Earth can be concealed when it moves in front of the Sun, thanks to laser techniques Istock

In the (unlikely) event that an alien civilisation decided to invade other planets, firing lasers into space could safely conceal the Earth, scientists claim. This scheme could also be reversed, to communicate with non-hostile extraterrestrial beings.

David M Kipping and Alex Teachey, from the University of Columbia, believe that if other forms of intelligent life exist in space, they would know how to cloak their presence or deliberately broadcast it through controlled laser emission. Similarly, they say that humans may use this knowledge either to protect themselves, or on the contrary, to search the universe for traces of other civilisations.

Hiding with a monochromatic laser

Planets are usually discovered because they move in front of other stars, blocking light in the process. In the case of the Earth, other stars see it moving in front of the Sun for 10 hours each year. According to the two scientists, shining a 30 megawatt monochromatic laser towards another star, during these 10 hours, would efficiently hide the Earth from the view of this star.

However, for a very advanced alien population, with the appropriate tools, seeing through this protective shield would not be complicated. Another, more sophisticated strategy to hide would be concealing only the atmospheric signatures, linked to traces of life and biological activity on the planet. This means artificially hiding the presence of oxygen, for example. To achieve this, scientists could use "a peak laser power of 160 kilowatts per transit in front of the sun", according to Kipping and Teachey.

Communicating with other worlds

Not all extraterrestrial beings should be feared, the scientists add. For those who believe aliens would be as friendly as ET, it would be interesting to communicate. Using the same lasers to artificially change the shape made by the Earth when it moves in front of the sun, humans could let aliens know of their presence, and start a dialogue with them

Kipping says aliens may have come up with the same idea. Therefore, scientists should look for artificial transit alteration around other stars. Going through transit data collected over the years, in particular thanks to Nasa satellite Kepler, the scientist hopes to find traces of such non-standard transit emissions, which could indicate the presence of a friendly alien planet.