See also:

• Science: Astronomy: Solar System: Kuiper Belt  (23)
• Society: Philosophy: Philosophy of Logic: Logic and Ontology: Natural Kinds  (3)

Gravity Rules: The Nature of Planethood - - Article discussing possible definitions that qualify objects, such as Pluto and Sedna in the Kuiper Belt, as being planets or not.

Is Pluto a Giant Comet? - - Discusses related discoveries and excerpts.

New Horizons: Is Pluto a Planet? - - Brief discussion of the controversy, and suggested classification of "Ice Dwarf" for Pluto, Charon, Sedna, and similar objects.

Pluto - - Argues that Pluto is the most important Kuiper Belt object, not the least important planet, based on its orbit and other properties. From astronomer Dave Jewitt, who studies comets and other primitive solar system bodies.

Pluto is a Planet - - Argues that Pluto meets the simplest and most coherent definition, rebuts opposing arguments, and lists various characteristics of all 9 planets to show what a diverse group they are. From astronomer John Stansberry of the Steward Observatory in Arizona, US.

What is a Planet - - Reviews newly-discovered objects that stretch the definition of the term, including massive superjupiters, free-floating planets, and other exoplanets. Suggests a definition based on the way an object is formed. From astronomer Gibor Basri.

Yes, Pluto Really is a Planet - - Argues that no commonly-accepted category fits it better. Includes a proposed definition of planet, and a list of known objects meeting it. From Lowell Observatory astronomer Marc W. Buie.

IAU: Trans-Neptunian Object 2003 UB313 - - Re-announces formation of a working group to produce a formal definition of a planet, in conjunction with the announcement of this Trans-Neptunian object larger than Pluto, which will not be named pending a formal definition. (August 4, 2005)

CBS News: Pluto: Planet Or Junk Snowball? - - Outlines the history of the debate. (February 14, 2005)

SciZone - Ontario Science Centre: Pluto: Planet or Not? - - Brief nontechnical introduction to Pluto and similar objects such as Sedna and Quaoar, and a summary of the features that make Pluto different than the other planets. Includes a capsule summary of the arguments for and against calling Pluto a planet. (April, 2004)

SPACE.com: Pluto's Planet Status Could be Jeopardized by Sedna Discovery - - Discusses the ongoing debate over the definition of the term "planet", and suggests that if Pluto should be considered a planet, so should Sedna and similar bodies. (March 17, 2004)

National Geographic News: Pluto: Planet or Comet? - - Discusses Pluto's similarity to other Kuiper Belt objects, and introduces a 5-way classification scheme for solar system objects to break down the lumping together of dissimilar planets. (February 23, 2001)

Much ado about Pluto - - News release from NASA affirming Pluto's planetary status. (February 17, 1999)

The Status of Pluto - - Clarification from the International Astronomical Union on Pluto's planetary status. (February 3, 1999)

When Is a Planet Not a Planet? - - Articles discusses the debate whether Pluto should be included among the planets. [Atlantic Monthly] (February 1, 1998)