As I recall, the definitions extended to planets' spherical moons, irregular moonlets or satellites (I don't recall the terms used), brown dwarves, etc. I also don't remember if the definitions included a class for large, non-stellar interstellar interlopers. I don't know the mass/gravitational threshold for spherical objects, nor do I possess the math and physics skills to calculate that. Maybe someone else knows? One could calculate the theoretical limit for becoming spherical, then define any object larger than that limit as a planet, provided of course it fits other criteria, such as orbiting a star or star-like object. Imperfections such as Earth's slightly pear-shaped "sphere" and the oblateness of Jupiter would then not matter. ----- Original Message ----- From: "Joe Bauman" <bau@desnews.com> To: "Utah Astronomy" <utah-astronomy@mailman.xmission.com> Sent: Tuesday, August 02, 2005 1:52 PM Subject: 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 | | _______________________________________________ | Utah-Astronomy mailing list | Utah-Astronomy@mailman.xmission.com | http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy | Visit the Photo Gallery: http://www.utahastronomy.com | | ______________________________________________________________________ | This e-mail has been scanned by Cut.Net Managed Email Content Service, using Skeptic(tm) technology powered by MessageLabs. For more information on Cut.Nets Content Service, visit http://www.cut.net | ______________________________________________________________________ | |