NASA's venerable Kepler space telescope's count of exoplanets has passed the magic 1,000 mark, including eight new planets and 544 candidate planets.
Of more than 1,000 verified planets found, eight are less than twice Earth-size and in their stars' habitable zone, the US space agency said.
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 - the 1,000th of which was recently verified.
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.
"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.
"The Kepler team and its science community continue to produce impressive results with the data from this venerable explorer," said Grunsfeld.
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.
"With each new discovery of these small, possibly rocky worlds, our confidence strengthens in the determination of the true frequency of planets like Earth," said co-author Doug Caldwell, SETI Institute Kepler scientist at NASA's Ames Research Centre at Moffett Field, California.
"The day is on the horizon when we'll know how common temperate, rocky planets like Earth are," said Caldwell.
With the detection of 554 more planet candidates from Kepler observations conducted 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 Ames who led the analysis of a new candidate catalogue.
The finding was published in The Astrophysical Journal.
