Context :

Aims : In 2010 , detailed observations have been published that seem to indicate another super-Earth planet in the system of Gliese 581 located in the midst of the stellar climatological habitable zone .
The mass of the planet , known as Gl 581g , has been estimated to be between 3.1 and 4.3 M _ { \oplus } .
In this study , we investigate the habitability of Gl 581g based on a previously used concept that explores its long-term possibility of photosynthetic biomass production , which has already been used to gauge the principal possibility of life regarding the super-Earths Gl 581c and Gl 581d .

Methods : A thermal evolution model for super-Earths is used to calculate the sources and sinks of atmospheric carbon dioxide .
The habitable zone is determined by the limits of photosynthetic biological productivity on the planetary surface .
Models with different ratios of land / ocean coverage are pursued .

Results : The maximum time span for habitable conditions is attained for water worlds at a position of about 0.14 \pm 0.015 AU , which deviates by just a few percent ( depending on the adopted stellar luminosity ) from the actual position of Gl 581g , an estimate that does however not reflect systematic uncertainties inherent in our model .
Therefore , in the framework of our model an almost perfect Goldilock position is realized .
The existence of habitability is found to critically depend on the relative planetary continental area , lending a considerable advantage to the possibility of life if Gl 581g ’ s ocean coverage is relatively high .

Conclusions : Our results are a further step toward identifying the possibility of life beyond the Solar System , especially concerning super-Earth planets , which appear to be more abundant than previously surmised .