2016/08/31 by Martin Turbet, Jeremy Leconte, Franck Selsis +5 · 1 citation
Physics and Astronomy · #astro-ph.EP
paper · pdf · doi:10.1051/0004-6361/201629577
published as A&A 596, A112 (2016) · Accepted for publication in Astronomy&Astrophysics, companion paper to Ribas et al
arxiv created 2016/09/28 · arxiv updated 2016/12/14
Radial velocity monitoring has found the signature of a M sin i = 1.3~M_⊕ planet located within the Habitable Zone (HZ) of Proxima Centauri \citepAnglada16. Despite a hotter past and an active host star the planet Proxima~b could have retained enough volatiles to sustain surface habitability \citepRibas2016. Here we use a 3D Global Climate Model (GCM) to simulate Proxima b's atmosphere and water cycle for its two likely rotation modes (1:1 and 3:2 spin-orbit resonances) while varying the unconstrained surface water inventory and atmospheric greenhouse effect. We find that a broad range of atmospheric compositions allow surface liquid water. On a tidally-locked planet with sufficient surface water inventory, liquid water is always present, at least in the substellar region. With a non-synchronous rotation, this requires a minimum greenhouse warming (∼10~mbar of CO2 and 1~bar of N2). If the planet is dryer, ∼0.5~bar/1.5~bars of CO2 (respectively for asynchronous/synchronous rotation) suffice to prevent the trapping of any arbitrary small water inventory into polar/nightside ice caps. We produce reflection/emission spectra and phase curves for the simulated climates. We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes. The angular separation of 7 λ/D at 1~μm (with the E-ELT) and a contrast of ∼10-7 will enable high-resolution spectroscopy and the search for molecular signatures, including H2O, O2, and CO2. The observation of thermal phase curves can be attempted with JWST, thanks to a contrast of 2×10-5 at 10~μm. Proxima~b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima~b and possibly determine whether this exoplanet's surface is habitable.