Considerations for the habitable zone of super-Earth planets in Gliese 581

We assess the possibility that planets Gliese 581 c and d are within the habitable zone. In analogy with our solar system, we use an empirical definition of the habitable zone. We include assumptions such as planetary climates, and atmospheric circulation on gravitationally locked synchronous rotation. Based on the different scenarios, we argue that both planets in Gliese 581 could develop conditions for a habitable zone. In an Earth-like environment planet d could be within a habitable zone, if an atmosphere producing greenhouse effect of 100K could have developed. If the planets are gravitationally locked-in, planet c could develop atmospheric circulation that would allow it to reach temperatures consistent with the existence of surface liquid water, which in turn could support life.