Washington: Scientists may have hit upon a new idea of tracking aliens, after years of seeking them through radio signals and ultra short laser pulses.
Avi Loeb, working with the Harvard-Smithsonian Centre for Astrophysics, proposes that searching for extraterrestrials` city lights could be one way of finding them.
"Looking for alien cities would be a long shot, but wouldn`t require extra resources. And if we succeed, it would change our perception of our place in the universe," said Loeb, the journal Astrobiology reports.
As with other methods, astrophysicists rely on the assumption that aliens would use earth-like technologies, according to a Harvard-Smithsonian statement.
This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.
How easy would it be to spot a city on a distant planet? Clearly, this light will have to be distinguished from the glare from the parent star.
As the planet orbits, it goes through phases similar to those of the Moon. When it`s in a dark phase, more artificial light from the night side would be visible from earth than reflected light from the day side.
So the total flux from a planet with city lighting will vary in a way that is measurably different from a planet that has no artificial lights.
Spotting this tiny signal would require future generations of telescopes. However, the technique could be tested closer to home, using objects at the edge of our solar system.
Loeb and Edwin Turner from Princeton University calculate that today`s best telescopes ought to be able to see the light generated by a Tokyo-sized megalopolis at the distance of the Kuiper Belt - the region occupied by Pluto, Eris and thousands of smaller icy bodies.
So if there are any cities out there, we ought to be able to see them now. By looking, astronomers can hone the technique and be ready to apply it when the first earth-sized worlds are found around distant stars in our galaxy.