Whether there's life beyond Earth is one of the most profound questions we can ask, and finding out is a cornerstone of many a space mission. But if there is anybody out there, they might also be wondering the same thing, so maybe making ourselves easier to find could be an important part of our first contact strategy. A new MIT study outlines a way to use existing or near-future tech to build a kind of laser lighthouse to signal to our cosmic neighbors.
The Search for Extraterrestrial Intelligence (SETI) program has been hunting for signs of life among the stars since the mid-80s, mostly by looking for radio signals and potentially laser flashes. Along with scouring nearby stars for radio chatter, anything anomalous immediately draws more attention – the unpredictable flickering of "Tabby's Star" was thought by some to be caused by some kind of alien megastructure, and SETI investigated the long-shot idea that 'Oumuamua, the first interstellar asteroid detected passing through the solar system, could have been an alien probe.
But rather than wait for E.T. to phone us, maybe our best bet is to make Earth one of these anomalies, to attract the attention of any alien astronomers that might be scanning our corner of the galaxy. According to a new feasibility study out of MIT, a high-powered laser used as a beacon could do just that. Any such device would need to be strong enough to outshine the Sun, and be detectable from a fairly long distance.
"This would be a challenging project but not an impossible one," says James Clark, author of the study. "The kinds of lasers and telescopes that are being built today can produce a detectable signal, so that an astronomer could take one look at our star and immediately see something unusual about its spectrum. I don't know if intelligent creatures around the Sun would be their first guess, but it would certainly attract further attention."
The study found two setups that produced the best results: a 2-megawatt laser pointed through a 30-m (98-ft) telescope, and a 1-megawatt laser directed through a 45-m (148-ft) telescope. Both of these setups could be detectable from as far as 20,000 light-years away, although at that distance the lag between sending and receiving is likely going to be a problem.
The team says the best targets are probably Proxima Centauri b, the closest known exoplanet at just four light-years away, or the seven-planet system around TRAPPIST-1, which is 40 light-years from Earth. Along with broadcasting our location, the laser could even be used to send messages in pulses, like Morse code.
"If we were to successfully close a handshake and start to communicate, we could flash a message, at a data rate of about a few hundred bits per second, which would get there in just a few years," says Clark.
Of course, there are a few hurdles to the concept. Neither the laser nor telescope technology is yet at the level needed for the beacon, but we are getting close. The US Air Force has been experimenting with Airborne Lasers for defense, which are theoretically powerful enough to be adapted into an interstellar laser lighthouse. And while there aren't yet any telescopes big enough to focus the beam, the Thirty-Meter Telescope has been proposed for Hawaii, and the European Extremely Large Telescope is currently under construction in Chile, with a diameter of 39 m (128 ft).
Other problems are more concerning. The study notes that a laser that powerful could damage the vision of anybody who looked directly at it, and might mess with the instruments of satellites that pass through the beam.
"If you wanted to build this thing on the far side of the Moon where no one's living or orbiting much, then that could be a safer place for it," says Clark. "In general, this was a feasibility study. Whether or not this is a good idea, that's a discussion for future work."
But there's another question to ask – should we be broadcasting our presence to the universe at all? After all, human history has taught us that first contact between two civilizations rarely goes well for both parties. Other scientists believe we should instead be using this kind of technology to actively cloak Earth from prying alien eyes.
The study was published in The Astrophysical Journal.
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