Using transit detection—looking for the dip in light when a planet passes in front of the star it orbits—is a technique we Earthlings have been utilizing in our search for other worlds. Thanks to projects such as NASA’s Kepler mission, this method has yielded the discovery of more than 1,000 planets—several of which are comparable in size to Earth.
Stephen Hawking and other prominent scientists, however, have long cautioned that advanced alien civilizations could be utilizing the same technique—which means they could very well locate our planet, drifting along cozily in the Sun’s habitable zone, just waiting to be colonized.
“We’ve been broadcasting our presence into space since World War II with TV, FM radio, and radar. These signals could be picked up by advanced aliens,” Seth Shostak, director of the Center for SETI Research, told CNN.
Now, two astronomers at Columbia University, David Kipping and Alex Teachey, have stepped up, suggesting that lasers could conceal Earth from extraterrestrial searches—avoiding the kind of hostile alien invasion a la Independence Day.
According to Kipping and Teachey, emitting a 30 MW laser at visible light for 10 hours, once a year (at the precise moment Earth crosses in front of the Sun), would eliminate the dip in light that characterizes Earth’s transit signal.
(This 30 MW energy expenditure is comparable to the energy collected by the International Space Station in a year.)
“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 per transit,” Teachey said in the Royal Astronomical Society press release. “To another civilization, this should make the Earth appear as if life never took hold on our world.”
Taking these solutions one step further, scientists could build a bigger, badder chromatic cloak, effective at all wavelengths and requiring a large array of tunable lasers that would eat up 250 MW of power. That solution, however, could backfire; the lasers could modify the way light from the Sun drops during a transit—an obvious sign that the transit is artificial.
“Imagine if humans found indirect evidence for a planet, but for some reason, couldn’t see the…thing at all,” Teachey told Gizmodo. “We’d probably start paying very close attention.”
Of course, if Earth is capable of cloaking its presence, then so do alien worlds. Teachey and Kipping encourage that the Search of Extraterrestrial Intelligence (SETI), in its constant quest to find out if we’re truly alone in the universe, broaden its search to include artificial transits.