Two weeks ago, while on my amazingly cool Astronomy course, my teacher decided the class to debate about wether or not Pluto should be a planet. before we started arguing though, she gave us the three definitions of a planet, according to the IAU:
1. It orbits the Sun 2. has enough mass and gravity to become almost spherical (hydrostatic equilibrium) 3. Has cleared the neighborhood around it
Now, if you look closely you may realize that number 3 is highly debatable (Number 2 in a sense as well): What is the definition of cleared up? You'd think it were 'the planet has absorbed, or thrown out of orbit all nearby objects. If that were true, then Jupiter wouldn't be a planet, because it has two asteroid groups orbiting with it.
I don't want to get into a lengthy tale about what happened in our classroom (It was mostly one group saying 'You're racists against little planets' and 'If we took out number three, we'd have 500,000 planets in the Solar System). Now I ask you:
Is Pluto a planet?
P.S: I don't want to hear a simple 'yes' or 'no', I want to hear why. This is a very debatable topic (So is everything else in Astronomy, but...), and I just want to hear what everyone thinks. I might debate a bit myself if this gets interesting.
Its orbit is very inclined; the other 8 planets' orbits are all more or less on a plane. This suggests it was formed in a different way to the other planets, and so it can be argued that it should be classified differently. Also, it may be orbiting around Charon in a double planet, rather than a planet with a moon.
Pluto has been considered a planet for a long while I think it should be still considerd a planet because of how l0ng its been called a planet
LOL that is stupid!If something has called long time for wrong name, name need to be changed!We must move forvard! And I think that Pluto should be called planet.Planets are gas or rock and Pluto is ice..And that Pluto have a moon wont matter, asteroids have moons too!
Well after my little research is Pluto in our solar system a "Dwarf" planet like Eris (largest dwarf planet known) Soo both of them (and 2 other) are dwarfy but both are still planets...
Pluto meets this criterion and is therefore a planet. Under this definition, our solar system has 13 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.
That's interesting. The moon is round. It's not a planet. It's also bigger than pluto. And interesting you include Haumea in your comment, because it is elliptical in shape, not round.
I think that it is necessary to point out that prior to 2006 we had no standardized definition of what a planet truly is. It is a result of the discovery of the many transneptune objects in our solar system that prompted this. The discovery of eris, quaor, and sedna caused this controversy in the first place. Judging by our initial concept of what a planet is these would have all been planets, however there were many major differences between them and the other planets in our solar system, making a recognized and standard definition necessary.
NASa's New Horizon mission to the Kuiper Belt, I think we should wait until 2015 to weigh in on the OP's question. My opinion is it's too soon to tell if Pluto is a true planet but since 2006 it's been classified as a "Dwarf Planet".
