Scientists have been rethinking the so-called Goldilocks zone commonly used to roughly estimated if a planet is habitable. The Goldilocks zone is the area around the solar system where the temperature would be just right for liquid water on the planet's surface. The problem is a refreshing of the Goldilocks zone definition has pushed some planets previously believed to be in the habitable zone outside that range.
One of the planets that have been pushed outside the Goldilocks zone is Kepler-22b. That particular planet was once deemed the most habitable world outside of our solar system. However, under the new definition the planet no longer looks as though it would support life. Scientists Ravi Kopparapu from Penn State University says that the definition of a habitable zone hadn't been updated in 20 years.
He and colleagues settled on a new definition that involves a host stars temperature and estimates of how well the atmosphere of the planet would absorb heat from the parent star. Laboratory experiments conducted in recent years have offered new figures for how water and carbon dioxide absorb light from different types of stars. These experiments in turn were integrated into a new formula and some planets previously believed to be in this habitable zone are now outside it.
This means that some planets that scientists previously believed could be habitable are now too hot. At the same time, it also means the planets scientists had previously believed to be too cold are now in the habitable zone. Interestingly, the Earth is now not as habitable according to the new Goldilocks definition as it was once believed to be. Under the previous definition, the Earth was exactly in the middle of the Goldilocks zone in our solar system. The scientists now believe that the earth is actually only a few million kilometers away from the edge of our solar system's Goldilocks zone where the planet would be too hot to support life.
The scientists believe that this could be because the current Goldilocks zone definition still doesn't take into account clouds and how they might reflect heat from the parent star. The scientists are unable to take into account cloud cover on the planet because we can't see exoplanets to determine if they have cloud cover. Anyone who's been through a Texas summer will agree that environment here on earth is very close to being uninhabitable in some areas.