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Title: HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY

Abstract

In the outer regions of the habitable zone, the risk of transitioning into a globally frozen 'snowball' state poses a threat to the habitability of planets with the capacity to host water-based life. Here, we use a one-dimensional energy balance climate model (EBM) to examine how obliquity, spin rate, orbital eccentricity, and the fraction of the surface covered by ocean might influence the onset of such a snowball state. For an exoplanet, these parameters may be strikingly different from the values observed for Earth. Since, for a constant semimajor axis, the annual mean stellar irradiation scales with (1 - e {sup 2}){sup -1/2}, one might expect the greatest habitable semimajor axis (for fixed atmospheric composition) to scale as (1 - e {sup 2}){sup -1/4}. We find that this standard simple ansatz provides a reasonable lower bound on the outer boundary of the habitable zone, but the influence of both obliquity and ocean fraction can be profound in the context of planets on eccentric orbits. For planets with eccentricity 0.5, for instance, our EBM suggests that the greatest habitable semimajor axis can vary by more than 0.8 AU (78%) depending on obliquity, with higher obliquity worlds generally more stable against snowballmore » transitions. One might also expect that the long winter at an eccentric planet's apoastron would render it more susceptible to global freezing. Our models suggest that this is not a significant risk for Earth-like planets around Sun-like stars, as considered here, since such planets are buffered by the thermal inertia provided by oceans covering at least 10% of their surface. Since planets on eccentric orbits spend much of their year particularly far from the star, such worlds might turnout to be especially good targets for direct observations with missions such as TPF-Darwin. Nevertheless, the extreme temperature variations achieved on highly eccentric exo-Earths raise questions about the adaptability of life to marginally or transiently habitable conditions.« less

Authors:
;  [1];  [2];  [3]
  1. Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544 (United States)
  2. Columbia Astrobiology Center, Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
  3. Kavli Institute for Theoretical Physics, UCSB, Santa Barbara, CA 93106-4030 (United States)
Publication Date:
OSTI Identifier:
21471313
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 721; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/721/2/1295; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLIMATE MODELS; CLIMATES; ENERGY BALANCE; MOMENT OF INERTIA; ONE-DIMENSIONAL CALCULATIONS; PLANETS; SUN; MAIN SEQUENCE STARS; MATHEMATICAL MODELS; STARS

Citation Formats

Dressing, Courtney D, Spiegel, David S, Scharf, Caleb A, Menou, Kristen, and Raymond, Sean N., E-mail: courtney@astro.princeton.ed, E-mail: dsp@astro.princeton.ed, E-mail: kristen@astro.columbia.ed, E-mail: caleb@astro.columbia.ed, E-mail: raymond@obs.u-bordeaux1.f. HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY. United States: N. p., 2010. Web. doi:10.1088/0004-637X/721/2/1295.
Dressing, Courtney D, Spiegel, David S, Scharf, Caleb A, Menou, Kristen, & Raymond, Sean N., E-mail: courtney@astro.princeton.ed, E-mail: dsp@astro.princeton.ed, E-mail: kristen@astro.columbia.ed, E-mail: caleb@astro.columbia.ed, E-mail: raymond@obs.u-bordeaux1.f. HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY. United States. doi:10.1088/0004-637X/721/2/1295.
Dressing, Courtney D, Spiegel, David S, Scharf, Caleb A, Menou, Kristen, and Raymond, Sean N., E-mail: courtney@astro.princeton.ed, E-mail: dsp@astro.princeton.ed, E-mail: kristen@astro.columbia.ed, E-mail: caleb@astro.columbia.ed, E-mail: raymond@obs.u-bordeaux1.f. Fri . "HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY". United States. doi:10.1088/0004-637X/721/2/1295.
@article{osti_21471313,
title = {HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY},
author = {Dressing, Courtney D and Spiegel, David S and Scharf, Caleb A and Menou, Kristen and Raymond, Sean N., E-mail: courtney@astro.princeton.ed, E-mail: dsp@astro.princeton.ed, E-mail: kristen@astro.columbia.ed, E-mail: caleb@astro.columbia.ed, E-mail: raymond@obs.u-bordeaux1.f},
abstractNote = {In the outer regions of the habitable zone, the risk of transitioning into a globally frozen 'snowball' state poses a threat to the habitability of planets with the capacity to host water-based life. Here, we use a one-dimensional energy balance climate model (EBM) to examine how obliquity, spin rate, orbital eccentricity, and the fraction of the surface covered by ocean might influence the onset of such a snowball state. For an exoplanet, these parameters may be strikingly different from the values observed for Earth. Since, for a constant semimajor axis, the annual mean stellar irradiation scales with (1 - e {sup 2}){sup -1/2}, one might expect the greatest habitable semimajor axis (for fixed atmospheric composition) to scale as (1 - e {sup 2}){sup -1/4}. We find that this standard simple ansatz provides a reasonable lower bound on the outer boundary of the habitable zone, but the influence of both obliquity and ocean fraction can be profound in the context of planets on eccentric orbits. For planets with eccentricity 0.5, for instance, our EBM suggests that the greatest habitable semimajor axis can vary by more than 0.8 AU (78%) depending on obliquity, with higher obliquity worlds generally more stable against snowball transitions. One might also expect that the long winter at an eccentric planet's apoastron would render it more susceptible to global freezing. Our models suggest that this is not a significant risk for Earth-like planets around Sun-like stars, as considered here, since such planets are buffered by the thermal inertia provided by oceans covering at least 10% of their surface. Since planets on eccentric orbits spend much of their year particularly far from the star, such worlds might turnout to be especially good targets for direct observations with missions such as TPF-Darwin. Nevertheless, the extreme temperature variations achieved on highly eccentric exo-Earths raise questions about the adaptability of life to marginally or transiently habitable conditions.},
doi = {10.1088/0004-637X/721/2/1295},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 721,
place = {United States},
year = {2010},
month = {10}
}