Monday, August 14, 2006

Who decides what "a planet" is?

The International Astronomical Union is meeting in Prague to try to decide just what officially constitutes a planet. Or to put it in real terms, to decide whether or not Pluto is one.

I'm reminded of the many lengthy debates amongst academics and students over just which is "England's third oldest university", nearly all of which seem to come down to a proposal for the key point (doors opening, charters being issues, formal conferrment of university status, formal conferrment of degree awarding powers) which conveniently gives the answer as the institution the proposer personally wants to be the oldest. Or the film The Englishman Who Went Up a Hill But Came Down a Mountain which shows how rigid scientific definitions can clash with popular usage and understanding. Or even the long running debate amongst some Doctor Who fans over what certain stories should be called (I'm serious - there really are people who argue this ad infinitum), where the term "official" is thrown around as though to mean "That Is The End Of The Matter" and never has any effect on the raging arguments.

Which leads me to wonder whether any decision by this meeting that ultimately says "Pluto is not a planet - that's official" will actually be accepted by the population at large. But if the definition that is eventually adopted is made with public perceptions in mind, one has to wonder whether or not the exercise is necessary at all. The public does not always respond well to scientists rewriting the vocabulary - look how long it has taken for the Brontosaurus to disappear from popular perception - and when they are starting from the point where the term is not really widely accepted as being something determined by scientists in the first place, they are especially unlikely to accept a change that changes the popular conception.

Maybe the best solution that would command popular support would be the following:

One possible resolution to the debate is for new categories of planet to be introduced. Mercury, Venus, the Earth and Mars would be "rocky planets". The gas-giants Jupiter, Saturn, Uranus and Neptune would be a second category.

Pluto, 2003 UB313, and any other objects passing the "roundness test", would be reclassified as a third type of planet - perhaps "icy dwarfs".
We shall see what the meeting's outcome is...

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