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Habitable Zone Lifetime of Exoplanets around Main Sequence Stars

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rushby2013astrobiol833.pdf (608.9Kb)
Date
18/09/2013
Author
Rushby, Andrew
Claire, M.
Osborn, H.
Watson, A.
Keywords
Exoplanet habitability metrics
Continuously habitable zone
Stellar evolution
Planetary habitability
QB Astronomy
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Abstract
The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star’s main sequence lifetime. We describe the time that a planet spends within the HZ as its ‘‘habitable zone lifetime.’’ The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the ‘‘classic’’ HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a ‘‘hybrid’’ HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79 · 109 years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets’ HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns.
Citation
Rushby , A , Claire , M , Osborn , H & Watson , A 2013 , ' Habitable Zone Lifetime of Exoplanets around Main Sequence Stars ' , Astrobiology , vol. 13 , no. 9 , pp. 833-849 . https://doi.org/10.1089/ast.2012.0938
Publication
Astrobiology
Status
Peer reviewed
DOI
https://doi.org/10.1089/ast.2012.0938
ISSN
1531-1074
Type
Journal article
Rights
© 2013. Mary Ann Liebert, Inc. This is an open access article, available from http://online.liebertpub.com/doi/pdfplus/10.1089/ast.2012.0938
Description
Funding: Dean's Scholarship at the University of East Anglia.
Collections
  • University of St Andrews Research
URI
http://hdl.handle.net/10023/5071

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