The hunt for alien life may get easier; thanks to a ‘habitability index’ created by scientists that can point out which of the thousands of exoplanets discovered so far have a better chance of hosting life.Traditionally, astronomers have focused the search by looking for planets in their star’s “habitable zone” — more informally called the “Goldilocks zone” — which is the swath of space that’s “just right” to allow an orbiting Earth—like planet to have liquid water on its surface, perhaps giving life a chance.But so far that has been just a sort of binary designation, indicating only whether a planet is, or is not, within that area considered right for life.The new metric, called the “habitability index for transiting planets,” is more nuanced, producing a continuum of values that astronomers can punch into a Virtual Planetary Laboratory Web form to arrive at the single—number habitability index, representing the probability that a planet can maintain liquid water at its surface.
Scientists also accounted for a phenomenon called “eccentricity—albedo degeneracy,” which comments on a sort of balancing act between a planet’s albedo — the energy reflected back to space from its surface — and the circularity of its orbit, which affects how much energy it receives from its host star. The two counteract each other.The higher a planet’s albedo, the more light and energy are reflected off to space, leaving less at the surface to warm the world and aid possible life.
But the more noncircular or eccentric a planet’s orbit, the more intense is the energy it gets when passing close to its star in its elliptic journey.
A life—friendly energy equilibrium for a planet near the inner edge of the habitable zone — in danger of being too hot for life — would be a higher albedo, to cool the world by reflecting some of that heat into space, Barnes said.Conversely, a planet near the cool outer edge of the habitable zone would perhaps need a higher level of orbital eccentricity to provide the energy needed for life.