Thanks to NASA's now-crippled Kepler space telescope, astronomers say they now know there are billions of potentially habitable, Earth-size planets in the Milky Way galaxy.

That finding is a game changer, say NASA scientists, and it has ushered in a new era of astronomy.

"It's been nearly 20 years since the discovery of the first extrasolar planet around a normal star," said Andrew Howard, an astronomer with the Institute for Astronomy at the University of Hawaii.

"Since then, we have learned that most stars have planets of some size orbiting them, and that Earth-size planets are relatively common in close-in orbits that are too hot for life. With this, we've come home, in a sense, by showing that planets like our Earth are relatively common throughout the Milky Way galaxy," he added.

In August, NASA announced that Kepler, crippled by two broken wheels that control the telescope's orientation in space, had to end its hunt for Earth-like planets in the galaxy.

The telescope, launched in 2009, has given scientists enough data to keep scientists busy for another two to three years.

"The Kepler mission has been spectacularly successful," said William Borucki, Kepler's principal science investigator, in a statement earlier. "The most exciting discoveries are going to come in the next few years as we analyze this data."

Those words are ringing true this week as NASA reveals information about Earth-like planets at the second Kepler Science Conference at the Ames Research Center in Moffett Field, Calif.

At the Kepler conference in 2011, the mission team announced its first confirmed planet in a habitable zone -- Kepler-22b. Since then, four more habitable zone candidates have been confirmed, including two in a single system.

A habitable zone is a relatively small area around a star in which it's not too hot or too cold for life and water to be present in liquid form if conditions are right.

This year, the Kepler team outlined data on the discovery of 833 new Earth-like candidates. Ten of the planets are less than twice the size of Earth and orbit in their sun's habitable zone.

And according to scientists at the University of California at Berkeley and the University of Hawaii, Manoa, one in five of the 200 billion stars in the Milky Way have planets about the size of Earth with surface temperatures conducive to life.

"When you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye," said U.C. Berkeley graduate student Erik Petigura, who led the analysis of the Kepler data. "That is amazing."

Geoffrey Marcy, a professor of astronomy at Berkeley, cautioned that simply because a planet is relatively close to the size of Earth and orbits in a habitable zone, doesn't mean it will hold life or even be hospitable to life.

"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive," added Marcy in a statement. "Others may have rocky surfaces that could harbor liquid water suitable for living organisms. We don't know what range of planet types and their environments are suitable for life."

For NASA, the data compiled by Kepler is invaluable for planning future missions that hunt for Earth-like planets that could hold life.

"For NASA, this discovery is really important, because future missions will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are," Howard said. "An abundance of planets orbiting nearby stars simplifies such follow-up missions."

Kepler may no longer be operating but its data is changing scientists' view of the galaxy.

"Stars are the building blocks of the galaxy, driving its evolution and providing safe harbors for planets," said William Chaplin, professor for astrophysics at the University of Birmingham. "To study the stars, one truly explores the galaxy and our place within it. These are data we could only have dreamed of a few years ago."

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, or subscribe to Sharon's RSS feed . Her email address is sgaudin@computerworld.com.