Re: [Utah-astronomy] planets - or not

Very good point, Kim. When I was talking with my son, Sky, the other day he suggested the same definition for a planet, large enough that its gravity forms it into a sphere and in orbit around a star. The last part rules out moons that are big enough but are not planets. I think it's a fine definition. The question is, what is the lower limit for enough mass to create a sphere? And how perfect does the sphere have to be? (In a sense, Jupiter isn't a very good sphere -- it's oblate because it is so large and spins so fast and is so gaseous that it bulges at the belt).) -- Joe