Pluto is an oddball among planets. It has been kicked out of and invited back into the “Planetary Club†several times. I don’t even know if Pluto is even considered a planet right now. I do know that whether Pluto is a planet or not has been a debate among scientists and astronomers ever since its discovery. Today I’m going to talk about the history of Pluto, as well as my opinions of the small planet.
Percival Lowell was the first one to propose the possible existence of a planet beyond Neptune. He believed that he perceived irregular movements in Uranus’ orbit, and so he figured that there must be another planet’s gravity interacting with it. It is now believed that his observations about Uranus were false, but it did lead to the discovery of Pluto and the Kuiper Belt.
Lowell owned an observatory, and he hired Clyde Tombaugh to work under him. Eventually, Tombaugh discovered Pluto. It was so small that they could not well estimate the size, and were off by a factor of four-hundred. Lowell believed that Pluto was at least as big as Uranus, probably bigger. As telescope technology got better and better, Pluto’s size got smaller and smaller, until we arrived at its current size, at about three quarters of earth’s size.
Pluto is really irregular. First, we have to talk about its moon, Charon. Pluto’s orbit around the sun is altered by its moon, which is a characteristic particular to Pluto. Pluto’s orbit is also not on the same plane of orbit as the other planets; all the other planets orbit on pretty much the same vertical plane. Pluto goes below the other planets, and then above. Pluto also has a highly elliptical orbit, so there are times that it is actually closer to the sun than Neptune.
All of this brought into question whether Pluto was actually a planet or not. Until this time, anything orbiting the Sun had been considered a planet. With the discovery of the asteroid belt, the Kuiper belt, and dwarf planets like Pluto and Ceres, it brought in the question of how astronomers classify objects orbiting the Sun. Basically, scientist concluded that for something to be considered a planet, it had to meet the following criteria.
A planet must:
- Be nearly spherical
- Be Orbiting the Sun
- Have cleared its neighborhood
Pluto falls short in the third category. All the other planets have either captured the debris around them and they became moons (ie, the Gas Giants) or pulled the debris to the surface of the planet. Pluto, with its orbit in the Kuiper belt, did not have enough gravitational pull to clear out its neighborhood, and so it is not considered a planet anymore.
I think it would be cool to learn more about dwarf planets, because there are a LOT of dwarf planets in the Solar System. There are alll different types of planets, and, just because they’re small, we never learn about most of them in school.