MODEL SPECTRA OF THE FIRST POTENTIALLY HABITABLE SUPER-EARTH—Gl581d

Gl581d has a minimum mass of 7 M Earth 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-CO 2 atmospheres with and without biotic oxygen concentrations. We find that a minimum CO 2 partial pressure of about 7 bar, in an atmosphere with a total surface pressure of 7.6 bar, is needed to maintain a mean surface temperature above freezing on Gl581d. We model transmission and emergent synthetic spectra from 0.4 μm to 40 μm 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.