Welcome, Guest. Please Login.
Gravity Simulator
11/19/17 at 00:52:51
News: Registration for new users has been disabled to discourage spam. If you would like to join the forum please send me an email with your desired screen name to tony at gravitysimulator dot com.
Home Help Search Login


Pages: 1 2 
Send Topic Print
What is a planet? (discussion) (Read 16780 times)
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
What is a planet? (discussion)
08/15/06 at 17:57:43
 
The subject says it all ...
I'd like for other members to post their ideas on the matter before I do, so as to see true opinions.
Back to top
 
 
View Profile WWW   IP Logged
Tony
YaBB Administrator
*****




Posts: 1051
Gender: male
Re: What is a planet? (discussion)
Reply #1 - 08/16/06 at 19:51:47
 
The IAU's proposal was all over the news today.  If adopted, there'll be 12 planets plus 12 provisional planets, whatever that means.  Here's a simulation of our new 22-planet solar system:
 
http://orbitsimulator.com/gravity/simulations/provisionalplanets.gsim
Back to top
 
 
Email View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #2 - 08/19/06 at 17:41:17
 
There's a new proposal on the voting block for Proposition 5 at the IAU GA.
 
See a Copy of it here http://www.space.com/scienceastronomy/060819_new_proposal.html
 
This would effectively reduce the number of planets to 8
 
In addition here is more consequences of the 1st Prop 5...
http://www.gps.caltech.edu/~mbrown/embargo/howmanplanets.html
 
and the map of the new solar system
Back to top
 
 
View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #3 - 08/19/06 at 19:58:04
 
Here is something from a scifi site for classifying planets, I have to admit I rather like for terms of sub-classification.
 
http://arcbuilder.home.bresnan.net/PCL01.html
Back to top
 
 
View Profile WWW   IP Logged
mkruer
Uploader



I love YaBB 1G -
SP1!

Posts: 8
Re: What is a planet? (discussion)
Reply #4 - 08/19/06 at 21:42:55
 
Grin I think that the IAU GA should just adopt that, its there, its detailed, and It works.
Back to top
 
 
View Profile   IP Logged
Tony
YaBB Administrator
*****




Posts: 1051
Gender: male
Re: What is a planet? (discussion)
Reply #5 - 08/20/06 at 17:18:30
 
We should get Mike Brown hooked on Gravity Simulator.  My effort to reproduce his graphic yields a slightly more accurate one.  In his graphic Uranus' orbit should be more elliptical, and Ceres shouldn't produce such a fat orbit trail.  His table of objects includes Sedna, but his diagram doesn't show it.
 
Here's my effort using Gravity Simulator and the list of objects in his table:
Back to top
 
 
Email View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #6 - 08/23/06 at 19:47:38
 
Mystery Surrounds Thursday's Vote on Pluto's Fate  
 
http://space.com/scienceastronomy/060823_planet_vote.html
 
(also Cross posted in the News thread)
Back to top
 
 
View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #7 - 08/23/06 at 20:18:45
 
From The IAU GA - (Dissetatio Cum Nuncio Sidereo III, Page 8 http://astro.cas.cz/nuncius/nsiii_09.pdf Retrieved 08/23/2006 10PM CST)[minor formatting corrections]
 
Final Version of Resolution on the Definition of a Planet At the second session of the General Assembly which will be held 14:00 Thursday August 24 in the Congress Hall, members of the IAU will vote on the resolutions presented here. There will be separate sequential votes on Resolution 5A and Resolution 5B.
Similarly, there will be separate votes on Resolutions 6A and 6B. Resolution 5A is the principal definition for the IAU usage of “planet” and related terms. Resolution 5B adds the word “classical” to the collective name of the eight planets Mercury through Neptune. Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the proto-type. Resolution 6B introduces the name “plutonian objects” for this class.  
The Merriam-Webster dictionary defines “plutonian” as: Main Entry: plu•to•ni•an
– Pronunciation: plü-’tO-nE-&n – Function: adjective – Usage: often capitalized – : of, relating to, or characteristic of Pluto or the lower world.  
 
