The Allen Telescope Array in California, which is used for SETI. Image: SETI Institute
The Kepler Space Telescope has found several potential habitable exoplanets that exist in the same solar system—so, could there be intelligent life living on them that communicate back and forth with each other? Some experts in the Search for Extraterrestrial Intelligence think it's possible, and that intercepting their communications might be our best bet for proving the existence of aliens.
The idea is called "eavesdropping SETI," and its foundation relies on the principle that, if intelligent life is common in solar systems with Earth-like planets in the habitable zone, then it's not out of the realm of possibility that there may be two distinct alien civilizations living in solar systems with multiple planets in a star's habitable zone.
Alternatively, maybe an alien civilization had the wherewithal to colonize another planet in its solar system, kind of like how some humans would like to do with Mars. Either way, if there is intelligent life on multiple planets in a given solar system, then it only follows that they'd probably want to communicate with each other.
And that's where SETI scientists come in. Data from Kepler has already been used to identify several possible solar systems, and we already have the technology to track the planets' locations with respect to Earth. When two planets line up with Earth, we can point all of our radio telescopes at them, with hopes of "overhearing" communication between the two.
"Someday, we will colonize Mars—if so, we will want to communicate with people and machines on Mars or other planets in our solar system," Dan Werthimer, a SETI researcher at the University of California-Berkeley, said about the project. "Similarly, perhaps other civilizations are sending radio or laser signals between planets within their own solar system. Using recent data from NASA’s Kepler mission, we can predict exactly when two extrasolar planets will be lined up with Earth, and we can schedule our observations to attempt to detect another civilization’s inter-planetary communication."
Here's what it looks like:
Image: UC Berkeley
Werthimer says that it's highly likely that any sort of intelligent extraterrestrial life is sending these sorts of radio signals, because we have been doing the same thing—inadvertently—for roughly 100 years now, with our radio and television signals.
"Nearby stars have seen The Simpsons," he said. "We're broadcasting, we're either leaking signals or sending deliberate signals." And, maybe, other civilizations are, too.
We've already got some candidates. Take, for instance, the Gliese 667 star system, a meager 22 light years away from Earth. That one has three potentially habitable planets, so it'd make sense for Werthimer to target that one first. Beyond that, there's an estimated, oh, 500 million potentially habitable planets in the Milky Way alone.
Seth Shostak, a senior astronomer with the SETI Institute who told Congress last week that we'd probably find evidence of intelligent life within 20 years or so, said that eavesdropping SETI is one of three "horses" in the race to discover aliens.
The big money, he said, is to look in our own solar system for microbes. The second possibility is to "build very large instruments that can sniff the makeups of other atmospheres," looking for methane or carbon or other evidence of life. The third, and most active area of SETI, is to "eavesdrop on signals."
"I think that makes sense—even we, with just 100 years of development or so, have the technology to send information across light years," he said. "It's unproven whether there's any life, but I think that situation will change within our lifetimes…the fact we haven't found anything yet means nothing—it's like looking for megafauna in Africa and giving up after looking at one city block. The universe is [full of potential] habitats for life."
And, if we do find something, decoding it might not actually be so difficult.