Well, thought I might chime in on the whole “What is the definition of a planet?” debate. I know what I’m about to say here is going to be highly controversial, so please bear with me.
I’m a bit appalled about this uproar over defining the characteristics of a planet. It seems to me, that in an effort to save Pluto’s status as a planet, the International Astronomical Union has come up with the strangest definition:
A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.
Say what? Does that mean that every round rock, gas, or iceball out there that orbits the sun is now a planet? That could be just the case. Under the definition, recently discovered 2003 UB313, Ceres (formerly a very spherical astroid) and Charon (formerly Pluto’s own moon) now become planets. Had enough? Well, perhaps not the IAU, either. There’s more…rocks like Sedna, 2005_FY9, and even what I’d consider the least likely of the top candidates, 2003_EL61, could also be considered planets sometimes in the future.
Maybe I’m missing something here, but Pluto has always been a mystery to me, ever since I learned the names of the planets. Why is this icy rock with a very thin atmosphere considered a planet? Because it’s round and goes around the sun? Well, so does the moon (which also has a very thin atmosphere), but under the new definition, we’re still considering it a moon. So, I’m sure some of you might say, “Ok, but it’s spherical in nature, has gravity, and all that. It can’t be just an astroid or something else.” Fine, fair enough, you got me. So, what does all this tell me? Failed planet. Something that was going to potenitally form into a planet or a moon, but something happened where either a true atmosphere never formed, or it was blown away millions of years ago.
Would it not be simpler to define a planet this way? Well, at first glance, this might scrub Pluto off the list, along with the other rocks being considered, but not necessarily. What about two categories, so we’re not kidding anybody: Major Planet and Failed Planet. Group all the gaseous-type planets (like the big 8) in the first group. Then put all the rocks that have a spherical (none of this oblong stuff) that are rock or rock and partially ice into the second group. You could even further divide the two groups if you want. Here’s two of my proposed defintions. The first would be highly controversial (because of Pluto), and the second not so much:
1. A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (b) is in orbit around a star, and is neither a star nor a satellite of a planet, and (c) has an atmosphere thicker than [arbitrary number here].
2. A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a spherical or bulged spherical shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet. A planet shall be classifed into Major Planets or those that possess an atmosphere thicker than [number], and Failed Planets or those that do not possess an atmosphere or possess and atmosphere thinner than [number].
There, two definitions that might work. The first obviously gets rid of anything without an true atmosphere, and the second keeps Pluto and any astroid field and Kuiper Belt object that comes our way, but further clarifies how they’re labelled. Both kinds could also be Plutons, a planet that takes more than 200 Earth years to orbit the sun, and has a highly elliptical orbit.
I don’t know, it’s just always been hard for me to see Pluto as a planet in the first place (other than the fact the textbooks said so), and all this seems merely to be a compromise between those who’d like to see Pluto stay and those who’d like it gone. Is Pluto or these other considered objects a planet? Only you can decide. On a last note, I will boycott whoever supports the promotion of things like 2003_EL61 to a planet. That is a weird shaped rock, NOT a planet. I mean, look at its satellites. Those are not anywhere near spherical. At least Pluto/Charon, and 2003 UB313 have spherical moons.