Habitable worlds with no signs of life

Abstract

'Most habitable worlds in the cosmos will have no remotely detectable signs of life' is proposed as a biological hypothesis to be tested in studies of exoplanets. Habitable planets could be discovered elsewhere in the Universe, yet there are many hypothetical scenarios whereby the search for life on them could yield negative results. Scenarios for habitable worlds with no remotely detectable signatures of life include: planets that are habitable, but have no biosphere (Uninhabited Habitable Worlds); planets with life, but lacking any detectable surface signatures of that life (laboratory examples are provided) and planets with life, where the concentration of atmospheric gases produced or removed by biota are impossible to disentangle from abiotic processes because of the lack of detailed knowledge of planetary conditions (the 'problem of exoplanet thermodynamic uncertainty'). A rejection of the hypothesis would require that the origin of life usually occurs on habitable planets, that spectrally detectable pigments and/or metabolisms that produce unequivocal biosignature gases (e.g. oxygenic photosynthesis) usually evolve and that the organisms that harbour them usually achieve a sufficient biomass to produce biosignatures detectable to alien astronomers.

29 page, 3 figures, 1 table, accepted for publication in Philosophical Transactions of the Royal Society (Exoplanet discussion meeting)

References in corpus (5)

• Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
• Spectral signatures of photosynthesis I: Review of Earth organisms
• Spectral signatures of photosynthesis II: coevolution with other stars and the atmosphere on extrasolar worlds
• Formation of Early Water Oceans on Rocky Planets
• Colors of extreme exo-Earth environments

Cited by in corpus (11)

• Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
• Abiotic O${}_2$ Levels on Planets around F, G, K, and M Stars: Possible False Positives for Life?
• Subsurface Exolife
• Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System
• Dependence of Biological Activity on the Surface Water Fraction of Planets
• A population-based Habitable Zone perspective
• Biofluorescent Worlds II. Biological fluorescence induced by stellar UV flares, a new temporal biosignature
• Biosignature Surveys to Exoplanet Yields and Beyond
• Surface and Temporal Biosignatures
• A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone
• Direct Exoplanet Investigation using Interstellar Space Probes