Is Pluto a planet again? No, and we ask local astronomers to explain why

Lehigh University professor Joshua Pepper helps find exoplanets, so you’d think he would be on board with calling Pluto a planet.

“I agree that the current definition of a planet is both problematic and limiting, but I have not seen a better one,” Pepper said, “and I definitely believe that it does not make sense to call Pluto a planet.”

Why not? For one thing, such a definition would do more than restore status to our solar system’s ninth planet — there would be way more than that.

A column in Forbes by astrophysicist Ethan Siegel rebutting Stern and Grinspoon says that under their definition, 19 moons, one asteroid and 87 objects would make the cut. The solar system would have more than 100 planets!

It makes more sense, the argument goes, to describe other worlds with a prefix, like exoplanet, dwarf planet or rogue planet (which is one without a star).

“The names we give things should tell us something about them,” Pepper said. “As problematic as the IAU definition is, it helps us understand the relationships between objects in our solar system. And it tells us more than the alternate approach, which is just ‘round things smaller than stars.’”

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