Even amateur students of astronomy are likely familiar with the concept of a "habitable zone," that area around a star which experts for years have believed is a critical component for the formation of life. The idea is that a planet must exist in this zone—not too close to the star, not too far from it—in order to have stable bodies of liquid water and optimal temperatures for life to arise.

One group of scientists, though, have proposed that the class of planets capable of supporting life might be much broader than originally thought:

Liquid water — and potentially habitable conditions — could exist on the surfaces of planets far different from our own, according to a new study. ...

The new models, if verified with future research, open up the possibility that many different kinds of worlds could be habitable. ...

The study, published in the journal Nature Astronomy, used modeling to find that super-Earths — rocky worlds that are larger than our own — could support thick atmospheres that would allow water to persist on their surfaces even if they're far from their star.

The hypothesis is that planets may form with a primordial atmosphere that, if the planets are close enough to a star, may be dissipated by the star's intense radiation. Yet if the planet is far enough away from the star, "the atmospheres remain, [and] the right conditions for liquid water can occur."

Sunlight may not even be a necessary component to life on other planets:

"[W]here sufficient geothermal heat reaches the surface, radiation from a star like the Sun is not even necessary so that conditions prevail at the surface that allow the existence of liquid water."

If you drastically expand the criteria classifying the planets on which human beings can survive, what do you get?

It's exciting, folks!

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