'Goldilocks' zone for planets re-defined

US researchers say they've come up with a more precise model for the "goldilocks" or habitable zone around stars where planets could conceivably support life. A team in the Penn State University department of geosciences reports their modeling of habitable zones where planets could have liquid water that might sustain life suggests those zones are actually farther away from stars than previously thought. The researchers, using updated absorption databases of greenhouse gases with more accurate information on water and carbon dioxide than previously was available, have come up with new estimates of the position of a habitable zone in relation to a star. "This has implications for finding other planets with life on them," lead study investigator Ravi Kumar Kopparapu said. The new model suggests extrasolar planets previously believed to be in habitable zones of their stars' systems may, in fact, not be. Earth, it turns out, is barely within the sun's habitable zone under the new model, although the researchers acknowledge their model doesn't take into account feedback from clouds, which reflect radiation away from Earth and stabilize the climate.