The habitable zone is one of the few astrophysical terms that has actually entered the common lexicon. It describes the region around a star in which a planet could be capable of supporting liquid water on its surface. In other words, it must be not too hot and not too cold but just right, which is why it is also known as the Goldilocks zone.

Now the notion of the habitable zone is set to change dramatically. Today, René Heller at McMaster University in Hamilton, Canada, and John Armstrong at Weber State University in Ogden, Utah, say that the current definition zone needs to be drastically re-written.

These guys argue that this definition is unnecessarily Earth-centric and point out that factors other than distance to the parent star also determine whether a planet’s surface is warm enough to support liquid water.

And this means that some places could be even better than Earth for supporting the emergence of life. These places, say Heller and Armstrong, should be called “super-habitable”.

One important factor is tidal forces, that stretch and squeeze a body in an eccentric orbit and can dramatically heat a planet or moon. This is what generates the heat the maintains a watery ocean beneath the surface of Jupiter’s moon Europa.

There’s no reason, say Heller and Armstrong, why a similar effect couldn’t heat a planet in an eccentric orbit around its star. That would keep a planet beyond the traditional habitable zone warm enough to support liquid water and heat a planet inside the habitable zone beyond habitability, they say.

(However, tidal friction would tend to circularise an eccentric orbit over time, so such an orbit would need to be influenced by other objects such as more distant giant planets to maintain the eccentricity.”

Planets that are slightly more massive than Earth could also be super-habitable. Heller and Armstrong point out that they would have longer tectonic activity, which helps to recycle carbon dioxide that would otherwise be removed from the atmosphere causing the planet to cool into a snowball state; have a stronger magnetic field that would protect incipient life forms; have a smoother surface that allows shallower, more productive oceans and have a thicker atmosphere than Earth’s.

All these factors, and others too, would make these places better-suited for life than our home planet. And the best place to look for them is probably k-type dwarf stars, such as Alpha Centauri B, one of the our closest neighbours.

So it looks as if this neighbour might be amongst the most interesting systems out there—a star with a super-habitable zone.

Of course, whether life has actually evolved here or elsewhere is another question entirely but one that people are likely to become increasingly interested in exploring.

Ref: arxiv.org/abs/1401.2392 : Superhabitable Worlds