The Kepler Space Telescope was launched in 2009. Since then, it has aimed its giant mirror at one small spot in the sky. Its instruments are examining the light from about 145,000 main sequence stars, a tiny fraction of the 400 billion stars that make up our Milky Way galaxy. Kepler’s sensors are capable of detecting the small decreases in the amount of light pouring from the stars whenever a planet happens to swing in front of one of them.
In the three years Kepler has been operating, the telescope has detected evidence of more than 2000 potential planets, with about 700 of those now confirmed. It takes three transits of a planet across the face of its sun for scientists to be confident it’s really there and not just a stray glitch in the data. However, the accuracy of Kepler is such that they expect over 80 percent of the planet candidates to be confirmed as real.
Recently, the first roughly Earth-sized planet in what would be the habitable zone of its star has been confirmed. Known as Kepler 22b, it is 600 light years away. If it has an atmosphere, then its surface temperature will average about 72 degrees Fahrenheit. Rather comfortable.
At the moment, no details about the planet are known, beyond its existence and size. More observations will be necessary before its mass can be determined and any details about its composition and atmosphere can be known. Kepler will doubtless find hundreds more of similar planets before its mission comes to an end.
If something like Kepler were 600 light years away and looking at our solar system, it would just now, possibly, be confirming the existence of our home world, assuming it was edge on to that instrument. Only a fraction of stars with worlds around them will be angled toward us in such a way that Kepler will be able to see them.
The good news about the discovery of Earth-like worlds in the habitable zones of other stars is that it will begin to transform the search for extraterrestrial intelligence—called SETI for short. For the past fifty years of intermittent looking for radio waves from the sky, the search has been largely random. For the first time, thanks to Kepler, SETI scientists now have a place to point their radio telescopes.
The largest telescope dedicated to SETI is the Allen Telescope Array. It is a privately financed operation run jointly by the SETI Institute and the Radio Astronomy Laboratory at UC Berkeley. It was funded largely by Paul Allen, one of the cofounders of Microsoft. Back in April of 2011 the SETI Institute ran short of money had had to shut down temporarily. By August, however, they managed to raise enough funds so that they were able to resume operations on December 5, 2011. Kepler 22b will be one of the first places they look now, along with another fifty or so potentially habitable worlds that have been discovered by Kepler.
Although the odds of finding someone out there have risen thanks to Kepler, we still have no way of knowing whether intelligence is common among the stars. Even if there are other civilizations out there, how many might there be?
And then there’s another little problem. If someone on Kepler 22b were listening to Earth just now, they would be seeing our world as it existed not today, but how it was six hundred years ago. They are, after all, six hundred light years from us, and it takes light and radio waves six hundred years to travel the distance. So if they listen with radio telescopes, they won’t hear anything at all: Earth didn’t start broadcasting radio signals until about a hundred years ago. The first television broadcast was only in 1932. We’ve only been noisy for a very brief time. Six hundred years ago Columbus hadn’t even discovered the New World.
So even if someone is out there, what are the odds that they happen to be broadcasting TV and radio signals? How long does a civilization continue to do that? Does it get replaced with something else? What if we go all to cable and fiber optics? For most of human history, we’ve been silent. There could be a bunch of thriving civilizations out there that have yet to get past their equivalent of the nineteenth century; there could be a million Roman Empire clones, powerful and rich, that we can never know about because they haven’t invented radios yet.
And worse, current SETI really isn’t designed to overhear even the normal radio and television chatter of an extraterrestrial civilization. It’s instead hoping to hear a signal being sent out specifically to be heard by other civilizations around other stars: a purposely sent signal announcing, “here we are.”
But that’s something even we haven’t done; we’re listening, but we aren’t sending out much in the way of purposeful signals like that. What if everyone is just listening like us? It really isn’t much of a surprise that SETI has so far found nothing. A bigger surprise would have been if we’d already heard anything at all yet.
Is it a hopeless quest? A waste of money? No. The odds may not be very good, but the universe is huge. And the potential payoff is what makes SETI worthwhile.