And Then There Were Eight.

This day will go down in infamy as 'the day Pluto died.' That's right, the brilliant people at the International Astronomical Union have voted on a new definition of the word 'planet.' Guess they figured it was about time we had one, since people have only been looking at the skies since the fucking dawn of time. Basically, a classical planet is now defined as "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit." According to this definition, there are eight classical planets - Mercury through Neptune.

Pluto apparently doesn't cut it anymore. It - along with those other things out there like its partner Charon, the recently discovered ice ball nicknamed Xena, and the object nicknamed Sedna discovered in 2003 - is now classified as a "plutonian object," or a "trans-Neptunian object." This was all announced today, so I'm still a little unclear on what to call Pluto & company. But the point is that Pluto & company don't fit the definition of a classical planet - they have not cleared the neighborhood around their orbits. Pluto's orbit is tilted so that it crosses Neptune's, and Pluto and Charon are actually a double system: they revolve around each other. Earth's moon revolves around a center of gravity that is inside the planet Earth, making it a real satellite. Charon and Pluto revolve around a point in space, so they are a double system. I think Sedna and Xena are also not free and clear - they're part of the Kuiper Belt, a big cloud of millions of small bodies that float way out past Neptune's orbit. Pluto and Charon are actually on the inner part of the Belt too.

So... bye bye Pluto. We hardly knew ye. And when the New Horizons spacecraft that was launched just a few months ago reaches you in 2015, we probably won't give a damn if you are a dwarf planet or a trans-Neptunian object or something else entirely. We just wanna know more.

The captain started feeling around on all the trees!
"We're on Pluto!"
"How can you tell?"
"From the bark, you dummies!"