Axial Tilt And Life

An often ignored factor in determining the habitability of a planet is the tilt of that planet's axis of rotation, says astrobiologist Rene Heller. The tilt of Earth's polar axis creates the seasons, of course, but Heller says it does more than that-- it moderates and stabilizes the climate over long periods, allowing life to develop and thrive. Without the tilt, he argues, equatorial regions would becomes blazingly hot, and polar regions freeze solid. Life would be a challenge.

Heller goes beyond that. He notes the over the long term a star's gravity erases axial tilt, bringing all planets straight up and, eventually, into tidal lock-- that is, the same hemisphere of the planet would always face the star. That would not be conducive to life. Therefore, he argues, axial tilt is intimately related to habitability.