Pluto no longer a planet

[MMC]

Originally posted by snoopy369
The Death Star would take rather more offense than Pluto would I suspect to any such demotion

Nah... the Death Star would just demote any planet that dared to demote the Death Star

However... how many planets do you know of that can be destroyed by simply flying into their exhause pipe and launch a couple of ordinary missiles?

[Zoid]

According to sources on the web the Death Star is between 120-160 kilometers in diameter. This would be roughly a 1/20 of Pluto. It´s not even big by comparison with other Kuiper Belt Objects (KBO). It´s estimated that there is around 35000 KBOs over a 100 kilometers in diameter...

[Mercator]

Originally posted by Lord Avalon
Then shouldn't Neptune be disqualified for the same reason? It hasn't cleared Pluto out of its neighborhood.

I don't really get it either. The previous proposal we heard of was pretty clear about what was a planet and what wasn't. I don't quite understand where exactly the boundary between planet and "dwarf planet" is in this decision.

Does anyone know where to find a more detailed explanation than what's appeared in every news article I've seen about this?

Edit: Hmmm, the IAU website doesn't really say any more either. I suppose it's just clear enough for astronomers then.

[Dis]

Originally posted by DrS
It is more properly a Kuiper belt object. But still, I'd have preferred to see it grandfathered in. It's been a 'planet' for so long now, it's part of the collective culture.

think of all the atlases and encyclpedias that have to be changed. Not to mention game show and trivia game questions.

[Lord Avalon]

Originally posted by Lorizael
Although the actual line is, "He's headed for that small moon."

D'oh! I stand corrected.

Originally posted by Mercator
I don't really get it either. The previous proposal we heard of was pretty clear about what was a planet and what wasn't. I don't quite understand where exactly the boundary between planet and "dwarf planet" is in this decision.

Does anyone know where to find a more detailed explanation than what's appeared in every news article I've seen about this?

Edit: Hmmm, the IAU website doesn't really say any more either. I suppose it's just clear enough for astronomers then.

After further reflection, maybe it's because Charon isn't considered a moon of Pluto, but a dwarf planet in its own right, and "neighborhood" means their orbit. So because neither of them have cleared their orbit of each other, they're not planets, but Neptune is, because it doesn't share its orbit with anything larger than a moon. The explanation in the article wasn't good enough.

EDIT:

Originally posted by Dis
think of all the atlases and encyclpedias that have to be changed. Not to mention game show and trivia game questions.

And websites, like nineplanets.org.

[Will9]

Here is my defenition of a planet:

1. It must orbit a star.
2. It must have a almost round shape.

Pluto, your a planet in my eyes!

[Mercator]

Originally posted by Lord Avalon
After further reflection, maybe it's because Charon isn't considered a moon of Pluto, but a dwarf planet in its own right, and "neighborhood" means their orbit. So because neither of them have cleared their orbit of each other, they're not planets, but Neptune is, because it doesn't share its orbit with anything larger than a moon. The explanation in the article wasn't good enough.

I don't think Charon is considered a dwarf yet. And even so, what would happen in the case of twin planets? Say, two Earth-sized objects rotating around each other? In fact, "dwarf" seems to indicate something about size, but the definition doesn't seem to say much about size... Well, except maybe that "clearing the neighborhood" probably relates to the force of the planet's gravity.

[Zoid]

IAU 2006 General Assembly: Result of the IAU Resolution votes

24. August 2006, Prague



The first half of the Closing Ceremony of the 2006 International Astronomical Union (IAU) General Assembly has just concluded. The results of the Resolution votes are outlined here.



It is official: The 26th General Assembly for the International Astronomical Union was an astounding success! More than 2500 astronomers participated in six Symposia, 17 Joint Discussions, seven Special Sessions and four Special Sessions. New science results were vigorously discussed, new international collaborations were initiated, plans for future facilities put forward and much more.

In addition to all the exciting astronomy discussed at the General Assembly, six IAU Resolutions were also passed at the Closing Ceremony of the General Assembly:

1. Resolution 1 for GA-XXVI : "Precession Theory and Definition of the Ecliptic"
2. Resolution 2 for GA-XXVI: "Supplement to the IAU 2000 Resolutions on reference systems"
3. Resolution 3 for GA-XXVI: "Re-definition of Barycentric Dynamical Time, TDB"
4. Resolution 4 for GA-XXVI: "Endorsement of the Washington Charter for Communicating Astronomy with the Public"
5. Resolution 5A: "Definition of 'planet' "
6. Resolution 6A: "Definition of Pluto-class objects"


The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as 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.

