## How much is a planet worth?

Over at Boing Boing, Lee Billings has an interview with Greg Laughlin, an astrophysicist who recently came up with an equation for estimating the value of planets, a sort of Drake equation for cosmic economics.

This equation’s initial purpose, he wrote, was to put meaningful prices on the terrestrial exoplanets that Kepler was bound to discover. But he soon found it could be used equally well to place any planet-even our own-in a context that was simultaneously cosmic and commercial. In essence, you feed Laughlin’s equation some key parameters — a planet’s mass, its estimated temperature, and the age, type, and apparent brightness of its star — and out pops a number that should, Laughlin says, equate to cold, hard cash.

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.

## When will the first Earth-like planet be discovered?

Using the properties of previously discovered exoplanets (that is, planets outside of our solar system) and their dates of discovery, Sam Arbesman and Greg Laughlin predict that the discovery of the first Earth-like exoplanet will likely occur in early May 2011.

Of course, it’s a bit more complicated than that, but here’s an overview of what we did. Using the properties of previously discovered exoplanets, we developed a simple metric of habitability for each planet that uses its mass and temperature to rate it on a scale of 0 to 1, where 1 is Earth-like, and 0 is so very not Earth-like. Plotting these values over time and taking the upper envelope yields a nice march towards habitability.

The authors don’t address this directly in their paper, but I wondered what the Moore’s Law for planetary discovery might be — e.g. every X years (or months?), the habitability of the most habitable planet discovered doubles. So I emailed Sam Arbesman and he said that his quick back of the envelope calculation would be “half a month or so”…which is an astounding pace.

## More extrasolar planetary news

Oliver Morton fills us in on the current happenings in the search for planets outside of our solar system. A friend of his clued him in on a technique that could be used to not only discover planets but to determine if those planets show signs of supporting Earth-like life.

When they are passing in front of their stars, their atmospheres are backlit in a way that can make spectroscopic analysis of the different chemicals in their atmospheres comparatively easy: the wavelengths of light absorbed by the various chemicals will show up, in a tiny way, in the spectrum of the starlight. And this is what makes it possible to imagine looking at them for signs of life.

What scientists would look for are planets with unstable atmospheres, which James Lovelock said was an indication of life.

After the extragalactic planet post this morning, Sam Arbesman sent me a link to systemic, a blog dedicated to the search for extrasolar planets written by Greg Laughlin, one of the scientists involved in the effort. Here are two relevant posts. In Forward, Laughlin says we’re very close to finding a nearby Earth-like planet:

Detailed Monte-Carlo simulations indicate that there’s a 98% probability that TESS will locate a potentially habitable transiting terrestrial planet orbiting a red dwarf lying closer than 50 parsecs. When this planet is found, JWST (which will launch near the end of TESS’s two year mission) can take its spectrum and obtain resolved measurements of molecular absorption in the atmosphere.

In Too cheap to meter, Laughlin presents a formula for the land value of such a discovery that depends on how far away the planet is, the age of the star it orbits, and the star’s visual magnitude.

Applying the formula to an exact Earth-analog orbiting Alpha Cen B, the value is boosted to 6.4 billion dollars, which seems to be the right order of magnitude. And applying the formula to Earth (using the Sun’s apparent visual magnitude) one arrives at a figure close to 5 quadrillion dollars, which is roughly the economic value of Earth (~100x the Earth’s current yearly GDP)…