I’m somewhat chagrined than I didn’t pick up on this myself, but I’m amazed that no-one else did: in all the furore over whether Pluto was a planet or merely a borrowed geological term, no-one stopped to think of the nominative consequences for our own fair sphere. Anjana Ahuja reports in The Times on the views of the editor of Sky and Telescope magazine, Richard Fienberg:
According to the IAU’s General Assembly, which met in Prague this year, a celestial body can be called a planet only if a) it is in orbit around the Sun; b) it is round (in other words, is massive enough to be shaped into a ball by its own gravity); and c) it has cleared the neighbourhood around its own orbit.
It is c) that has proved awkward. The IAU meant that planets should orbit the Sun in isolation, rather than whizzing around with other bodies, such as asteroids. This clause did for Pluto, because it resides in the Kuiper Belt, a girdle of icy bodies that lies beyond Neptune.
But, Fienberg points out: “Our own world is threatened by . . . a host of other near-Earth asteroids whose paths around the Sun intersect ours. By strict application of the IAU’s new rules, this means Earth is no longer a planet either. Ditto for Mars, Jupiter and Neptune, all of which are accompanied in orbit by little asteroids. Ridiculous!”
Special plead your way out of that one, IAU. I confidently predict the appearance of a modified sub-clause which defines 'cleared' as 'not having any other bodies above a certain percentage of the size of the candidate planet' – if there isn’t one already. It’s not so much I’m convinced by this argument, but it just shows how easy it is to tie yourself in knots when you start preferring semantics to science. And this closing line is priceless:
Fienberg has come up with a fresh mnemonic, forged in pure bitterness, to describe the new Pluto-less planetary octet: Many Very Egotistical Malcontents Just Screwed Up Nomenclature.