Talk:2006 definition of planet

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/Archive 1 /Archive 2

Contents 1 Archived 2 the underlying reason for the redefinition 3 the possibility that the inner core will dominate the whole crust 4 2006 Planet definition 5 Extrasolar Planets 6 Controversial? 7 A new Idea

[edit] Archived

I've archived the talk page into Archive 2, it was getting way too long. -- Lego@lost _{Rocks Collide!} | 07:29, 27 September 2006 (UTC)

What happened to the archives??? They seem to be gone now. AstroHurricane001 22:23, 26 October 2006 (UTC)

They got left behind during the last page move. I've fixed it now. DanielCristofani 05:57, 27 October 2006 (UTC)

[edit] the underlying reason for the redefinition

i think we should include in the article the underlying reason that the definition was changed. i think that it was that under the old system, there would now be more planets, and having a lot of planets is supposed to be bad. (by the way i think thats the most asinine thing ive ever heard of)

[edit] the possibility that the inner core will dominate the whole crust

Is there Always a possibility that the inner core will dominate or rule over the whole crust?if yes..why? and if no..why?

Huh? -- MiguelMunoz 00:11, 12 January 2007 (UTC)

[edit] 2006 Planet definition

It is fine by me if you want to merge my article and yours it is fine.Asteroidz R not planetz 17:10, 26 November 2006 (UTC)

[edit] Extrasolar Planets

I took out a sentence that incorrectly claimed that this definition doesn't apply to extrasolar planets. The 2003 draft agreement on extrasolar planets explicitly said that the lower limit of a planet's size would be whatever astronomers settle on for the solar system's planets. So it was designed to complement whatever new definitions astronomers developed for our own system. -- MiguelMunoz 19:39, 11 January 2007 (UTC)

[edit] Controversial?

Is this still controversial? it hasn't been edited in a month, and the arguments have died down. I'll remove the category unless somebody objects. Totnesmartin 17:04, 9 March 2007 (UTC)

Looks pretty good to me. I think it would be useful to include when the next scheduled attempt to define planets will occur (probably during the next IAU meeting in 2009). -- KarlHallowell 20:32, 11 March 2007 (UTC)

[edit] A new Idea

Why not just make the definition to read so that it includes any body that has enough mass to be roughly spherical but also has enough mass to have a moon that that meets the same criteria without having a center of gravity shared by the two bodies that is outside the object in question. If the minimum mass to retain a spherical shape can be determined why can't we determine the minimum mass to have a moon that is also spherical while keeping the center of gravity within itself? In this way almost all of the smaller planetoids thats caused all of this fuss would be excluded from being a planet without having some arbitrary criteria base off of a random amount of mass or diameter. User:. 68.193.3.225 08:57, 15 March 2007

Well, this discussion isn't for us to decide, so it doesn't really belong here, but from what I understand, it isn't a good idea to make a moon a requirement. What would Mars and Venus become? Also, I think there's an asteroid, one much smaller than Ceres, that has a sattelite, and isn't large enough to maintain hydrodstatic equilibrium. I don't think requiring a moon would be a good idea. McKay 13:32, 15 March 2007 (UTC)

You misunderstand me, not that it would be a requirement to have a moon but, that if there where to be a hypothetical moon just large enough to hold a shperical shape that the shared center of gravity would be within the object in question. I didn't mean to suggest that planets would be definited by if they have a moon or not - that would, as you hinted at, exclude Venus. Mars two moons but even though neither one is shereical I would wager that Mars is large enough to hold hypothetically in its gravity a moon large enough to be spherical in shape with out moving the center of gravity outside of itself. I'm not a physicist or I would do the calculation myself.User:. 68.193.3.225 14:19, 15 March 2007

This is rather moot, as we do not make this decision, the IAU does. Your question also depends on the distance between hypothetical moon and planet (at distance 0 between surfaces, the barycenter will always be in the larger body for bodys of equal density). And if you require the moon to be outside the Roche Limit, I don't know if e.g. Mercury passes. --Stephan Schulz 16:34, 15 March 2007 (UTC)

Ahh, I think I understand you better, but then it's an arbitrary distinction. one can't speak of "moons just large enough to hold a spherical shape" without knowing of their composition and history. Enceladus, a moon, is "large enough" to maintain maintain hydrostatic equilibrium, but 4 Vesta, a larger asteroid, is not. Also in question is theory, it is theoretically possible for one via thought experiments to create theoretical moons which are of various sizes and masses, that would break the idea. McKay 16:41, 15 March 2007 (UTC)

'Large enough' might be a bad phrase to use, a better phrase might be 'has enough mass'. I could be wrong but I was under the impression that mass was the determining factor in wheather an object could maintain a hydrodstatic equilibrium, reguardless of actual size or diameter? If so having a hydrodstatic equilibrium would not be an arbitrary distinction and if an object had enough mass to maintain a hydrodstatic equilibrium and to hold in its gravity another object with the minimum amount of mass needed to also maintain a hydrodstatic equilibrium without displacing the first objects center of gravity outside outside of itself then my idea still holds water, right? User:. 68.193.3.225 14:54(EST), 15 March 2007

4 Vesta has more mass than Enceladus (moon), yet Enceladus is in hydrostatic equilibrium, and Vesta is not. It is not generally agreed by scientists that mass makes hydrostatic equilibrium. But even that aside, there's still problems with the idea:

• Let's assume (for simplicity) that we've just got two potential planets in a universe. One larger than the other, and both orbiting a barycenter in a circle. From Barycenter (and a little OR): With a radial distance of a, and a barycenter at position r from the center of the primary mass a/r = 1 + m1/m2 which for something like the earth moon system, m1/m2 is about 1.2%, so the ratio of the barycenter to the orbital radius is about 98%, for the pluto charon system, it's about 90%. so, this means if the moon were further from the earth (lets say three times?), than it would have a barycenter outside of the surface of the earth. And similarly, if Charon were closer to pluto (half the distance would suffice), then it would be within it's barycenter. But your argument was with something like Vespa (or something with about that mass), then it only depends on how close an object could be to it. So, any object that maintains hydrostatic equilibrium, could hold another such object, presuming it was close enough to it. Except in the case where an object has exactly the smallest mass, because then it's feasably impossible (though still theoretically possible) for it to have another object "in orbit" with barycenter inside itself, but it would require the other object to physically be touching it.
• We basically make the distinction for calling something a star if it (is massive enough to) create(s) internal fusion. Requiring that it also be large enough to support another star similarly is kinda silly. There are several binary star systems that have a barycenter outside of the surface of the primary star. Even in the case of very large stars vs very small stars. Does that make them any less stars?

(These problems make me say that this definition is arbitrary.) 20:14, 15 March 2007 (UTC)

Personally, I'd like to see more planets, not less - I'd rather add Eris and Ceres to the list of planets than take Pluto off. Since when did the IAU, an organization I've never heard of, have the final say on the definition of a planet anyways? CobraA1 07:32, 7 April 2007 (UTC)