groovychk: (science)

So Xena has been officially named Eris (after the greek goddess of discord) and her moon is Dysnomia (daughter of Eris and the spirit of lawlessness)

Like all small bodies in the solar system, such as dwarf planets and asteroids, Eris and Dysnomia were each given a sequential number.

Pluto, now just another of the probably dozens of dwarf planets, was further demoted by receiving a sequential number just as Eris and Dysnomia received... it now is officially called 134340 Pluto.
groovychk: (science)
The New Solar System
groovychk: (science)

Scientists decide Pluto’s no longer a planet

Historic new guidelines approved by astronomers in Prague

The IAU therefore resolves that planets and other bodies in our SolarSystem be defined into three distinct categories in the following way:

(1) A planet1is 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 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

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.

The following sentence is added to Resolution 6A:

This category is to be called "plutonian objects."

groovychk: (science)

"So the newest resolution includes the requirement for orbital dominance as a condition for full-fledged planethood, Dr. Gingerich said. That knocks out Pluto, which crosses the orbit of Neptune, and Xena, which orbits among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt. "


So the definition I posted previously is still in play but the additional criteria of orbital dominance takes Pluto (as well as Ceres and Xena) out of the running.
groovychk: (science)§ion=theworld

So now the IAU says we have 12 Planets!

Pluto & Charon

My very educated mother can't just use nine planets considering xena. (heh - weak - but the best I can do on short notice)

So the conclusion is that any star orbiting object (and not orbiting another planet) with gravity strong enough to pull itself into a sphere is a planet. Charon was formerly considered a moon of Pluto (along with Hydra and Nix) but is now considered a planet on its own making Pluto-Charon a double planet.

The Pluto type objects are being given a new classification of "Plutons"

... the IAU said Pluto meets its proposed new definition of a planet: any round object larger than 800 kilometers (nearly 500 miles) in diameter that orbits the sun and has a mass roughly one-12,000th that of Earth. Moons and asteroids will make the grade if they meet those basic tests.

Roundness is key, experts said, because it indicates an object has enough self-gravity to pull itself into a spherical shape. Yet Earth’s moon would not qualify because the two bodies’ common center of gravity lies below the surface of the Earth.

Of course this would also seem to mean Sedna and Quaoar will be planets as well. Also true for Orcus (90482 Orcus), Ixion (28978 Ixion), Varuna (20000 Varuna), "Easterbunny" (2005 FY9) and "Santa" (2003 EL61).

I'm glad to see Ceres in there - I always wanted it to be a planet. Click HERE for a great graphic of all the other objects being considered for planet status.

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