Reflections on O2 as a Biosignature in Exoplanetary Atmospheres.
TLDR
Environmental factors for abiotic O2 have been identified and will improve the ability to choose optimal targets and measurements to guard against false positives, and thorough evaluation of potential biosignatures works to increase confidence in life detection.Abstract:
Oxygenic photosynthesis is Earth's dominant metabolism, having evolved to harvest the largest expected energy source at the surface of most terrestrial habitable zone planets. Using CO2 and H2O—molecules that are expected to be abundant and widespread on habitable terrestrial planets—oxygenic photosynthesis is plausible as a significant planetary process with a global impact. Photosynthetic O2 has long been considered particularly robust as a sign of life on a habitable exoplanet, due to the lack of known “false positives”—geological or photochemical processes that could also produce large quantities of stable O2. O2 has other advantages as a biosignature, including its high abundance and uniform distribution throughout the atmospheric column and its distinct, strong absorption in the visible and near-infrared. However, recent modeling work has shown that false positives for abundant oxygen or ozone could be produced by abiotic mechanisms, including photochemistry and atmospheric escape. Environm...read more
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Evolution of a Habitable Planet
TL;DR: In this paper, it is shown that Earth's climate has remained conducive to life for the past 3.5 billion years or more, despite a large increase in solar luminosity, probably because of previous higher concentrations of CO 2 and/or CH4.
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Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment.
Victoria S. Meadows,Victoria S. Meadows,Christopher T. Reinhard,Christopher T. Reinhard,Giada Arney,Giada Arney,M. N. Parenteau,M. N. Parenteau,Edward W. Schwieterman,Shawn Domagal-Goldman,Shawn Domagal-Goldman,Andrew P. Lincowski,Andrew P. Lincowski,Karl R. Stapelfeldt,Heike Rauer,Shiladitya DasSarma,Siddharth Hegde,Norio Narita,Russell Deitrick,Russell Deitrick,Jacob Lustig-Yaeger,Jacob Lustig-Yaeger,Timothy W. Lyons,Timothy W. Lyons,N. Siegler,J. Lee Grenfell +25 more
TL;DR: The coevolution of life with the early Earth's environment is examined to identify how the interplay of sources and sinks may have suppressed O2 release into the atmosphere for several billion years, producing a false negative for biologically generated O2.
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Modeling Repeated M Dwarf Flaring at an Earth-like Planet in the Habitable Zone: Atmospheric Effects for an Unmagnetized Planet.
Matt A. Tilley,Matt A. Tilley,Antígona Segura,Antígona Segura,Victoria S. Meadows,Victoria S. Meadows,Suzanne L. Hawley,Suzanne L. Hawley,James R. A. Davenport,James R. A. Davenport +9 more
TL;DR: In this article, the impact of active M dwarf stars on the atmospheric equilibrium and surface conditions of a habitable zone Earth-like planet is investigated, which is key to assessing M dwarf planet habitability.
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Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System
Andrew P. Lincowski,Victoria S. Meadows,David Crisp,David Crisp,Tyler D. Robinson,Tyler D. Robinson,Rodrigo Luger,Jacob Lustig-Yaeger,Giada Arney,Giada Arney +9 more
TL;DR: In this paper, a 1D terrestrial-planet climate model with line-by-line radiative transfer and mixing length convection (VPL Climate) coupled with a terrestrial photochemistry model was used to simulate environmental states for the TRAPPIST-1 planets.
Evidence for free oxygen in the Neoarchean ocean based on coupled iron-molybdenum isotope fractionation
Andrew D. Czaja,Clark M. Johnson,Eric E. Roden,Brian L. Beard,Andrea R. Voegelin,Thomas F. Nägler,Nicolas J. Beukes,Martin Wille +7 more
TL;DR: In this article, a combination of Fe and Mo isotope systematics of Ca-Mg carbonates and shales from the 2.68 to 2.50 Ga Campbellrand-Malmani carbonate platform of the Kaapvaal Craton in South Africa was used to constrain free O2 levels in the photic zone of a Late Archean marine basin by the combined use of Fe-Mo isotope systems.
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