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2003 Ub 313: The Incredible Shrinking Planet?, No bigger than Pluto?
Guest_BruceMoomaw_*
post Jan 31 2006, 09:20 PM
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(Thanks to Emily Lakdawalla):

http://sciencenow.sciencemag.org/cgi/content/full/2006/127/1
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Betelgeuze
post Apr 12 2006, 05:15 AM
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The problem is that it's easy to say that now with just one solar system and nine (or eight or ten, depending on who's counting) planets. What happens when we start finding solar systems where the equivalent of Mercury is the size of Europa or Triton? Is the response of astronomers to be: Sorry, you have to be "this big" to qualify as a planet.

For some reason the exoplanets in the PSR 1257+12 system never get a lot of attention, yet they are as small or even smaller as Pluto. Did we discover small planets or are they the first asteroids/minor planets we found around another star?
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Jyril
post Apr 12 2006, 05:45 AM
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PSR 1257+12 B and C are a few times more massive than the Earth, A is about the size of the Moon. There's probably yet another body, but not even the discoverers call it a planet as it is has only one fifth the mass of Pluto.


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Stephen
post Apr 12 2006, 06:05 AM
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QUOTE (Jyril @ Apr 12 2006, 05:45 AM) *
PSR 1257+12 B and C are a few times more massive than the Earth, A is about the size of the Moon. There's probably yet another body, but not even the discoverers call it a planet as it is has only one fifth the mass of Pluto.

Interesting.

Yet again it seems to be only the term "planet" which attracts this debate. Consider neutron stars. They are not even as big as many asteroids or Kuiper belt objects, much less Pluto, yet no astronomer seems to be suggesting that their diminutive size means we should stop calling them "neutron stars" and dub them (say) "neutron objects" or "neutron dwarfs" instead.

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tedstryk
post Apr 14 2006, 04:28 AM
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QUOTE (Stephen @ Apr 12 2006, 06:05 AM) *
Interesting.

Yet again it seems to be only the term "planet" which attracts this debate. Consider neutron stars. They are not even as big as many asteroids or Kuiper belt objects, much less Pluto, yet no astronomer seems to be suggesting that their diminutive size means we should stop calling them "neutron stars" and dub them (say) "neutron objects" or "neutron dwarfs" instead.

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Stars have a clear definition, in that they are capable or were capable of sustained nuclear fusion. So there are clear criteria here. The problem is that, despite what Britt thinks, the term planet is still largely pre-scientific, without clear criteria behind it.

QUOTE (nprev @ Apr 12 2006, 03:41 AM) *
The IAU & everyone else has to face up to one fundamental fact: the objects in the Solar System exist along a continuum of sizes, from individual hydrogen atoms to Jupiter. Defining what is and is not a planet will always be a purely arbitrary convention by any objective standard, except for the apparent distinction that a planet has to independently orbit the Sun. Maybe it's time to throw out the concept entirely...?

Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!)


That works until we find a KBO larger than Mercury.


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Guest_BruceMoomaw_*
post Apr 14 2006, 07:21 PM
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QUOTE (tedstryk @ Apr 14 2006, 04:28 AM) *
That works until we find a KBO larger than Mercury.


Actually, it doesn't work right now. The trouble is that some of those super-Mercurian iceballs may be in the Oort Cloud, and if so we'll NEVER know whether they exist there or not -- they're too far away for any conceivable type of direct observation. (The remarkable orbit of Sedna, which is pretty big itself, is suggestive.) Alan Stern suggested long ago that there's a real chance of some icy planetesimals out there bigger than Earth (indeed, we can't quite rule them out in the Kuiper Belt at this point).

Alan HAS suggested an alternative "scientific" definition for the minimum size of a planet -- namely, objects big enough to round themselves gravitationally. The trouble is that

(1) This definition, too, has seriously fuzzy edges -- consider Iapetus' distinct but not overwhelming departure from the spherical, and the fact that Proteus looks like a marshamallow. The last straw may have been the discovery of the remarkable rapid spin rate and resulting high elongation of 2003 EL61, which approaches Pluto's diameter on its long axis -- but is only half that on its short axis. Unlike the upper-size scientific definition of a planet -- an object too small to ignite deuterium fusion in its interior, as brown dwarfs do -- the "roundness" definition seems to me just too seriously shaky.

