[X] My Assistant

[SFJCody]

http://groups.yahoo.com/group/mpml/message/15111

[dvandorn]

If real estate doesn't matter and you classify planet vs. non-planet based solely on size and mass (i.e., is it big enough to have pulled itself into a ball), then what about a majority of the moons of the gas giants? Remember, real estate cannot be a factor in the equation.

Under the classification system that everything massive or large enough to pull itself into a sphere (more or less) is a planet, we have to admit Ceres, Vesta, the Galilean moons of Jupiter, many other Jovian moons, a lot of Saturnian moons, a lot of Uranian and Neptunian moons, plus possibly thousands of KBOs, all into the League of Planets.

Oh, and while it's not usually called a planet, our own Moon would have to be considered a planet, too.

If you're going to make an exception for bodies that orbit other planets to call them moons, then you're allowing real estate to enter the equation, and once you do that, you're simply applying arbitrary dividing lines...

-the other Doug

[Alan Stern]

If real estate doesn't matter and you classify planet vs. non-planet based solely on size and mass (i.e., is it big enough to have pulled itself into a ball), then what about a majority of the moons of the gas giants?  Remember, real estate cannot be a factor in the equation.

Under the classification system that everything massive or large enough to pull itself into a sphere (more or less) is a planet, we have to admit Ceres, Vesta, the Galilean moons of Jupiter, many other Jovian moons, a lot of Saturnian moons, a lot of Uranian and Neptunian moons, plus possibly thousands of KBOs, all into the League of Planets.

Oh, and while it's not usually called a planet, our own Moon would have to be considered a planet, too.

If you're going to make an exception for bodies that orbit other planets to call them moons, then you're allowing real estate to enter the equation, and once you do that, you're simply applying arbitrary dividing lines...

-the other Doug

We dealt with the satellites issue in a long IAU article which I am happy to share if
anyone wants it; just email me and I'll send it.

Here's what we said: if an object fitting the planetary definition orbits another planet
then it is called a satellite of the planet and a "planetary body", but not a planet.

[dvandorn]

OK -- fair enough. Though that *is* allowing a gravitational definition of real estate to affect the terminology...

Isn't there some theory out there that Triton was once a KBO that was later captured by Neptune? If that's the case, then you would say that Triton is a planetary body that was once a planet but is now a satellite?

I think the reason people are so energized over the classification issue is that most people have a need for a world around them that they can hold in their heads at one time. When we think of a city, for example, we think in sequential sequences of roughly ten-square-block areas that we can characterize in our minds "at once." We even give names to these small, handle-able chunks, calling them districts or neighborhoods. But we chop things into segments that we feel comfortable dealing with as single entities.

If you want people to feel like they have a place in a larger Universe, you need to give them relatively "small" chunks to deal with. Giving school kids ever-widening chunks (Earth as a planet, Earth/Moon System, Inner Solar System, Solar System) you keep the number of elements of each "chunk" under 10. That seems to be a good limit, since anything that gets a lot more complex is difficult for an average person to handle in one "chunk."

So, I think it is important to give people some kind of system that identifies a Solar System consisting of a number of objects (in the vicinty of 10 or so objects) that they can grasp in one "chunk." When you add thousands of objects, you need to add them "en masse," is with the Asteroid Belt, the Kuiper Belt, the Oort Cloud -- note that those are all singular, not plural, nounds. Otherwise, people begin to feel lost and overwhelmed by the sheer number of "things" they need to consider or account for within a given system.

(Note -- I'm not talking about the scientists and engineers, here, who are trained, or have an affinity, to think in different scales. I'm talking about your normal, salt-of-the-Earth kinds of people who make up 95% of the world's population...)

-the other Doug