Analysis of the radiative budget of the Venusian atmosphere based on infrared Net Exchange Rate formalism

Lebonnois, Sébastien; Eymet, Vincent; Lee, Christopher; d'Ollone, Jan Vatant

doi:10.1002/2015je004794

Cited by 37 publications

(51 citation statements)

References 40 publications

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“…In the Appendix B we present spectra and phase curves obtained with different compositions and rotations. As the planet could have experienced a fate similar to Venus (Ingersoll 1969), we also present reflection spectra and phase curves for a Venus-like atmosphere (Lebonnois et al 2015), including sulphur-bearing aerosols known to produce a high albedo at visible wavelength, and then exposed to the irradiance of Proxima at the orbital distance of Proxima b.…”

Section: Prospects For Direct Imagingmentioning

confidence: 99%

The habitability of Proxima Centauri b

Turbet

Leconte

Selsis

et al. 2016

A&A

241

262

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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 (Anglada-Escudé 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 (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. Any low-obliquity low-eccentricity planet within the HZ of its star should be in one of the climate regimes discussed here. 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 CO 2 and 1 bar of N 2 ). If the planet is dryer, ∼0.5 bar/1.5 bars of CO 2 (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 7λ/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 H 2 O, O 2 , and CO 2 . 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.

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Section: Prospects For Direct Imagingmentioning

confidence: 99%

The habitability of Proxima Centauri b

Turbet

Leconte

Selsis

et al. 2016

A&A

241

262

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“…The role of thermal tides to transport angular momentum vertically in low latitudes has been confirmed (Lebonnois et al 2010;Takagi & Matsuda 2007). It has also been noticed that the latitudinal distribution of zonal wind at cloud tops may result from an equilibrium between the impact of thermal tides and the angular momentum transport by the meridional circulation (Lebonnois et al 2010), providing grounds for systematic and simultaneous observations of both zonal and meridional regimes.…”

Section: Introductionmentioning

confidence: 87%

“…Characterizing the meridional circulation is also important for understanding the maintenance of the super-rotation, by determining the global mean and eddy circulations and the associated meridional transport of angular momentum and energy (e.g., Limaye & Rengel 2013). The role of thermal tides to transport angular momentum vertically in low latitudes has been confirmed (Lebonnois et al 2010;Takagi & Matsuda 2007). It has also been noticed that the latitudinal distribution of zonal wind at cloud tops may result from an equilibrium between the impact of thermal tides and the angular momentum transport by the meridional circulation (Lebonnois et al 2010), providing grounds for systematic and simultaneous observations of both zonal and meridional regimes.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric circulation of Venus measured with visible imaging spectroscopy at the THEMIS observatory

Gaulme

Schmider

Widemann

et al. 2019

A&A

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Measuring the atmospheric circulation of Venus at different altitudes is important for understanding its complex dynamics, in particular the mechanisms driving super-rotation. Observationally, Doppler imaging spectroscopy is in principle the most reliable way to measure wind speeds of planetary atmospheres because it directly provides the projected speed of atmospheric particles. However, high-resolution imaging spectroscopy is challenging, especially in the visible domain, and most knowledge about atmospheric dynamics has been obtained with the cloud tracking technique. The objective of the present work is to measure the global properties of the atmospheric dynamics of Venus at the altitude of the uppermost clouds, which is probed by reflected solar lines in the visible domain. Our results are based on high-resolution spectroscopic observations with the long-slit spectrometer of the solar telescope THEMIS. We present the first instantaneous "radial-velocity snapshot" of any planet of the solar system in the visible domain, i.e., a complete radial-velocity map of the planet obtained by stacking data on less than 10 % of its rotation period. From this, we measured the properties of the zonal and meridional winds, which we unambiguously detect. We identify a wind circulation pattern that significantly differs from previous knowledge about Venus. The zonal wind reveals a "hot spot" structure, featuring about 200 m s −1 at sunrise and 70 m s −1 at noon in the equatorial region. Regarding meridional winds, we detect an equator-to-pole meridional flow peaking at 45 m s −1 at mid-latitudes, i.e., about twice as large as what has been reported so far.

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“…The effects of topography are ignored and the surface of the planet is thus considered as an isotropic sphere of albedo A s " 0.2 and thermal inertia I gr " 2000 J.m´2.s´1 {2 .K´1, which is a typical value for Venus-like soils (see e.g. Lebonnois et al 2010) 2 . All of these parameters remain unchanged for the whole study and are summarized in Table 1.…”

Section: Physical Setup Of the 3d Simulationsmentioning

confidence: 99%

“…We do not attempt to reproduce exactly the composition and dynamics of the Venus atmosphere, which is a complex problem beyond the scope of this study (see e.g. Lebonnois et al 2010Lebonnois et al , 2016, but to simply retrieve its main features (optical opacity, clouds absorption, etc.). As a consequence, we opt for a generic approach excluding a fine tuning of the atmospheric properties.…”

Section: Appendix A: Normalized Spherical Harmonicsmentioning

confidence: 99%

Generic frequency dependence for the atmospheric tidal torque of terrestrial planets

Auclair-Desrotour

Leconte

Mergny

2019

A&A

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Context. Thermal atmospheric tides have a strong impact on the rotation of terrestrial planets. They can lock these planets into an asynchronous rotation state of equilibrium. Aims. We aim at characterizing the dependence of the tidal torque resulting from the semidiurnal thermal tide on the tidal frequency, the planet orbital radius, and the atmospheric surface pressure. Methods. The tidal torque is computed from full 3D simulations of the atmospheric climate and mean flows using a generic version of the LMDZ general circulation model (GCM) in the case of a nitrogen-dominated atmosphere. Numerical results are discussed with the help of an updated linear analytical framework. Power scaling laws governing the evolution of the torque with the planet orbital radius and surface pressure are derived. Results. The tidal torque exhibits i) a thermal peak in the vicinity of synchronization, ii) a resonant peak associated with the excitation of the Lamb mode in the high frequency range, and iii) well defined frequency slopes outside these resonances. These features are well explained by our linear theory. Whatever the star-planet distance and surface pressure, the torque frequency spectrum -when rescaled with the relevant power laws -always presents the same behaviour. This allows us to provide a single and easily usable empirical formula describing the atmospheric tidal torque over the whole parameter space. With such a formula, the effect of the atmospheric tidal torque can be implemented in evolutionary models of the rotational dynamics of a planet in a computationally efficient, and yet relatively accurate way.Key words. hydrodynamics -planet-star interactions -waves -planets and satellites: atmospheres tween the two effects locks the planet into an asynchronous rotation state of equilibrium, which explains the departure of the rotation rate of Venus to spin-orbit synchronization.Article number, page 1 of 23

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Analysis of the radiative budget of the Venusian atmosphere based on infrared Net Exchange Rate formalism

Cited by 37 publications

References 40 publications

The habitability of Proxima Centauri b

The habitability of Proxima Centauri b

Atmospheric circulation of Venus measured with visible imaging spectroscopy at the THEMIS observatory

Generic frequency dependence for the atmospheric tidal torque of terrestrial planets

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