Life on Earth-like planets can exist at least ten times farther away from their stars than previously thought, scientists found, putting in question our whole perspective on habitable zone distances.
A new paper published in the journal, Planetary and Space Science, describes how living organisms have just as much chance of surviving in areas below their uninhabitable planets’ surfaces.
This includes planets a staggering distance away from their stars, as well as even those that were recently discovered to be drifting in space by themselves, with no apparent host star.
The previous commonly accepted assertion was that the so-called ‘Goldilocks’ zone was a requirement. It is the zone both far away and near enough to its star to provide the kind of climate capable of sustaining life. In our understanding, it should support water that is neither boiling hot nor frozen.
Now a team of researchers from Aberdeen and St. Andrews universities has an updated view of things. PhD student Sean McMahon, author of the paper, says “that theory fails to take into account life that can exist beneath a planet's surface. As you get deeper …the temperature increases, and once you get down to a temperature where liquid water can exist – life can exist there too.”
To prove this, the scientists devised a computer model to cleverly approximate temperatures below the surfaces of planets by inputting the distance to their respective stars and crossing that with the planet’s size.
Using that model they discovered that the radius around a star, capable of supporting life, increased three-fold if new data on depth at which life can exist below the surface of a given planet were taken into account.
"The deepest known life on Earth is 5.3 km below the surface, but there may well be life even 10 km deep in places on Earth that haven't yet been drilled,” McMahon said.
What adds to the excitement is that the model allows for potentially expanding the habitable zone even more. If indeed we do find life 10km below the Earth’s surface, the math tells us that Earth-like planets could support life as far as 14 times the distance previously considered to be the Goldilocks zone.
To put this into perspective – our current habitable zone is considered to reach out as far as Mars. But new measurements that account for life existing under rocky surfaces take that radius as far as Jupiter and Saturn.
For example, the recently discovered Gliese 581 d could be a candidate. Sure, it is about 20 trillion kilometers away, but its cold surface could well hide life a couple of kilometers below the surface, scientists assume.
Scientists are excited at the subsurface theory on sustaining life. We can now widen our search for life, they hope, adding that the new findings are so radical that the fact of life on Earth (which itself is very different from the thousands of planets we know about) could itself be anomalous because life receives much more protection inside a warm, mineral-rich rock than risking survival on its inhospitable surface.