Watch Stephen Colbert Talk Pluto Flyby with Neil deGrasse Tyson (Video)

Astronomer Neil deGrasse Tyson famously insists that Pluto should not be considered a planet — and Stephen Colbert, former host of "The Colbert Report," put that conviction to the test in a recent interview with the famed astronomer.

Colbert talked with Tyson in a new video posted Tuesday (July 14) in advance of the September premier of "The Late Show with Stephen Colbert" on CBS. Tyson, who is the director of the Hayden Planetarium and a popular spokesperson for science, talked about the incredible photographs of Pluto taken by the New Horizons probe during its close flyby of the dwarf planet.

"It looks like an illustration in a dictionary that says 'Planet,'" Colbert said in reference to the most recent Pluto image, while talking to Tyson. "It looks like a planet, it's got atmosphere, it even has a heart — unlike you, who will give it no love." [Poll: Should Pluto Be a Dwarf Planet or Full-Fledged World?]

In the new video, Colbert pressed Tyson on the reasons why Pluto was demoted from planet to dwarf planet in 2006. Tyson famously supports Pluto's demotion because of its small size and because it shares its neighborhood, the Kuiper Belt, with several other objects that are similar in size. That makes Pluto unlike the other eight planets, which have each gravitationally gobbled up nearby debris to create clean orbits. However, Tyson called Pluto "the king of the Kuiper Belt."

On a scale of "1 to awesome," Tyson said he rated the flyby "awesome minus 10 percent." Even if Pluto is slightly larger than scientists previously suspected, it's still much smaller than researchers initially speculated. When Pluto was discovered, Tyson said, it was thought to be Earth's size. In reality, it is five times smaller in diameter than Earth and is half as wide as Mercury. If Neptune was a Chevy Impala parked at the curb, in Tyson's example, Pluto would be a Matchbox car.

But Pluto wasn't the only planet that might deserve to be demoted, Tyson said: All the rocky planets are "dwarf planets" compared with the gas giants. He said he'd take all four rocky planets in our solar system — Earth, Mars, Mercury and Venus — and call them dwarf planets rather than admit Pluto to the planet club.

If we lived on Jupiter (whose diameter is 11 times larger than Earth's), Tyson said, "We would look at these puny, rocky things and say, 'What? They want to call themselves a planet like us? No.'"

The extreme close-ups from the New Horizons Pluto flyby are still worthy of celebration, though. "It's not every day where you get to be the first eyes to set upon a completely undiscovered land," Tyson told Colbert. "It is especially beautiful and especially exciting because no one has seen this before yesterday."

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Sarah Lewin
Associate Editor

Sarah Lewin started writing for in June of 2015 as a Staff Writer and became Associate Editor in 2019 . Her work has been featured by Scientific American, IEEE Spectrum, Quanta Magazine, Wired, The Scientist, Science Friday and WGBH's Inside NOVA. Sarah has an MA from NYU's Science, Health and Environmental Reporting Program and an AB in mathematics from Brown University. When not writing, reading or thinking about space, Sarah enjoys musical theatre and mathematical papercraft. She is currently Assistant News Editor at Scientific American. You can follow her on Twitter @SarahExplains.