A powerful laser is just the thing to announce our presence as a technological species in this arm of the galaxy. Engineers would line up to work on that project. But is it a good idea to let any mysterious galactic neighbours know we’re here?

A pair of scientists at the Massachusetts Institute of Technology (MIT) have published a paper outlining how a powerful laser could be built to communicate our presence to any other technological civilizations in our galactic vicinity. James R. Clark, one of the authors of the paper, and a graduate student in MIT’s Department of Aeronautics and Astronautics, says such a laser could be built with technology that’s within our reach. Clark emphasizes that the paper is a ‘feasibility study’ rather than an actionable plan.

“I wanted to see if I could take the kinds of telescopes and lasers that we’re building today, and make a detectable beacon out of them.” James Clark, grad student, MIT Dept. of Aeronautics and Astronautics.

The laser would have to be powerful, between 1 to 2 megawatts. That’s pretty powerful, but not anywhere near the world’s most powerful. Japan fired a 2 petawatt (2 quadrillion watt) laser in 2015, but only for 1 trillionth of a second. And other researchers around the world are working on more powerful lasers than that. Clark points to the US Air Force’s Airborne Laser project, which was designed to shoot down ballistic missiles. It was in the same power range needed for Clark’s system, and was tested successfully, so the idea is not far-fetched.

The US Air Force’s Airborne Laser anti-missile system inside the turret on the Boeing 747. Image Credit: Air Force photo by Bobby Jones – http://news.com.com/2300-1008_3-6192767-4.html?tag=ne.gall.pg, Public Domain

But this feasibility study isn’t only about the laser. It involves telescopes, too. The powerful laser would be fired through a telescope some 30 to 45 meters in diameter. Kind of like frying bugs on the sidewalk with a magnifying glass when you were a kid. (Do kids still do that?)

There are telescopes under construction in that range. The Thirty Meter Telescope (TMT) and the European Extremely Large Telescope (EELT), which has a 39.3 meter primary mirror. So the telescope technology is not far-fetched.

The laser has to be this powerful, because to any distant alien astronomer, the light of our Sun would drown out a lower-powered laser. The laser would be tuned to the infrared range and it would stand out from the Sun’s natural variation of infrared emissions. The signal would be visible to any alien observers within about 20,000 light years if they were looking closely enough.

Alien astronomers in our own neighbourhood would see the beacon if they were conducting only a cursory survey. The well-known TRAPPIST-1 star is only about 40 light years away, and it is home to 7 exoplanets, some of them in the habitable zone. Our nearest stellar neighbour, Proxima Centauri, is only about 4 light years way, and it has a planet that is potentially in the habitable zone.

“If we were to successfully close a handshake and start to communicate, we could flash a message…” – James Clark, grad student, MIT Dept. of Aeronautics and Astronautics.

The beacon could be used as a communications system by sending pulses similar to the 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, a graduate student in MIT’s Department of Aeronautics and Astronautics and author of the study.

Clark analyzed what combinations of laser powers and telescope sizes would be needed to produce a beacon that would stand out from the blinding glare of the Sun. He concluded that a 2-megawatt laser pointed through a 30-meter telescope could create a strong enough signal to reach Proxima Centauri B. A laser with half that power—only 1 megawatt—if directed through a 45 meter telescope, would be visible to alien astronomers in the TRAPPIST-1 system.

But it’s a bit too early to be thinking of specific targets for this beacon, and the whole idea may seem questionable at first glance. It’s more of a thought experiment than a plan. The idea was to study the combinations of lasers and telescopes necessary and to see how they would perform. “I wanted to see if I could take the kinds of telescopes and lasers that we’re building today, and make a detectable beacon out of them,” Clark says.

If a system like this was ever built, it would be placed atop a mountain just like our best observatories. This would limit atmospheric interference. Makes sense, but there is a dangerous element to the whole idea, too.

A 2 megawatt laser is nothing to fool around with. A typical laser in eye surgery is only 40 watts. The powerful laser in this interstellar beacon system would be very destructive, if someone were to look at it. Since it would be in the infrared, we wouldn’t be able to see it, but it could still damage eyeballs. It poses a more realistic danger to any spacecraft or satellites that passed directly overhead. The beam has the potential to scramble any Earth-directed camera systems.

But both those problems could probably be planned for and dealt with. By building it on the Moon, maybe?

“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,” Clark says. “In general, this was a feasibility study. Whether or not this is a good idea, that’s a discussion for future work.”

Once Clark established the types of technology needed to construct this powerful laser beacon, he looked at it from the other side. What technology would be needed to see it? How advanced would any alien observers need to be to detect it? How likely is it that they would even look in our direction?

Clark concluded that a telescope with only a 1 meter primary telescope would detect the signal, but, and this is a big but, it would have to be pointed directly at the source. He says that’s pretty unlikely. “It is vanishingly unlikely that a telescope survey would actually observe an extraterrestrial laser, unless we restrict our survey to the very nearest stars,” Clark says.

According to Clark, this whole idea ties in to our other science objectives around exoplanets. He hopes the study will encourage the development of infrared imaging techniques, not only to spot any laser beacons that might be produced by alien astronomers, but also to identify gases in a distant planet’s atmosphere that might be indications of life. We’re already constructing technology to look for bio-markers in the atmospheres of exoplanets, so as we get better at that, maybe we’ll get lucky and see someone else’s infrared beacon.

“With current survey methods and instruments, it is unlikely that we would actually be lucky enough to image a beacon flash, assuming that extraterrestrials exist and are making them.” – James Clark, grad student, MIT Dept. of Aeronautics and Astronautics.

“With current survey methods and instruments, it is unlikely that we would actually be lucky enough to image a beacon flash, assuming that extraterrestrials exist and are making them,” Clark says. “However, as the infrared spectra of exoplanets are studied for traces of gases that indicate the viability of life, and as full-sky surveys attain greater coverage and become more rapid, we can be more certain that, if E.T. is phoning, we will detect it.”

But hold on a second. Even if we can build this beacon, or one even more powerful, should we? Anyone who’s read any science fiction would likely be cautious.

If we build this big light, is there a risk of attracting some sort of hideous moth species? Will we have to build another, more powerful “bug-zapper” laser to deal with them? Where will this laser building end? Will humanity get swept up in some sort of galactic arms race?

Stephen Hawking warned us to be wary of eagerly advertising our presence. Assuming life on another world was subject to evolution by natural selection, we can also assume that any dominant species would have a pronounced aggressive trait, just like humans do. Otherwise, how would they have advanced to the technological stage?

“Whether or not this is a good idea, that’s a discussion for future work.” – James Clark, grad student, MIT Dept. of Aeronautics and Astronautics.

Let the discussion begin!

Sources

• MIT Press Release: “E.T., we’re home“
• Research Paper: “Optical Detection of Lasers with Near-term Technology at Interstellar Distances“
• Wikipedia Page: Boeing YAL-1″