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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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Guest_BruceMoomaw_*
post Apr 18 2006, 06:40 AM
Post #2





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Well, you've got to set the goalposts at SOME point. And the case for setting them at just a bit smaller than Pluto is pretty good, precisely because Pluto has been thought of as a planet for so long -- given the rate at which KBOs are being discovered now, it's unlikely that there will ever again be a gap so long between the discovery of KBOs more than 2000 km wide.

Of course, we should also very definitely be teaching kids that at this point the word "planet" doesn't have any scientific significance, that all it means is "object bigger than such-and-such a diameter", and that at this point we have no idea how many "planets" the Sun has even by that arbitrary criterion (and, for that matter, we never WILL know, thanks to the possibility of big Oort Cloud objects). If we're not going to admit that "planet" is strictly an arbitrary standard, we should stop using the word at all -- but I very much doubt that's going to happen. All we can do is make sure that people know what it actually signifies at this point.
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AndyG
post Apr 18 2006, 09:08 AM
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QUOTE (BruceMoomaw @ Apr 18 2006, 07:40 AM) *
Well, you've got to set the goalposts at SOME point.

Why not set goalposts using the highest surface escape velocity? This neatly captures elements of diameter and mass, and avoids issues of how to define 'rotundity'.

Set limits something like:

asteroid < 750m/s
> 750m/s small planet < 2500m/s
> 2500 m/s medium planet <5000m/s
> 5000m/s large planet

Ceres has an escape velocity of ~500m/s. It's an asteroid, albeit a large one.

Pluto is ~1070m/s. Small planet.

Mercury & Mars are medium planets. Earth & Venus are large.

If the body orbits a planet, it's a moon. Change "planet" to "moon" and set the size qualifier one higher. "Asteroid" changes to "moonlet". So Titan and Ganymede (~2770m/s) become "large moons" and Europa (2040m/s), as with our Moon, become "medium moons". Miranda is a moonlet. And quite right too.

Andy G
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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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