Welcome Moons, Asteroids and TV Princesses!


The nomenclatural melee now unfolding among the astronomers presently convening in Prague has yielded some interesting results.

We've gotten much closer to an organized definition of 'planet', but many folks are unhappy with the repercussions to which this definition leads.

Okay, no one's terribly surprised by the recommendation that 2003 UB313, the icy body both larger than Pluto and orbiting out past it in the distant reaches of our solar system, be considered a planet. It had to go that way, didn't it?

All I must ask is: Why, oh why, can't we just stick with calling it Xena? How cool to boast of our first-ever planet named after a fictitious television heroine (as if somehow classical mythology and contemporary pop-culture don't serve parallel roles in the collective consciousness). Scientists' planetary naming conventions, be damned!

Then, it's on to Pluto, who, also not surprisingly, had his planetary status saved—probably due more to cultural affection than scientific logic.

Or is it the other way around?

Thanks to our societal fervor for keeping Pluto a planet, we're likely to inherit at least a dozen more planets (or even all the way up to a total of 53, just for the time being)… all because the proposed definition—the body must have a large enough mass so that gravity forms it into a sphere, and it must orbit around a star—bowed to the pro-Pluto-as-planet pressures.

(My favorite comment comes from a NY Times opinion piece, which closes on this overdramatic note: 'All this just to keep Pluto as a planet. Whatever merit the new definition may have scientifically, it is an abomination culturally.')

But I certainly didn't expect Pluto's largest moon, Charon, to receive an invitation to join the planet club—because it doesn't simply orbit around Pluto, but orbits with Pluto around a center of mass outside both of them (which I suppose ultimately points us back to the Sun?).

This new conceptual creation of a Pluto/Charon 'binary planet' system has only minute consequences for our tracking of their zodiacal position. However, in terms of astrological interpretation, the effects could be dramatic. Where we previously had a single point of interest, we now confront a pair of twins. This only confirms my instinct that resolving the 'what is a planet?' controversy would have a serious interpretative impact on our understanding of the Pluto archetype ('there's more out there than we thought'). Beyond that, it's too early to say.

And Ceres, too? Yes, Ceres, the largest body in the asteroid belt between Mars and Jupiter, also qualifies for planetary classification under the current proposal. Interestingly, a glance back through history shows that initially, upon its discovery in 1801, Ceres was considered a planet… and remained as such for the next half-century or so, until the new 'asteroid' label was created. (For all the historical details, check this out.)

How often do we go back 200 years in scientific history, only to conclude that our more recent ideas have proven insufficient to handle the expanding data set… and we were originally correct in our so-called 'outdated' notions?

These truly are interesting times in which to live.

Far Out: Nine Planets? (San Francisco Chronicle)
What makes a planet? (Michael Brown, Cal Tech)
The Continuing Discovery of Pluto (Planet Waves)
Planets, Get Your Planets Here! (Philip Sedgwick)