This means that the Solar System consists of eight "planets" Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called "dwarf planets" was also decided. It was agreed that "planets" and "dwarf planets" are two distinct classes of objects. The first members of the "dwarf planet" category are Ceres, Pluto and 2003 UB313 (temporary name). More "dwarf planets" are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate "dwarf planets" are listed on IAU's "dwarf planet" watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.

The "dwarf planet" Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects. The IAU will set up a process to name these objects.

Below are the planet definition Resolutions that were passed.

Notes for editors
A press conference about the Closing Ceremony of the General Assembly, including the results of the planet-definition vote, will be held at 18:00, in Meeting Room 3.3 of the Prague Congress Center. (It will NOT be possible for journalists to ring in to this conference: they must be there in person.)

The panel for the press conference will be:

* Ron Ekers (outgoing IAU President)
* Catherine Cesarsky (incoming IAU President, Member of the Planet Definition Committee)
* Jan Palous (Chair of the National Organising Committee)
* Richard Binzel (Member of the Planet Definition Committee)
* Karel van der Hucht (incoming Secretary General)

This press conference will conclude around 18:30 CEST.

The IAU is the international astronomical organisation that brings together distinguished astronomers from all nations of the world. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. Founded in 1919, the IAU is the world's largest professional body for astronomers. The IAU General Assembly is held every three years and is one of the largest and most diverse meetings on the astronomical community's calendar.

Contacts
Following the vote, some of the members of the planet definition committee will be available for interviews (after the final vote):

Richard Binzel
Member of the Planet Definition Committee
Prague Conference Center, Meeting Room 3.1
Tel: +420-261-177-110
Cell: +420-776-806-297 (during the General Assembly)

Junichi Watanabe
Member of the Planet Definition Committee
Prague Conference Center, Meeting Room 3.3
Tel: +420-261-177-081
Cell: +420-776-806-265 (during the General Assembly)

Iwan Williams
President, IAU Division III Planetary Systems Sciences
Prague Conference Center, Meeting Room 244
Tel: +420-261-177-064
Cell: +420-776-157-769 (during the General Assembly)

Owen Gingerich
Chair of the IAU Planet Definition Committee
Tel: via the Press Room +420-261-177-075

Professor Ron Ekers
IAU President
Tel: via the Press Room +420-261-177-075

Catherine Cesarsky
IAU President-Elect and member of the Planet Definition Committee
Tel: via the Press Room +420-261-177-075

PIO contact
Lars Lindberg Christensen
IAU Press Officer
IAU GA 2006 Press office, Meeting Room 3.2
Prague Congress Center
Tel: +420-261-177-075/+420-261-222-130
Cellular: +49-173-3872-621
E-mail: lars@eso.org

Links

* Programme for the Closing Ceremony: http://www.astronomy2006.com/second-...g-ceremony.php
* Live public webcast of the Closing Ceremony: http://astronomy2006.com/tv/
* Live press webcast of the Closing Ceremony (press only, please do not distribute): http://www.astronomy2006.com/tv-press
* The IAU Web page: http://www.iau.org
* IAU News during the 2006 General Assembly: http://www.iau2006.org
* IAU General Assembly: http://www.astronomy2006.com
* Free registration for the media: http://www.astronomy2006.com/media-accreditation.php



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 (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) shape2 , (c) 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".

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.


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

[Lord Avalon]

Originally posted by Mercator

I don't think Charon is considered a dwarf yet. And even so, what would happen in the case of twin planets? Say, two Earth-sized objects rotating around each other? In fact, "dwarf" seems to indicate something about size, but the definition doesn't seem to say much about size... Well, except maybe that "clearing the neighborhood" probably relates to the force of the planet's gravity.

Under one of the proposed definitions, Ceres, Pluto, Charon and "Xena" would have been planets, making 12.

The new definition isn't specific about size in terms of a number for mass, but size is implied in having enough gravity to assume a round shape and "clearing the neighborhood."

If you had a binary system of bodies large enough to otherwise be planets, then I'm guessing it would not be stable, and eventually they would assume different orbits - i.e., clearing the neighborhood of each other.

[Guynemer]

I think I speak for the vast majority of people trained and practicing in the sciences, when I say,

WHO GIVES A ****?!

[Zoid]

Well, I do!

[chequita guevara]

I say a planet is anything with sufficient gravity to pull itself into a round shape and hold an atmosphere and isn't a star.

[Colonâ„¢]

Or orbiting another planet.

[Unspeakable Horror]

[Whoha]

pluto should be grandfathered in. If they had only named that recently found object planet X then there would have been none of this difficulty.