The Effect of Orbital Configuration on the Possible Climates and Habitability of Kepler-62f

Aomawa L. Shields1,* (email: ashields@astro.ucla.edu) , Rory Barnes2,*, Eric Agol2,*, Benjamin Charnay2,*, Cecilia Bitz3,*, Victoria S. Meadows2,* 1UC Irvine/UCLA, Department of Physics and Astronomy and Harvard-Smithsonian Center for Astrophysics; 2University of Washington, Department of Astronomy and Astrobiology Program;

3University of Washington, Department of Atmospheric Sciences; *NASA Astrobiology Institute’s Virtual Planetary Laboratory

ACKNOWLEDGMENTS: This material is based upon work supported by the National Science Foundation under Award No. 1401554, and Grant Nos. DGE-0718124 and DGE-1256082, and by a University of California President’s Postdoctoral Fellowship. We would also like to acknowledge high-performance computing support from the Hyak supercomputer system at the University of Washington, and Yellowstone (ark:/85065/d7wd3xhc) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by the National Science Foundation.

REFERENCES: [1] Borucki et al. (2013) Science, 340, 6132

[2] Shields et al. (2016) Astrobiology, 16, 6

A Good Prospect for a Habitable World

o  Using an n-body model, we identify 0.00 ≤ e ≤ 0.32 as the range of stable initial eccentricities possible for Kepler-62f.

o  Kepler-62f could be habitable for a fairly wide range of plausible CO2 concentrations, or in a low-CO2 scenario, rare but possible orbital configurations.

o  If Kepler-62f is synchronously rotating, more than 3 bar of atmospheric CO2 would likely be required for open water at the substellar point, and atmospheric stability on the night side of the planet. [2].

A Potentially Habitable World

Photo: Martin Cox

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Star&

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Equinox&

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Fig. 1 – The Kepler-62 system consists of five closely spaced planets orbiting a K-dwarf star 1200 light years away. Kepler-62f (1.41RE) sits near the outer edge of the habitable zone, with a relatively low incoming stellar insolation (40% of what Earth receives from the Sun). However, the planet could avoid freezing with a sufficient greenhouse effect.

Abstract

Using n-body model constraints as well as tidal model simulation results as input to three-dimensional (3D) global climate model (GCM) simulations, we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on the potentially habitable planet Kepler-62f [1].

Where there could be water, there could be life…

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Fig. 9-10 – Left: Evolution of the spin period for Kepler-62f, using the Constant Phase Lag model. Only the extremely fast-rotating and high-obliquity cases do not tidally lock within 5 Gyr. Right: Surface temperature for a synchronously-rotating Kepler-62f with 3 bar of CO2 in the atmosphere. The planet is globally ice-covered, the substellar point is just above freezing, and the night side is right at the condensation limit for CO2 at this surface pressure.

Fig. 5-6 – Surface temperature as a function of the month of the year for Kepler-62f (left) after 40-year CCSM4 GCM simulations, assuming a 12-month annual cycle, Earth-like CO2, an obliquity of 60° and an eccentricity of 0.32. Temperatures reach above freezing during southern hemisphere summer months. This is because we have assumed a specific orbital configuration (right), where the angle of the vernal equinox with respect to pericenter is 90°, similar to Earth (102.7°). This maximizes the effects of high obliquity and eccentricity, and could melt ice sheets formed during colder seasons.

Summer&sols*ce&at&closest&approach&

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stable e_fmax = 0.32

unstable

Stable eccentricity range for Kepler-62f 0.00 ≤ e ≤ 0.32

24-hr, Obl 23.5°

8-hr, Obl 80°

10-d, Obl 5°

e=0.00 e=0.32

Fig. 2 – Fraction of stable configurations after a 106-year HNBody integration for initial eccentricities between 0.0 and 0.9 for Kepler-62f. The eccentricities of all other planets in the Kepler-62 system were set to zero.

Fig. 3 – Sea ice cover fraction as a function of latitude for Kepler-62f after 160-year LMD Generic GCM simulations. With 3 bar of CO2 in the atmosphere, open water is only possible at the maximum stable initial eccentricity (e = 0.32), and an extreme obliquity (90°), with an Earth-like rotation rate.

Fig. 4 – Surface temperature as a function of latitude for Kepler-62f with 5 bar CO2 in the planet’s atmosphere. Open water is present throughout the entire stable eccentricity range, 0.00 ≤ e ≤ 0.32.

Image credit: NASA Ames/JPL-Caltech