Just as astronomers on Earth are incessantly scanning the universe for signs of life, alien civilizations might be doing the same – and their search could light upon us.
And because we can't rule out the possibility that such aliens could be malevolent, scientists suggest we should be thinking about whether to cloak our planet from their questing eyes, and they have a strategy.
By employing the principles behind our own search for promising planets, argue researchers in a paper published Wednesday, we could potentially shield our home from those who would wish us harm.
“So a lot of scientists, including Stephen Hawking, have said it actually might be dangerous for other civilizations out there to know that we exist,” co-author Alex Teachey of Columbia University told Scientific American.
“If you look at the history of humanity there have been cases where two civilizations have come in contact for the first time, one of these civilizations with a slightly more advanced technology, and that group has ended up subjugating the other group,” he said.
The concern is that this could happen to us, on a planetary scale, just as literature and Hollywood like to remind us in stories such as “War of the Worlds” and “Independence Day."
To avoid such a scenario, researchers looked at the way in which our own scientists locate planets outside of our solar system, known as exoplanets.
Most such planets have been discovered by staring at distant suns and looking for temporary dips in the amount of light coming our way, indicating the likely passing of a planet in front of said star. NASA’s Kepler telescope has identified more than a thousand planets in this way.
And so could aliens discover the existence of Earth.
“If you wanted to cloak a planet, if you wanted to make it look like the planet is not there at all, you’ve got to get rid of that dip,” explains Mr. Teachey in a Youtube video. “You’ve got to fill in the missing starlight.”
We could do this, explain the researchers in the Monthly Notices of the Royal Astronomical Society, by firing lasers into space, to compensate for the sunlight hidden by the passing Earth, tricking any observers into thinking nothing at all was happening.
A single 30-megawatt laser, pumping out its beam for a mere 10 hours once a year, would do the trick – requiring energy equivalent to that consumed annually by about 70 homes.
"It doesn't have to be one huge laser; it could be an array positioned around the Earth,” co-author David Kipping told the BBC. “Or you could put it in space as a satellite, and we've calculated that the International Space Station already collects exactly the amount of energy we would need."
And yet light is not the only way by which a planet can be found. There are other means, such as the gravitational pull it exerts on a star.
If an extraterrestrial race were to detect the presence of a planet in one of these other ways, and yet fail to see the drop in light as it passed by the sun, it could pique their curiosity. Better, perhaps, to let them see the planet, but to erase all indication that it might host conditions favorable to life.
Such a “bio-cloak” would require less energy than full concealment, and it would work by altering the apparent wavelength of light passing from the sun through our atmosphere – a characteristic that can be used to determine the makeup of a planet’s atmosphere.
"We can actually cancel those features out, such as oxygen," Dr. Kipping told Space.com. "The alien civilization is going to detect your planetary transit. They're going to detect your planetary radial velocity, but then when they 'smell' the atmosphere, it would not look like a tasty planet. It would just look like a dead world."