Sure, astronomers might not call it a planet anymore, but every schoolchild knows how badass Pluto really is. It’s got a giant moon, Charon, and two smaller ones, Hydra and Nix.
In addition to being colder than ice with an average temperature of 44 Kelvin (that’s colder than liquid nitrogen), I’m here to bring you the news that despite the fact that it’s so cold and so far from the Sun, Pluto has been melting!
Since its discovery by Clyde Tombaugh in 1930, astronomers have been fascinated with Pluto, making very careful observations of it, trying to learn more about this bizarre, icy sphere so far-flung from the Sun. Recently, a team of scientists led by Bradley Schaefer took a look at 75 years of accumulated data on Pluto, and found something incredible.
You see, much like our Moon, Pluto has one hemisphere darker than the other. For our Moon, the side that faces us is darker than the side that faces away:
Astronomers call the difference between the brightness (or reflectivity) of a planet albedo. Pluto’s northern hemisphere has a darker albedo than its southern hemisphere, and that explains why Pluto appeared to get darker from 1954 to the 1980s.
And their best explanation is that since Pluto has a very thin atmosphere (made of Nitrogen, just like ours), when one of the poles is continuously exposed to the Sun, the light and heat causes the frost on the poles to sublimate (or boil off directly from the solid phase). Because frost has a different reflectivity than the rest of the reddish Plutonian crust (which is mostly solid methane), that causes the observed change in albedo. And hence, Pluto is melting!
Now, where will the Plutonians go to live? And will we have to wait until the New Horizons mission reaches Pluto in 2015 to find out?