Habitability of the Goldilocks Planet Gliese 581g: Results from Geodynamic Models

TL;DR

This study uses geodynamic models to assess the long-term habitability of the super-Earth Gliese 581g, focusing on its potential for supporting photosynthetic life based on its position and land/ocean coverage.

Contribution

It introduces a thermal evolution model to evaluate habitability of super-Earths, specifically analyzing the impact of land and ocean distribution on long-term biological productivity.

Findings

Maximum habitability occurs near 0.14 AU from the star.

High ocean coverage increases the likelihood of habitability.

Gliese 581g's position is nearly optimal for habitability within model uncertainties.

Abstract

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 Earth masses. 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 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.