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Habitability of Exomoons at the Hill or Tidal Locking Radius

Hinkel, Natalie R. and Kane, Stephen R. (2013) Habitability of Exomoons at the Hill or Tidal Locking Radius. Astrophysical Journal, 774 (1). Art. No. 27. ISSN 0004-637X. doi:10.1088/0004-637X/774/1/27.

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Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets μ Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated flux on a moon at its furthest, stable distance from the planet achieves its largest flux gradient, which places a limit on the flux ranges expected for subsequent (observed) moons closer in orbit to the planet. We have also analyzed the effect of planetary eccentricity on the flux on the moon, examining planets that traverse the habitable zone either fully or partially during their orbit. Looking solely at the stellar contributions, we find that moons around planets that are totally within the habitable zone experience thermal equilibrium temperatures above the runaway greenhouse limit, requiring a small heat redistribution efficiency. In contrast, exomoons orbiting planets that only spend a fraction of their time within the habitable zone require a heat redistribution efficiency near 100% in order to achieve temperatures suitable for habitability. This means that a planet does not need to spend its entire orbit within the habitable zone in order for the exomoon to be habitable. Because the applied systems comprise giant planets around bright stars, we believe that the transit detection method is most likely to yield an exomoon discovery.

Item Type:Article
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URLURL TypeDescription Paper
Hinkel, Natalie R.0000-0003-0595-5132
Kane, Stephen R.0000-0002-7084-0529
Additional Information:© 2013 American Astronomical Society. Received 2013 February 20; accepted 2013 July 17; published 2013 August 12. The authors acknowledge financial support from the National Science Foundation through grant AST-1109662. This work has made use of the Habitable Zone Gallery at The authors thank René Heller for use of his publicly accessible and well documented code,, as well as his useful suggestions and insight. N.R.H. thanks CJ Messinger, Esq., for his inspiration and CHW3 for his support.
Funding AgencyGrant Number
Subject Keywords:astrobiology; planetary systems; planets and satellites: individual (μ Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b)
Issue or Number:1
Record Number:CaltechAUTHORS:20130924-114841297
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Official Citation:Habitability of Exomoons at the Hill or Tidal Locking Radius Natalie R. Hinkel and Stephen R. Kane 2013 ApJ 774 27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41505
Deposited By: Ruth Sustaita
Deposited On:24 Sep 2013 20:07
Last Modified:10 Nov 2021 04:31

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