A populist uprising restores a space favorite to the planetary ranks. Will the astronomers listen?
When Pluto was hurled from the pantheon of planets back in 2006, it could simply have slinked away, accepting its new title of “dwarf planet” without a fuss. But thanks to the undying support of its millions of fans—not just schoolchildren, but many astronomers as well—the little planet that could is still a contender.
The latest evidence: a debate at the Harvard-Smithsonian Center for Astrophysics, in which three astronomers squared off to present both sides of the question: “Is Pluto a Planet?” And when the dust settled, the audience, made up mostly of ordinary citizens, declared once again that the answer is “duh, obviously.”
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Three may seem like one side too many, but David Aguilar, the Center’s director of public affairs, who set up the debate, wanted to look at the question not just from a scientific perspective, but also through the lens of history. The first speaker, therefore, was the eminent Harvard astronomer and historian of science Owen Gingerich. “Planet,” he pointed out, “is a culturally defined word that has changed its meaning over the ages.”
In fact, the word itself comes from an ancient Greek word meaning “wanderer.” Unlike the stars, which seem fixed in place, the planets are objects that wander from one constellation to another in the sky—and since the Sun and the Moon do that too, they were originally considered planets as well.