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Title: Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Abstract

Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO{sub 2}, under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures ( T {sub s}); snowball ( T {sub s} ≤ 235 K), waterbelt (235 K ≤ T {sub s} ≤ 250 K), temperate (275 K ≤ T {sub s} ≤ 315 K), and moist greenhouse ( T {sub s} ≥ 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having Tmore » {sub s} ∼ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ∼1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO{sub 2}, habitability can be maintained for an upper limit of ∼2.2, ∼2.4, and ∼4.7 Gyr around F-, G-, and K-dwarf stars respectively, due to main sequence brightening.« less

Authors:
;  [1];  [2]; ;  [3]
  1. Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO (United States)
  2. University of California, Irvine, Department of Physics and Astronomy, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States)
  3. NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195 (United States)
Publication Date:
OSTI Identifier:
22661300
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 837; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON DIOXIDE; CLIMATES; COMPUTERIZED SIMULATION; DIFFUSION; DWARF STARS; EARTH PLANET; GENERAL CIRCULATION MODELS; HEAT EXCHANGERS; ICE; LIMITING VALUES; LOSSES; MAIN SEQUENCE STARS; SATELLITE ATMOSPHERES; SATELLITES; SPACE; THERMAL RADIATION; THERMODYNAMICS

Citation Formats

Wolf, Eric T., Toon, Owen B., Shields, Aomawa L., Kopparapu, Ravi K., and Haqq-Misra, Jacob, E-mail: eric.wolf@colorado.edu. Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5FFC.
Wolf, Eric T., Toon, Owen B., Shields, Aomawa L., Kopparapu, Ravi K., & Haqq-Misra, Jacob, E-mail: eric.wolf@colorado.edu. Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model. United States. doi:10.3847/1538-4357/AA5FFC.
Wolf, Eric T., Toon, Owen B., Shields, Aomawa L., Kopparapu, Ravi K., and Haqq-Misra, Jacob, E-mail: eric.wolf@colorado.edu. Fri . "Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model". United States. doi:10.3847/1538-4357/AA5FFC.
@article{osti_22661300,
title = {Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model},
author = {Wolf, Eric T. and Toon, Owen B. and Shields, Aomawa L. and Kopparapu, Ravi K. and Haqq-Misra, Jacob, E-mail: eric.wolf@colorado.edu},
abstractNote = {Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO{sub 2}, under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures ( T {sub s}); snowball ( T {sub s} ≤ 235 K), waterbelt (235 K ≤ T {sub s} ≤ 250 K), temperate (275 K ≤ T {sub s} ≤ 315 K), and moist greenhouse ( T {sub s} ≥ 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having T {sub s} ∼ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ∼1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO{sub 2}, habitability can be maintained for an upper limit of ∼2.2, ∼2.4, and ∼4.7 Gyr around F-, G-, and K-dwarf stars respectively, due to main sequence brightening.},
doi = {10.3847/1538-4357/AA5FFC},
journal = {Astrophysical Journal},
number = 2,
volume = 837,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2017},
month = {Fri Mar 10 00:00:00 EST 2017}
}