As a planetary scientist, I don't know what else to call Pluto: It's big and round and thousands of miles wide.

There was a time when Pluto - which NASA's New Horizons spacecraft at last explored in 2015, a mission I led - was considered the last planet. We now know there are thousands of other - possibly inhabited - planets.

We really just didn't realize the diversity of planetary types in our solar system. Pluto looked like a misfit because it was the only one we saw. And just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies. They're large enough to make themselves round by self gravity, and they surely pass the test of planethood.

The Kuiper Belt is the largest mapped structure in our planetary system, three times as big as all the territory from the sun out to Neptune's orbit.

Just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies.

I don't believe we should classify planetary objects by location. We should use properties of the objects as a guide.