There's no objective definition for the term "planet", other than what people say. It's only a matter of which people you listen to. If you don't go by anything that people say, it means you're making up your own definition.
Actually, just the opposite is true. What people say is scientifically irrelevant; in the long run, what determines how scientific concepts get defined is what the actual objective evidence shows. People used to say that Andromeda was a "spiral nebula," believing it was a cloud of gas fairly nearby. But the evidence showed tht it was actually a whole galaxy even bigger than our own, made up of hundreds of billions of stars and a good three million light-years distant. What people said was absolutely, profoundly irrelevant to what it actually was. Science is about evidence, not opinion.
Scientists: Sucking the fun out of the solar system. Enjoy.
There are 9 planets. Sure, there are also hundreds, or thousands of planet-sized things out there, but screw them. If they get a cool name they can be planets also.
You know... for centuries, people thought there were seven planets, including the Sun and Moon, which all circled the Earth. Then they figured out that the Earth was one of six known planets circling the Sun. Then Uranus and Neptune were discovered, and people thought there were seven planets, then eight. Then Ceres and the next few asteroids were discovered, and they were initially assumed to be planets, and the number went up to ten, twelve, ultimately dozens of planets in our system. It was over sixty years before Ceres and its kin were redefined as non-planets (based on the growing evidence proving that they were far smaller than originally assumed) and the number "officially" fell to eight. Then, a mere 78 years ago, Pluto was discovered and called a planet, and we started thinking there were nine. Now we've discovered Eris, which is bigger than Pluto, and it's very likely that the 98% of trans-Neptunian bodies we haven't discovered yet contain dozens of other bodies bigger than Pluto. Maybe even as big as Mars or Earth.
There's nothing special or constant about the idea of there being nine planets. Heck, I have relatives who were alive when we thought there were eight planets. Our estimates of the number of planets have varied many times in the past, and will change again in the future. It's illogical to have any attachment to a particular number of planets just because it's the one you're used to. There's nothing special about the old and familiar. Surely it's more wondrous to embrace the new, to celebrate the discovery of new planets rather than closing one's mind to the idea of changing an old assumption.
