Nasa's venerable Kepler space telescope has confirmed eight new alien planets, with three of them located in habitable zone - orbiting their stars at just the right distance to have liquid water, and possibly life.
Eight new worlds beyond our solar system, including two of the most Earth-like planets discovered so far, boost the number of Kepler's confirmed planets to over 1,000.
Kepler continuously monitored more than 150,000 stars beyond our solar system, and to date has offered scientists an assortment of more than 4,000 candidate planets for further study.
Using Kepler data, scientists reached this millinery milestone after validating that eight more candidates spotted by the planet-hunting telescope are, in fact, planets.
The Kepler team also has added another 554 candidates to the roll of potential planets, six of which are near-Earth-size and orbit in the habitable zone of stars similar to our Sun.
Three of the newly-validated planets are located in their distant Suns' habitable zone, the range of distances from the host star where liquid water might exist on the surface of an orbiting planet. Of the three, two are likely made of rock, like Earth, Nasa said.
"Each result from the planet-hunting Kepler mission's treasure trove of data takes us another step closer to answering the question of whether we are alone in the Universe," said John Grunsfeld, associate administrator of Nasa's Science Mission Directorate at the agency's headquarters in Washington.
To determine whether a planet is made of rock, water or gas, scientists must know its size and mass. When its mass can't be directly determined, scientists can infer what the planet is made of based on its size.
Two of the newly validated planets, Kepler-438b and Kepler-442b, are less than 1.5 times the diameter of Earth.
Kepler-438b, 475 light-years away, is 12% bigger than Earth and orbits its star once every 35.2 days.
Kepler-442b, 1,100 light-years away, is 33% bigger than Earth and orbits its star once every 112 days.
Both Kepler-438b and Kepler-442b orbit stars smaller and cooler than our Sun, making the habitable zone closer to their parent star, in the direction of the constellation Lyra.
With the detection of 554 more planet candidates from Kepler observations conducted from May 2009 to April 2013, the Kepler team has raised the candidate count to 4,175.
"We're closer than we've ever been to finding Earth twins around other Sun-like stars. These are the planets we're looking for," said Fergal Mullally, SETI Institute Kepler scientist at NASA's Ames Research Centre, who led the analysis of a new candidate catalogue.
The finding was published in The Astrophysical Journal.