Research Note

Habitability of the Goldilocks planet Gliese 581g: results from geodynamic models

¹ Potsdam Institute for Climate Impact Research, PO Box 60 12 03, 14412 Potsdam, Germany
e-mail: bloh@pik-potsdam.de
² Department of Physics, University of Texas at Arlington, Box 19059, Arlington, TX 76019, USA

Received: 18 January 2011
Accepted: 14 February 2011

Abstract

Aims. In 2010, detailed observations have been published that seem to indicate another super-Earth planet in the system of Gliese 581, which is 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_⊕. 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 ± 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 another 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.