This conclusion is based on studies of life here on Earth

Jan 21, 2012 09:44 GMT  ·  By

The fact that the Earth has a tilted axis when compared to that of the Sun does wonders for our planet, helping it regulate its climate, display seasonal variations, and ultimately support life. Astrobiologists say that the same positive aspects should apply to extrasolar planets as well.

Thus far, experts searching for Earth-like worlds among the stars have primarily been interested in finding planets where liquid water is possible on the surface. But examples such as Mars and the Saturnine moons Titan and Enceladus show that that is not really that important.

But planetary tilt, a characteristic known as obliquity, may play a very important role in differentiating an Earth-analog planet that can potentially support life from another just like it. In other words, the two worlds may share all other traits, including proximity to their parent stars, except their axial tilt.

Investigators with the Leibniz Institute for Astrophysics (LIA) in Potsdam, Germany, say that scientists have only paid marginal attention to this important planetary trait up until now. Postdoctoral research associate René Heller says that this characteristic must now be added to astrobiologists' list.

This list contains all the conditions that an exoplanet must meet in order to be cataloged as potentially habitable. This includes lying in its parent star's habitable zone, displaying liquid water and an atmosphere, being rocky and of similar mass and diameter to Earth and so on.

But Heller says that tilt should never slip out of sight again. “Obliquity and seasonal aspects are an important issue in understanding exoplanet habitability that has mostly been neglected so far,” the investigator explains, quoted by Space.

If exoplanets display an obliquity of less than 5 degrees, then they may be unsuitable for life. This setup would imply that the equatorial regions of that planet would be blasted by solar radiation, and driven to exhibit extreme temperatures.

At the same time, the polar regions would receive only minimal amounts of sunlight. Such a state of affairs would lead to a situation where the exoplanet would display extreme temperature variations based on latitude. It would also display only minimal traces of seasons.

There is of course the scenario where mid-latitude zones remain temperate, allowing for potentially-habitable, albeit confined, areas. But that may not happen at all on zero-obliquity worlds, where the planet may simply be incapable of holding on to its atmosphere.

“Obliquity is definitely a very important variable. [It]can certainly end up being the critical linchpin of determining whether or not any part of a planet could be considered habitable,” Columbia University Astrobiology Center director Caleb Scharf concludes. He was not a part of the study.