Gliese 581g, Mono Lake and the Drake Equation

In September 2010, scientists discovered a new extrasolor planet, Gliese 581g, that is to date the planet the most similar to earth that we found. It is in the Gliese 581 star system, only 20 Light-years from us, and orbits its sun at the right distance to have liquid water, so it is not too warm and not too cold. It has a gravity similar to earth (between 1.1 and 1.7 G) strong enough to maintain a thick atmosphere.

These characteristics make it the planet the most succeptible to have life on it. So much in fact that it's discoverer, Professor Steven S. Vogt from the University of California, Santa Cruz said "my own personal feeling is that the chances of life on this planet are 100%. I have almost no doubt about it."

Now, the most surprising thing about this discovery is the fact that we found such a planet so fast and so close to us. The search for extrasolar planets started only a few years ago, and the current telescope technology only allows us to investigate solar systems that are very close to us, say just a few hundred light-years from us. That is a very small fraction of the total stars in our galaxy, which is 100,000 light-years wide.

Detecting a small planet like earth is very hard, most of the 519 extra solar planets discovered so far are giant planets like Jupiter. Which means there might be even more planets like Gliese 581g in our neighborhood.

These facts led scientists to believe that the fraction of stars with potentially habitable planets is on the order of a few tens of percent, and if the Sun's stellar neighborhood is a typical sample of the galaxy, then the discovery of Gliese 581g in the habitable zone of its star points to the potential of billions, maybe a hundred billion Earth-like planets in our Milky Way galaxy alone.


In an unrelated scientific discovery, NASA researchers found a new type of microorganism thriving in the highly toxic environment of Mono Lake, California. The bacteria, named GFAJ-1 use Arsenic instead of Phosphorous as a building block for its DNA, and is the only known life-form to do so.

That discovery tells us that life is able to develop in environments much different than our own, and so it raises the probablity of finding it on other planets.

And that leads us to the Drake Equation.

The Drake Equation is a formula used to estimate the number of detectable extraterrestrial civilizations in the Milky Way galaxy.

                   N = N* x  fp x  ne x  fℓ x  fi x  fc x  L

Where:

          N* = The number of stars in the galaxy
          fp = the fraction of those stars that have planets
         ne = the average number of planets that can potentially support life per star that has planets
         fℓ = the fraction of the above that actually go on to develop life at some point
        fi = the fraction of the above that actually go on to develop intelligent life
        fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
        L = the fraction of those civilizations that are still alive today

activemind.com has a fun calculator if you want to try the Drake Equation yourself.

Until recently, N was estimated to be from 1 to 10. Only a handful of civilizations in our galaxy. But the discoveries of Gliese 581g and Mono Lake seem to indicate that ne and  fℓ are higher that we previously thought.   fp x ne could be from 20% to 50%, and fℓ could be close to 100%. This would mean that the number of advanced extraterestrial civilizations out there could be in the thousands or even millions. That would make the Star Trek universe look like a deserted island.

So if there are thousands of advanced extraterestrial civilizations, how come we never heard from them, right? Well, that will be the subject of my next blog entry, the Fermi Paradox.

Links: Gliese 581g, the Drake Equation, Extrasolar planets