Thursday, August 24, 2006

A Little Distraction


I am sure everyone in the noosphere is following the controversy about Pluto. You're not? Where have you been hiding? Seems the International Astronomical Union (IAU) has been debating whether or not Pluto 'deserves' to be classified as a planet or not.

Pluto's classification change doesn't bother me. After all we have known for some time that Pluto might not be a planet-at least not in the same sense as Earth or Jupiter. The whole controversy reminds me of the sorts of controversies that happen in biological taxonomy between splitters and lumpers.

Splitters are those taxonomists who make fine distinctions between species and group them into many small catagories. Lumpers take the same sets of species and lump them into a smaller number of more inclusive categories. Indeed the IAU recently considered a scheme that lumped the eight 'classical' planets plus Pluto as planets along with Ceres and a small number of Pluto type bodies, expanding the ranks of objects called planets. Seems like the astronomical splitters won though.

According to the IAU determination a planet is defined in the following way:

"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 neighborhood around its orbit."

Looks to me like Pluto does not meet criterion c since sometimes it's closer to the Sun than Neptune, so it joins Ceres and some other bodies as what the IAU calls dwarf planets. If it will make Pluto fans feel better, the IAU calls Pluto the "...Prototype of a new category of trans-neptunium objects. "

Pluto in the meantime will keep on it's lonely funky orbit around the Sun.

Other links:

Good background on Pluto and images of Pluto and its moon:
http://www.nineplanets.org/pluto.html

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