Cryptic photosynthesis, Extrasolar planetary oxygen without a surface biological signature

TL;DR

This paper explores the possibility of detecting extraterrestrial life through atmospheric biomarkers on planets with cryptic photosynthetic communities that lack surface spectral signatures, challenging traditional biosignature detection methods.

Contribution

It introduces the concept of cryptic photosynthesis as a potential biosignature and links geomicrobiology with astronomy by modeling spectra of such hidden biota on exoplanets.

Findings

Cryptic photosynthetic communities are widespread and significant for planetary productivity.

Such communities can produce detectable atmospheric biomarkers without surface spectral signatures.

Earth-analog planets with cryptic biospheres could be identified through atmospheric analysis.

Abstract

On the Earth, photosynthetic organisms are responsible for the production of virtually all of the oxygen in the atmosphere. On the land, vegetation reflects in the visible, leading to a red edge that developed about 450 Myr ago and has been proposed as a biosignature for life on extrasolar planets. However, in many regions of the Earth, and particularly where surface conditions are extreme, for example in hot and cold deserts, photosynthetic organisms can be driven into and under substrates where light is still sufficient for photosynthesis. These communities exhibit no detectable surface spectral signature to indicate life. The same is true of the assemblages of photosynthetic organisms at more than a few metres depth in water bodies. These communities are widespread and dominate local photosynthetic productivity. We review known cryptic photosynthetic communities and their productivity. We link geomicrobiology with observational astronomy by calculating the disk-averaged spectra of cryptic habitats and identifying detectable features on an exoplanet dominated by such a biota. The hypothetical cryptic photosynthesis worlds discussed here are Earth-analogs that show detectable atmospheric biomarkers like our own planet, but do not exhibit a discernable biological surface feature in the disc-averaged spectrum.