Detectability of red-edge-shifted vegetation on terrestrial planets orbiting M stars

Abstract

We have explored the detectability of exovegetation on the surface of a terrestrial planet orbiting an M star. The exovegetation is responsible for producing a pigment-derived surface signature that is redshifted with respect to the Earth vegetation's red edge. The redshift was estimated using a model of leaf optical property spectra (Jacquemoud & Baret) combined with a 3 photon photosynthetic scheme calculated by Wolstencroft & Raven for a possible exovegetation growing on an M star planet. To study the detectability of this surface biosignature on an M star terrestrial planet, we have used the three-dimensional model developed by Tinetti et al. for the case of the Earth. This model can generate disk-averaged spectra and broadband integrated fluxes, which will be useful for future terrestrial planet exploration missions, such as the NASA Terrestrial Planet Finder Coronagraph. Input to this model were the atmospheric profiles and cloud distributions predicted by Joshi and coworkers for a synchronous planet orbiting an M dwarf and the distinctive surface reflectance of the exovegetation. While on Earth this pigment-derived surface feature would be almost completely masked by water absorption, even in a cloud-free atmosphere, we found that the strength of the edge feature on our simulated M star terrestrial planet can exceed that on Earth, given the right conditions. Obviously, the detectability of such biosignatures would be highly dependent on the extent of vegetation surface area, cloud cover, and viewing angle.

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