Source: Quanta Magazine, Feb 2016
As future telescopes widen the survey of Earth-like worlds, it’s only a matter of time before a potential biosignature gas is detected in a faraway sky. It will look like the discovery of all time: evidence that we are not alone. But how will we know for sure?
At a 2013 symposium, Seager presented a revised version of the Drake equation, Frank Drake’s famous 1961 formula for gauging the odds that SETI would succeed. Whereas the Drake equation multiplied a string of mostly unknown factors to estimate the number of radio-broadcasting civilizations in the galaxy, Seager’s equation estimates the number of planets with detectable biosignature gases. With the modern capacity to look for any life regardless of whether it’s intellectually capable of beaming messages into space, the calculation of our chances of success no longer depends on uncertainties like the rareness of intelligence as an evolutionary outcome or the galactic popularity of radio technology.
Scheduled to speak last at the symposium, Seager set a light-hearted tone for the after party. “I put it all in our favor,” she said, positing that life has a 100 percent chance of arising on Earth-like planets, and that half of these biospheres will produce detectable biosignature gases — another uncertainty in her equation. Crunching these wildly optimistic numbers yielded the prediction that two signs of alien life would be found in the next decade.