Phil Plait author of Bad Astronomy writes, it’s silly to try to scientifically define a class of objects that are really only defined culturally, these definitions are still unsatisfying to me. A planet-sized object between stars is not a planet? How round is round? How do you define its "neighborhood"?
Has Jupiter 'cleared its neighborhood, given the existance of the Trojans? What about Earth's co-orbital? What is the scientific definition of 'cleared'?
Meanwhile S&T blogger Bob Naeye writes " But there are several gaping holes in the IAU’s definition, including one that is so immediately obvious that it boggles my mind that intelligent people could actually vote for it. The definition is anti-Copernican in the sense that it defines planets as objects orbiting the Sun. In other words, only solar-system objects can be considered true planets. Excuse me, but even under the most liberal definition for “planet†that one could seriously propose, we know of about 50 planets in our solar system right now. We already know of more than 200 planets outside the solar system." I also suspect we’ll find systems that through some kind of freak dynamical evolution, have left planet-mass objects in zones of rubble. Heck, even Earth shares its region of space with tens of thousands of asteroids of various sizes. One could counter that these bodies are in unstable orbits. But both Jupiter and Neptune harbor vast populations of Trojan asteroids that will remain in their orbits for billions of years. And even many trans-Neptunian bodies, such as Pluto, cross Neptune’s orbit. Under the IAU’s vague new rules, we could rule out Earth, Jupiter, and Neptune, and perhaps other planets as well. And by not setting a specific size or mass requirement, the IAU has left itself wide open for criticism as soon as astronomers find Mercury-, Mars-, and perhaps even Earth-sized bodies in the distant solar system. Such discoveries are only a matter of time, given the limited nature of surveys to date.
A unnecessarily precipitous definition, lacking in sufficient scientific rigor, sadly typical of political hack work done by other international committees.
Sic Transit Gloria IAU.
Web Astronomers' Blog Reaction to IAU Planet Definition
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- Web Astronomers' Blog Reaction to IAU Planet Definition