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Project Progress

In this project we focus on understanding what we can learn about an extrasolar terrestrial planet from remotely sensed, disk-averaged spectra, as a function of spectral resolution and instrument sensitivity. With these spectroscopic studies we will build a spectral library of terrestrial planets for use in Terrestrial Planet Finder (TPF) mission planning and data analysis, and better understand the wavelength-dependent surface ultraviolet (UV) fluxes, to determine what constraints these might provide on planetary habitability and biological evolution.

We have used a range of Earth-like, self-consistent planetary atmospheres with different oxygen abundances around F2V, G2V and K2V stars (Krelove, Segura and Kasting) as the basis for this study. Using a spectrum resolving (line-by-line) atmospheric/surface radiative transfer model (Crisp) and a detailed spectra description of the parent star (Cohen), we have generated synthetic spectra of these planetary atmospheres, from the UV to the far-infrared (IR) (Meadows). These spectra clearly show the delectability of biosignatures such as O₂, O₃, CH₄ and N₂O, and also atmospheric CO₂. Figure 1 shows our results on ozone as a function of atmospheric oxygen abundance for a planet around a G2V star and Figure 2 shows the spectrum for as “Earth” around stars of different spectral type and the differences in detectability of atmospheric features. To further explore planetary habitability, and planetary conditions for life, Kasting, Segura and Sommerlatt have computed surface UV fluxes and UV dose rates for erythema and deoxyribonucleic acid (DNA) damage. Interestingly, planetary UV surface fluxes are low for high-oxygen planets orbiting the high-UV output F stars, because of the creation of a protective “super” ozone layer.

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