Assessing Conditions for the Origin of Life on exoplanets

The assessment of planet habitability for extrasolar planets is commonly linked to the measurement of certain characteristic atmospheric gases such as water, carbon dioxide, oxygen, ozone and methane. However, the detection of these “biosignatures” often lacks a mechanism that relates those detections to the biogeochemical cycling taking place between the atmosphere, surface and ocean. This lack of context can lead to a limited assessment of a potential habitable environment and allows for unresolvable false positive scenarios for any biosignatures that may be detected. Understanding habitability on terrestrial exoplanets, and interpreting atmospheric signatures from the future Habitable Worlds Observatory (HWO), requires a deeper knowledge of this geochemical cycling—not just that of carbon, oxygen or hydrogen, but of the other bioessential elements of CHNOPS (nitrogen, phosphorus and sulfur) and iron (Fe). In this work we present arguments and suggested pathways for assessing the origin of life (OOL) on exoplanets in advance of HWO. Both OOL and planet habitability are required for extant life. Here we define the OOL as as a transcription and translation (DNA -> RNA -> proteins) system, with enzyme-driven metabolic networks contained within a cellular membrane (Goldman et al. 2016). It is this transition from mineral-catalyzed to enzyme-driven organic redox chemistry that we will focus our study here. In this work we will aim to answer the question—if we fundamentally assume that the OOL on exoplanets started with some of the same mineral-enzyme transitions as on Earth, can we detect chemical signatures that could tell us whether those transitions could exist on an exoplanet?