Today, debate still rages over how to classify the little celestial body, along with others orbiting the sun, but the IAU stands by its definition. "I think that most of the astronomical community has come to terms with the fact that we now know that the solar system has a continuous distribution of objects from very large down to very small," said Lars Lindberg Christensen, a spokesman for the IAU. "We now know that what we call the different objects has to necessarily change with time." Don't tell that to Plutophiles still seething about the decision.

While Tyson emphasises the things that set Pluto apart from the eight official planets, like its cluttered and elongated orbit, he does not argue against calling it a planet. We should spend less time classifying objects as planet or non-planet, he says, and more time thinking about the myriad ways to group them, from size and composition to formation history and weather. He makes a good case for moving beyond the definition debate, but it is unlikely to sway the hordes of devoted Plutophiles — especially the angry correspondent who told Tyson: "Pluto is a planet because I say so."

To the best of our knowledge, no people live on Pluto. But at least a few "Pluto people" live right here on Earth. And they want to see us get closer to the far planet. One of these Plutophiles is Clyde W. Tombaugh, 84, an astronomer at New Mexico State University at Las Cruces.