Talk:Definition of planet/Archive 3

message: When Ceres was discovered in 1801. At first, everyone was like "Oh, it definently a planet! It's right where we excpected it to be! In the huge empty gap between Mars and Jupiter!" And it was obvious. Sure, the best telescopes couldn't resolved it as anything more then a point of light, but that's ok. And everyone was happy. Until Pallas was discovered. "Well, that's ok. We'll have another planet!" And then came Juno. "And another!" After some time, they eventually realised that thousands of these odd "Asteroids" would be found, and that they couldn't fit in well with the big planets known at the time (Mercury to Neptune). So then the planet count went back down to 8. Until Pluto was discovered. Pretty much the same thing happened, it was definently a planet, although an oddball too. Until 1992. Something else was found beyond Neptune. It was smaller, but it was in the same area. Doubt lingered, but then along came some others. Sedna, Quaoar, and then "X". We face the same problem today. We know that out there is something like an asteroid belt, but with ice instead of rock. Perhaps "X" and Pluto would just be really big comets in the Kuiper Belt.  Maybe if something is mostly made of ice, it can't be a planet, because if brought close to the Sun, it vanishes pretty quickly. It would look nice sure, in it's death pangs, but when all is said and done... the system I thought they'd choose wouldn't have an arbitrary barrier at 800 km for size, but at say... Mercury. It's made of rock, round, big, is very close to the Sun, but still not vaporised. Seems logical to me. But what do I know? I'm not one in the commitee of "7 elderly astronomers who decide the faith of the Sol-system". When we discovered about say, 50 of these things, just "Nuke and Pave" the bloated list, with Mercury being the smallest.--Planetary 18:59, 16 August 2006 (UTC)
replies: text: We already have discovered over 50 of them. This definition, love it or shove it, is for the long haul. Serendipodous 19:05, 16 August 2006 (UTC)

text: I already know about Hot Jupiters. That isn't what I really meant. If you could push Pluto inside Mars's orbit, say, it would evaporate pretty quickly (relatively speaking). That probably won't happened, though. Pluto's still pretty big, and hard to move. By 50, I meant 50 planet-sized KBOs, not all of them. I know there are almost 1000 already. I just think the current definition for planet isn't strict enough.  IMHO, Mercury should be the smallest planet. We can call the others "planetoids". If something is discovered out there larger then Mercury, I'm all for it. Just my opinion. Just noting similarities now to about 200 years ago, when this sort fo thing was happening with the asteroids. I think making Ceres a planet would just make things worse. If they wanted to, they could even set the limit at "X"'s size, but Ceres is just much too small. As for translation issues, I can already think of something in my native language that says the same thing as Plutons. But I recommend planetoids or minor planets. --Planetary 20:13, 16 August 2006 (UTC)
replies: text:  We have already found more that 50 planet-sized KBOs. At least according to Mike Brown, and he should know. Serendipodous 20:51, 16 August 2006 (UTC)

