Scientists rethink the habitable zone

摘要

When considering where to look for extraterrestrial life, astronomers have mostly stuck with what's familiar. The best candidates for habitable planets are considered the ones most like Earth: small, rocky, with breathable atmospheres and a clement amount of warmth from their parent stars. But as more exoplanets have been discovered, astronomers have debated the usefulness of this definition. Some planets in a star's so-called habitable zone, where temperatures are right for liquid water, are probably not good for life at all. Others outside that designated area might be perfectly comfortable. Now, two studies propose revising the concept of the habitable zone. One new definition brings more planets into the habitable fold; the other nudges some out. "Both papers focus on questioning the classical idea of the habitable zone," says Penn State astronomer Noah Tuchow. "We should extend the range of places that we look, so we don't miss habitable planets."