Talk:Definition of planet/definition of planet archive 3

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[edit] the proposed definitions

In the subheading of The IAU Debate it mentions three possible definitions of planet that they are considering. Wouldn't, under the third definition, 90377 Sedna be considered a planet? It clearly lies out of the Kuiper belt, and clearly closer than the Oort Cloud. (2003 UB313, and 50000 Quaoar are in the Kuiper belt?) Wouldn't that make Sedna a planet under this definition (and revert pluto's planetary status to that of a kuiper belt object)? McKay 07:08, 5 July 2006 (UTC)

The general consensus appears to be that Sedna is part of a population. 2000 CR105 has a similar orbit to Sedna, though not quite as extreme. Mike Brown has said that, since Sedna's orbit is so elliptical, there was only a one-in-sixty chance that anyone pointing to the sky would have seen it at this time. That means, essentially, thet there must be at least sixty more Sednas out there. Not sure if that logic holds, but then I'm not a math type. 2003 UB313 is considered part of the "scattered disc", a region of Kuiper belt objects sent into higher elliptical orbits. Quaoar is a KBO. Serendipodous 11:14, 5 July 2006 (UTC)

Re: your math. If there's a 1 in 60 chance for anyone to see an object like Sedna, and there were 60 such objects, then the probability of one of those objects being viewable is about 63%. (1 - (1 - 1/60)^60) Which does seem approximately reasonable. (i.e. Sure, I like your answer.) McKay 09:12, 22 July 2006 (UTC)

[edit] illustrating the sub-stars section

Can we get a better image for the substars section? The current one is fairly misleading in terms of scale: the planets of 55 Cancri are not equally spaced as depicted (the first three planets are bunched very close to the star, and the fourth is around 20 times further out), and it depicts a fictitious system of planets/moons around the sub-brown dwarf (not the known dust disc). Perhaps an image of 2M1207b would be appropriate here? If we do keep the current image, the caption should be changed. Chaos syndrome 15:52, 8 July 2006 (UTC)

An image of 2M1207b would not be appropriate for that section, first because there is already an image of Gliese 229B in orbit around its star in the "brown dwarfs" section, and second because it is specifically Cha 110913-773444 that is under discussion within the "sub-stars" section. If we were to locate another image, it would have to be another image of Cha 110913-773444. In light of your comments, I have already modified the caption to de-specify the larger star system within that image, and as to your concerns about the image depicting Cha's as-yet unidentified "planets", I do see your point but I am not particularly alarmed, mainly because at the px level I have set the image at, the planets are virtually indistinguishable, and the orbits merely look like rings. Also, this is an artist's impression of a hypothetical scene. Much like artistic renditions of the skies of extrasolar planets or the view from inside Saturn, a certain amount of artistic licence is to be expected. There may be no planets as yet observed around Cha, but that doesn't mean that there aren't any. Serendipodous 16:16, 8 July 2006 (UTC)

I suggested 2M1207b because it too is a planetary mass object (some argue that it is a sub-brown dwarf [1]) with a dust disc. The new wording is an improvement though. Maybe creating a new comparison image (similar to the one used near the bottom of this page on SolStation, though that image is subject to copyright) might be better - comparison of the Sun versus Cha 1109-7734 versus Jupiter. Chaos syndrome 19:08, 8 July 2006 (UTC)

That would be a good idea; though I don't really know how to do it. The reason I'm specifying Cha is because it is a planet-sized object not tied to any star, and thus blurs the line between planet and star. Any sub-brown dwarf in orbit around a star wouldn't make the same point. Serendipodous 19:17, 8 July 2006 (UTC)

I'd be able to render something in POV-Ray. Instead of rendered versions of the Sun and Jupiter, we could use actual images, though I'm not entirely sure if that can be done while still adhering to the NASA licenses. Chaos syndrome 19:28, 8 July 2006 (UTC)

That'd be great, if you could do it. I always assumed that NASA's images were in the public domain. Serendipodous 19:41, 8 July 2006 (UTC)

Ok, I've uploaded the new image. Chaos syndrome 20:00, 11 July 2006 (UTC)

Very nice! Thanks for putting the effort in. It looks great. Serendipodous 11:22, 12 July 2006 (UTC)

[edit] Size comparison with Jupiter

The picture comparing the sizes of Pluto with the Earth, the Moon and other KBOs suggests a false qualitative difference between Earth and the other objects. It is important to counter this with the observation that planets come in a huge range of sizes. The differences between Earth and Jupiter are much greater then the differences between Earth and Pluto, and that is important to deciding what a planet is. Algr 04:29, 15 July 2006 (UTC)

Hmm. I think the main problem is that the listed picture doesn't reflect the topic of the section anymore either. It's been part of this article for a long time and was specially made for it, so I am rather attatched to it, but the fact is that the issue raised in that section is not the small size of the KBOs/asteroids, but their large sizes relative to each other. I may swap it out with a more appropriate image, but I would like to find a way to keep it in, so I'll repost it here until I can figure out how.

The relative sizes of Earth (on the left) with (from top to bottom) the Moon, Pluto and its largest moon Charon, Sedna, Quaoar, and Ceres on the right.

Serendipodous 07:43, 15 July 2006 (UTC)

[edit] Merging with "Planet"

Just a headsup; when the IAU announces its final definition in September, I'm planning to merge this article with planet. Just wanted to make sure everyone's OK with that.Serendipodous 19:21, 23 July 2006 (UTC)

Can I suggest keeping it seperate for a small while, maybe 3 months or so, just to ensure that the the defintion is accepted by most astronomers... I'm sure it wouldn't be the first time that a definition from a regulatory body was rejected by the people who will use it.

After that time I'd be tempted to keep a lot of the info in an article like this as it makes for an interesting read, with a possible renaming to something like 2000's Definition of planet debate (or controversy, or some other term) - I can imagine this being an interesting matter for study in the history and/or philosophy of science, and it makes the point in an interesting manner that some things in science are not determined by nature, but by the whim of man... --Neo 21:14, 23 July 2006 (UTC)