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.
To show that this is the case, the researchers used a computer model to approximate temperatures below the surfaces of planets by entering the distance to their respective stars while referencing it to the size of the planet. This allowed them to come up with a subsurface habitable zone (SSHZ) map.
Life In Other Planets
Results showed that the habitable radius around a star increases three-fold if life can exist 3.3 miles (5.3 km) below the surface (which is the case on Earth). If it can exist as far as 6 miles (10 km) down (not impossible), that would extend our solar system's SSHZ by a factor of 14. That's beyond Saturn — a range that would have to include moons like Europa and Ganymede, both of which are thought to host subsurface oceans.
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