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Neil deGrasse Tyson refuses to debate Alan Stern on Pluto as a planet

Neil deGrasse Tyson
Neil deGrasse Tyson
Photo by Cindy Ord

With the New Horizons probe just about a year away from its flyby encounter with Pluto, which was once considered the ninth planet in the Solar System, its principle investigator Dr. Alan Stern has challenged Dr. Neil deGrasse Tyson to a debate over whether or not Pluto should be considered a planet. Tyson, a celebrity astrophysicist whose updated version of Cosmos has just finished its run, has thus far refused to do so, according to a Tuesday story on

Tyson explained his refusal to debate Stern on his Facebook page. “As a general rule, I don't debate people. Done it once or twice before, but abandoned the effort. What's behind it is that I don't have opinions that I require other people to have. So debates don't interest me for this reason.” Tyson, aside from his Cosmos series, is a fixture on television and radio talk shows. He is generally treated with deference by interviewers such as Stephen Colbert and Bill Maher with his positions on a variety of subjects ranging from Pluto to climate change going unchallenged.

This elicited a sharp retort by Stern on his own Facebook page. “Tyson says he won't debate. All scientists engage in debate over competing ideas. If he persists in not supporting his position by engaging in debate, I'll consider it evidence he knows the position isn't supportable.” Stern has threatened to debate an empty chair if Tyson does not reconsider his position. Stern’s challenge and Tyson’s refusal has kicked up something of a social media firestorm.

Pluto, which was discovered in 1930, was considered the ninth planet of the solar system for the next 75 years. Tyson was a driving force in getting Pluto demoted to a “dwarf planet,” even going so far as to exclude it in a display at the Hayden Planetarium as the facility’s director. Tyson’s view is that Pluto, for various reasons, is no different from the uncounted celestial bodies that inhabit the Kuiper Belt and is not a proper planet at all. The International Astronomical Union agreed with this view in 2006 when it reclassified Pluto as a dwarf planet.

Stern has been a dissenter to this decision, pointing out that less than five percent of working astronomers voted in favor of the reclassification. He has also suggested that under the IAU definition of what a planet is, Earth. Mars. Jupiter, and Neptune would also be excluded. The reason is that a planet, according to the IAU, must have cleared its neighborhood of other objects. These four planets are in close proximity to a large number of asteroids and therefore, Stern contends, are not strictly speaking planets according to the IAU.