The planet, called Proxima b, orbits Proxima Centauri - the closet star to our solar system - and is about 1.3 times bigger than Earth.
Because Proxima Centauri radiates much less heat than the Sun, the planet occupies the "habitable zone" where temperatures are mild enough to allow liquid surface water.
Proxima b is only four light years away from Earth and Professor Abraham Loeb, from Harvard University, has raised the possibility of humans one day colonising the planet.
"The lifetime of Proxima is several trillion years, almost a thousand times longer than the remaining lifetime of the Sun," he said.
"Hence, a habitable rocky planet around Proxima would be the most natural location to where our civilisation could aspire to move after the Sun will die, five billions years from now."
Proxima b is only 7.5 million kilometres from its parent star - some 5% of the distance between the Earth and the Sun - and it takes just 11.2 days to complete one orbit.
Russian billionaire Yuri Milner is planning to send a fleet of miniature interstellar probes fitted with cameras there on a 20-year mission to search for alien life.
The £75m Breakthrough Starshot project - which is backed by Professor Stephen Hawking - aims to accelerate the tiny one gram "nanocraft" to 20% of the speed of light using "sails" pushed by a powerful laser.
Prof Loeb, who chairs the Breakthrough Starshot advisory board, said the aim was to launch the "nanocraft" towards Proxima Centauri within the next two to three decades.
"It will take 20 years to reach Proxima and four more years for the photos to get back to Earth," he added.
