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Titel |
Habitability of planets on eccentric orbits: limits of the mean flux approximation |
VerfasserIn |
Emeline Bolmont, Anne-Sophie Libert, Jérémy Leconte, Franck Selsis, Martin Turbet, François Forget |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250121598
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Publikation (Nr.) |
EGU/EGU2016-382.pdf |
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Zusammenfassung |
A few of the planets found in the insolation habitable zone (region in which a planet with an
atmosphere can sustain surface liquid water, Kasting et al. 1993) are on eccentric
orbits, such as GJ 667Cc (eccentricity of < 0.3, Anglada-Escude et al. 2012) or
HD 16175 b (eccentricity of 0.6, Peek et al. 2009). This raises the question of the
potential habitability of planets that only spend a fraction of their orbit in the habitable
zone.
Usually for a planet of semi-major axis a and eccentricity e, the averaged flux over one
orbit received by the planet is considered. This averaged flux corresponds to the flux received
by a planet on a circular orbit of radius r = a(1 −e2)1∕4. If this orbital distance is within the
habitable zone, the planet is said “habitable”. However, for a hot star, for which the habitable
zone is far from the star, the climate can be degraded when the planet is temporarily outside
the habitable zone.
We investigate here the limits of validity of the mean flux approximation used to assess
the potential habitability of eccentric planets. For this study, we consider ocean
planets in synchronized rotation and planets with a rotation period of 24 hr. We
investigate the influence of the type of host star and the eccentricity of the orbit on
the climate of a planet. We do so by scaling the duration of its orbital period and
its apastron and periastron distance to ensure that it receives in average the same
incoming flux as Earth’s. We performed sets of 3D simulations using the Global
Climate Model LMDz (Wordsworth et al. 2011, Forget et al. 2013, Leconte et al.
2013). The atmosphere is composed of N2, CO2 and H2O (gas, liquid, solid) in
Earth-like proportions. First, we do not take into account the spectral difference
between a low luminosity star and a Sun-like star. Second, the dependence of the
albedo of ice and snow on the spectra of the host star is taken into account. This
influences the positive ice-albedo feedback and can lead to a different climatic
evolution.
We show that the higher the eccentricity and the higher the luminosity of the star, the less
reliable the mean flux approximation. |
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