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How Many Planets? We're Agnostic We at The Planetary Society love all worlds and advocate for their exploration—no matter which ones the scientific community decides to call planets. Mat Kaplan, host of Planetary Radio, occasionally hosts guests on his show that have very strong opinions on this subject. On the left, Mat and Cassini imaging team lead Carolyn Porco show solidarity for 8 planets, and on the right, Mat joins New Horizons principal investigator Alan Stern and astrobiologist David Grinspoon in flashing the symbol for 9 planets. The Planetary Society