That’d be the Drake equation, which was developed over half a century ago to determine where life might lurk in the universe. Until now, the formulation that promises to pin down the number of intelligent civilizations in the cosmos has suffered one big limitation: There’s been no actual data to constrain most of its parameters.
All that’s been changing since numbers started coming in from the Kepler mission over the past few years. We now know that small, Earth-sized planets are scattered throughout the galaxy, and that many lie within the habitable zone of a Sun-like star.
Using the new Kepler data, astrobiologist Amri Wandel did some calculations to estimate the density of life-bearing worlds in our corner of the universe. The exciting news is there are probably millions to billions of biotic planets in the Milky Way.
But before we start packing our bags, a sobering reality check: Our corner of the cosmos may be dark. Wandel’s math shows the closest life-bearing world is ten to a hundred light years distance from Earth. And that’s just to find a world that harbors single-celled life. The closest intelligent aliens may be thousands of light years further.
The Arecibo Radio Telescope in Puerto Rico, which does a small amount of searching for extraterrestrial life. Image:
Wandel’s findings, which will be published next year in the International Journal of Astrobiology, were released in pre-print yesterday. He restricted his analysis to Earth-sized planets within their star’s habitable zone—that is, the zone that’s neither too hot nor too cold for Earth-like organisms to potentially evolve.
There are a lot of assumptions here: For one, that alien biology will have comparable physical requirements to our own. If biotic life isn’t limited to Earth-sized planets in the habitable zone—a restriction that precludes the icy moons Europa and Titan—the number of life-harboring worlds could actually be much higher.
It’s important to bear in mind that Wandel came to his estimates by updating just one Drake equation parameter: The number of potentially habitable worlds. His new calculations say nothing about the probability of finding life on a “potentially habitable” world. This remains the key missing factor for constraining the distance to our closest alien neighbors.
But in the near future, spectral observations of exoplanet atmospheres may allow us to start pinpointing life’s fingerprints from afar. If we could locate a few planets with promising biosignatures, we could at least make an educated guess about the probability of life evolving there—and start honing in on the actual distance to our nearest neighbors.
Whatever that distance ends up being, let’s hope we start refining cryosleep technology pretty soon. However you slice it, if Wandel’s numbers are even close, it’s going to be a long, dark haul to first contact.