My Definition of “Planet”

Pluto's Two Newest Moons
Is Pluto a planet or not? Its three moons don't help to categorize it.
OK, I've thought more about it. Here's my suggestion for the IAU (actually, S&T editor in chief Rick Fienberg said he made similar suggestions to the astronomers already):

There are eight planets. Everything else is an asteroid. That would leave moons as moons (a.k.a. satellites) and leave comets as a separate class of object. Asteroid is a perfectly fine word. No need for "minor" or "dwarf" planets or "small solar system objects."

We have main-belt asteroids, near-Earth asteroids, Trojan asteroids, Centaur asteroids, and Kuiper-belt asteroids (like Pluto) — all which will be managed by the, uh, Asteroid Center.

We'll worry about extrasolar planets and "rogue" planets (loner worlds unattached to stars — like the Moon was in Space: 1999) later.

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.


This site uses Akismet to reduce spam. Learn how your comment data is processed.