Talk:Definition of planet

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Help with this template Comments: edit – history – watch – refresh There seem to bad formulations in the subsection Definition of planet#Double planets. See Talk:Definition of planet#Definition of natural satellite. Therefore the article currently doesn't deserve FA rating. Andres 13:20, 27 August 2006 (UTC)

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Contents 1 Removed paragraph 2 Definitions of planets in fiction 3 Minor inaccuracy removed 4 The new diagram 5 Future of the Definition?

[edit] Removed paragraph

I have removed this paragraph from the "Double planets" section:

This is true of any moon sufficiently far enough away from its parent body that its orbital speed round the planet is slower than the planet's speed round the Sun. The required distance from the planet to the moon depends on the mass of the planet, and the distance from the planet to the Sun, but not the mass of the moon. If the distance from the Sun to the planet increases, or the planet's mass decreases, then the required distance between the planet and moon increases. Consequently, the same argument could be used that Jupiter and Callisto or Saturn and Iapetus form double planets.

This may be true, but it has never been sourced, and I can't verify it. If someone can, I'd be happy to see it put back. Serendipodous 22:44, 8 November 2006 (UTC)

[edit] Definitions of planets in fiction

what about adding a pra. about the Definition of planet in fiction (tv,books etc.) like Star Trek planet classifications 89.1.30.64 03:18, 3 February 2007 (UTC)

This article is about the scientific definition of a planet, so it would be inappropriate to add fictional information. However, you may be interested in reading Stars and planetary systems in fiction‎. Cheers. --Ckatz^chat_spy 03:56, 3 February 2007 (UTC)

[edit] Minor inaccuracy removed

Following the sentence describing Eris as a "Dwarf Planet," I removed this dubious claim: "...although the Minor Planet Center has given it a full minor planet designation: 136199 Eris." This suggests that the designation "Minor planet" is more specific than "dwarf planet" In fact, all 136199+ known small bodies are designated "minor planets." --MiguelMunoz 10:49, 12 February 2007 (UTC)

Indeed, Pluto has also recently been assigned a minor planet designation - 134340. --Neo 12:11, 12 February 2007 (UTC)

[edit] The new diagram

The new diagram listing the changing numbers of planets is quite nice, but it does contradict the article slightly. Galileo considered his four moons "planets", though I don't know yet whether this term was widely used for them, or for how long. Until we sort this out it might be a good idea to take the diagram down for now. I'll place it here until I can get some better information.

Serendipodous 09:30, 22 February 2007 (UTC)

[edit] Future of the Definition?

Does anyone know if the IAU is planning to revisit or revise the new definition of the planet? I have heard of multiple petitions from both the scientific community and public that urge them to do so. --Sly 18:12, 15 March 2007 (UTC)

Tough call. Alan Stern and Mark Sykes have circulated a petition, and the definition of planet will have to be a topic at the next IAU congress in 2009, if only to deal with the extrasolar issue. However, realistically, I don't think there's any going back. Pluto was placed in the Minor Planet Catalogue, and by the time it comes up for reconsideration in 2009, 42,000 new objects will be ahead of it in the list. Since minor planets are named in chronological order, that would mean that, were Pluto removed from the catalogue, every single one of the 42,000 new objects will need to have its number changed, and not only that, but every single paper that mentioned any of those 42,000 objects would need to be altered as well. My feeling is that, eventually, "Dwarf planet" will be considered a subclass of "planet" and so Pluto will get at least some of its planetary dignity back. However it will still remain a dwarf planet. Perhaps they can add a new designation in the catalogue to list the dwarf planets as special among the minor planets. Serendipodous 19:00, 15 March 2007 (UTC)

Not to be difficult, but if the decision were made to redesignate, I doubt that something as minor as the numbering would stand in the way. There's no reason to renumber the following objects, no more than there is to retrieve and renumber your cheques if you have to cancel one. Worst case scenario, they could declare 134340 permanently empty ("retired"?) and move on. (Don't forget that Pluto - having been assigned a number 76 years after its discovery - isn't in chronological order anyways.) --Ckatz^chat_spy 08:56, 16 March 2007 (UTC)

