Space/Science — HabitableZone

Space/Science » in reply to Do we have to "obey" the IAU?

And the issue is?
Adam — (archived)

Hi Larry

Their current observational redefinition of 'planet' makes more sense than any other theory-dependent argument I've heard. If an object is round from gravity and orbits a star in its own orbit - better than saying "if it's leftover junk from planet formation then it's not a planet." But it's only leftover junk if you follow that particular theory.

Ceres is an end-point of accretion - nothing bigger came to be between Mars and Jupiter, and perhaps nothing could. That it's surrounded by unaccreted bits is immaterial because most of the planets have debris sharing their orbits too (think Trojan asteroids.) So why not call it a planet? Likewise Pluto and its kin. If the Solar System has dozens of ice dwarf planets/Plutons then it's a bigger place, and more wonderful for it.

The astronomers wanted an observational definition with a minimum of theory, and they got it. If we fall back to the old Greek meaning of "planetes" then technically Uranus and Neptune drop off the list too as they're not naked eye objects.

As for exoplanets, what were you trying to say? Why aren't they planets???

Adam

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