Astronomers say the findings were made after conducting a survey of red dwarf stars, which account for about four out of five stars in the Milky Way galaxy.
Buddhist thangka depiction of the ten-thousandfold worlds in space
They calculate that around 40 per cent of red dwarfs have a rocky planet not much bigger than Earth orbiting the "habitable zone," in which liquid surface water can exist.
Scientists say that where there is water, there also could be life although they add that being in the habitable zone is no guarantee that life has evolved on a planet.
Dr. Xavier Bonfils, from Grenoble University in France, who led the international team, said: ''Because red dwarfs are so common -- there are about 160 billion of them in the Milky Way -- this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.'' More