It's been a busy time in the search for extraterrestrial intelligence, an endeavor nicknamed SETI that began 50 years ago with a scan for alien radio waves from Tau Ceti and Epsilon Eridani.
NASA's planet-hunting Kepler Telescope is returning a rich harvest of potential targets. So far, scientists have found 1,253 stars that likely have planets in tow, including 55 with worlds that appear to be in life-friendly zones.
"It's a new game. We can start pointing our telescopes where we know there are planets, rather than pointing at stars where we thought there might be habitable planets. It's exciting," Jill Tarter, director of SETI research for the California-based SETI Institute, told Discovery News.
Tarter's team already has scanned Kepler's prime targets for signs of artificially generated radio signals, which would be evidence of a past or present technologically advanced civilization. No signs of ET among those, but researchers are far from discouraged.
Extrapolating from Kepler's data, which was collected from just a tiny sliver of the galaxy, scientists estimate there are about 50 billion planets in the Milky Way, of which about 500 million may be habitable -- located at a proper distance from the parent star for liquid water to pool on the planet's surface. Water is believed to be a key ingredient for life.
"There's a lot more real estate out there than we might once have thought," Tarter said.
Along with good targets to scan, the Kepler survey could help the search for E.T. by identifying types of stars more likely to host planets.
"If it turned out that G-type stars of a certain age or something were more likely to have these kinds of worlds... that would shift the approach," SETI astronomer Seth Shostak told Discovery News.
"The bottom line on Kepler is that the fraction of stars that might have a cousin of Earth, if you will, seems to be something on the order of 5 percent, maybe 3 percent, maybe 10 percent... somewhere in that range," he added. "That's good news. It could have been one in 10,000. It could have been one in 100,000. It could have been one in a million, and it's not.
"It means that if you have 100 star systems, you can feel fairly confident that some of them are going to worlds that are suitable for life. Even though it doesn't change your strategy very much, it means you have more hope of it succeeding," Shostak said.