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The Conversation USA

The Conversation USA

Planetary confusion -- why astronomers keep changing what it means to be a planet

  • Written by Christopher Palma, Associate Dean for Undergraduate Students and Teaching Professor of Astronomy & Astrophysics, Pennsylvania State University
In 2015, NASA’s New Horizons spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon. NASA/JHUAPL/SwRI

As an astronomer, the question I hear the most is why isn’t Pluto a planet anymore? More than 10 years ago, astronomers famously voted...

Read more: Planetary confusion -- why astronomers keep changing what it means to be a planet

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