According to the IAU, there are now eight planets. Pluto has been demoted, and three other bodies (Ceres, Charon and Xena) being considered for promotion to planet status did not make the cut. Now Pluto and Ceres are considered "dwarf planets" and Charon is left as "Pluto's largest moon". Xena is not the official name of the other celestial body, according to Wikipedia :
Claims that 2003 UB313 has been officially named "Xena" or "Lila" are incorrect; "Xena" is an informal codename used by its discoverers among themselves, and "Lila" is a name in the address of the website where the object was announced, after the newly-born daughter of one of the discoverers. Neither name was submitted to the IAU.
So the poor thing has the unromantic title of "2003 UB313". I prefer "Xena," myself.
The final definition of "planet," agreed upon yesterday by the body of the IAU, according to the Wikipedia current event article, is the following (found here):
The IAU...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] except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
Footnotes:
[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.
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.
And who is the IAU to be redefining planets? The International Astronomical Union, an organization recognized by astronomers around the world as the "official authority for naming stars, planets, asteroids and other celestial bodies and phenomena, and is the official body of astronomy." (Wikipedia article on the IAU)
Very interesting. I wonder how long the decision will stick? It looks like they had a lot of heated discussion and debate before they agreed on a definition.
1 comment:
These silly scientists always think they know everything, but look how often they change their minds. ;)
Poor Pluto will always be number nine to me.
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