Other planets have been listed and then demoted, stripped of the right to call themselves planets. I like using terms like that, because after all, every planet is just a hunk of matter spinning around in space where no one can hear it scream, let alone complain about naming rights. Hunks of matter don't have volition, let alone vocabularies! Anyway, the sun used to be a planet, but when scientists established that there had been a heretical misunderstanding and it didn't revolve around the earth, it was slapped with the label "star" and told to hush up. The moon also lost planetary status, but it took it well.
Then new planets were found -- Uranus (aka Herschall), Ceres, Neptune (or Leverrier), Pallas, Vesta, Flora, Iris, Vulcan -- what? what? I'm not listing them in order from the sun, just in order that I remember them. Some of them later got transmogrified into asteroids, and Vulcan was relabeled a figment of the imagination. Yes, Vulcan disappeared completely without survivors. And then Pluto.
I like reading about the partnership between mathematicians and astronomers, because mathematicians are just cool. Gauss figured out the orbit of Pallas with basically two sightings and a paper clip. John Adams sent accurate predictions of Neptune's orbit to Britain's Royal Astronomer, who ignored him because Adams had a proletarian accent, thereby ceding Neptune's discovery to the FRENCH. Oops.
Why are Marschall and Maran on opposite camps? Marschall is comfortable with the IAU's definition of planets, which acknowledges Pluto's non-unique Kuiper belt status. Maran points out that the main reason there the IAU has a definition of "planet" is to figure out how to name new objects, which is not an issue with Pluto, and that astronomers never get the final word on what to call things anyway -- things end up with the name everyone uses, which is why no one has heard of Hershall or Leverrier and why Jupiter's moons aren't named after the Medici's. Both are right, and both agree that the name isn't really that important but wow isn't it great that people get so excited about this? Science is fun!