Hunt for alien life homes in on Earth 2.0, a planet of similar size to our own

The hunt for potential life in outer space has taken a step forward - an international team of researchers has discovered the first earth-sized planet within the "habitable zone" of another star.

The exoplanet dubbed Kepler-186f was first spotted by scientists using Nasa's Kepler telescope, according to research published on Thursday in the US journal Science.

The exoplanet, located some 500 light years from earth, orbits in what is seen as the sweet spot around its star known as the "Goldilocks zone": not too close and not too far, so it could have liquid water, considered a crucial component to possibly hosting life. "The discovery of Kepler-186f is a significant step toward finding worlds like our planet earth," said Paul Hertz, who is Nasa's Astrophysics Division director at the agency's headquarters.

The planet was "the right size and is at the right distance to have properties that are similar to our home planet", said Elisa Quintana of the SETI Institute at Nasa's Ames Research Centre in California, the lead author of the paper published in Science.

"We can now say that other potentially habitable worlds, similar in size to earth, can exist. It's no longer in the realm of science fiction," she said, speaking at a press conference.

Kepler-186f is about 1.1-times the size of earth, which researchers say is key to predicting the composition of the surface and its atmosphere.

When planets are 1.5 times the size of earth or larger, many of them seem to attract a thick hydrogen and helium layer that makes them start to resemble gas giants such as Jupiter or Saturn.