Gravity and Life

Astronomers have traditionally seen the "habitable zone" around a star-- the area in which a planet might support life-- as a function of the energy output of the star. The universe being what it is, though, things might be more complicated than that.

A recent study suggests gravity might expand the habitable zone of a solar system. If a planet is in a highly elliptical orbit, the pull of gravity from the parent star will constantly vary, constantly stressing the internal structure of the planet. The reaction to that stress will generate heat, which would make its way to the surface, possibly supporting life at the surface or below it even though heat from the star might not be enough for life. Presumably, such a situation would be unlikely as the home of a civilization, but simple life forms are another matter.

We see smaller versions of such a scenario close to home. Going strictly by the Sun's energy output, both Europa and Enceladus would be well beyond the solar habitable zones. Both are seen as possible abodes of life, however, because they are not frozen solid. Their interiors are stressed, and internal heat is produced, by the constant manipulation of the gravity of Jupiter and Saturn, respectively.