E.T., We’re Home

Estimated reading time: 5 minutes

Clark envisions that, like these massive observatories, a laser beacon should be built atop a mountain, to minimize the amount of atmosphere the laser would have to penetrate before beaming out into space.

He acknowledges that a megawatt laser would come with some safety issues. Such a 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. While the beam wouldn’t be visible, it could still damage people’s vision if they were to look directly at it. The beam could also potentially scramble any cameras aboard spacecraft that happen to pass through it.

“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.”

Taking E.T.’s Call 

Having established that a planetary beacon is technically feasible, Clark then flipped the problem and looked at whether today’s imaging techniques would be able to detect such an infrared beacon if it were produced by astronomers elsewhere in the galaxy. He found that, while a telescope 1 meter or larger would be capable of spotting such a beacon, it would have to point in the signal’s exact direction to see it.

“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.

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.

“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.”

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