our whole solar system could change soon!!!
astronomers are busy in prague voting on their proposed new and finally official definition of a planet. we've identified 9 planets in our solar system in the past: mercury, venus, earth, mars, jupiter, saturn, uranus, neptune and pluto (my very fine mother just sent us nine pizzas!). the first planet was identified over 200 years ago as an object that moved across the sky in a different way than the stagnant distant points of light... the stars. no formal definition of a planet currently exists.
the proposed definition is that in order for a celestial object to be a "planet" it must:
1) orbit around a star, but not actually be a star (a star is an object that burns at least hydrogen in its interior)
2) and be made up of enough stuff (mass) that its own gravity pulls it together to be nearly spherical.
roughly, an object less than 1% the mass of our moon within a diameter way less than the length of california could satisfy the second point. so.... we could wake up soon in a solar system containing 12 planets? if the new definition gets voted in.... we would add ceres between mars and jupiter, keep pluto, throw in pluto's moon charon, and the unromantically named 2003 UB313.
i think there are some ambiguities that still plague the nearly new definition of a planet. for instance, pluto's orbit around the sun is not in the same plane as the other currently existing 8 planets and pluto's orbit is more eccentric (less circular) than the other planets. also, there are objects out there that arent officially stars because they dont burn hydrogen in their cores, called brown dwarfs, but they are 12-75 times bigger than juptier-like giant planets and they dont orbit around other stars. do we need another name for objects that are bigger than juptier, but smaller than brown dwarfs and are not orbiting around stars?
hmmmm.... pygmy planets, plutons, globules, gray dwarfs, pixie planets ;)
i dont think any of those names are clever enough to stick..... any ideas??