In Brief

Is Pluto a Planet? Definition Takes Center Stage in Webcast Tonight

Pluto Artist's Impression
Artist’s concept of how the surface of Pluto might look. (Image credit: ESO/L. Calcada)

If you're confused about what exactly a planet is, don't feel bad: Astronomers are still arguing over the term eight years after the International Astronomical Union (IAU) came up with a controversial new definition that demoted Pluto to "dwarf planet" status.

You can get an inside look at the ongoing debate tonight (Sept. 18) at 7:30 p.m. EDT (2330 GMT) during an event organized by the Harvard-Smithsonian Center for Astrophysics (CfA) called "What Is a Planet?" You can watch the lecture live here on, courtesy of the CfA, or on the CfA's "Observatory Nights" YouTube channel:

Three experts will participate in tonight's event, CfA representatives said in a media advisory:

"Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, will present the historical viewpoint. Dr. Gareth Williams, associate director of the Minor Planet Center, will present the IAU’s viewpoint. And Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, will present the exoplanet scientist’s viewpoint."

At the end of the debate, the audience will get to vote on its preferred definition of "planet," and whether or not Pluto makes the cut. Results will be announced Friday (Sept. 19), CfA representatives said.

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.