Pluto couldn’t give a rat’s ass what we call it
For centuries we sort of toddled along without a real definition of a “planet”, but we finally got one at the recent meeting of the International Astronomer’s Union in Prague:
- it must be in orbit around the Sun
- it must be large enough that it takes on a nearly round shape
- it has cleared its orbit of other objects
Really a pretty good definition. Planets don’t orbit other planets; those are moons. Planets are big enough to pull into hydrostatic equilibrium, so they’ll be pretty much round – thus excluding every irregular chunk of rock from being called a planet. And a planet’s orbit will be cleared of other stuff, either by the planet pulling it in, or winging it off with its gravitational field. This alone excludes Pluto from being called a planet, since its orbit transects the plane of Neptune’s orbit. Only the obliquity of their respective orbits has kept Neptune from clearing Pluto…
But people are pissed off about it. Predictably, someone’s making money selling T-shirts and “Honk if Pluto is still a planet” bumper-stickers (I wish I’d thought of it!). All I can say is, with all the issues there are in the world, if your choice for the advertising space on the back of your car is whether Pluto is called a planet, you need to get out more. It’s just nomenclature.
The universe cares nothing for the Post-It notes we stick on every object. It doesn’t even make a practical difference to us, other than as a convenience. What matters is the physical reality of the object. Our labels do not make a millimeter’s difference in Pluto’s orbit, nor a gram’s difference to it’s mass, or its potential as a future tourist location (none).
On another level what matters (to us, not the universe) is sound, predictive scientific theory. Newton’s “laws” (really theories) of motion give us a predictive handle on the stuff wheeling around in our solar system. That could be really important someday, given the energy differences of our planetary orbit and that of a misdirected asteroid.
We could call Pluto a turnip if we wanted, but then we’d have to call turnips something else.
- Angry Astronomer, Musings On Pluto