January 17, 2014 – It turns out that “not too cold” has been redefined by researchers at the University of Aberdeen when it comes to determining habitable planets. In a paper called Circumstellar habitable zones for deep terrestrial biospheres, published in Planetary and Space Science, the Aberdeen authors state that previously considered uninhabitable rocky planets may be life friendly after all. That life, however, may be underground.
Just like discoveries made here life can be found deep inside a planet – as much as 5.3 kilometers (3.29 miles) based on what we have discovered so far on Earth. And as we drill further into the crust scientists speculate that we will find life as deep as 10 kilometers (6.2 miles) beneath the surface.
Based on the 5.3 kilometer metric the researchers developed a model that indicates Earth-like planets orbiting a Sun-like star could support life at a distance of three Astronomical Units, that is three times greater than our present Earth-Sun orbital distance. At that distance and depth liquid water would exist and where we find liquid on Earth we find life. And based on the 10 kilometer metric that habitable zone grows to orbits 14 Astronomical Units. So even though rocky planets like Mars may have thin atmospheres that we would never consider suitable for life, below the surface they may be teeming with it. Similarly moons orbiting planets within these zones may also harbor subsurface life even if orbiting gas giants that fit within the model.
For some of the recent planets Kepler identified such as Gliese 581d (seen below based on artist rendering), they may prove hospitable to life after all if these new parameters prove themselves as we seek life elsewhere in our Solar System and in neighboring systems within the Milky Way Galaxy.