The Kepler spacecraft has now discovered an additional 1,284 planets orbiting other stars, adding to the thousands of discoveries made by the rugged observatory. Of these worlds, NASA investigators believe nine of them may possibly be habitable. All of these finds have been verified by other astronomers around the globe.

Analysis of 4,302 samples showed 550 are likely to be rocky worlds. Nine of these orbit within the so-called habitable zone from their parent sun. This is the distance from a star at which liquid water may be possible on an alien world.

Kepler results are typically calculated by a tedious process of examining each candidate one at a time. A new statistical analysis method, developed to examine many cases simultaneously, was utilized to decipher thousands of records noted by Kepler in July 2015. Candidate signals were not declared to be a planet unless analysis found a 99 percent confidence the body was, indeed, an exoplanet.

"Planet candidates can be thought of like bread crumbs. If you drop a few large crumbs on the floor, you can pick them up one by one. But, if you spill a whole bag of tiny crumbs, you're going to need a broom. This statistical analysis is our broom," Timothy Morton from Princeton University said.

Exoplanets were, until recently, the stuff of science fiction. In the 1980s, as Carl Sagan was bringing his masterwork Cosmos to the general public, astronomers did not know of a single planet orbiting an alien star. Today, astronomers have examined almost 5,000 planetary candidates, confirming over 3,200 alien worlds. Of these, 21 are most likely composed of rocks and are in the correct orbits for liquid water to flow their surface.

Kepler launched into space in 2009, on a mission to detect exoplanets orbiting alien suns. In 2013, the vehicle suffered equipment failure, threatening the observatory. However, astronomers found methods to continue their observations with the planet-hunting spacecraft.

This new study is the largest find of exoplanets ever made by astronomers. In addition to the newly confirmed worlds, the study also found an additional 1,327 candidates that are likely exoplanets but whose signals did not make the 99 percent threshold. These will be examined using other methods.

Analysis of the new data from Kepler revealing nearly 1,300 previously unknown worlds around other stars was published in The Astrophysical Journal.