Poor Pluto can't get no respect. Remember that conference they were going to have where all the astronomy bigwigs were planning to decide what makes a planet a planet? The International Astronomical Union (IAU) General Assembly were scheduled to gather this week and cast their ballots for which astronomical bodies in our sun's orbit get invited to be on the official solar system "Who's Who" list. Well, today the vote happened, and Pluto is not going to get an invite. According to Spaceweather.com, Pluto, along with two others, Ceres and 2003 UB313 (I think that might be the one they call Xena) are being classified as "dwarf planets."
Now, from what I read before, a dwarf planet Pluto might have still been classed as a planet, except for the fact it doesn't meet one of the three planetary requirements that the IAU determined would be the standard by which planethood is to be judged. The three criteria are as follows (from Spaceweather.com):
(1) It must have enough mass and gravity to gather itself into a ball.
(2) It must orbit the sun.
(3) It must reign supreme in its own orbit, having "cleared the neighborhood" of other competing bodies.
So, Pluto fails to achieve full planet stature because he isn't a bully. He hasn't kicked out all the other kids in the neighborhood (or made them his satellite toadies.) There are loads of other large objects floating around out there in the Kuiper Belt where Pluto hangs out, thousands in fact. You could say that Pluto lives out in the suburbs with lots of other middle class objects, none of them important enough to live on their own private estates like Jupiter, Saturn and the other solar system hotshots with private gates and chauffeurs (and very high property taxes.)
I don't think this is as big a demotion as it sounds. Sure there are now officially only eight planets in our solar system, but there is also a new category just for Pluto, Ceres and 2003 UB313. Dwarf planets may not sound very important, but they're important enough to call a whole conference over, and have a vote and everything, and create a special category just for them; so Pluto's got to feel good about that. He's important enough to cause a fuss, and what more could any of us want, really? Actually, he may be better off this way. By Kuiper Belt standards, Pluto's still a big fish in a small pond, which might be preferable to being given full planet status and then having to try to keep up with the big boys. No, I think Pluto and the other dwarf planets can be very satisfied with today's decision. They get to feel superior to the mere asteroids in the neighborhood, without having to face a lot of planetary peer pressure--and their taxes will probably stay low, so who could complain about that?
|