Olivia Venot | Université Paris-Est Créteil (original) (raw)
Papers by Olivia Venot
We present as ’proof of concept’ a 3D global circulation model for the fast rotating (Porb = 0.83... more We present as ’proof of concept’ a 3D global circulation model for the fast rotating (Porb = 0.835 days), high surface gravity (g = 47.4 m/s) hot Jupiter WASP-43b [1] with anomalous dynamics that at least partly breaks the ’superrotation paradigm’. We will discuss the difference between this model and a 3D model for HD 209458b, the dynamics of which is dominated by unperturbed superrotation. We will show that the anomalous dynamical effect can at the very least explain the reduced east-ward hot spot shift in hot Jupiters and naturally leads to very large day to night side temperature gradients. Our results suggest that we have to fundamentally question basic assumptions in 3D atmosphere modelling of exoplanets to explain observations of some hot to ultra-hot Jupiter atmospheres. Indeed, there are currently two exoplanets that outright question the paradigm that the hottest spot of a hot Jupiter is always eastward shifted due to superrotation: CoRoT-2b with an apparent westward shift...
Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retr... more Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retrievals. As the James Webb Space Telescope (JWST) and Ariel launch draw near, assessing the underlying biases and assumptions made when applying self-consistent chemistry into spectral retrievals is crucial. Here we use the flexibility of TauREx 3.1 to cross-compare three state of the art chemical equilibrium codes: ACE, FastChem and GGchem. We simulate JWST spectra for ACE, FastChem, GGchem and GGchem+condensation containing only C, H, O, N elements and spectra for FastChem, GGchem and GGchem+condensation with a more extensive range of elements giving seven simulated JWST spectra in total and then cross-retrieve giving a total of 49 retrievals. Our analysis demonstrates that like-for-like, all chemical codes retrieve the correct parameters to < 1% of the truth. However, retrievals, where the contained elements do not match the truth, parameters such as metallicity deviate by 20% while...
We will review the observations of species useful to constrain the O/H ratio in the interior of t... more We will review the observations of species useful to constrain the O/H ratio in the interior of the ice giants. We will apply a comprehensive thermochemical and diffusion model to the ice giants and derive constraints on their deep O/H ratios.
Bulletin of the American Astronomical Society, 2019
We have developed a photo-thermo-chemical model adapted to the study of the hot terrestrial atmos... more We have developed a photo-thermo-chemical model adapted to the study of the hot terrestrial atmospheres. Such a model is essential to interpret future observations and to predict the composition of hot extrasolar terrestrial planets. It is also important to understand the formation and the evolution of some of their key atmospheric species. We investigate here the effect of an increase of the temperature on the predicted abundances of some of these key species, such as ozone O3 and carbon dioxide CO2.
We have created a new model to study the atmosphere of exoplanets. Derivated from a car engine co... more We have created a new model to study the atmosphere of exoplanets. Derivated from a car engine combustion model, it is particularly adapted to the high temperature chemistry occuring in the atmosphere of hot Jupiters. Such a model appears essential to interpret recent and future observations, predict the composition and understand the formation and evolution of these planetary bodies. Preliminary results of a 1D thermo-photochemical model for HD 209458b are presented.
The Astronomical Journal
We present the analysis of the hot-Jupiter KELT-7 b using transmission and emission spectroscopy ... more We present the analysis of the hot-Jupiter KELT-7 b using transmission and emission spectroscopy from the Hubble Space Telescope, both taken with the Wide Field Camera 3. Our study uncovers a rich transmission spectrum that is consistent with a cloud-free atmosphere and suggests the presence of H 2 O and H −. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature-pressure profile, collision induced absorption, and H −. KELT-7 b had also been studied with other space-based instruments and we explore the effects of introducing these additional data sets. Further observations with Hubble, or the next generation of space-based telescopes, are needed to allow for the optical opacity source in transmission to be confirmed and for molecular features to be disentangled in emission. Unified Astronomy Thesaurus concepts: Transmission spectroscopy (2133); Exoplanet atmospheres (487); Astronomy data analysis (1858)
We have developed a new model to study the atmospheres of exoplanets, adapted to the high tempera... more We have developed a new model to study the atmospheres of exoplanets, adapted to the high temperature and conditions of the atmospheres of hot Jupiters. Such a model appears essential to interpret recent and future observations, predict the composition and understand the formation and evolution of these planetary bodies. Results of a 1D thermo-photochemical model for HD 209458b are presented. An important problem of photochemical model is the lack of high temperature photochemical data. In order to improve this situation, we have begun a campaign of measurement of VUV absorption cross section at high temperature for H2O, CO2, CH4 and CO. We will present the influence of these new experimental data on the thermo-photochemical model.
