how to define planets

[bdaunno]

these people are forgetting the most simple thing that can clear up this mess<br /><br />planets should orbit a star, have enough gravity to become round, AND<br /><br />not be a member of an asteroid belt or similar system. pluto should be eliminated and recategorized as a kuiper belt object. this would also free xena, ceres, and charon.<br /><br />8 planets is what we have, and they should not be defined based on the disappointment of 5th graders.

 

[cuddlyrocket]

Define asteroid belt and similar system. Define Kuiper Belt object.<br /><br />Remember, the definition must apply to other solar systems.

 

[harmonicaman]

<b>CuddlyRocket -</b><br /><br /><i>"Define asteroid belt and similar system. Define Kuiper Belt object."</i><br /><br />These two areas of our Solar System are sufficiently defined at this time and require no further disambiguation. <br /><br /><i>"Remember, the definition must apply to other solar systems."</i><br /><br />Why? I don't think this is a very realistic goal. The Extrasolar planetary systems are so alien in their form, that they have little or no resemblance to our own Solar system. How would our narrow planetary classification system relate to a Brown Dwarf Solar System or a Black Hole Solar System?<br /><br />This decision is a flagrant example of the flawed "Design by Committee" concept, and the result will be increased confusion about what's really what in the Solar System - science is supposed to be about making things more clear!<br /><br />This decision is exactly the same as classifying animals by their size alone - there are other important considerations which are being totally ignored here!

 

[bdaunno]

harmonica i think you are in way over your head. you are seperating dog from man while the rest of the community is seperating lizard from mammal. And in this case, size is the major issue defining planets.<br /><br />The larger end of the spectrum is much easier to define as you approach stellar limits. The smaller end, however, is exactly what's under debate. You can't put an exact value to it because whose to say a 2000 kilometer object is a planet and a 1999 kilometer object is not? This is why we need to use other variables. In this case, I reccomend adding whether or not anything else composes an objects orbit, and not just the orbit around the sun itself.<br /><br />Sort of like seperating the ideas of "land lizards" from "sea lizards." <img src="/images/icons/smile.gif" /> (don't think specifics like alligator from iguana, just the general idea)

 

[alokmohan]

If you call mercury a planet ,why call ganymede a moon?We may say solar system has four planets called gas giants and moons named terrestrial planet.Will you agree?

 

[cuddlyrocket]

No.<br /><br />Ganymede is not a planet because it does not orbit a star. It orbits a planet.

 

[harmonicaman]

<b>Bdaunno -</b><br /><br /><i>"you are seperating dog from man while the rest of the community is seperating lizard from mammal. And in this case, size is the major issue defining planets."</i><br /><br />I agree that size is a factor, but this silly plan makes size <i>the only</i> factor under consideration! I think the Solar System is a bit more complicated than that. <br /><br />An asteroid is like other asteroids and shouldn't be confused with planetary bodies. The KBOs and Oort cloud objects are just that; they also shouldn't be lumped in together with the other planets.<br /><br />Why weren't factors like material composition, location, albedo and other attributes considered in the definition of what constitutes a planet?<br /><br />How does this definition of a planet make the Solar System less ambiguous? Isn't this the goal of science?<br /><br />Why does there have to be a planet definition now? We really have a lot more to learn about the Solar System and this arbitrary definition is likely 50 years premature.<br /><br />The IAU just got it wrong; they'll just have to straighten it out later when we learn even more about the components of the Solar System.

 

[cuddlyrocket]

"...but this silly plan makes size the only factor under consideration!"<br /><br />No it doesn't. An object must also be orbiting a star. <br /><br />"An asteroid is like other asteroids and shouldn't be confused with planetary bodies."<br /><br />I agree with you - now they won't be. Ceres is not an asteroid.<br /><br />"The KBOs and Oort cloud objects are just that; they also shouldn't be lumped in together with the other planets."<br /><br />That's a matter of opinion. There's no reason why definitions can't overlap. 'Xena' is both a planet (and a pluton) and a KBO.<br /><br />"Why weren't factors like material composition, location, albedo and other attributes considered in the definition of what constitutes a planet?"<br /><br />The definition was designed to be usable for objects around other stars, as the science of extra-solar planets if developing rapidly. These matters would either be arbitrary or difficult to establish for such planets. In any event, what definition for these would include <i>all</i> the eight 'classical planets'. And there's something to be said for a relatively simple definition.<br /><br />"How does this definition of a planet make the Solar System less ambiguous?"<br /><br />You now know Xena <i>is</i> a planet.<br /><br />"Why does there have to be a planet definition now?"<br /><br />The IAU wouldn't have taken the matter up if there hadn't been a lot of pressure for a definition. Was Xena' a planet? The press (and school textbook and encyclopaedia editors) kept asking - and it made the astronomical community look silly that they could not answer the simple question 'what is a planet?'.<br /><br />"We really have a lot more to learn about the Solar System and this arbitrary definition is likely 50 years premature."<br /><br />The definition is not arbitrary. You might not like it, but that's a different matter. And there's no way the astronomical community could wait 50 years not knowing the answer to 'what is a planet?'.<br /><br />"The IAU just got it wrong

 

[mythrz]

I know how to "knip this in the bud". Lose the definition "planet" entirely! Since so many people are holding on to the name "planet" and what they want it to mean. This is sad, that something so simple as a definition could cause so much fuss.

