHEME<br /> <br /><b>General Definition: </b><br /><br />A <i>planet</i> is a celestial body that is low enough in mass that it can never generate energy in its interior from self-sustaining nuclear fusion, and is large enough that its shape becomes determined by gravity so that it reaches a state of hydrostatic equilibrium. <br /><br /><b>Categories Based on Dynamical Role and Orbit: </b><br /><br />A <i>major planet</i> is in orbit around a star and is dynamically significant enough that it dominates its orbit of neighboring bodies.<br /><br />A <i>minor planet</i> is in orbit around a star and is dynamically insignificant enough that it does not dominate its orbit of neighboring bodies. <br /><br />A <i>secondary planet</i> is in orbit around another planet and is thus dynamically insignificant. <br /><br />An <i>isolated planet</i> is unbound to a stellar system and is thus dynamically insignificant. <br /><br /><b>Categories Based on Physical Structure and Size: </b><br /><br />A <i>supergiant planet</i> is high enough in mass that it contains degenerate matter in its core, but low enough in mass that at no time can it become a star.<br /><br />A <i>giant planet</i> is high enough in mass that it contains a liquid metallic hydrogen layer in its interior, but low enough in mass that it is not a supergiant planet.<br /><br />A <i>subgiant planet</i> is large enough that it contains an outer layer of hydrogen or helium gas, but low enough in mass that it is not a giant planet.<br /><br />A <i>dwarf planet</i> is large enough that it can modify its initial chemical composition in its interior, but small enough that it is not a subgiant planet.<br /> <br />A <i>subdwarf planet</i> is large enough that it is
 
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kheider

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<font color="yellow">Earth is a major dwarf planet.</font><br /><br />This classification scheme might be useable in the future. But given how emotional the general public was reacting to Pluto being classified as a 'Dwarf Planet', it would almost create global chaos if the IAU started officially calling our home world a 'Major Dwarf Planet'. You think "clearing its neighborhood of comparable objects" is difficult to explain? Try explaining the oxymoron "Major Dwarf" to the general public. <img src="/images/icons/rolleyes.gif" /><br /><br /><font color="yellow">Ganymede is a secondary dwarf planet</font><br /><br />I'm not sure the public wants to call spherical moons as planets. Currently (for better or worse) we define both planets and moons by their surroundings. I don't think the public wants to call Luna a 'secondary dwarf planet moon'.<br /><br />Right now we just need a definition of a Planet. Currently Planets need to be dominant objects, were as worlds do not.<br /><br /><font color="yellow">There are also the eight major planets.</font><br /><br />This is the way it is for now. We have 8 Planets, 16+ 'Dwarf Planets' (compound noun), and 136,563+ asteroids (known as minor planets until August 2006).<br /><br />-- Kevin Heider
 
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