When you look up in the night sky, you see … well, mostly nothing anymore. On a clear night, if you’re lucky enough to live in an area without much light pollution: the moon, a planet (probably Venus), and the brightest of stars. But there’s more out there — billions of stars and maybe some extraterrestrials.
The Search for Extra-Terrestrial Intelligence (SETI) Institute, a nonprofit research group near Silicon Valley, is still trying to guess the chance that other beings exist and that we could make contact. Scientist Frank Drake developed an equation to find an estimate. The equation uses seven variables: the rate of star formation, the fraction of stars with planets, the number of planets suitable for life, the fraction of those planets where life appeared, the number that became intelligent, and how long that civilization lasted. When Drake first plotted the numbers 60 years ago, his low estimate was 1,000 stars with civilizations able to make contact. But as research churns out more data, that number only goes up.
Here’s Drake’s Equation, where N equals the number of communicable civilizations:
Of the seven variables, the rate of star formation remains relatively fixed. Drake’s original estimate of one star formed per year was low, but not drastically so. Each new star gives the possibility of extra terrestrials, but so does each star already in the Milky Way.
According to NASA, there are already between 100 and 400 billions stars in our galaxy alone. Each star could have planets very much like ours, which concerns the second and third variables in Drake’s equation. NASA’s Kepler Mission returned the most recent data on this front to us over the last few years. It has discovered more than 4,000 possible planets, including 1,000 that meet NASA’s minimum criteria for being planet-like. When looking at the stars, finding planets turned out to be relatively easy for Kepler. What this seems to suggest is that more often than not, a star has satellite planets. But can they support life?
Thanks to Kepler’s ability to identify planets, it has also provided the data on planets in what is called the Goldilocks Zone. Since our planet isn’t too hot like Venus or too cold like Uranus and has large planets in Saturn and Jupiter protecting it from asteroids, it is in a position “just right” to support life. Kepler has discovered nearly a dozen such planets, and one planet in particular — Kepler-452b — is only slightly larger than Earth. This discovery, however, does not factor into the possibility of life existing on planets unlike ours. Just as life exists in almost any climate on Earth, the possibility of life existing in different climates elsewhere in the universe is high. Tardigrades, known also as Water Bears, are micro-organisms that can survive temperatures above boiling water and near absolute zero (nearly -450º Fahrenheit). These creatures have even been known to survive trips outside Earth’s atmosphere.
Most important to Drake’s equation are the final four propositions, which are the most difficult to pin down because Earth is the only planet we know of that supports life. That’s why Drake put his original estimate at 100 percent certitude that a planet in the Goldilocks Zone would spring intelligent life. And he might not be wrong. Building upon his work, scientists Caleb Scharf and Leroy Cronin developed an equation for the probability of abiogenesis, or the chance that life can spring up in a given circumstance. Their equation, like Drake’s, is optimistic in nature, and says that where the building blocks are available, life will find a way. That life will be subject to the same evolution principle that life on Earth is, producing a tree of life unique to that planet’s habitat.
What it doesn’t say is whether that planet will ever produce intelligent and civilized life curious about its place in the universe. Here we are forced to look at our own planet and the species that have arisen from our own tree of life. Of all the species to have ever existed, only humans have communicated outside our solar system.
This brings us to the last piece of the equation — the length of time a civilization releases detectable signals. Our species, for instance, took hundreds of millions of years of evolution to move from primordial gook to upright apes, yet thousands to get us from farming to space travel. We humans have released detectable signals for barely a century, but that’s enough time to reach dozens of stars with dozens of possible planets. So why haven’t we heard back from anyone yet?
Maybe we have. Or maybe we won’t ever. Even with 100 billion stars in our galaxy, there are 2 trillion galaxies in the known universe. If there were only one civilization capable of communication in every 100 trillion planets, there would still be 20 billion planets with communicable civilizations. Most of them would simply be too far for us to contact. But that does not mean they aren’t there. The importance of Drake’s equation and the Scharf/Cronin equation is that they ask questions, not provide answers.
Are we alone in the galaxy? Drake’s Equation seems to tell us that it is highly improbable that we are not, but without proof, it can’t say for certain. So we keep looking, curious as ever. Until then, it is a humbling thought to look to the night sky and wonder what civilizations might be looking to their night sky, maybe moonless, a different planet or three, and wondering the exact same thing.
Chris Gilson is not dead. He writes about music for Pancakes & Whiskey, and his work has appeared in the New York Times, Paste, Splitsider, and elsewhere.