Is Pluto A Planet? Here's What Neil deGrasse Tyson Believes

Pluto — the celestial body, not the beloved Disney character — was demoted from its planetary status in 2006 by the International Astronomical Union (IAU). The argument had been over whether the little spheroid was big enough to be considered a planet in the first place. 

Until then, the term "planet" had actually been a quaint colloquialism for any large celestial object within the solar system. It was only during the 2006 General Assembly of the IAU that the definition of what defined a "planet" came into existence... and literally changed everything.

For a large celestial object to be considered a planet, the IAU decided it needed to have two defining characteristics. First, it had to be big enough that its gravitational orbit around the sun made it round, and secondly, it had to be big enough to fight off any nearby planetary objects or debris. Basically, it had to be a space-faring bully. 

Pluto definitely had the first element — it was round, but it wasn't big enough to "shoo away" its neighbors. Thus, Pluto went from being the ninth planet in our solar system to one of five dwarf planets, with the IAU having said at the time that Pluto is "an important proto-type of a new class of trans-Neptunian objects."

Neil deGrasse Tyson, who is still the director of the Hayden Planetarium at the American Museum of Natural History in New York, first noticed something was different about Pluto back in the 1990s. During a 2009 interview with NPR, Tyson stated that other celestial bodies of ice discovered in the outer solar system acted similarly to Pluto because they crossed orbits with other planets.

According to Tyson, that's simply not how a large celestial body considered a "planet" should behave. The astrophysicist went on to say that Pluto's demotion as a "planet" shouldn't be looked at negatively. Instead, Pluto should be considered the first object discovered in an area of the outer solar system known as the Kuiper belt. 

That didn't stop Tyson from poking fun at Pluto's diminutive size when he appeared on "The Late Show with Stephen Colbert" in 2017. During the brief interview, he said the Earth's moon has five times the mass of Pluto, and yet it's a "moon," not a planet. In fact, Pluto is only about two-thirds the moon's diameter with a circumference of 4,627 miles, according to Space.com. 

So, according to Tyson, Pluto is still not a planet and should "stay in its lane," sticking to his perspective despite continued controversy over the matter in the wider scientific community.