If scientists wanted aliens to find Earth, how would they arrange such an encounter? A new paper from MIT suggests that a giant laser, magnified by a giant telescope and aimed out into space, could do the trick.
In what author James Clark calls a "feasibility study," he proposes that a high-powered 1-to 2-megawatt laser be focused directly into space. While the Earth has been sending signals like radio waves into space for over a century, like those famously seen in the , it's possible that solar entities like the sun and exoplanets beyond the solar system have been interfering with signals, making it harder for potential aliens to touch base.
The goal of the laser-telescope rig is the creation of an energy beam, meant to stand out amid all of the excess noise in the solar system. Its target would be areas like Proxima Centauri, the closest star to Earth, and TRAPPIST-1, a star around 40 light-years away with seven exoplanets in orbit. Scientists say 3 of those exoplanets are potentially habitable.
"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, in a .
The planetary beacon is technically feasible, Clark says. He compares it to the Air Force's Airborne Laser program, , a prototype from the Reagan era which consisted of a 747 with a giant laser grafted onto the nose, meant to shoot down ballistic missiles. The YAL was never seriously considered for combat due to the project's tremendous cost, but it nonetheless demonstrated such tech was possible.
At 35 to 45 meters large, the telescope needed for the project would dwarf anything currently seen on the Earth. However, Clark points out, that could soon change: The is currently under construction by the European Space Organization, with its projected size of 39 meters in diameter. The project has a , or approximately $1.3 billion.
The real challenge with Clark's beacon is safety. MIT warns that the "beam would produce a flux density of about 800 watts of power per square meter, which is approaching that of the sun, which generates about 1,300 watts per square meter." Shooting off a laser with the power of the sun could cause massive corneal damage for anyone looking in its direction.
A giant, fantastically expensive laser with the ability to blind mass sections of the populace calls to mind James Bond-style villainy as much as it does Carl Sagan. Clark's plan for the telescope's safety is one straight out of Moonraker: put the laser on the Moon.
"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."
Scientists in the public and private sectors are advancing bold ideas, such as SpaceX's dream of future colonization. The giant laser Clark proposes might never come to pass, but if there's a way to find life on TRAPPIST-1, it certainly seems more viable than other current options.
"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."