Are There Signals Coming from Deep Space?
By Seth Shostak, Senior Astronomer
The star KIC 8462852 may have an unpronounceable name, but just about everyone with an interest in aliens has been talking about it. As of today, they can elaborate their discourse with some new results.
The conversations started about three weeks ago, when a paper written by a small battalion of astronomers pointed out that this star - an imposing 1400 light-years from where you're sitting - occasionally dips its headlights. Every few weeks or months, it will blink, temporarily dimming to as little as 80 percent of its normal brightness. There is no indication (and little likelihood) that this bizarre behavior is caused by planets orbiting the star. Even Jupiter-size worlds would only block about one percent of the star's light.
So what is going on? The astronomers who discovered this strange behavior considered several possible explanations for the dimming. Their favorite was the presence of cometary debris in orbit around the star - an idea they liked, but didn't love.
However others - and especially the press - were jumping on another, sexier bandwagon. The occasional dimming of KIC 8462852 might be due to "megastructures" - giant astroengineering projects that aliens had undertaken in their solar system. These could be space habitats or phalanxes of orbiting solar energy collectors (so-called Dyson swarms, named after the physicist who popularized the idea). They might even be giant, opaque "cut outs" whose blockage of starlight would be a beacon to other worlds, indicating that KIC 8462852 was an oasis of intelligence in the galactic desert.
All nice ideas. Exciting ideas. But how would you prove any of them?
One straightforward approach would be to search for radio signals coming from KIC 8462852. Not naturally produced radio signals, but rather the kind that would indicate the presence of broadcast-savvy extraterrestrials.
Consequently, the SETI Institute immediately swung the antennas of its Allen Telescope Array in this star's direction, and for two weeks has been searching for transmissions that would tell us someone is home. The Array was tuned to frequencies from 1 to 10 gigaherz, which is way, way higher than those covered by your radio or TV. But this microwave part of the dial makes a lot of sense for interstellar broadcasting for reasons that you can look up, should you be technically obsessed.
The Institute team actually looked for two different types of signals: The first would be extremely narrow-band transmissions - which is to say, signals that would be at only one, very constricted spot on the dial. That's the kind of broadcast that would work best as a "hailing channel" because it concentrates all of the transmitter's energy into a tiny slice of the radio spectrum. In that sense, it's akin to a laser pointer, which can be intensely bright despite being low power - all the energy goes into a very specific color.
The second type of data analysis looked for much broader transmissions. The idea is that if KIC 8462852 is really home turf to some clever aliens who've moved from infrastructure to megastructure, then there might be fleets of transport rockets servicing this construction. A good way to propel these rockets would be with intense microwave radio beams - and they would produce a broad-band signal that the Allen Telescope Array might pick up.
So that's what we've looked for. But we didn't find either type of signal.
What does that mean? It might be that we missed out because our measures were not sensitive enough. Even if the putative inhabitants of KIC 8462852 were deliberately sending a narrow-band hailing signal, their transmitter would need to be a 100 thousand-trillion watt beast for us to hear it. This star system is very far away, remember.
The required power is obviously high if the signal is broadcast equally in all directions. But on the other hand, if the aliens had some inclination to target their broadcast in our direction, the required transmitter power would be enormously lower. And as a final point, it's worth noting that any society able to build a Dyson swarm has mega-oodles of energy available - more than enough to power the mother of all transmitters.
So yes, it's still possible that the odd behavior of this star might indeed be due to large-scale public works projects by aliens. But given the results of this first search, I think the smart money should go elsewhere. Hundreds of years of astronomical study has taught us something important: Every time we've turned our telescopes to the heavens and found mysterious phenomena, there were folks who immediately assumed we had uncovered evidence of cosmic companions. But each time, the truth turned out to be less exotic: we had discovered some previously unknown natural phenomenon (or, in the case of the Martian canals, no phenomenon at all).
So while it's nice to hope for megastructures, don't bet the family farm on it.