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The newspaper of The Johns Hopkins University May 19, 2008 | Vol. 37 No. 35
What Is a Planet? APL Conference Will Grapple With Definitions

By Michael Buckley
Applied Physics Laboratory

Top scientists and educators will convene in Maryland this summer to explore a basic, but controversial, question: What is a planet?

The Great Planet Debate: Science as Process conference will be held Aug. 14-16 at Johns Hopkins' Applied Physics Laboratory and will include scientific sessions, a debate and an educators workshop addressing the processes leading to planet formation and characteristics and the criteria used to define and categorize planets.

"The time is ripe to hold a scientific conference to examine how planets form and evolve, both within our solar system and around other stars, as well as their physical characteristics," said Mark Sykes, a conference organizer and director of the Planetary Science Institute, Tucson, Ariz. "This event provides researchers with a unique opportunity to examine all sides of this issue and talk about it face to face. They can also sit down with educators to discuss how to broach the planet definition controversy in the classroom."

In August 2006, the International Astronomical Union, the organization that assigns names and classifications to astronomical objects, passed a resolution defining new criteria for "planets," governed by their mass and location. Under the IAU definition, only eight of the original nine planets in our solar system qualify, with Pluto and similar bodies falling into a new category of "dwarf planets." Segments of the planetary science community objected to the IAU criteria, and the debate continues among professional scientists, educators and the public.

Hal Weaver of APL, one of the conference organizers, said, "No votes will be taken at this conference to put specific objects in or out of the family of planets. But we will have advocates of the IAU definition and proponents of alternative definitions presenting their cases." This includes a public debate between Sykes and Neil deGrasse Tyson of the American Museum of Natural History, New York, on the afternoon of Aug. 14.

After two days of scientific sessions, the educators workshop on Aug. 16 will provide a forum on how the planet debate can be used to spark scientific inquiry in the classroom.

"This topic provides the perfect opportunity to teach science as a process, not a collection of facts," said organizing committee member Keith Noll of the Space Telescope Science Institute, Baltimore. "We also need to stress the importance of incorporating new discoveries to continually improve our understanding of the diverse objects within planetary systems."

For more information on the conference and workshop, including the schedule of invited talks, go to


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