Also known as the Goldilocks zone, because temperatures are "just right" for life there, the habitable zone is the main tool that exoplanet hunters have to rank their finds. But researchers are still using a definition coined in 1993. "Those habitable zones have not been updated in the last 20 years," says Ravi Kopparapuof Penn State University.
He and his colleagues have a new definition. The zone's boundaries have always depended on the star's temperature, plus estimates of how well the atmospheres of any planets would absorb heat from their star. But in recent years, lab experiments have turned up new figures for how water and carbon dioxide absorb light from different types of stars. The redefinition is based on these figures – and pushes the zone further from the star than the old definition.
Now, many planets, including supposedly balmy Kepler-22b, look too hot. However, the redefinition should also bring into the habitable fold planets that were thought to be too cold.
An even better planet than our current one may be waiting for us ...