Model Spectra of the First Potentially Habitable Super-Earth - Gl581d

TL;DR

This study models the atmospheres and spectra of Gl581d, a potentially habitable super-Earth, to identify observable indicators of habitability and biological activity for future telescopic observations.

Contribution

It provides the first detailed spectroscopic models of Gl581d's atmosphere assuming Earth-like compositions, exploring conditions for habitability and biosignature detectability.

Findings

A minimum CO2 pressure of 7 bar is needed for surface temperatures above freezing.

Synthetic spectra indicate observable biosignatures in future telescopic observations.

The model demonstrates how atmospheric features relate to habitability conditions.

Abstract

Gl581d has a minimum mass of 7 MEarth and is the first detected potentially habitable rocky Super-Earth. Our models confirm that a habitable atmosphere can exist on Gl581d. We derive spectroscopic features for atmospheres, assuming an Earth-like composition for this planet, from high oxygen atmosphere analogous to Earth's to high CO2 atmospheres with and without biotic oxygen concentrations. We find that a minimum CO2 partial pressure of about 7 bar, in an atmosphere with a total surface pressure of 7.6 bar, are needed to maintain a mean surface temperature above freezing on Gl581d. We model transmission and emergent synthetic spectra from 0.4{\mu}m to 40{\mu}m and show where indicators of biological activities in such a planet's atmosphere could be observed by future ground- and space-based telescopes. The model we present here only represents one possible nature - an Earth-like composition - of a planet like Gl581d in a wide parameter space. Future observations of atmospheric features can be used to examine if our concept of habitability and its dependence on the carbonate-silicate cycle is correct, and assess whether Gl581d is indeed a habitable super-Earth.