Tuesday, November 30, 2010

Rocky and giant and dwarf ... oh my!

I refer, of course, to the current official categorization scheme for planets -- and what isn't a planet.

(That's not the moon. Earth is only there for scale. Read on.) 

In our solar system the rocky -- or as some prefer to call them, terrestrial -- planets are Earth and its close neighbors: Mercury, Venus, and Mars. The gas-giant planets, of course, are Jupiter, Saturn, Uranus, and Neptune. The dwarf planets -- not really planets --  include Ceres (in the main asteroid belt) and a cast of, probably, hundreds in the Kuiper belt.

It is into that last/new/contentious category that the International Astronomical Union reassigned -- many say, demoted -- Pluto in 2006.

Much has been written about whether Pluto is, or is not, properly a planet. Most of it, IMO, has been silly. I was delighted to encounter a cogent, clear-thinking piece on the topic on Space.com, entitled Fighting for Pluto's Planet Title: Q & A With Planetary Scientist Alan Stern.

The whole interview is well worth reading, but most compelling to me is the observation that rule three of the IAU 3-part definition of a planet -- the rationale by which Pluto was reclassified -- is time- and location-dependent. An apropos quote: "Earth — the one object I think everyone agrees is a planet — is too small to clear Pluto's zone in the age of the solar system, and would not be a planet by the IAU's way of thinking." 

So: let's hear it for Pluto.

And with so many planets, dwarf or otherwise, likely waiting to be discovered in the Kuiper belt, wouldn't Goofy also be a great [dwarf] planet name?  Why shouldn't well-known cartoon characters supplant ever-more-obscure mythological names as the inspiration for celestial bodies?

To all you planetary astronomers out there: here's a list of Warner Brothers toon characters to get those nomination juices flowing ... 


Lawrence St. John McGee said...

I still like "Persephone" as a name, personally. And wasn't Goofy a Disney character? Haha.

Edward M. Lerner said...

Goofy *is* a Disney name -- like (in one manner of speaking) Pluto.

Persephone, being (in myth) Pluto's consort would make a lot of sense for a body near Pluto. IMO, Persephone would have been a better choice than Charon for Pluto's large moon.

Curiously, the IAU never asks my opinion :-)

- Ed

Erik said...

I wonder if the fleet would still be classifiable as planets under this criteria. Technically they orbit around a common barycenter and would have to clear the objects in their orbital zone (each other) in order to satisfy the definition. I think the idea is enough to drive a puppeteer mad.
On the other hand you could argue that the fleet are a 5-ary planet, and that n-ary planets do not have to clear each other from their orbits. In that case the fleet could be classified as a 5-ary planet.
New Terra is going to be much tougher to classify.

Edward M. Lerner said...

Once the Fleet of Worlds cut loose from its star, it (singly and in its several parts) failed the first test for a planet: orbiting a sun.