Tyson’s demotion of Pluto only came to the public’s attention when Kenneth Chang, a New York Times reporter, noticed there were only eight planets featured at the Rose Center. When Chang asked other astronomers to comment, they called the decision absurd. Letters of protest poured into the museum. But Tyson held firm, and in the years that followed, astronomers discovered other icy bodies at the edge of the solar system that were even bigger than Pluto. In 2006, the International Astronomical Union decided to classify it as a dwarf planet.

“By the way,” Tyson said, scanning the crowd. “Who’s the kid who said, ‘Pluto is a planet?’ What’s your name?”

The boy answered, “Sebastian.”

“Sebastian, a question for you. You know Pluto is small, right?”

“Yes.”

“Do you know how small it is?”

“No.”

“No, you don’t know how small it is!” Tyson roared. When he works a crowd, he doesn’t maintain a cool composure, like his hero Carl Sagan. He has a touch of Chris Rock. “So how can you say Pluto must be a planet? For example, if the planet Saturn were a car, how big a car would Pluto be sitting next to it? Do you have any idea? If Saturn, the car, were like Saturn the planet, how little would you have to make a car to be the size of Pluto? Do you have any idea? Would it be like a Mini Cooper? Or what’s that, the Smart Car? That little stubby car that’s got no butt?” Tyson sidled around on stage, as the crowd laughed at the living essence of a car without a butt. “That little thing? You’ve seen those. Great for parking. You think it’s that small, maybe?”

Tyson stood tall again. “I’ll tell you how small!” he shouted. “To make Pluto the size of a car relative to Saturn the car, it would have to be the size of a matchbox car sitting on the curb.” He squeezed his fingers. “Like that. There are six moons in the solar system bigger than Pluto—including Earth’s moon. And practically everybody I know saying ‘Pluto must be a planet,’ did not know that. Did you also know that Pluto is mostly ice by volume? So that if you slid it into where Earth is right now, heat from the sun would evaporate that ice and it would grow a tail. That’s no kind of behavior for a planet, I wouldn’t think. There’s a word for things with tails. What do we call them?”

The crowd answered, “Comets!”

“Comets, thank you. No, I think Pluto is happier now as the king of the comets, instead of being a pipsqueak planet.”

Tyson glared again at Sebastian. “So you agree with me? You admit it?”

Sebastian, arms folded, gave a nod.

“We have a convert, right there,” Tyson declared.