Earth 'twins' discovered
Five potential Earth twins with conditions capable of supporting life have been discovered orbiting Sun-like stars.
Other planet candidates identified by the American space agency Nasa's new Kepler space telescope could have life-bearing moons.
Astronomers also confirmed the existence of a six-planet solar system centred on a Sun-like star named Kepler-11.
The wealth of observation data has amazed scientists and greatly boosted the chances of life evolving beyond the Earth.
Nasa administrator and former astronaut Charles Boden said: "In one generation we have gone from extraterrestrial planets being a mainstay of science fiction to the present, where Kepler has helped turn science fiction into today's reality."
The latest batch of Kepler data identified what are believed to be several hundred new planets orbiting distant stars.
Of these, 54 sit within the habitable or "Goldilocks zone" - the region just the right distance from the parent star to allow conditions that are not too hot and not too cold for liquid surface water and life to exist.
Five of the candidate planets, yet to be verified by follow-up observations, are near-Earth sized.
They are likely to be small, rocky planets with atmospheres and possibly oceans and rivers of flowing water. Any or all of them could be places where primitive or advanced life exists.
The remaining 49 habitable-zone candidates range from "super-Earth" worlds up to twice the size of Earth to planets bigger than Jupiter.
But even giant planets with crushing gravity and pressure could have life-sustaining moons if they lie within the "Goldilocks zone".
Kepler's principal investigator, Dr William Borucki, from Nasa's Ames Research Centre in Moffett Field, California, said: "The fact that we've found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting Sun-like stars in our galaxy.
"We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone, some of which could have moons with liquid water."
Among the stars with planetary candidates, 170 show evidence of possessing multi-world solar systems.
Kepler-11, around 2,000 light years from Earth, has six confirmed planets all with orbits smaller than Venus's and is the most tightly packed planetary system yet discovered.
Findings from Kepler-11 appear in the latest issue of the journal Nature.
All the star's planets are larger than Earth, with the biggest being comparable to Uranus and Neptune.
The innermost planet, Kepler-11b, is 10 times closer to its star than Earth is to the Sun.
Moving outwards, the other planets are Kepler-11c, Kepler-11d, Kepler-11e, Kepler-11f and Kepler-11g which is half the Earth-Sun distance from its star.
Kepler science team member Dr Jack Lissauer, also from Ames, said: "Kepler-11 is a remarkable system whose architecture and dynamics provide clues about its formation.
"These six planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets' mass, while the gas takes up most of their volume.
"By measuring the sizes and masses of the five inner planets, we determined they are among the lowest mass confirmed planets beyond our solar system."
The latest discoveries increase the total number of planet candidates identified by Kepler since the telescope was launched into orbit in 2009 to 1,235.
Of these, 68 are approximately Earth-sized, 288 are "super-Earth" sized, 662 are Neptune-sized, 165 are the size of Jupiter, and 19 are larger than Jupiter.
Kepler is designed to look for the tiny dimming of star light caused by planets crossing or "transiting" their stars.
The transits of habitable zone planets orbiting Sun-like stars occur about once a year, and three transits are required to verify the observations. It may therefore take three years for astronomers to confirm the discoveries of Earth-like planets.
Kepler's telescope "eye" has been sweeping an area covering about one four hundredth of the sky containing more than 156,000 stars.