Pluto Making a Comeback

anthemaniac writes "Space.com reports that the American Astronomical Unions Division of Planetary Scientists recognizes the IAU's authority to make a new planet defintion but expects it to be altered. Separately, 300 astronomers have signed a petition saying they won't use the definition. All this stems from the discontent over how only 424 astronomers voted on the proposal that demoted Pluto. Looks like this little dog is on the comeback trail."

Comments

i just wrote a story about this at kuro5hin.org

[circletimessquare]

So... What is a Planet Again?

the issue centers on one the IAU itself says it hasn't addressed with it's new definition of a planet: extrasolar systems. as new telescopes come on line with more resolving power, our bestiary of planets is going to grow by leaps and bounds. it will render the debate over pluto moot

i think a definition of planet should be:
-round, with a significant atmosphere
-this is distinct from a gas giant, which should be considered closer to stars than to planets (round, mostly gas: really just stars without enough critical mass to ignite fusion)
-and distinct from a moon (no atmosphere, but still round)
-asteroids, comets, etc make up the miscellany

and notice, most importantly, i said nothing about what something orbits. what something orbits is really secondary in consideration to what something is composed of. if we find an earth-like "moon" orbiting a gas giant in another solar system, is what it orbits really the first consideration in picking what to call it? no, composition should come first, orbit second. so you could have a moon of the sun (pluto), or a planet of saturn (titan), or an asteroid of mars (deimos/ phobos, etc.)

so this system demotes not only pluto, but also mercury. while promoting titan. so our solar system is composed of:
-4 planets (venus, earth, mars, titan)
-4 gas giants (jupiter, saturn, neptune, uranus)
-and countless moons (of the sun and the planets)/ asteroids (of the sun and the planets)/ comets/ ring systems/ kuiper belt, oort cloud objects/ etc

really, as we see more and more exotic arrangements in extrasolar systems as new telescopes come on line, this debate about pluto will look more and more pedantic. and the IAU should really begin focusing on a more rigid definition no matter what, something they said they weren't doing at their last congress. we will soon have a vastly larger catalogue of strange orbital objects/ arrangements out there. pluto is small potatoes... literally

Consistent terminology is crucial to any field

[teal_]

Oh but it is, it's very important. A precise terminology is critical to get anything done in any field.

Nostalgia or neat names your kids like are no reason to violate the rules of your field. AIDS was orginally categorized as a form of cancer, but then we found that it's not a cancer, so we stopped calling it a cancer. It's simple, really. Once you disprove something, it makes no sense to go on believing it.

The simple truth is that if you call Pluto a planet, then you also have to call Ceres and potentially hundreds of bodies in the Kuiper belt planets as well. Pluto does not dominate its orbit around the sun, it shares it with Charon, they spin around each other, one is not a moon of the other. None of the other planets in the solar system have such a symbiosis, they all have moons that orbit them. What shall we do when we manage to spot specific planetary bodies in distant solar systems? "let's see... hrm, that's a class-M planet, that's a gas giant, that's a dead rock, all of these have moons and they're spherical and dominate their orbits, but hey, here's a neat looking body there dancing with another body, I guess that's a planet too, let's call it Mickey and forget the thing it's spinning with." Where does it end? We need a concise definition that works every time, no exceptions.

As it is, with that gold disc in the voyager spacecrafts showing the planets of our system, it's doubtful ET will find us now since he'll see our system has only 8 planets but his directions said there would be 9. If he stumbles into the system anyway, and finds that's he's got the right place, he's going to think we're a bunch of retards for saying we have 9 planets :)