It’s an idea seen again and again in movies: Extraterrestrial life seeks us out—and then tries to snuff us out. Thankfully, two astronomers from Columbia University have an idea that could help hide our planet from unwanted visitors until we’re ready to face them: a laser cloaking device.
Currently, there are plans to broadcast messages across the galaxy in hopes that intelligent life on a distant planet will pick up the call. But many prominent scientists have cautioned against such ideas, as extraterrestrials might seek out our life-bearing planet for all the wrong reasons—maybe to take our resources for themselves. Or, even if they are less hostile, there could be devastating unintended consequences along the lines of Europeans bringing new diseases to the Americas—which killed up to 90 percent of the native population.
And even without yelling to the universe that we’re here, our planet wouldn’t be hard to find if you know what you’re looking for. For example, when the Kepler spacecraft looks for planets that might host life, it looks to the stars: When a planet moves in front of the star it orbits, there is a noticeable dip in the light. Using this simple technique alone, more than 1,000 planets have been identified. From there, scientists check to see if the planets fall in the habitable zone of their stars, meaning they are warm enough for liquid water and thus a good place to check for life—like Earth.
Should extraterrestrials know to look for these clues, and should they have more advanced technology and bad intentions, we could be in deep, deep doo doo (to put it scientifically).
Hiding the Earth from Alien invaders
Luckily for us, Professor David Kipping and graduate student Alex Teachey of Columbia have a solution. If the Earth passing the Sun causes a visible dip in the light seen by other planets, then a laser could be turned on to compensate for the darkness—making it appear that the light is constant and that our planet is not there.
According to the authors in their paper in Monthly Notices of the Royal Astronomical Society, this would require that we emit a continuous 30 megawatt laser for ten hours when our planet blocks the sunlight heading towards a planet that could harbor life—apparently requiring the same amount of energy that the International Space Station collects in a year. A chromatic cloak, meanwhile—which is effective at all wavelengths—would require 250 megawatts.
“Alternatively, we could cloak only the atmospheric signatures associated with biological activity, such as oxygen, which is achievable with a peak laser power of just 160 kW [kilowatts] per transit [period of blocking the sun for a potential life-bearing planet]. To another civilization, this should make the Earth appear as if life never took hold on our world,” said Teachey in a statement.
Should we decide not to hide ourselves from aliens, these laser arrays could also be used for communication purposes. For example, modifying the way the light from the Sun dips during the transit could make it obviously artificial, shouting to the universe that we exist.
“There is an ongoing debate as to whether we should advertise ourselves or hide from advanced civilizations potentially living on planets elsewhere in the Galaxy,” said Kipping. “Our work offers humanity a choice, at least for transit events, and we should think about what we want to do.”
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Image credit: ESO / G. Hüdepohl
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