Shining a laser beam toward a planet whose inhabitants might see the Earth pass in front of the sun could replace the light the Earth blocks out.
New York: Humans could use controlled laser emission to conceal the Earth from searches by advanced extraterrestrial civilisations who might wish to exploit our planet's bountiful resources.
Several prominent scientists, including Stephen Hawking, have cautioned against humanity broadcasting our presence to intelligent life on other planets.
Other civilisations might try to find Earth-like planets using the same techniques we do, including looking for the dip in light when a planet moves directly in front of the star it orbits, researchers from Columbia University in New York said.
These events - transits - are the main way that the Kepler mission and similar projects search for planets around other stars.
So far Kepler alone has confirmed more than 1,000 planets using this technique, with tens of these worlds similar in size to the Earth, researchers said.
Alien scientists may use this approach to locate our planet, which will be clearly in the 'habitable zone' of the Sun, where the temperature is right for liquid water, and so be a promising place for life, researchers suggest.
Hawking and others are concerned that extraterrestrials might wish to take advantage of the Earth's resources, and that their visit, rather than being friendly, could be as devastating as when Europeans first travelled to the Americas.
Researchers suggest that transits could be masked by controlled laser emission, with the beam directed at the star where the aliens might live. When the transit takes place, the laser would be switched on to compensate for the dip in light.
According to researchers, emitting a continuous 30 Mega Watt (MW) laser for about 10 hours, once a year, would be enough to eliminate the transit signal, at least in visible light. The energy needed is comparable to that collected by the International Space Station (ISS) in a year.
A chromatic cloak, effective at all wavelengths, is more challenging, and would need a large array of tuneable lasers with a total power of 250 MW, researchers said.
"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 kilowatt (KW) per transit," said Alex Teachey from Columbia University.
"To another civilisation, this should make the Earth appear as if life never took hold on our world," said Teachey.
As well as cloaking our presence, the lasers could also be used to modify the way the light from the Sun drops during a transit to make it obviously artificial, and thus broadcast our existence, researchers said.
Researchers suggest that we could transmit information along the laser beams at the same time, providing a means of communication.
The findings were published in the journal Monthly Notices of the Royal Astronomical Society.
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