The thing most people don't understand is that astronomers have been finding objects in the solar system that are larger that Pluto is, and yet we do not also classify them as planets. There was never a solid definition of what exactly makes a planet, and so that's what the IAU did. Unfortunately it meant that Pluto didn't make the cut. Because if we had lowered the standards to include Pluto, then it would also include a ton of other bodies and we'd have like 30 planets or something.
We decided Pluto was a planet in the first place because there was speculation on "Planet X" based on irregularities in Uranus's and Neptune's orbits, which was later corrected by the Voyager 2 mission, AND because it was discovered so early so we didn't know about all these other trans-Neptunian objects.
I'm happy with the current Captcha.
I have an idea: Change the question to something related to this forum, like "Who founded Aperture Science?" or "What is the name of the acress that plays GLaDOS?".
Yes, because spam bots would never think of using Portal related answers to Portal related questions on a Portal related website.
Does Cave Johnson beat Charlie Nash?