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Pluto has been demoted to dwarf planet status

DailyTech reported last week that Pluto was coming close to being dismissed as an official planet of our solar system. Pluto, which was first discovered in 1930, has been the subject of debate for astronomers for over 70 years. The International Astronomical Union's 2,500 astronomers (representing 75 countries) gathered to decide the fate of Pluto and the results are in.

The International Astronomical Union (IAU) voted to demote Pluto from the ranks of the solar system's now 8 planets.  The decision comes as Pluto no longer fits the newly ratified definition of a planet decided upon by the IAU this week. The new definition states that a planet is “a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ...nearly round shape, and has cleared the neighborhood around its orbit.”

Pluto does not clear the neighborhood around its orbit because its orbit overlaps with its much larger neighbor Neptune. This therefore disqualifies it from planet status according to the IAU. Instead, Pluto will be classified as a dwarf planet and join the ranks of other dwarf planets such as Ceres, which lies between Mars and Jupiter and 2003 UB313 or ‘Xena’ as discoverer Michael Brown of the California Institute of Technology has nicknamed it. ‘Xena’ is an icy object that lies after Pluto and is slightly larger than the now dwarf planet.



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Definition of a Planet
By epsilonparadox on 8/24/2006 12:47:48 PM , Rating: 4
quote:
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 classical 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".


These resolutions would also rule out neptune.




RE: Definition of a Planet
By Trisped on 8/24/2006 12:50:04 PM , Rating: 2
Just what I was going to say.


RE: Definition of a Planet
By Nightmare225 on 8/24/2006 12:51:36 PM , Rating: 2
Beat me to it! You're right. Somethings awfully screwy here...


RE: Definition of a Planet
By skyyspam on 8/24/2006 1:06:00 PM , Rating: 2
How? Neptune's a gas giant planet, I thought.


RE: Definition of a Planet
By psychobriggsy on 8/24/2006 1:11:21 PM , Rating: 2
Pluto's orbit is eccentric and skewed from the solar equator enough that the orbital paths of both planets don't overlap.

i.e., when Pluto's in Neptune's area of space, it's bazillions of miles above or below Neptune. The usual 2D overhead orbit diagrams don't usually show this depth issue.

(that's what I read elsewhere anyway)


RE: Definition of a Planet
By Nanobaud on 8/24/2006 1:26:28 PM , Rating: 2
Depends on what is meant by 'cleared'. It must not require collecting every bit of matter along the orbital sweep to the object and it's moons, and would be somewhat subjective. Perhaps it is a relative criteria and a larger body can 'clear' its orbit with more residual matter than a smaller body. Also, since Pluto's orbital inclination is about 15° higher than Neptune's, does aither ever really cross the others path?


RE: Definition of a Planet
By SilthDraeth on 8/24/2006 3:16:11 PM , Rating: 2
Not really.

The part that Pluto does not meet is:
c) has cleared the neighbourhood around its orbit.

Neptune does meet that. Pretty much Neptune fits all other definitions of a planet, and has a normal orbit of the Sun. Pluto does not, and does not match any other planet's orbital patterns. Neptune never crosses the path of Uranus, and since it has a regular path, then Pluto is crossing it's path, and not the other way around.

http://www.space.com/scienceastronomy/solarsystem/...
"Pluto's orbit is inclined, or tilted, 17.1 degrees from the ecliptic -- the plane that Earth orbits in. Except for Mercury's inclination of 7 degrees, all the other planets orbit more closely to the ecliptic."


RE: Definition of a Planet
By Chernobyl68 on 8/24/2006 3:40:30 PM , Rating: 2
The asteroid Ceres would have been classified a planet had they not included the bit about cleared its neighborhood.

Personally, I think they should have "grandfathered" Pluto's status in, to make everyone happy.



RE: Definition of a Planet
By SilthDraeth on 8/25/2006 10:38:24 AM , Rating: 2
I believe that would have been a good idea.


"I modded down, down, down, and the flames went higher." -- Sven Olsen

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