A team of astrobiologists has redefined conventional notions of where life can exist within a solar system. They've suggested that life could exist inside planets with inhospitable surfaces. Dubbed "subsurface habitable zones," this new definition of habitable zones means that alien life may be far more prevalent than we ever imagined.
Typically, a solar system's habitable zone, or so-called "Goldilocks zone," is a fairly narrow band within which planets can foster liquid water at the surface and cling to a stable atmosphere. For our solar system, this life-imbuing region of space extends from Venus to Mars.
Scratching the Surface
But as a team of researchers from Aberdeen and St. Andrews universities are now arguing, this traditional definition fails to take into account life that can exist beneath a planet's surface. Indeed, as extremophiles on Earth have shown, life can be incredibly resilient. What's more, temperatures increase as depth increases; once temperatures can foster liquid water, it's conceivable that life can exist there, too.