Hawking and others are concerned that extraterrestrials might wish to take advantage of the Earth's resources, and that their visit, rather than being benign, could be as devastating as when Europeans first travelled to the Americas.
The two authors of the new study 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 the authors, emitting a continuous 30 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 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."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. To another civilisation, this should make the Earth appear as if life never took hold on our world", said Alex. more
