The habitability of super-Earths in Gliese 581

TL;DR

This study assesses the habitability of super-Earths in the Gliese 581 system, finding that Gl 581d may support primitive life despite challenging conditions, making it a promising target for future biomarker searches.

Contribution

It introduces a thermal evolution model to evaluate habitability of super-Earths considering land/ocean coverage and biological productivity limits.

Findings

Gl 581c is outside the habitable zone due to proximity to the star.

Gl 581d is a tidally locked super-Earth near the habitable zone's outer edge.

Primitive life could potentially exist on Gl 581d despite adverse conditions.

Abstract

Aims: The planetary system around the M star Gliese 581 consists of a hot Neptune (Gl 581b) and two super-Earths (Gl 581c and Gl 581d). The habitability of this system with respect to the super-Earths is investigated following a concept that studies the long-term possibility of photosynthetic biomass production on a dynamically active planet. Methods: A thermal evolution model for a super-Earth is used to calculate the sources and sinks of atmospheric carbon dioxide. The habitable zone is determined by the limits of biological productivity on the planetary surface. Models with different ratios of land / ocean coverage are investigated. Results: The super-Earth Gl 581c is clearly outside the habitable zone, since it is too close to the star. In contrast, Gl 581d is a tidally locked habitable super-Earth near the outer edge of the habitable zone. Despite the adverse conditions on this planet, at least some primitive forms of life may be able to exist on its surface.Therefore, Gl 581d is an interesting target for the planned TPF/Darwin missions to search for biomarkers in planetary atmospheres.