Talk:Definition of planet/Archive 2

message: It appears that Hygiea is actually pretty oblong, but in the low resolution images that made it look kind of spherical it was just seen from a particular viewing angle that made it appear so. The main evidence is lightcurve analysis (check out this article, in particular pages 375 & 376. By the way, IMHO it's pretty cool how they can arrive at the shape models). I'm not sure how accurate the smaller details of the shape model are, but the strong change seen in Hygiea's lightcurves as it moves in its orbit is pretty solid evidence that it is irregular. The spherical-like low resolution Hubble images were probably taken when it was oriented like in the left-hand shape picture there. It is interesting to compare to a similar analysis of Pallas (known to be slightly irregular from occultations), which can be found here, (page 350 in particular). The change in Hygiea's lightcurve with viewing geometry is much larger than for Pallas's lightcurve, which pretty strongly indicates that Hygiea is more irregular (unless it has some pretty major albedo variations on its surface, which seems fairly unlikely). Deuar 19:50, 23 April 2006 (UTC)
thread_title: The shape of Hygiea

message: As I have said, I know zip about math, but I feel this "spheroid" information is very useful in providing a quantifiable basis for the argument. However it is making the "Size" section rather unwieldy. There are two issues here; what is meant by "spheroid", and which objects in our Solar system are spheroidal. The article currently spends more time discussing the definition of "spheroid" than it does discussing Solar system objects. 
I've just reworded and redrafted the section. I think it makes the argument clearer; if you feel there are any inconsistencies, please change them. 
By the way, RandomCritic, when you changed Vesta from "Spheroid" to "irregular", and Mimas from "Spheroid" to "Ellipsoid" you forgot to change the colour of the fields. I swapped them for now, though I imagine this debate isn't over yet. 
Question: Where does this definition leave EL61? Can it still be called an ellipsoid by this definition? It seems to me that it would be a highly oblate spheroid now. If that's the case, then perhaps we should drop it from the table.  Serendipodous 22:04, 26 March 2006 (UTC)
thread_title: Straying from the topic

message: We need to add a discution over what is a moon: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=643 --Pedro 23:14, 30 March 2006 (UTC)
replies: text: I see your point, but really the argument is pretty much the same as whether Ceres is a planet or an asteroid. The Sun has several "rings" (the asteroid and Kuiper belts) and many "planetlets" within those rings, along with rubble and dust, just as Saturn's rings have moonlets.  The same logic applies to planets as applies to moons: how large does a planet/moon need to be before it can be called a planet/moon?. The real question, and this is addressed in the article, is whether moons can be considered planets in their own right. Serendipodous 23:23, 30 March 2006 (UTC)

text: Ceres is round, so bad example really but, as the roundess debate has clearly shown in recent days, the line between "round" and "not round" is a fuzzy one. Is Vesta round? Clearly some here think yes and others think no. Myself I have no idea; but since the purpose of this article is not to find a definition for "planet" but to illustrate just how hard it is to come up with one, that's not really a problem. The same logic applies to moons as applies to asteroids. When is a moon a moon? When it's round? How round is round? And so on. The size table doesn't distinguish between asteroids and moons, nor should it, since it deals with physical characteristics, rather than whatever other objects the asteroid or moon happens to be near. The term "moonlet" seems to be en vogue to describe these tiny moons, which is no less aprapos than, say, "planetoid" to describe a hunk of rock orbiting the Sun. Serendipodous 23:59, 31 March 2006 (UTC)
thread_title: moons

message: 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)
replies: text: 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)
replies: text: 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)
thread_title:  the proposed definitions 

message: 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)
replies: text: 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)
replies: text: I suggested 2M1207b because it too is a planetary mass object (some argue that it is a sub-brown dwarf ) 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)
replies: text: 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)
replies: text: 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)
replies: text: 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)
replies: text: Ok, I've uploaded the new image. Chaos syndrome 20:00, 11 July 2006 (UTC)

text: Very nice! Thanks for putting the effort in. It looks great. Serendipodous 11:22, 12 July 2006 (UTC)
thread_title:  illustrating the sub-stars section 

message: The IAU meeting is underway, and press coverage is beginning.  Here is an article I've encountered 
(Associated Press, at the website for the Boston Globe): http://www.boston.com/news/science/articles/2006/08/14/astronomers_meet_to_define_planet/. GRBerry 21:19, 14 August 2006 (UTC)
thread_title:  Press coverage 

message: At Talk:2006 redefinition of planet#Image removal rationale, concerns have been brought up regarding the use of :Image:Newplanets.jpg. I'd like to know what the general opinion here is. I personally would remove the image for the reasons given on the above page. Nick Mks 19:19, 17 August 2006 (UTC)
replies: text: Well, as the person who imported that image I should justify my action at least. There has been a great deal of supposition and fudging released by the IAU in the last few days that has been picked up by the media as established fact; the most notable being, of course, that there are now 12 planets. This is wrong. There could be (and indeed should be, if the definition were to be scientific rather than cultural) dozens of planets in our solar system. That image demonstrates a fixed, scientific limit for the total number of planets in our system. Anything below it would have to be justified in some way other than, "But that's just too many!" Serendipodous 19:49, 17 August 2006 (UTC)
replies: text: I think the image is great. Sure, it's a little rough, but I think it's cool. The rationale for the 12 planets is that those are the ones we have relative certainty of their Hydrostatic equilibrium. The other 53-12=41 Mike Brown thinks are probably round enough, but we don't have enough information. More information will most likely bring the number to around 53 quickly, and several hundred (thousand) in the future. McKay 20:40, 17 August 2006 (UTC)
thread_title:  [[:Image:Newplanets.jpg]] 

message: from IAU:
:Q: What is a “satellite” of a planet?
:A: For a body that is large enough (massive enough) to satisfy the definition of “planet”, an object in orbit around the planet is called a “satellite” of the planet if the point that represents their common centre of gravity (called the “barycentre”) is located inside the surface of the planet.
*so this means that objects smaller than Mimas are no longer considered to be moons?! Or I missunderstood it?!--Pedro 23:32, 17 August 2006 (UTC)
replies: text: As I read it, all satellites are still satellites even if they are large enough to be planets. But I agree, that is a bit ambiguous. Serendipodous 14:13, 18 August 2006 (UTC)
thread_title: Definition of moon aka "satellite"

message: This may be a silly question, but what happens if a planet-like object that maybe once was in orbit around a star but was ripped out of orbit by some passing star and is now kind of floating around is discovered? What's that? --Elliskev 19:23, 16 August 2006 (UTC)
replies: text: Not a planet. But we already know objects that are way too small to be even brown dwarfs (>13 MJupiter). There are several suggested terms like sub-brown dwarfs (hardly apt in this case), rogue planet and planemo.--JyriL talk 19:29, 16 August 2006 (UTC)

text: One thing it's not is a silly question :). In fact this is considered one of the major flaws in the IAU's definition by some see here, for example. The issue of what constitutes a star and what constitutes a "rogue planet" is not dealt with by this definition, the main purpose of which was to decide what to do about "Xena." Serendipodous 19:32, 16 August 2006 (UTC)
thread_title: Rogue planets