Is Pluto a Planet?

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You know what a planet is, right? A big round thing that orbits a star. Uh, not so fast. The surprisingly vicious debate over the planetary status of Pluto has given us a fascinating glimpse into what a scientific definition really is. And perhaps the word planet is too vague to be used as a scientific definition at all.

Hosted by Matt O'Dowd Written by Drew Rosen and Matt O'Dowd Graphics by Leonardo Scholzer Directed by: Andrew Kornhaber Produced By: Kornhaber Brown

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We love to classify things. Labels help us keep stuff organized in our heads. In science, categorization provides a fast and easy way to know the properties of a member of the group just by knowing what group it belongs to. Chemists group elements on the periodic table, those groups exhibit similar chemical behavior that reflect outer-shell electron number. Biologists group organisms by similar physical characteristics, and this taxonomy reflects genetic relationships. Astronomers are all about space taxonomy. We classify galaxies based on their shape, black holes based on how they feed, stars based on their colour and brightness, and planets by… well, by a set of criteria that has caused more tension and heartbreak than any made-up grouping scheme really should. Because a change in that scheme demoted Pluto from planet to not-planet. Today we’re going to settle whether this was reasonable, and whether we should keep the word “planet” at all.

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