The Habitable Zone and the Generalized Greenhouse Effect
It is generally tacitly assumed that the atmosphere of a habitable planet absorbs in the infrared and is transparent in the visible. We consider the cases in which the optical depth in the visible is not negligible. We show that such planets can harbor life under conditions similar to those found on Earth. Moreover, it is conceivable that planetary evolution starts with phases in which the optical depth in the visible is not negligible and evolves out of it or passes through such a phase during the evolution of the planet.
To this goal, we present a generalized theory of the greenhouse effect (GHE) as a function of the optical depths in the visible and the infrared and solve it under the radiative boundary conditions relevant to Earth. We then investigate the parameter space to search for domains with adequate average surface temperature and show how the optical depths in the visible and infrared combine to create a range of life-supporting temperatures and hence extend the habitable zone significantly.
KeywordsOptical Depth Greenhouse Effect Saturation Temperature Molecular Absorption Central Star
- Kasting JF, Pavlov AA (2002) Methane greenhouses and anti-greenhouses during the Archean Era. AGU Fall meeting abstracts, December, C3, San Francisco, CaliforniaGoogle Scholar
- Rothman LS, Gordon IE (2009) HITRAN2008 est ARRIVÉE. In: 64th international symposium on molecular spectroscopy, Ohio State University, Ohio, USAGoogle Scholar
- Shaviv G, Wehrse R (1991) Continuous energy distributions of accretion discs. Astron Astrophys 251:117–132Google Scholar
- Simpson GC (1927) Some studies in terrestrial radiation. Mem R Meteorol Soc II 1015 (16), 69, A195, 1016Google Scholar
- Stracke B, Godolt M, Grenfell JL, von Paris P, Patzer B, Rauer H (2012) The inner boundary of the habitable zone: loss processes of liquid water from terrestrial planet surfaces. Page 8313 of: Abbasi A, Giesen N (eds) EGU General Assembly conference abstracts. EGU General Assembly conference abstracts, vol 14Google Scholar