OT: The solar system has 12 planets

[Renegade 13]

henk brouwer said:
http://oklo.org/?p=120#comments
Apperently our moon will magically be promoted into planethood 30 billion years from now if this definition is accepted. (if the solar system is not destroyed before)

Within 30 billion years, the Sun will long since have gone into its red giant phase, with it's diameter increasing so much as to possibly engluf the Earth and Moon in its outer atmosphere. We won't care where the Earth/Moon barycenter is at that point All we'd have left of our Sun is the remnants of a really pretty planetary nebula.

[henk brouwer]

Very true
It's still an akward definition for a planet though, what if Charon had been in an eleptical orbit, so the barycenter would sometimes be inside, and sometimes outside of pluto, would charon change planet-moon status during it's orbit?

The whole double planet thing seems unnecessary, just name the heavier of the two objects the planet and the lighter one the moon, you're unlikely to find two bodies orbiting each other with exactly the same mass. If you do, just dump a couple of tons of material on one of them and your problem is solved.

[capnq]

henk brouwer said: what if Charon had been in an eleptical orbit, so the barycenter would sometimes be inside, and sometimes outside of pluto, would charon change planet-moon status during it's orbit?

If I'm understanding the definition of barycenter correctly, a barycenter does not move relative to the objects that define it.

[henk brouwer]

Hmm the barycentre is indeed defined by the *average* distance between the two objects. Still, if they are in eleptical orbits the distance to the barycentre can change, if I understand correctly, actually it would have to because the objects move closer to each other, so one or both of them have to get closer to the barycentre. the wiki page on 'center of mass'( http://en.wikipedia.org/wiki/Center_of_mass )has an animation of two objects orbiting around their barycentre in an eleptical orbit when you scroll down a bit. in this animation the distance between the objects and the barycentre changes. If the radius of one of them had been a bit over twice as large the barycentre would disapear in it for part of each orbit. (I really should do the math, but that scares me a bit actually, I just hope I'm right )

[Cipher7071]

It would seem that the barycenter for two perfectly spherical bodies would never move. But, if either or both were oddly shaped and rotating, then the barycenter could shift somewhat.

I find the definition of a pluton that depends on the object's origin compelling. Otherwise, how to decide according to size or orbit seems abitrary to me. They shouldn't spend too much time arguing over it, as much of the argument is semantic.

[ToddT]

Nah, i have a very cynical take on this. Given the perodic discussion as to whether pluto is a planet or not, and now the discovery of other objects almost as big, the ones pushing for planet status of the planets and ensuring pluto's status, or looking make a name for themselves to find other planets in the solar system, which is more glamorous, finding a large rock or a small planet. From what i remember, if pluto had been found several years later it would most likely not have been classified as a planet.
pluto was found while ppl where looking for a 9th planet that had been mathmatically calculated to exist, when it was found it was for smaller than expected, hence part of the reason to found the everelusive tenth planet. I think that was before they new the exist of the ort cloaud and kiper belt.

[Cipher7071]

You're right about one thing: Where egos are involved, what's logical will often take a back seat.