(2) If we do accept it, then there's also a veritable swarm of new objects which will have to be called planets, including at least four asteroids and a very big collection of KBOs. This may be acceptable to scientists, but the public will raise hell.

Combine these two factors, and I think that in the end we have to accept that the definition of "planet" will be unavoidably highly arbitrary. (2003 EL61 produces enough problems by itself; its long diameter is about 2000 km, which would fit my own proposal for defining a "planet" -- but its short axes don't.)
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Posts in this topic
- BruceMoomaw   2003 Ub 313: The Incredible Shrinking Planet?   Jan 31 2006, 09:20 PM
- - elakdawalla   QUOTE (BruceMoomaw @ Jan 31 2006, 01:20 PM)(T...   Jan 31 2006, 09:36 PM
|- - SFJCody   QUOTE (elakdawalla @ Jan 31 2006, 09:36 PM)Ac...   Feb 1 2006, 12:19 AM
||- - Rob Pinnegar   QUOTE (SFJCody @ Jan 31 2006, 06:19 PM)There...   Feb 1 2006, 02:12 AM
|- - AlexBlackwell   QUOTE (elakdawalla @ Jan 31 2006, 09:36 PM)Si...   Feb 1 2006, 05:48 PM
|- - JRehling   Incidentally, don't forget that Pluto "sh...   Feb 1 2006, 07:17 PM
|- - TritonAntares   QUOTE (JRehling @ Feb 1 2006, 09:17 PM)Incide...   Feb 2 2006, 12:27 PM
|- - Rob Pinnegar   QUOTE (TritonAntares @ Feb 2 2006, 06:27 AM)A...   Feb 3 2006, 07:18 PM
||- - ljk4-1   For what this is worth, Sky & Telescope is now...   Feb 10 2006, 04:52 PM
|- - angel1801   QUOTE (TritonAntares @ Feb 2 2006, 09:57 ...   Apr 12 2006, 02:01 PM
|- - Planet X   QUOTE (angel1801 @ Apr 12 2006, 09:01 AM)...   Apr 12 2006, 04:48 PM
- - MichaelT   I just read that the Max-Planck-Institute for Radi...   Feb 1 2006, 10:32 AM
- - SigurRosFan   Here's the detailed press release: - http://w...   Feb 1 2006, 01:19 PM
|- - David   QUOTE (SigurRosFan @ Feb 1 2006, 01:19 PM)Her...   Feb 1 2006, 01:34 PM
|- - Rob Pinnegar   QUOTE (SigurRosFan @ Feb 1 2006, 07:19 AM)A j...   Feb 1 2006, 02:46 PM
- - Big_Gazza   I have heard a rumour that one of the Mormons secr...   Feb 3 2006, 11:01 AM
|- - Bob Shaw   QUOTE (Big_Gazza @ Feb 3 2006, 12:01 PM)I hav...   Feb 3 2006, 01:24 PM
||- - AndyG   QUOTE (Bob Shaw @ Feb 3 2006, 01:24 PM)Do you...   Feb 3 2006, 03:35 PM
|- - JRehling   QUOTE (Big_Gazza @ Feb 3 2006, 03:01 AM)I hav...   Feb 10 2006, 05:50 PM
||- - punkboi   QUOTE (JRehling @ Feb 10 2006, 10:50 AM)http:...   Feb 10 2006, 05:54 PM
||- - Katie   QUOTE (JRehling @ Feb 10 2006, 10:50 AM)http:...   Feb 11 2006, 08:30 AM
||- - ljk4-1   I like the idea that when you die you get to evolv...   Feb 11 2006, 07:12 PM
||- - ljk4-1   Looks a lot like Europa! UB 313: Larger t...   Feb 11 2006, 09:53 PM
|||- - David   QUOTE (ljk4-1 @ Feb 11 2006, 09:53 P...   Feb 12 2006, 03:48 PM