Resolutions Committee members will be available at the IAU Exhibit (situated in the exhibition area, 2nd floor of Congress Hall, Foyer 2) from 13:00–13:30 today (Thursday). However, only minor corrections can be accommodated at this stage.  A French version of the Resolutions will be available at the door.
IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation ‘planets’. The word ‘planet’ originally described ‘wanderers’ that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.
 
Resolution 5A
 
The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:
 
(1) A planet[1] is a celestial body that  
  • (a) is in orbit around the Sun,  
  • (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,  
    and
  • (c) has cleared the neighbourhood around its orbit.

(2) A dwarf planet is a celestial body that  
  • (a) is in orbit around the Sun,  
  • (b) has sufficient mass for its self-gravity to overcome
    rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape[2],  
  • (c) has not cleared the neighbourhood around its orbit,  
    and  
  • (d) is not a satellite.

 
(3) All other objects[3] orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.
 
[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
[2] An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

 
Resolution 5B
 
Insert the word “classical” before the word “planet” in Resolution 5A, Section (1), and footnote 1. Thus reading:
(1) A classical planet[1] is a celestial body . . .
and
[1] The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
 
IAU Resolution: Pluto
 
Resolution 6A
The IAU further resolves:
Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
 
Resolution 6B
The following sentence is added to Resolution 6A:
This category is to be called “plutonian objects.”
 
250 words for
Compromise. Achieving a planet definition has been all about compromise. There are two equally valid descriptions of what should be the principal criterion for defi ning a planet. One is dynamical, an object that has “cleared out its zone.” The other is based on the physical nature of the body itself. The pendulum of argument has swung both ways during the General Assembly discussions. But now it has swung too far.
Resolution 5B is all about finding the middle ground. Using qualifiers gives equal status to both points of view and leaves open the possibility to define other types of planets in our Universe. Resolution 5B restores the “global and cultural points of view” that the Planet Definition Committee had responsibility to achieve. The public recognizes Mars, for example, as a “planet” not because it has cleared out its zone, but because it is a fascinating world.
To illustrate why Resolution 5B is cultural, and not silly semantics, consider how you must answer two questions: How many planets are there? Is Pluto a planet? A vote in favor of 5B yields: “There are 8 classical planets and many dwarf planets yet to be discovered” and “Pluto is a planet, but in the dwarf planet category.” These answers highlight and communicate the tremendous revolution of new discoveries in our outer Solar System. Further, it saves enormous public backlash by still being able to say the words “Pluto is a planet, but”. Do not underestimate the global cultural importance of these fi rst four words. The word “planet” deserves to be shared equally.
250 words against
Resolution 5B represents a small but significant change to
Resolution 5A. The key issue is the definition of “planet”. Resolution 5A is close to the version agreed by consensus on Tuesday evening where it was made clear that three distinct categories of objects orbiting the Sun were being defined: planets, dwarfplanets, and small bodies. The logical implications from the rules of grammar cannot be ignored. By using the name “planet” with two different adjectives “classical” and “dwarf” a larger category of planets is implied. This contradicts the first paragraph of both Resolutions 5A and 5B and transforms three distinct categories into two (planets and small bodies) and two sub-groups of planets.
To the question “is Pluto a planet?” the two resolutions give different solutions – “Yes” for 5B and “No” for 5A. To the question “How many planets are there?” Resolution 5A gives 8, Resolution 5B currently gives 12 and soon at least 50. The total number of planets may not matter to scientists,  it is critical for education and the dissemination of science. For scientists, it is relevant that dynamical and cosmogonical criteria, which are now the source for the defi nition of planets, would in Resolution 5B be relegated to a secondary role.  
In Resolution 5A the arguments from geophysics and from dynamical astronomy are given equal weight. Such a balanced solution had received very strong support in the meeting of Division III (Planetary Systems Science) and the Planet Definition Information Meeting.  
Resolution 5B is misleading and should be rejected.

