One of the hottest debates in all of astronomy is whether or not Pluto is a planet. After a long battle the IAU decided that Pluto was no longer a planet, and that it would be reclassified to reflect that. Since then, the answer of whether Pluto is a planet or not has not been settled, and some still say that Pluto is a planet. Regardless of what you think Pluto is, Pluto officially is not a planet, and there is some good evidence for why it isn’t. Here are a few reasons why Pluto is not a planet.
First of all, the orbit of Pluto is very eccentric, and indicates that it isn’t really a planet, but an object that comes from the Kuiper belt. This belt is an area of space that is left over from the making of the solar system, and that Pluto may even been just be a former moon of Neptune that was flung out into its orbit by some sort of gravitational tug.
Pluto has a moon that is nearly as big as Pluto is. Its moon Charon is almost as big as Pluto, and some are wondering if Charon and Pluto rotate around a single point in space, as opposed to being a planet-moon system. If this is true, then Pluto wouldn’t be a planet because it wouldn’t have cleared out the area of its orbit, which is required to be a planet.
The biggest reason that Pluto is not a planet is because it was probably mislabeled from the very beginning. It doesn’t make sense that you would have several gas giant planets, and then have some sort of small planet right after that. There have been asteroids in the past that have been mislabeled, such as Ceres, which was mistaken for a planet as well upon discovery.
Obviously we don’t see Ceres as a planet, and so we shouldn’t see Pluto as a planet either. Pluto is in a 3:2 resonance with Neptune, and this is similar to other Kuiper Belt objects, and other objects just beyond the orbit of Neptune. This resonance means that for every time Neptune orbits three times, the objects that are in resonance will orbit twice.
They are gravitationally bound so that they won’t collide, yet the orbit of Pluto comes inside that of Neptune. This eccentric orbit suggests that Pluto is not a planet because all the other planets have more of a circular orbit.
So, there are plenty of reasons why Pluto is not a planet. While the debate will rage on for years to come I am sure, I think that no one will really know what Pluto is. For the sake of nostalgia, we can call Pluto a planet, regardless of whether it technically is or not.