||- - tty   QUOTE (ljk4-1 @ Feb 11 2006, 08:12 P...   Feb 12 2006, 07:31 PM
|- - Katie   QUOTE (Big_Gazza @ Feb 3 2006, 03:01 AM) ...   Feb 13 2006, 04:06 AM
|- - ljk4-1   QUOTE (Katie @ Feb 12 2006, 11:06 PM) Bei...   Feb 13 2006, 04:55 AM
|- - Bob Shaw   QUOTE (ljk4-1 @ Feb 13 2006, 04:55 A...   Feb 13 2006, 12:05 PM
- - BruceMoomaw   QUOTE (Big_Gazza @ Feb 3 2006, 11:01 AM)I hav...   Feb 11 2006, 08:56 AM
- - BruceMoomaw   If they declare Pluto a planet but 2003 UB313 a no...   Feb 12 2006, 06:08 AM
- - BruceMoomaw   Actually, it's kind of flattering that the Gre...   Feb 13 2006, 11:37 PM
|- - Bob Shaw   QUOTE (BruceMoomaw @ Feb 13 2006, 11:37 P...   Feb 14 2006, 08:57 AM
- - edstrick   "I can't believe I ate the ***WHOLE*** TH...   Feb 14 2006, 10:41 AM
- - dvandorn   Personally, I'd be more worried about your stu...   Feb 14 2006, 03:34 PM
- - BruceMoomaw   QUOTE (Bob Shaw @ Feb 14 2006, 08:57 AM) ...   Feb 14 2006, 10:07 PM
|- - SFJCody   Brown to discuss 'Xena' discovery http://...   Feb 19 2006, 12:34 PM
|- - SFJCody   Amateurs spot 10th planet http://www.spaceflightno...   Feb 21 2006, 10:22 AM
|- - SFJCody   The IAU will publish beginning of September 2006 t...   Mar 4 2006, 10:27 AM
- - BruceMoomaw   Dear God, I hope they don't decide that Pluto ...   Mar 4 2006, 10:48 PM
|- - Bob Shaw   QUOTE (BruceMoomaw @ Mar 4 2006, 10:48 PM...   Mar 4 2006, 10:58 PM
|- - SFJCody   No news for a while, which is kind of a shame. I h...   Mar 19 2006, 10:42 PM
- - Rob Pinnegar   Well, it's only been a month or so since the l...   Mar 20 2006, 05:09 PM
|- - SFJCody   UPDATE! http://www.gps.caltech.edu/~mbrown/pl...   Apr 11 2006, 05:45 PM
- - ljk4-1   FOR RELEASE: 1:00 pm (EDT) April 11, 2006 Erica ...   Apr 11 2006, 06:08 PM
- - BruceMoomaw   Robert Roy Britt, in his blog on this subject ( ht...   Apr 12 2006, 12:09 AM
|- - Bob Shaw   QUOTE (BruceMoomaw @ Apr 12 2006, 01:09 A...   Apr 12 2006, 12:31 AM
|- - David   QUOTE (BruceMoomaw @ Apr 12 2006, 12:09 A...   Apr 12 2006, 01:22 AM
|- - Stephen   QUOTE (BruceMoomaw @ Apr 12 2006, 12:09 A...   Apr 12 2006, 03:37 AM
- - nprev   The IAU & everyone else has to face up to one ...   Apr 12 2006, 03:41 AM
|- - Stephen   QUOTE (nprev @ Apr 12 2006, 03:41 AM) Wel...   Apr 12 2006, 04:45 AM
|- - David   QUOTE (nprev @ Apr 12 2006, 03:41 AM) The...   Apr 12 2006, 08:28 AM
|- - AndyG   QUOTE (nprev @ Apr 12 2006, 04:41 AM) Def...   Apr 12 2006, 01:46 PM
- - BruceMoomaw   I remain convinced of what I said in 1999: if you ...   Apr 12 2006, 04:51 AM
- - Betelgeuze   QUOTE The problem is that it's easy to say tha...   Apr 12 2006, 05:15 AM
|- - Jyril   PSR 1257+12 B and C are a few times more massive t...   Apr 12 2006, 05:45 AM
