I have a bit of a pet peeve. And its not a very common one. I absolutely hate when people say that they feel sorry for Pluto being demoted to dwarf planet status. Pluto does not have feelings. Pluto is practically a giant rock. Giant rocks do not have feelings. There are actually a lot of really important reasons why Pluto is not a planet and is a dwarf planet. Pluto is no longer deemed a planet because a lot of really smart people put a lot of work into proving that its not.So the purpose of this blog post is to talk a little bit about why Pluto is no longer a planet, what makes it different from the other planets and who was behind the change.
1. Pluto does not have a circular orbit. Everything orbits around two fixed points. In the case of all the other planets, these points are so close together that the orbit is circular. Pluto's orbit points are far away, meaning it orbits in an elliptical. This means that at points in it's orbit it's actually closer to the sun than Neptune. This completely messes up the order of the solar system. It also means that its distance from the sun is not constant, and changes greatly with time.
2. Pluto does not have a large enough gravitational field. There are 3 criteria that need to be met for on object to be considered a planet. They need to 1) Orbit the sun 2) Be spherical and 3) Have 'cleared the neighbourhood' of its orbit. Pluto checks 1 and 2 but 3 is where it falls down. This means that there will be no other objects of a comparable mass in the area of its orbit. Pluto doesn't meet this criteria as it's only 0.07 times the mass of other objects in its orbit. Earth for example is 17 million times the mass of other objects in its orbit. Source.
3. Pluto doesn't fit in. Pluto is a small rocky planet. Its similar to the rocky planets(Mercury, Venus, Earth and Mars) but is found after the gaseous planets(Jupiter, Saturn, Uranus and Neptune). Its a bit weird. In theory it should be made of gas but its not. Some scientists believe that Pluto did not originate in our solar system but was caught by the Sun's gravitational field and is now stuck here. Source.
When was Pluto denounced from its planet status?
After a 'planet' larger than Pluto was discovered beyond Pluto(Eris) a massive debate was started as to what defined a planet and whether both Pluto and Eris were planets or not. This debate led to the International Astronomical Union officially define a 'planet' in 2006. This definition states that a planet is a celestial body that is A) In orbit around the sun B) Has sufficient mass to assume hydrostatic equilibrium(ie it is spherical) and C) Has 'cleared the neighbourhood of its orbit'. As I've already gone into, Pluto does not do C and neither does Eris. So Pluto was denoted to dwarf planet status along with Eris.
So there you go. There's some more information about what makes a planet a planet and why Pluto cannot be considered as a planet. If you were one of those people that felt sorry for Pluto I hope this has helped you see the light -wink wink-. Trust me, Pluto is not sad, its with its own kind now.