It’s hard to mourn the death of something that was never alive. But in this case, people do. From the years 1930 to 2006, the former planet Pluto lived in harmony with the other eight in our solar system. But in 2006, astronomer Dr. Mike Brown and his team demoted Pluto from the status of planet to that of the lowly dwarf planet along with the briefly-known tenth planet, planet X (also known as Eris). Dr. Brown says that Pluto and Eris, while still a part of our solar system, are just too different to be called planets along with the other eight. Talk about your ultimate case of “one of these things is not like the others”.
For someone like me who knows very little about the final frontier, and even less about science, Dr. Brown was able to put into simple terms why Pluto just didn’t fit in with its peers. Dr. Brown says that, for one thing, Pluto isn’t nearly as big as the others (planet envy perhaps?). It is, in fact, only approximately 1400 miles in diameter while our own moon is about 2100 miles in diameter. Pluto’s orbit around the sun isn’t the same as those of the eight planets it used to be grouped with, either. While the other eight have circular orbits around the sun, Pluto has an elliptical orbit that tilts about twenty degrees and overlaps slightly with Neptune’s. To be perfectly blunt, Dr. Brown says that the main reason why Pluto is now only a dwarf planet is because it just can’t be classified well with the other eight. It is, however, classified very well with Eris and the other dwarf planets, of which there are estimated to be sixty out there past Neptune. Pluto is just, as Dr. Brown put it, “a funny oddball at the end of the solar system.”
Dr. Brown surprised me with his sense of humor during his talk here. I suppose I had the false notion, when I walked in, that he would be all business and very stern, with no regrets over his decision to punt Pluto out of the Big Eight. But, like he says, Pluto is just so comparatively small it is hard to call it a planet. Dr. Brown also cleared up some common astronomy-related misconceptions. He says that some people think that “anything round is a planet” or that a planet is a planet when it is big enough to be controlled by gravity. Not so, he says. He also said that some people think that if a large body has a moon (or two or three) then it is classified as a planet. This is also untrue. Mercury and Venus don’t have moons, he points out, and they’re still planets… for now.