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The habitability of Proxima Centauri b II. Possible climates and Observability

Abstract : Radial velocity monitoring has found the signature of a $M \sin i = 1.3$~M$_\oplus$ planet located within the Habitable Zone of Proxima Centauri, (Anglada-Escud\'e et al. 2016). Despite a hotter past and an active host star the planet Proxima~b could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model to simulate Proxima b's atmosphere and water cycle for its two likely rotation modes (1:1 and 3:2 resonances) while varying the unconstrained surface water inventory and atmospheric greenhouse effect. We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water inventory larger than 0.6 Earth ocean, liquid water is always present, at least in the substellar region. Liquid water covers the whole planet for CO$_2$ partial pressures $\gtrsim 1$~bar. For smaller water inventories, water can be trapped on the night side, forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO$_2$ pressure is required to avoid falling into a completely frozen snowball state if water is abundant. If the planet is dryer, $\sim$0.5~bar of CO$_2$ would suffice to prevent the trapping of any arbitrary small water inventory into polar ice caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes discussed here. We use our GCM to produce reflection/emission spectra and phase curves. We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular separation of $7 \lambda/D$ at 1~$\mu$m (with the E-ELT) and a contrast of $\sim 10^{-7}$. The magnitude of the planet will allow for high-resolution spectroscopy and the search for molecular signatures.
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Contributor : Marie-Paule Pomies <>
Submitted on : Friday, September 2, 2016 - 3:02:37 PM
Last modification on : Friday, November 29, 2019 - 3:28:05 PM

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Martin, Turbet, J. Leconte, Franck Selsis, Emeline, Bolmont, Francois, Forget, et al.. The habitability of Proxima Centauri b II. Possible climates and Observability. Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 596, ⟨10.1051/0004-6361/201629577⟩. ⟨hal-01359518⟩



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