Home > Science & Technology > Pluto couldn’t give a rat’s ass what we call it

Pluto couldn’t give a rat’s ass what we call it

August 27, 2006

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.

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Categories: Science & Technology
  1. Ed
    August 27, 2006 at 20:47 | #1

    But what was the whole point of “redefining” what a planet is (or isn’t).  According the some in the IAU the thought of large numbers of “planets” within the Oort Cloud would be overwhelming.  So what!  Do we need to redefine the definition of the word “star” to exclude white/red/brown dwarfs because the number of solar objects is overwhelming?  Who cares if there are hundreds of “planets” beyond Pluto? The first nine planets can be named and “revered” somewhat, let’s add to the number and be excited about any new discovery.

    You’re right, it’s just nomenclature and Pluto won’t disappear because we have re-listed it as a “dwarf planet”.  But the reason behind it is a combination of ego and stupidity, and adds to the confusion of a already blase public.  Why not spend the time debating what can be done about light pollution, or funding cuts for research and science that go to a set of manned missions that will be abandoned when the public gets bored?

  2. August 27, 2006 at 21:03 | #2

    I like your alternatives.  As I walk across campus, I see new light fixtures that spill light up into the night sky – and our campus has a very active planetarium and an astronomy club!  And funding for manned spaceflight (without any actual mission) just makes my blood boil.

    It’s good to have a definition, but I wouldn’t have demoted Pluto because people get all freaked out over it.  I’d just have given it an asterisk instead.

  3. August 30, 2006 at 11:01 | #3

    Don’t think I will be losing a whole lot of sleep over it.

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