Friday, August 25, 2006

So is the Earth a planet?

Astronomers in Prague have voted a definition of a "planet" that excludes Pluto. And now the backlash begins and we will see whether the world at large will actually accept the International Astronomical Union as having the power to do this. Already some scientists have declared they will not be changing their textbooks.

One point that's come up is that the definition of "planet" that the IAU voted on may exclude the Earth as well!

One of the three criteria for planethood states that a planet must have "cleared the neighbourhood around its orbit". The largest objects in the Solar System will either aggregate material in their path or fling it out of the way with a gravitational swipe.

Pluto was disqualified because its highly elliptical orbit overlaps with that of Neptune.

But Dr Stern pointed out that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path.
So do we have yet another mess?

And if even the head of NASA's mission to Pluto is not going to accept the new definition, why should anyone else feel bound by the IAU's decision?

1 comment:

ajd said...

It's all about politics. Of the 10,000 strong astronomy community, only 400 voted. Of the 2000 who attended the meeting, only 400 voted.

And you know why? They held the vote at the very end of the 10 day meeting, which meant most scientists had already left. There was some politics in there...

As a scientist, however, I am perfectly happy that Pluto is not a planet anymore. If we defined Pluto as a planet, our solar system would have in the region of 100 of them. Making an exception to the rule is always messy (i.e leaving as-is), so the only option was to demote Pluto. I just wish it was done in a cleaner way...

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