Habitable planets may exist closer to stars than previously thought

Habitable planets orbiting distant stars may exist closer to their parent stars than previously thought, French researchers say. Scientists at the Institut Pierre Simon Laplace in Paris have reported in the journal Nature a study in which their modeling of the "runaway greenhouse" effect, which would cause oceans to evaporate, showed it is initiated at a higher level of solar radiation than previously estimated. The finding suggests the habitable zone around any star, the distance at which a planet could have liquid water and potentially support life, extends further inward than previously believed, they said. Researcher Jeremy Leconte and colleagues included a three-dimensional climate model in their study, which yielded the finding of an increased threshold for the initiation of a runaway greenhouse effect. Based on their research, they suggest the inner edge of the habitable zone for any Earth-like planets around a star should be moved inward to about 0.95 astronomical units (one astronomical unit is the mean distance from the Earth to the Sun).