Habitability of Super-Earths: Gliese 581c and 581d

TL;DR

This paper models the thermal evolution of super-Earths to assess their habitability, focusing on the Gliese 581 system, and finds that one planet may support primitive life while the other likely does not.

Contribution

It introduces a thermal evolution model for super-Earths to evaluate habitability based on atmospheric CO2 and biological productivity limits.

Findings

Gl 581c is outside the habitable zone

Gl 581d is at the edge of the habitable zone

Gl 581d could harbor primitive life

Abstract

The unexpected diversity of exoplanets includes a growing number of super-Earth planets, i.e., exoplanets with masses smaller than 10 Earth masses. Unlike the larger exoplanets previously found, these smaller planets are more likely to have a similar chemical and mineralogical composition to the Earth. We present a thermal evolution model for super-Earth planets to identify the sources and sinks of atmospheric carbon dioxide. The photosynthesis-sustaining habitable zone (pHZ) is determined by the limits of biological productivity on the planetary surface. We apply our model to calculate the habitability of the two super-Earths in the Gliese 581 system. The super-Earth Gl 581c is clearly outside the pHZ, while Gl 581d is at the outer edge of the pHZ. Therefore it could at least harbor some primitive forms of life.