By Alan Boyle

Feb 20, MSNBC

How do you define a planet? Officials at the International Astronomical Union thought the matter was settled more than a year ago when it drew up a definition of planethood that separated little Pluto from its eight bigger siblings and put it in the dwarf-planet category. Boy, were they wrong.

Many astronomers say the definition that the IAU came up doesn't adequately reflect the diversity of worlds we see even in our own solar system - and arguably, might even exclude Jupiter as an official planet. Now a replay of the "Great Planet Debate" has been scheduled for August. Pluto may remain in the pint-size pigeonhole - but the other planets, in our solar system and beyond, would get their own pigeonholes as well.

The "Great Planet Debate" is due to begin on Aug. 14 at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md.

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photo: Pluto and its satellite Charon are the larger objects in this Hubble Space elescope image. Two even smaller satellites, Nix and Hydra, can be seen to the right (STScI / NASA)