From Alan Boyle's Cosmic Log:
An analysis of data from NASA's Kepler planet-hunting mission suggests that about 6 percent of all red dwarf stars should have habitable, Earth-sized planets — and because red dwarfs are the most common stars in our galaxy, the nearest Earthlike planet could be as close as 13 light-years.
"We thought we would have to search vast distances to find an Earthlike planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted," Harvard astronomer Courtney Dressing, the lead author of the data-crunching study, said in a news release.
... Red dwarfs are thought to account for about 75 percent of the stars in the Milky Way: They're smaller, cooler and fainter than our sun — so faint, in fact, that no red dwarf is visible to the naked eye. But the fact that they're cooler means that closer-in planets are more likely to be habitable.
... Dressing and her colleagues sifted through the 158,000 stars targeted by the Kepler probe to identify all the red dwarfs. She said the stars' sizes and temperatures were calculated using computer models "that are more appropriate for these small red stars." Previously, those stellar characteristics were derived using a less precise, one-size-fits-all type of computer model, she said.The article goes on to note, however, that such planets would probably be tidally locked.
The fresh analysis showed that almost all of the stars were smaller and cooler than previously thought. That means the worlds detected around those planets would be proportionately smaller as well, bringing more of them into the Earth-sized category.
The astronomers identified 95 Kepler candidate planets that are circling red dwarfs. When they ran those candidates through their fine-tuned computer model, they found that three of them were roughly Earth-sized, with the right temperature to sustain liquid water and life. And when they factored in their estimates for the proportion of planets that would have gone undetected, due to the limitations of the Kepler mission's observing method, they concluded that 6 percent of all red dwarfs should have an Earth-sized, habitable planet.
"That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought," the CfA's David Charbonneau, a co-author of the study, said in Wednesday's news release.Because our sun is surrounded by a swarm of red dwarfs, the statistics suggest that the most probable distance for such a habitable planet would be 13 light-years, if all the surrounding stars could be examined with a suitable telescope. Kepler isn't designed for such a survey — but a new type of space telescope, or a big enough network of ground-based telescopes, could take on the job.