Cryptic photosynthesis, Extrasolar planetary oxygen without a surface biological signature

摘要

On the Earth, photosynthetic organisms are responsible for the production ofvirtually all of the oxygen in the atmosphere. On the land, vegetation reflectsin the visible, leading to a red edge that developed about 450 Myr ago and hasbeen proposed as a biosignature for life on extrasolar planets. However, inmany regions of the Earth, and particularly where surface conditions areextreme, for example in hot and cold deserts, photosynthetic organisms can bedriven into and under substrates where light is still sufficient forphotosynthesis. These communities exhibit no detectable surface spectralsignature to indicate life. The same is true of the assemblages ofphotosynthetic organisms at more than a few metres depth in water bodies. Thesecommunities are widespread and dominate local photosynthetic productivity. Wereview known cryptic photosynthetic communities and their productivity. We linkgeomicrobiology with observational astronomy by calculating the disk-averagedspectra of cryptic habitats and identifying detectable features on an exoplanetdominated by such a biota. The hypothetical cryptic photosynthesis worldsdiscussed here are Earth-analogs that show detectable atmospheric biomarkerslike our own planet, but do not exhibit a discernable biological surfacefeature in the disc-averaged spectrum.