The four most likely cradles of life outside our solar system have been identified by scientists.
They contain so-called 'K' stars, whose planets may have just the right atmospheres to be harbouring aliens.
K stars are dimmer than our Sun, but brighter than the faintest stars, known as 'M' stars' or red dwarfs.
"I like to think that K stars are in a 'sweet spot' between Sun-like stars and M stars," said planetary scientist Dr Giada Arney, of NASA's Goddard Space Flight Centre.
This dramatically narrows down the number of worlds that maybe habitable, according to astronomers.
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