 

[MeteorWayne]

If it's so simple, what would be your definition?<br /><img src="/images/icons/wink.gif" /> <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>

 

[acevonwildfire]

Personally I like the proposed definition. Though I would make a minor modification. Below is my opinion of what the draft should be:<br /><br />Draft Resolution 5 for GA-XXVI: Definition of a Planet<br />Contemporary observations are changing our understanding of the Solar System, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries force us to create a new definition, which we can make using currently available scientific information. (Here we are not concerned with the upper boundary between "planet" and "star".)<br />The IAU therefore resolves that planets and other Solar System bodies be defined in the following way:<br />(1) A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape1, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.2<br />(2) We distinguish between the eight classical planets discovered before 1900, which move in nearly circular orbits close to the ecliptic plane, and other planetary objects in orbit around the Sun. All of these other objects are smaller than Mercury. We recognize that Ceres is a planet by the above scientific definition.<br />(3) We recognize Pluto to be a planet by the above scientific definition, as are one or more recently discovered large Trans-Neptunian Objects. In contrast to the classical planets, these objects typically have highly inclined orbits with large eccentricities and orbital periods in excess of 200 years. We designate this category of planetary objects, of which Pluto is the prototype, as a new class that we call "plutons". <br />(4) All non-planet objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".4<br />(5) Any obj

 

[MeteorWayne]

It's hard to tell reading through the whole thing. What were your modifications? <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>

 

[acevonwildfire]

ORIGINAL (2) We distinguish between the eight classical planets discovered before 1900, which move in nearly circular orbits close to the ecliptic plane, and other planetary objects in orbit around the Sun. All of these other objects are smaller than Mercury. We recognize that Ceres is a planet by the above scientific definition. For historical reasons, one may choose to distinguish Ceres from the classical planets by referring to it as a "dwarf planet."3 /ORIGINAL<br /><br />MODIFIED (2) We distinguish between the eight classical planets discovered before 1900, which move in nearly circular orbits close to the ecliptic plane, and other planetary objects in orbit around the Sun. All of these other objects are smaller than Mercury. We recognize that Ceres is a planet by the above scientific definition. /MODIFIED<br /><br />ADDED (5) Any object, recognized as a planet by the aforementioned definition, that does not fit the definition of a “pluton”, and is smaller than the diameter of Mercury shall be designated as a new class called “dwarf planets”. /ADDED

 

[MeteorWayne]

Thanks.<br />I agree that dwarf planet should be an official designation.<br />Though the dwarves might be pissed. <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>

 

[acevonwildfire]

My modification would make 3 distinct classes inside of the definition of 'planet'. This would also prevent pluto from being classified as a planet AND a dwarf planet AND a pluton.<br />Ace Von Wildfire

 

[MeteorWayne]

I like the planetoid idea. It does feel better than dwarf planet.<br />At least it's not offensive to dwarves.<br />Where the line gets drawn, I'm still a ponderin' <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>

 

[mythrz]

<i>If it's so simple, what would be your definition?</i><br /><br /><br />Of course it's simple..... we shall call everything "IFO". Identified Floating Object. Then name and number it and as an infamous cook would say "BAM" there you go!

 

[scepterium]

I don't get why we can't just call a planet something that is round because it has enough gravity to become round, and only orbits a star. Really, that's all they should look for when defining planets I think. It's like they think that what a planet is is a fact like a math equation they haven't figured out yet when it's not and is not anywhere near that important at all!

 

[MeteorWayne]

Well, they're not floating, they are orbiting.<br />One down, next suggestion <img src="/images/icons/smile.gif" /> <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>

 

[MeteorWayne]

That's pretty much what the proposed IAU definition is. <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>

 

[mythrz]

IOO, then.............BAM!

 

[scepterium]

Ok I just read the IAU proposals definition and agree with it %100.

 

[MeteorWayne]

Unfortunately, the term planet has a significant meaning for the 20% of humans who care about what's up there at all. You can't just BAM away centuries of human history.<br />No one is going to accept the term IOO!<br />See, things are hard until you actually try and do them. <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>

 

[brandbll]

I don't get why Charon is going to be calssified as a planet? Anyone get that? I thought they went overboard on the whole thing. I'm willing to bet 90% of people in the US didn't even know about Ceres before this. Well this can lead to a rise in interest in objects(hmmm, objects, seems like a fairly objective name) such as Ceres and could in turn help push for missions to said places. I think Charon seems to be the oddest choice of them all, but maybe that's just because i don't know much about it. <br /><br />Also, if Pluto and Charon are orbiting each other, doesn't that mean we won't have a "farthest planet from the sun" anymore since it will constantly be changing? <div class="Discussion_UserSignature"> <p><font size="3">You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard!</font></p> </div>

 

[cuddlyrocket]

'Xena' is the furthest planet from the Sun (at least at the moment).<br /><br />And Pluto isn't always the furthest planet from the Sun. At times it is closer to the Sun than Neptune.