NASA has discovered 1,200 possible planets orbiting other stars in the Milky Way, according to a much-anticipated report just released by the space agency's Kepler mission; that discovery could potentially triple the existing number of known planets in the universe. The big news, though, is that Kepler, a space observatory specifically designed to discover Earth-like planets, has finally done just that.

"This is the first big step forward to answering the ancient question, 'How common are other Earths?"

In the habitable zone, the name for the region in space in which liquid water can exist on a planet's surface, Kepler found 54 new candidates and five of those are similar in size to Earth. "Candidates require follow-up observations to verify they are actual planets," NASA explained in a press release, but that hasn't cooled the excitement. In anticipation of today's press release, Greg Laughlin, the blogger behind Systemic, a site that reports on recent developments in the study of extrasolar planets, prepared a characterization flowchat that will help amateur astronomers follow-up on data released by Kepler. Laughlin's flowchart, which was created with the help of Konstantin Batygin, was designed to "aid fellow exoplanet prospectors in sifting potentially interesting systems -- a template for the treasure map."

And as those astronomers begin to conduct follow-up observations, more details are sure to emerge. "For the first time in human history we have a pool of potentially rocky habitable zone planets," Sara Seager of the Massachusetts Institute of Technology told the New York Times. "This is the first big step forward to answering the ancient question, 'How common are other Earths?'"

As Kepler covers only 1/400 of the sky, and the new report is based on just four months worth of data from a planned 3 1/2-year mission, extrapolating the numbers would suggest that there are about 20,000 planets in the habitable zone within 3,000 light years of Earth.

Also announced today, Kepler discovered a six-planet system orbiting a sun-like star, known as Kepler-11. "This is the largest group of transiting planets orbiting a single star yet discovered outside out solar system," NASA explained. Located about 2,000 light years from Earth, Kepler-11 is described by NASA's scientists as the "most tightly packed planetary system yet discovered." All six of its planets are larger than Earth and move in tighter orbits than that of Venus. More details will be published in the February 3 issue of Nature.