Again, people forget that this is not only about Pluto. If for some reason Pluto gets back its planethood, it would mean that at least some of the other dwarf planets would also become planets. I don't think that returning to pre-2006 situation is possible. Eight or dozens of planets, but not nine.--JyriL ^talk 21:54, 17 March 2007 (UTC)

what the true problem is is that people are getting stuck over a definition. what you call it does not change what it is. i MY opinion, everything that directly orbits the sun and has enough mass to be round is a planet. the true root of the problem is that then there would be like 16 planets, and having a lot of planets is supposed to be bad. i dont understand why anyone thinks this way.

There wouldn't be 16 planets; there be more like 1600. We just haven't found them all yet. Try getting kids to memorise all those in school. Serendipodous 04:30, 21 March 2007 (UTC)

i doubt there would be that many, but i get your point. however, i dont see why we have to not call them planets. i dont think it would be that hard to memorize them all. i can remember the 50 states. a planet is pretty much a big thing that orbits a star. if there happens to be a lot of them, so be it.

This is a common misconception. It's not the number of planets that some astronomers consider a problem; it's their orbits - highly eccentric, or highly inclined, or both; and with huge semi-major axes that are sometimes hard to understand in their own right. Having an object is one thing; explaining how it got there is quite another. Compared to the nearly circular orbits of everything large inside Neptune, that tells you something different has been going on. So it's partially a dynamical and formation issue as well. Spiral Wave 19:49, 28 March 2007 (UTC)

That may be so of some astronomers, but the definition itself, as decided, is all about number. The distinction between a planet and a dwarf planet is the ratio of its own mass to the mass within its orbital zone. Serendipodous 09:46, 29 March 2007 (UTC)

I agree. i think that, to the astronomers, it is all about number. i think the true thing that makes this definition strange is that, suddenly, because of where it is, or the shape of its orbit, it is suddenly something else. i think we should exclude what it is DOING and focus on what it IS. i think we should take the planet as if it were alone in a void. nothing else around it. no orbits, no other planets, nothing. then, apply some test (like a size or roundness test) and see if it was a planet. if it passes, its a planet, no matter where it is or how many there are. (i.e. if a strawberry grew out of my nose, you would still call it a strawberry, and if there were suddenly 1000 George Bushes, they wouldnt suddenly not be George Bush) —The preceding unsigned comment was added by 69.177.203.87 (talk) 18:39, 29 March 2007 (UTC).

True, but then satellites like the Moon and Titan would have to be given similar consideration. I think that would be a perfectly adequate definition of planet, though again perhaps a little difficult for the kiddies to memorise in school.Serendipodous 18:43, 29 March 2007 (UTC)

Well, we just call them all planets and classify them. you have terrestrial planets, ice planets (pluto like things), gas giants, and moons. —The preceding unsigned comment was added by 64.252.194.190 (talk) 19:04, 30 March 2007 (UTC).

Not all moons, TNOs or terrestrial objects are planets though. Serendipodous 19:28, 30 March 2007 (UTC)

The thing is that there are families of objects which go roughly like this IMHO

• Lumps of Ice and Rock which orbit the Sun
  • Giants
    • Gas Giants - Jupiter and Saturn
    • Ice Giants - Uranus and Neptune
  • Terrestials - Mercury, Venus, Earth and Mars
  • Planetoids
    • Asteroids - Ceres, Pallas, Juno, etc.
    • Kupier Belt Objects - Eris, Pluto, etc.
  • Comets

The term planet itself is somewhat outdated - refering IMHO to the terrestials and giants together when there is little to connect them beyond easy visibility from Earth. If I were to plan school curriculums then this is how I would teach it - there's not much point making kids learn the names of the nine planets as abstract concepts, but learning something of the nature of the bodies as well is surely better. --Neo 11:48, 21 March 2007 (UTC)