The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth.
| Autor: | Arney G; 1 Astronomy Department, University of Washington , Seattle, Washington, USA .; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 3 Astrobiology Program, University of Washington , Seattle, Washington, USA .; 4 Now at: NASA Goddard Space Flight Center , Greenbelt, Maryland, USA .; 5 Now at: NASA Postdoctoral Program, Universities Space Research Association , Columbia, Maryland, USA ., Domagal-Goldman SD; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 6 NASA Goddard Space Flight Center , Greenbelt, Maryland, USA ., Meadows VS; 1 Astronomy Department, University of Washington , Seattle, Washington, USA .; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 3 Astrobiology Program, University of Washington , Seattle, Washington, USA ., Wolf ET; 7 Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder , Boulder, Colorado, USA ., Schwieterman E; 1 Astronomy Department, University of Washington , Seattle, Washington, USA .; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 3 Astrobiology Program, University of Washington , Seattle, Washington, USA .; 5 Now at: NASA Postdoctoral Program, Universities Space Research Association , Columbia, Maryland, USA .; 8 Now at: University of California at Riverside , Riverside, California, USA .; 9 Blue Marble Institute of Science , Seattle, Washington, USA ., Charnay B; 1 Astronomy Department, University of Washington , Seattle, Washington, USA .; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 3 Astrobiology Program, University of Washington , Seattle, Washington, USA .; 10 Now at: Paris-Meudon Observatory , Paris, France ., Claire M; 2 NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington , Seattle, Washington, USA .; 9 Blue Marble Institute of Science , Seattle, Washington, USA .; 11 Department of Earth and Environmental Sciences, University of St Andrews , St Andrews, UK ., Hébrard E; 6 NASA Goddard Space Flight Center , Greenbelt, Maryland, USA .; 12 University of Exeter , Exeter, Devon, UK ., Trainer MG; 6 NASA Goddard Space Flight Center , Greenbelt, Maryland, USA . |
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| Jazyk: | angličtina |
| Zdroj: | Astrobiology [Astrobiology] 2016 Nov; Vol. 16 (11), pp. 873-899. Date of Electronic Publication: 2016 Oct 28. |
| DOI: | 10.1089/ast.2015.1422 |
| Abstrakt: | Recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere contained a Titan-like, organic-rich haze. Prior work has claimed a haze-rich Archean Earth (3.8-2.5 billion years ago) would be frozen due to the haze's cooling effects. However, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. Here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 K, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young Sun. We find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. Hazes may even enhance planetary habitability through UV shielding, reducing surface UV flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7-2.6 billion years ago. The broad UV absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. The haze in Archean Earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of CO Competing Interests: Author Disclosure Statement No competing financial interests exist. |
| Databáze: | MEDLINE |
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