|- - Stephen   QUOTE (Jyril @ Apr 12 2006, 05:45 AM) PSR...   Apr 12 2006, 06:05 AM
|- - Jyril   It's the mass that dominates. Even the least m...   Apr 12 2006, 08:16 AM
|- - tedstryk   QUOTE (Stephen @ Apr 12 2006, 06:05 AM) I...   Apr 14 2006, 04:28 AM
|- - BruceMoomaw   QUOTE (tedstryk @ Apr 14 2006, 04:28 AM) ...   Apr 14 2006, 07:21 PM
|- - David   QUOTE (BruceMoomaw @ Apr 14 2006, 07:21 P...   Apr 14 2006, 08:18 PM
|- - BruceMoomaw   QUOTE (David @ Apr 14 2006, 08:18 PM) But...   Apr 17 2006, 06:45 PM
|- - David   QUOTE (BruceMoomaw @ Apr 17 2006, 06:45 P...   Apr 17 2006, 07:17 PM
|- - JRehling   As if this issue hadn't already been faced on ...   Apr 17 2006, 07:59 PM
|- - The Messenger   QUOTE (JRehling @ Apr 17 2006, 01:59 PM) ...   Apr 17 2006, 08:45 PM
- - edstrick   ....it was good enough for Zaljyx, and it's go...   Apr 12 2006, 09:31 AM
|- - David   QUOTE (edstrick @ Apr 12 2006, 09:31 AM) ...   Apr 13 2006, 07:46 PM
- - Decepticon   Here is a image comparison... http://www.nasa.gov/...   Apr 12 2006, 01:24 PM
- - JamesFox   When I read that blog by Robert Roy Britt, I notic...   Apr 12 2006, 01:37 PM
- - ljk4-1   Astrophysics, abstract astro-ph/0604245 From: Mi...   Apr 12 2006, 06:08 PM
- - ljk4-1   Tenth planet as bright as fresh snow It is only s...   Apr 12 2006, 09:37 PM
- - edstrick   "Don't care what the latest rage is...Gim...   Apr 14 2006, 09:50 AM
|- - Bob Shaw   QUOTE (edstrick @ Apr 14 2006, 10:50 AM) ...   Apr 14 2006, 11:51 AM
- - Planet X   I came up with a unique definition according to ma...   Apr 14 2006, 09:08 PM
- - SigurRosFan   Interesting comment: - Comment on the recent Hubb...   Apr 17 2006, 04:52 PM
|- - SFJCody   Brown et al make more measurements with Keck. http...   Apr 17 2006, 06:17 PM
- - dvandorn   Well -- for scientific purposes, it would be far m...   Apr 17 2006, 08:47 PM
- - BruceMoomaw   Size makes more sense than discovery date, by any ...   Apr 17 2006, 09:59 PM
|- - Stephen   QUOTE (BruceMoomaw @ Apr 17 2006, 09:59 P...   Apr 18 2006, 04:15 AM
- - JamesFox   When it comes to 2003 EL61, it's odd shape is ...   Apr 18 2006, 01:56 AM
- - BruceMoomaw   Well, you've got to set the goalposts at SOME ...   Apr 18 2006, 06:40 AM
|- - AndyG   QUOTE (BruceMoomaw @ Apr 18 2006, 07:40 A...   Apr 18 2006, 09:08 AM
|- - ugordan   QUOTE (AndyG @ Apr 18 2006, 10:08 AM) ...   Apr 18 2006, 09:21 AM
|- - David   QUOTE (AndyG @ Apr 18 2006, 09:08 AM) Why...   Apr 19 2006, 08:31 PM
- - edstrick   Also... at all 4 giant planets, there is a clear d...   Apr 18 2006, 10:23 AM
- - edstrick   The arm-waving idea I've posted here before is...   Apr 20 2006, 09:36 AM
- - ljk4-1   Though it is not online, the July 24, 2006 issue o...   Jul 21 2006, 02:40 PM


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