text: Since there is the odd belief the removing Pluto's planethood will result in riots. But then, cartoons can result in riots.--Planetary 21:05, 16 August 2006 (UTC)
replies: text: Well, the unsigned comment above (about opinion) reminds me about the decision made to turn pounds into a unit of mass and not force (discussion at weight). Even though officially according to virtually standards organization, the pound (and ounce and ton...) are units of mass, even the top class scientists use them the old way. Regardless of whether they like it or not, no matter what they say, Pluto will remain a planet. As I've been thinking about this discussion, I can't help but think about how I would make the distinction. I personally like taking away the status of Pluto, because I don't think it's very scientific. So, giving it the smaller status is a reasonable compromise. A couple sentances ago, I made the statement that I didn't think that calling pluto a planet was very scientific. Until the past couple days, my reasoning for thinking that it wasn't very scientific, wasn't very scientific. See, within the past 20 years, we've found other objects within the gravitational well of Sol that seem more like planets than Pluto does. (most notably "Xena"). But within the past couple of days, I've thought about it more. And I've been thinking, "Well, how would someone who wasn't familiar with just the Sol System define the term. This is hard for us – as humans who haven't left our system – to do, but picking a size and sticking to it is kinda stupid. (anything smaller than 2000km?) As it's very arbitrary. I liked the "larger than the combined masses of other objects in the same orbit" definition (which would kick out pluto), but it would kick out other planets just because some other masses got a little larger. I really do like the current proposed definition of having enough gravity to maintain Hydrostatic equilibrium. It doesn't seem arbitrary. sure, badastronomy.com likes to say that if a material is made of a softer substance like pluto, (cf 4 Vesta), it attains this status easier, but it isn't arbitrary, it's an established phenomenon. I want to say something (potentially about size) to exclude the potentially millions of KB or OC objects that might attain this status, but either it's too arbitrary, or  excludes planets like earth. Pedro is right, all other characteristics of celestial bodies are characteristics based on mass. A black hole is an object that is so massive that the escape velocity is greater than the speed of light. A star is an object not a black hole that's so massive that it generates internal fusion. Why not, A planet is something not a star that's so massive that it attains hydrostatic equilibrium. It think it makes perfect sense the more I think about it. McKay 13:20, 17 August 2006 (UTC)

text: Agree on horoscopes, Yes, mass is an arbitrary parameter Hydrostatic Equilibrium isn't. Sure, Ceres is kinda an asteroid, but an asteroid Usually considered a hunk of rock, and usually not really in hydrostatic equilibrium, because there isn't a liquid core. So, Ceres isn't really an asteroid. It may have been one at one point, but because of it's size it compressed its core, and reached a state of hydrostatic equilibrium. So, unless you can define asteroid differently, then that might be something. Also, mercury is smaller than many moons, should we have a new designator for Planets that are smaller than moons? McKay 18:37, 17 August 2006 (UTC)

text: Let's see, what's know about Ceres? Not much. Pluto is about 2 and a half times larger the Ceres. If we set the limit at Pluto exact size (will be known very well in 2015), we'd have 11 planets, with Pluto and "X" the new editions (2003 UB313 is too long a name, Xena is hideous, so for me it's just "X"). If we set the limit at Mercury, there would be 8. Yes, there are 2 larger moons in the solar system, one of which has a significant atmosphere. However, they all very clearly can't be planets by basically all definitions, because the center of mass of the system is deep inside the gaseous planet, which is much more massive. If Titan or Ganymede were free-orbiting objects, yes they'd definently be planets, based on sheer size. But they aren't. They're deep in the gravity well of their parent bodies. Another bonus of setting the universal lower limit for planethood at Mercury is that we don't have to wonder about Pluto-Charon counting as 2 planets or not. The difficulty with this whole issue is that we don;t know very much about the objects in question. "X" is just a point of light at best. Ceres is a ball of pixels. Pluto and Charon no better. We might just have to wait a few years, until New Horizons and Dawn reach their mission objectives.--Planetary 20:26, 17 August 2006 (UTC)
thread_title:  This whole things reminds me of...  

message: Why this obsession with roundness?  We don't define "moon" based on shape, which is why Jupiter and Saturn have so many of them.
For the traditionalists who want to keep 9 planets because they don't want to memorize more, I have a new mnemonic, good at least until they rename UB313 or add more planets:
My Very Educated Mother Considers Just Slightly Understood Nine Planet Concept Uneducated Roger 20:43, 16 August 2006 (UTC)
replies: text: Man Very Early Made Clay Jars Stand Up Nearly Perpendicular, Clearly Upright. GBC 17:03, 17 August 2006 (UTC)
thread_title:  MVEMCJSUNPCU 

message: PSR B1257+12 D could be defined as a planet if this passes... it's larger than Ceres. 132.205.93.195 03:23, 18 August 2006 (UTC)
thread_title:  PSR B1257+12 D