Editorial: Planet definition has clear’ flaw

Published 12:00 am Friday, August 25, 2006

Shame on Pluto. It forgot to &8220;clear the neighborhood around its orbit.&8221;

What in the solar system does that mean?

The International Astronomical Union’s new definition for planet is: &8220;a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape, and has cleared the neighborhood around its orbit.&8221;

Astronomers from around the world debated Thursday what is and what is not a planet. When the smoke cleared, the new definition meant that Pluto is no longer a planet.

Pluto doesn’t make the cut because of its oblong orbit overlaps Neptune’s orbit. This means it hasn’t cleared the neighborhood. Pluto is now classified as a dwarf planet.

But wait a moment. Couldn’t it be said that Neptune is the one not clearing its neighborhood? If Neptune’s orbit were cleared, Pluto wouldn’t be in it.

The definition is flawed. Neptune, which by the way has a few other objects that cross its orbit, doesn’t fit the IAU definition of a planet either.

We aren’t the only ones this occurred to when we first read the definition. We found out while researching this piece that, in fact, many astronomers refused to vote &045; some because of outright dissent but many because of the confusion we mention here. The debate over what is a planet was so heated and fractured at the convention in Prague, Czech Republic, that only about 300 out of the 2,500 astronomers from 75 countries cast ballots.

We understand the need to classify a definition and aren’t sentimental about keeping Pluto a planet, but even non-scientists can see the &8220;neighborhood&8221; clause needs to be worked out a little more.

Oh, and for anyone who got the answer to the number-of-planets question wrong on a test in school, it’s too bad your grade won’t change. However, you’ll have the satisfaction of knowing that not even the experts can answer that question.