[转载] 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 defi nition 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.
After having received inputs from many sides — especially the geological community — the term “Pluton” is no longer being considered.
IAU Resolution: Defi nition 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 refl ect 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 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, ( c ) has not cleared the neighbourhood around its orbit, and ( d ) is not a satellite.
(3) All other objects 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 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“
原文见http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html
原本想翻译一下的，但那个“cleared the neighbourhood”应该如何理解还没拿捏好。刚看了CCTV的新闻，我倒，居然把Dwarf Planets和Small Solar System Bodies混为一谈了……想想前两天某某某报纸扯着周济林老师的名字胡说八道，我就不说他啥好了……
8月25日补记：最终结果，Resolution 5A、6A获得通过，5B、6B遭否决。这果然是“Pluralitas non est ponenda sine necessitate”哈……本来就是一些没什么必要增添的概念么……不过“cleared the neighbourhood”的定义对于木星是不是有问题啊？
另：祝贺北京取得2012年第28届IAU大会的主办权，congratulations and good luck! I hope I could attend this meeting then……
