Mankind doesn’t explore space solely in search of extraterrestrials, but we keep our eyes peeled. Still, scientists know that the chances of happening across a fellow traveler in the great beyond are minimal — and they wrap their heads around the infinitesimal odds using the Drake Equation, a seven-variable way of deriving the chance of active civilizations existing beyond Earth.
But equations get older and equations get wrong. The Drake Equation, which takes into account various factors like the rate of star formation, the fraction of stars that could form planetary systems, the number habitable planets in those systems, and so on, is now 55 years old. It doesn’t reflect the new information SETI researchers have collected since the 1960s.
A new study published in the journal Astrobiology seeks to integrate new exoplanet data as part of the Drake Equation while demonstrating the role of “pessimism” and “optimism” in estimating the odds of finding E.T. (you don’t find what you don’t look for).
“The question of whether advanced civilizations exist elsewhere in the universe has always been vexed with three large uncertainties in the Drake equation,” said University of Rochester astronomer and study coauthor Adam Frank in a statement. “We’ve known for a long time approximately how many stars exist. We didn’t know how many of those stars had planets that could potentially harbor life, how often life might evolve and lead to intelligent beings, and how long any civilizations might last before becoming extinct.”
Estimates derived by projects running under NASA’s Kepler satellite and a few other instruments suggest that out of the estimated 2 x 10^22 stars in the known universe, 20 percent have planets that reside in habitable zones that have temperatures, atmospheres, and other traits that could support life. So that takes care of one uncertainty.
That leaves two other questions:
- How often would life evolve?
- How long could those civilizations survive for?
That last one is a particularly tough question to answer, since we can only really work off the history of human civilization — and we haven’t died off yet.
That’s where the notion of pessimism and optimism arise. Frank and Sullivan write that their method requires only establishing how low the probability that humans are the only intelligent species to have ever evolved is. They call this the pessimism line. “If the actual probability is greater than the pessimism line,” said Frank, “then a technological species and civilization has likely happened before.”
Using current SETI and exoplanet data, Frank and Sullivan ended up calculating this number at one in 10 billion trillion. That’s incredibly small — which means the odds that another intelligent species has evolved are very, very good.
“Think of it this way,” said Frank. “Before our result you’d be considered a pessimist if you imagined the probability of evolving a civilization on a habitable planet were, say, one in a trillion. But even that guess, one chance in a trillion, implies that what has happened here on Earth with humanity has in fact happened about a 10 billion other times over cosmic history!”
The researchers emphasize that this revised interpretation of the Drake equation accounts for the entire 13.78 billion year history of the universe — while the original localizes the odds of finding E.T. to the present day.
That being said, optimism for finding alien life has never been higher. After all, three famous names just started a multi-million dollar project to look for aliens in Alpha Centauri — the closest star system to the Earth — and some prominent scientists think there’s a good chance we’ll find something special. There’s certainly never been a time to be an E.T. optimist.Photos via NASA/JPL-Caltech/ESA/CXC/STScI