"This carefully measured catalogue is the foundation for directly answering one of astronomy's most compelling questions - how many planets like our Earth are in the galaxy?" said Susan Thompson, a research scientist at the SETI Institute, which searches for signs of extraterrestrial life.
Nasa said in a statement: "There are now 4034 planet candidates identified by Kepler. Of which, 2335 have been verified as exoplanets. Of roughly 50 near-Earth size habitable zone candidates detected by Kepler, more than 30 have been verified.
"Additionally, results using Kepler data suggest two distinct size groupings of small planets. Both results have significant implications for the search for life."