Counting Kepler and the other ground- and space-based planet searches underway, scientists have discovered a total of more than 700 confirmed alien planets. They're still on the hunt for a Twin Earth in the habitable zone --roughly the right size and temperature to host life.
Nick Gautier, Kepler project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Francois Fressin, the lead scientist on the new discovery, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
David Charbonneau, professor of astronomy at Harvard University
Linda Elkins-Tanton, director of the Carnegie Institution for Science's Department of Terrestrial Magnetism in Washington
The public can listen in on the alien planet announcement using NASA's News Audio website.
The $600 million Kepler mission is slated to run until at least November 2012, though its science team is hoping for an extension of the mission until 2016 or so.
NASA's Kepler mission has confirmed its first planet in the "habitable zone," the region where liquid water could exist on a planet’s surface. Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.
The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a star similar to our sun. The planet is about 2.4 times the radius of Earth. Scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.
Previous research hinted at the existence of near-Earth-size planets in habitable zones, but clear confirmation proved elusive. Two other small planets orbiting stars smaller and cooler than our sun recently were confirmed on the very edges of the habitable zone, with orbits more closely resembling those of Venus and Mars.
"This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Kepler's results continue to demonstrate the importance of NASA's science missions, which aim to answer some of the biggest questions about our place in the universe."
Kepler has discovered 1,235 exoplanets that revolve around a sun, in an area that represents around 1/400th of the Milky Way. By extrapolating these numbers, the Kepler team has estimated that there are at least 50 billion exoplanets in our galaxy — 500 million of which sit inside the habitable "Goldilocks" zones of their suns, the area that it is neither too hot nor too cold to support life.
Astronomers estimate that there are 100 billion galaxies in the universe. If you want to extrapolate those numbers, that means there are around 50,000,000,000,000,000,000 (50 quintillion) potentially habitable planets in the universe.
As Arthur C. Clarke, physicist and author of 2001: A Space Odyssey wrote, "The idea that we are the only intelligent creatures in a cosmos of a hundred billion galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume therefore, that they are out there and to consider the manner in which this may impinge upon human society."