Definition Of The Word Planet

[LJP07]

From those knowledgable about the subject, what would be your definition of a planet if you have one, I find it a difficult one to define, however I would disappointingly guess:

 

One which has similar chemical and physical properties, similar orbital patterns around a host star.

 

24 August 2006:

 

But the new definition was given and links are given below:

[kmarinas86]

Rules for a planet:

A planet cannot orbit another planet.

Of a set of worlds orbiting a barycenter (such as Pluto, Charon, and the two newly discovered objects in that system), the heaviest object of that system is the only planet in that system.

A planet is smaller than a brown drawf.

If it has a solid surface, it must be possible to use a latitude and longitude coordinate system on that solid surface.

[Tormod]

The International Astronomical Union are working on a new definition right now:

 

http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html

 

According to the new draft definition, two conditions must be satisfied for an object to be called a "planet." First, the object must be in orbit around a star, while not being itself a star. Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. The shape of objects with mass above 5 x 10²⁰ kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation.

[cwes99_03]

I recommend searching Hypography, since there are other threads that are already discussing this exact issue.

 

http://hypography.com/forums/astronomy-cosmology/8038-vote-iau-draft-resolution-definition-planet.html?highlight=planet

 

http://hypography.com/forums/astronomy-cosmology/8012-pluto-not-planet.html?highlight=planet

[LJP07]

Ok, thanks Cwes......I keep on searching the Database for matches and can never find one, then I post the thread, and I find out theres already one....:):):hihi::):doh:

[cwes99_03]

I know what you mean. I think these threads started at the same time, or maybe even after your thread, but they have been the more popular ones.

[Southtown]

Dark, orbits a star, and has gravity stronger than its density (round). That last one I stole from a scientist on the Science channel... some documentary about Pluto being demoted to a Kuiper Belt Object.

 

Edit: Tormod beat me to it.

[Southtown]

The new definition has been decided upon, and Pluto is out. Our solar system now consists of only eight known planets.

 

http://www.iht.com/articles/ap/2006/08/24/europe/EU_SCI_Planet_Conundrum.php

 

They left out the requirement that a planet not be a star, from what I read. I wonder about binaries, then.

[LJP07]

Didn't expect that myself however, the article does read :

 

PRAGUE, Czech Republic Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight.

 

I'm surprised that since it was discovered in 1930, it has been a planet for 76 years and only gets demoted now, but maybe it is the correct move after all considering the new definition of the word planet.

[Southtown]

Well, I disagree with the whole "cleared the neighborhood around its orbit" mumbo-jumbo. Honestly, what the hell does that have to do with anything? It's as if they purposefully set out to demote Pluto to a Kuiper Belt Object to make further studies more straight forward.

 

Also, it doesn't look like the article quotes the new definition verbatim, and I'm having trouble loading iau.org to read it for real, but I still think it should specify that planets be dark.

[Tormod]

I was going to post the press release but I can't access the iau.org site either.

 

But basically they have created a new class of planets called "dwarf planets", and decided that Pluto is one of them. So the "official" count of "major" planets in the Solar System is now 8.

[cwes99_03]

Actually there were updates yesterday. Pluto is no longer a planet, and as far as I can see neither are Charon or Ceres. Not sure abou Xena.

 

It said is the dominant object in it's orbital path. This implies that since Pluto comes inside Neptunes orbit and shares an orbit with Charon that neither can be the dominant. Ceres would likely fall the same way since it resides in the asteroid belt.

 

Not sure about Xena, but if it truly resides in the Juiper belt then it too would be out.

[cwes99_03]

RESOLUTIONS

Resolution 5A is the principal definition for the IAU usage of "planet" and related terms.

 

Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. The IAU will set up a process to name these objects.

 

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 © 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) shape2 , © has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

 

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

 

 

 

 

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1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

 

 

 

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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.1

 

 

This just in from the iau.org site.

 

I stand corrected in the wording.

[Eclogite]

This decision will not stand. It is ill conceived and ambiguous.

 

Only delegates present at the conference were allowed to vote on it - this was no more than 5% of IAU members. It's as if you were to decide who was going to be President of the US on the basis of the vote of a single state, such as Florida. I mean, how crazy can you get.:hihi:

[Southtown]

I hope it doesn't stand. I mean, binary stars can now qualify for planet status, but Pluto can't? And "dwarf planet"?! Who the hell decided to add more complexity at the situation?

[InfiniteNow]

Only delegates present at the conference were allowed to vote on it - this was no more than 5% of IAU members. It's as if you were to decide who was going to be President of the US on the basis of the vote of a single state, such as Florida. I mean, how crazy can you get.:shocked:

Funny. :eek:

 

 

They should have opened a web-based voting option with security setup such that the only voters allowed were IAU members. Then, ensure the decision was made with a cut off at 66% vote, but ensure options were limited to 2 or 3.

 

 

Funny though. :xx:

[Tormod]

But it *was* announced that they would make a decision in this matter on the IAU's General Assembly. I'd be very surprised if members of the IAU were unaware of what was going on.