Back to top
 
 
View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #8 - 08/24/06 at 05:40:11
 
Three New Planets with the Stroke of a Pen? Great News for Science Teachers  
http://www.space.com/searchforlife/060824_seti_12planets.html
 
(crossposted in News)
Back to top
 
 
View Profile WWW   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #9 - 08/24/06 at 08:21:48
 
BREAKING NEWS: Pluto Demoted, No Longer a Planet  
http://www.space.com/scienceastronomy/060824_planet_definition.html
 
Crossposted in Planet Definition discussion
Back to top
 
 
View Profile WWW   IP Logged
Ceres
YaBB Newbies
*


I love YaBB 1G -
SP1!

Posts: 1
Gender: male
Re: What is a planet? (discussion)
Reply #10 - 08/24/06 at 16:54:16
 
Quote from abyssoft   on 08/24/06 at 08:21:48:
BREAKING NEWS: Pluto Demoted, No Longer a Planet
http://www.space.com/scienceastronomy/060824_planet_definition.html

Crossposted in Planet Definition discussion

So this mean Charon is also a dwarf planet?
Back to top
 
 
View Profile   IP Logged
abyssoft
YaBB Administrator
*****


I love YaBB 1G -
SP1!

Posts: 302
Re: What is a planet? (discussion)
Reply #11 - 08/24/06 at 16:56:05
 
Indeed it does, so we have a double dwarf planet   GrinTongue
Back to top
 
 
View Profile WWW   IP Logged
Michael_C._Emmert
Uploader



I love YaBB 1G -
SP1!

Posts: 12
Re: What is a planet? (discussion)
Reply #12 - 08/25/06 at 08:11:04
 
I like the new definition  Smiley .  But  they haven't defined what they meant by "cleared out" it's orbit.  I read a great paper:
 
http://xxx.lanl.gov/abs/astro-ph/0608359
 
which shows a little better than the IAU definition what a planet is.
 
I notice that in the definition voted on here, a planet is greater than 50% of the rest of the material in the orbit.  The paper says >10000 makes sense, however there would be pathological cases, such as Neptune = 8500> Pluto, which is a result of there being nothing (known) outside of Neptune to perturb plutinos back into Neptune, such as Neptune did for Uranus.  They suggest >100 x the mass of the rest of the stuff in similar orbits, including (I presume) 1:1, 2:3, 3:5 etc. resonances.  That's reasonable.
 
For our solar system.
 
We're in trouble for those stars that have suffered some kind of major chaotic disaster, and of the ones discovered so far, this seems to be a majoritiy of the cases!  I thought this definition would be general  Roll Eyes  ???   Shocked .
Back to top
 
 
Email View Profile   IP Logged
Tony
YaBB Administrator
*****




Posts: 1051
Gender: male
Re: What is a planet? (discussion)
Reply #13 - 08/25/06 at 13:12:22
 
Quote from Michael_C._Emmert   on 08/25/06 at 08:11:04:
...which is a result of there being nothing (known) outside of Neptune to perturb plutinos back into Neptune, such as Neptune did for Uranus...

That's a very interesting point.  I don't believe Uranus has any known resonant objects.  But after a quick search through the paper for "Uranus" I didn't see this mentioned in the paper.  Was that your conclusion?
 
Thanks for the great link. Cheesy
Back to top
 
 
Email View Profile WWW   IP Logged
Michael_C._Emmert
Uploader



I love YaBB 1G -
SP1!

Posts: 12
Re: What is a planet? (discussion)
Reply #14 - 08/25/06 at 13:36:32
 
Yes, indeed it was my conclusion that Neptune perturbed Uranus' resonant objects back into Uranus , or into other planets (including Neptune) in a few cases.  I'll own up to that.  Sorry if I left an impression that the paper said that.
 
I have done a whole bunch of GravSims of Neptune resonances.  So I've got a pretty good feel for objects that get thrown out of Neptune's orbit.  If there was another planet beyond Neptune, the ones thrown to the outside would not be stable.  Since there's nothing substantial outside of Neptune then Neptune became a pathological case.  But it still outweighs everything in it's sphere.
Back to top
 
 
Email View Profile   IP Logged
Pages: 1 2 
Send Topic Print