The laser technique could also be used to broadcast the Earth's presence in the universe

Laser cloaking device could hide Earth from aliens

Powerful lasers could be used by astronomers to prevent aliens from discovering Earth according to two astronomers at Columbia University in New York.

Several prominent scientists, including Stephen Hawking, have cautioned in the past against humanity broadcasting its presence to intelligent life on other planets.

It is thought that other civilisations could find Earth-like planets using the same techniques that we do, searching for the dip in light when a planet moves directly in front of the star it orbits.

This process constitutes the main way that the Kepler mission and similar projects search for planets around other stars; it has confirmed more than 1,000 planets using this technique, with many of these worlds similar in size to the Earth.

Astronomers David Kipping and Alex Teachey have speculated that aliens could use the same 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.

Their solution involves emitting a continuous 30 MW laser for about 10 hours once a year that would eliminate the light blip that could be used to find Earth.

The laser would have to be pointed at the star where the aliens might live at the exact time of the year that the earth disrupts the light passage from our sun.

The energy needed is comparable to that collected by the International Space Station in a year.

However, 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 Teachey.

Although Hawking is concerned that extra-terrestrials might wish to take advantage of the Earth’s resources rather than engage in peaceful contact, the technology could be used to promote the Earth’s presence in the universe should we wish to advertise ourselves to other civilisations.

The lasers can 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.

The astronomers even state that we could transmit information along the laser beams at the same time, thus providing a means of communication.

"There is an ongoing debate as to whether we should advertise ourselves or hide from advanced civilisations 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."

Yesterday, NASA announced it had selected a team to build a new instrument that will detect planets outside our solar system, known as exoplanets, by measuring the minuscule ‘wobbling’ of stars. 

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