12 Planets, Maybe More???
The International Astronomical Union has finally taken up the task of creating an official scientific definition of what constitutes a planet: http://www.msnbc.msn.com/id/14364833/
I’ve been watching astronomers argue about this for the past few years. The debate heated up with the recent discoveries of Sedna and 2003 UB313 (“Xena”) in the outer reaches of the solar system.
The definition gaining the most favor is this:
"A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."
Under this plan, not only would Sedna and Xena both be considered planets, but so would the asteroid Ceres, which orbits the Sun in the asteroid belt between Mars and Jupiter. There is also a weird corollary to the definition that means Charon, Pluto’s moon, would also be considered a planet. Since it isn’t technically a satellite of Pluto, it’s part of a “double planet system,” which means Pluto and Charon count separately.
That raises the official tally of planets to 12, and I can think of a few more that might have to be added: Quaoar and (perhaps) Ixion. Both reside in the Kuiper Belt with Sedna and Xena.
I’m just wondering what others think of this: would you like to see the number of planets possibly raised to include as many as 53 objects, or would you rather stick with the “official” 9 planets, even though it’s scientifically arbitrary?
As for myself, I think the definition currently under consideration is about as scientifically sound as it can possibly be. Any other standard sacrifices science for tradition and convenience. If it’s massive enough for gravity to make it round, and it orbits a star, it’s a planet. There might be sub-classifications, like gas giant, dwarf planet, etc., but it’s still a planet.
Here’s a graphic of our “new” solar system:
Last edited by DRayRaven; 08-16-2006 at 07:46 AM.