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-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, 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.