No email voting was allowed for the decision – it was made by a show of hands – and that meant that less than 5% of the nearly 9000 IAU members actually voted.The exclusivity objection:
The definition stipulates that to be a planet, an object must have cleared the neighbourhood around its orbit. But Earth's orbital neighbourhood is filled with thousands of near-Earth asteroids, Stern says.The wrong motives objection:
And Mars, Jupiter and Neptune have so-called "Trojan" asteroids sharing their orbits. "This is a half-baked criterion for planethood," he says.
[Stern] says the new definition was pushed by people who are unhappy with having large numbers of planets – an earlier proposal would have potentially allowed hundreds of new planets into the fold.The it's-unenforceable objection:
"It's just people that say things like, 'School kids will have to memorise too many names.' Do we limit the number of stars because children have to think of too many names?
In any case, he says, astronomers are not obligated to use the new definition, since the IAU does not have the power to enforce it. "I don't think it's going to be very widely followed," he says.And, lastly, the it-doesn't-even-matter objection:
As best I can tell, 'dwarf' is an adjective and 'planet' is a noun," [David Weintraub] told New Scientist. "I think the IAU thinks they defined Pluto to not be a planet. But they in fact have defined Pluto to be a planet – a particular kind of planet."