Neil deGrasse Tyon on Pluto getting demoted from major planet to “dwarf planet”:

"So Pluto is not only the littlest planet, all right, that alone shouldn’t hurt it, but more than half of its volume is ice. No other planet has that. So if you moved it to where Earth is right now, heat from the sun would evaporate the ice and it would grow a tail. That’s no kind of behavior for a planet!

Pluto, its orbit is elongated so severely that it crosses the orbit of Neptune. Now, we have words for objects that cross the orbits of other planets and are made of mostly ice; they’re called comets. By the way, there are six moons in the solar system that are bigger than Pluto including Earth’s moon, which is five times the mass of Pluto. So really, Pluto was never the ninth planet; it was the first of a new class of objects that we didn’t really discover the rest of until the early 1990s.”