Monday, May 30, 2016

Introducing the Life Supporting Zone Concept as an Alternative to the Habitable Zone

Effective stellar flux calculations for limits of Life-supporting zones of Exoplanets


Ludwig et al


Habitable zones (HZ) are key concepts in the quest for finding extrasolar planets that may host life as we know it. HZs encompass regions around a star that would allow for liquid water to be present on the surface of a rocky planet. However, water may not be the only solvent capable of producing and sustaining biospheres (e.g. Schulze-Makuch & Irwin 2006), so the concept of life-supporting zones (LSZ) was introduced as a generalization of the classical HZ for a broader range of solvents (Leitner et al. 2010) . The aim of this work is to offer a straightforward means of calculating LSZs similar to those presented by Kopparapu et al. (2014) for the HZ. We used a 1D radiative convective model to determine LSZ limits for water/ammonia mixtures and sulfuric acid. A simplified cloud model was used for offline sulfuric acid cloud simulation. Water clouds were accounted for by variations of surface albedo values. Compared to recently updated results by Kopparapu et al. (2014), our results lie well within the uncertainty range of the Toon algorithm (Toon et al. 1989) for flux calculations. We found an inner limit of the LSZ closer and an outer limit further away from the star than the limits for the HZ would be. Recently discovered exoplanets (like Kepler 452-b) are shown to be positioned very well in the LSZ. The concept of LSZs adds additional perspectives to an exoplanet's ability to maintain life on its surface.

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