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Quarles B, Barnes JW, Lissauer JJ, Chambers J. Obliquity Evolution of the Potentially Habitable Exoplanet Kepler-62f. ASTROBIOLOGY 2020; 20:73-90. [PMID: 31613645 DOI: 10.1089/ast.2018.1932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Variations in the axial tilt, or obliquity, of terrestrial planets can affect their climates and therefore their habitability. Kepler-62f is a 1.4 R⊕ planet orbiting within the habitable zone of its K2 dwarf host star. We perform N-body simulations that monitor the evolution of obliquity of Kepler-62f for 10-million-year timescales to explore the effects on model assumptions, such as the masses of the Kepler-62 planets and the possibility of outer bodies. Significant obliquity variation occurs when the rotational precession frequency overlaps with one or more of the secular orbital frequencies, but most variations are limited to ≲10°. Moderate variations (∼10-20°) can occur over a broader range of initial obliquities when the relative nodal longitude (ΔΩ) overlaps with the frequency and phase of a given secular mode. However, we find that adding outer gas giants on long-period orbits (∼1000 days) can produce large (∼60°) variations in obliquity if Kepler-62f has a very rapid (4 h) rotation period. The possibility of giant planets on long-period orbits impacts the climate and habitability of Kepler-62f through variations in the latitudinal surface flux, where large variations can occur on million year timescales.
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Affiliation(s)
- Billy Quarles
- Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, Georgia
| | - Jason W Barnes
- Department of Physics, University of Idaho, Moscow, Idaho
| | - Jack J Lissauer
- NASA Ames Research Center, Astrobiology and Space Science Division MS 245-3, Moffett Field, California
| | - John Chambers
- Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, District of Columbia
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Del Genio AD, Kiang NY, Way MJ, Amundsen DS, Sohl LE, Fujii Y, Chandler M, Aleinov I, Colose CM, Guzewich SD, Kelley M. Albedos, Equilibrium Temperatures, and Surface Temperatures of Habitable Planets. THE ASTROPHYSICAL JOURNAL 2019; 884:75. [PMID: 33100349 PMCID: PMC7580787 DOI: 10.3847/1538-4357/ab3be8] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The potential habitability of known exoplanets is often categorized by a nominal equilibrium temperature assuming a Bond albedo of either ∼0.3, similar to Earth, or 0. As an indicator of habitability, this leaves much to be desired, because albedos of other planets can be very different, and because surface temperature exceeds equilibrium temperature due to the atmospheric greenhouse effect. We use an ensemble of general circulation model simulations to show that for a range of habitable planets, much of the variability of Bond albedo, equilibrium temperature and even surface temperature can be predicted with useful accuracy from incident stellar flux and stellar temperature, two known parameters for every confirmed exoplanet. Earth's Bond albedo is near the minimum possible for habitable planets orbiting G stars, because of increasing contributions from clouds and sea ice/snow at higher and lower instellations, respectively. For habitable M star planets, Bond albedo is usually lower than Earth's because of near-IR H2O absorption, except at high instellation where clouds are important. We apply relationships derived from this behavior to several known exoplanets to derive zeroth-order estimates of their potential habitability. More expansive multivariate statistical models that include currently non-observable parameters show that greenhouse gas variations produce significant variance in albedo and surface temperature, while increasing length of day and land fraction decrease surface temperature; insights for other parameters are limited by our sampling. We discuss how emerging information from global climate models might resolve some degeneracies and help focus scarce observing resources on the most promising planets.
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Affiliation(s)
- Anthony D Del Genio
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Nancy Y Kiang
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Michael J Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - David S Amundsen
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Linda E Sohl
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Yuka Fujii
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8550, Japan
| | - Mark Chandler
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Igor Aleinov
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Christopher M Colose
- NASA Postdoctoral Program, Goddard Institute for Space Studies, New York, NY 10025, USA
| | | | - Maxwell Kelley
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- SciSpace LLC, 2880 Broadway, New York, NY 10025, USA
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Way M, Del Genio AD, Aleinov I, Clune TL, Kelley M, Kiang NY. Climates of Warm Earth-like Planets I: 3-D Model Simulations. THE ASTROPHYSICAL JOURNAL. SUPPLEMENT SERIES 2018; 239:24. [PMID: 30948861 PMCID: PMC6443379 DOI: 10.3847/1538-4365/aae9e1] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We present a large ensemble of simulations of an Earth-like world with increasing insolation and rotation rate. Unlike previous work utilizing idealized aquaplanet configurations we focus our simulations on modern Earth-like topography. The orbital period is the same as modern Earth, but with zero obliquity and eccentricity. The atmosphere is 1 bar N2-dominated with CO2=400 ppmv and CH4=1 ppmv. The simulations include two types of oceans; one without ocean heat transport (OHT) between grid cells as has been commonly used in the exoplanet literature, while the other is a fully coupled dynamic bathtub type ocean. The dynamical regime transitions that occur as day length increases induce climate feedbacks producing cooler temperatures, first via the reduction of water vapor with increasing rotation period despite decreasing shortwave cooling by clouds, and then via decreasing water vapor and increasing shortwave cloud cooling, except at the highest insolations. Simulations without OHT are more sensitive to insolation changes for fast rotations while slower rotations are relatively insensitive to ocean choice. OHT runs with faster rotations tend to be similar with gyres transporting heat poleward making them warmer than those without OHT. For slower rotations OHT is directed equator-ward and no high latitude gyres are apparent. Uncertainties in cloud parameterization preclude a precise determination of habitability but do not affect robust aspects of exoplanet climate sensitivity. This is the first paper in a series that will investigate aspects of habitability in the simulations presented herein. The datasets from this study are opensource and publicly available.
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Affiliation(s)
- M.J. Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA
- Department of Physics and Astronomy, Uppsala University, Uppsala, 75120, Sweden
| | - Anthony D. Del Genio
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA
| | - Igor Aleinov
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10025, USA
| | - Thomas L. Clune
- Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, USA
| | - Maxwell Kelley
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA
| | - Nancy Y. Kiang
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA
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