I get forwarded stuff.  A forward I got today is for a week-old BoingBoing post about Greg Laughlin’s “exoplanet valuation” equation.  Laughlin is essentially trying to find a way to quantitatively compare the importance of each exoplanet discovery.  In this case, he’s trying to put it in terms of dollars and cents.  I don’t see where on his site he does the derivation for the equation, and I haven’t tried running any of the numbers yet (I’m still looking for a complete list of all 1200 new candidates), but the BoingBoing post says that so far:

At the time, the exoplanet Gliese 581 c was thought to be the most Earth-like world known beyond our solar system. The equation said it was worth a measly $160. Mars fared better, priced at $14,000. And Earth? Our planet’s value emerged as nearly 5 quadrillion dollars. That’s about 100 times Earth’s yearly GDP, and perhaps, Laughlin thought, not a bad ballpark estimate for the total economic value of our world and the technological civilization it supports.

The BoingBoing link breaks down the equation, but you can find Laughlin using it everywhere on his blog.