Oxygen-rich deep interiors of the Giant Planets cannot explain the discovery of H2O and CO2 in th... more Oxygen-rich deep interiors of the Giant Planets cannot explain the discovery of H2O and CO2 in the stratospheres of the Giant Planets by Feuchtgruber et al. (1997) because these species are trapped by condensation around their tropopause levels (except CO2 in Jupiter and Saturn). Therefore, several sources in the direct or far environment of the Giant Planets have been proposed: icy rings and/or satellites, interplanetary dust particles and large comet impacts. CO does not condense at the tropopauses of Giant Planets, so that oxygen-rich interiors are a valid source. An internal component has indeed been observed in the vertical profile of CO in Jupiter (Bezard et al., 2002) and in Neptune (Lellouch et al., 2005), while an upper limit has been set on its magnitude by for Saturn (Cavalie et al., 2009). In addition to interiors, large comets seem to be the dominant external source, as shown by various studies: Bezard et al. (2002) for Jupiter, Cavalie et al. (2010) for Saturn and Lell...
We have developed a new model to study the atmosphere of exoplanets adapted to the characteristic... more We have developed a new model to study the atmosphere of exoplanets adapted to the characteristics of the atmospheres of hot Jupiters and hot Neptunes. Such a model appears essential to interpret recent and future observations, to predict the composition and to understand the formation and the evolution of these planetary bodies. As the chemistry of nitrogen compounds is not well constrained, we investigated several sub-networks for nitrogen-bearing species and investigate their impact on the predicted abundances and spectra of HD 189733b. We present these results. An important problem of photochemical models is the lack of high temperature photochemical data. In order to improve this situation, we have begun a campaign of measurement of VUV absorption cross section at high temperature for H2O, CO2 and NH3. We will present the influence of these new experimental data on the thermo-photochemical model.
arXiv: Earth and Planetary Astrophysics, 2014
We developed a 1D photo-thermochemical model to study the atmosphere of warm exoplanets. The chem... more We developed a 1D photo-thermochemical model to study the atmosphere of warm exoplanets. The chemical scheme used in this model is completely new in planetology and has been constructed in collaboration with specialists of combustion. It has been validated as a whole through experiments on a large range of temperature (300 - 2500 K) and pressure (1 mbar - 100 bar), allowing to study a wide variety of exoplanets. We have used this chemical model to study the atmosphere of two warm Neptunes, GJ3470b and GJ436b, and the influence of different parameters (vertical mixing, metallicity, temperature, . . . ) on their chemical composition. We present here the results obtained in these studies.
At the time when the existence of nearly 2000 exoplanets have been confirmed, it is known that a ... more At the time when the existence of nearly 2000 exoplanets have been confirmed, it is known that a wide variety of elemental chemical composition exists, that is to say different metallicities and C/N/O/H ratios [1, 2, 3, 4]. Atmospheres with a high C/O ratio (above 1) are expected to contains an important quantity of hydrocarbons, including heavy molecules (with more than 2 carbon atoms). To study correctly these kind of atmospheres, a chemical scheme adapted to this composition is necessary. In this context, we have implemented a new chemical scheme than can describe the kinetics of species with up to 6 carbon atoms (C6 scheme). This chemical scheme is totally new in planetology because it has been developed with specialists of combustion and validated through experiments on a wide range of temperature (300 2500 K) and pressure (0.01-100 bar). This large range of validation allow us to study a broad variety of atmospheres. To determine in which studies this enhanced chemical scheme ...
Coronagraphic imaging and direct spectroscopy of young planets with the James Webb Space Telescop... more Coronagraphic imaging and direct spectroscopy of young planets with the James Webb Space Telescope (JWST) will add new insights into our understanding of the formation and evolution of exoplanets. This White Paper focuses on how JWST will add to our knowledge of young giant planets located at orbits beyond a few AU for the closest stars and a few 10s of AU for more distant ones. Companion White Papers concentrate on the study of mature planets via transit spectroscopy (White Paper by Greene et al.) and on the connection between exoplanets and planets within our own solar system (White Paper by Lunine et al.)
ABSTRACT Transit spectra have recently allowed to characterise the atmosphere of smaller planets ... more ABSTRACT Transit spectra have recently allowed to characterise the atmosphere of smaller planets than hot Jupiters, i.e. (sub-)Neptune size planets. For instance, the Neptune size planet GJ 436b and the mini Neptune or super-Earth GJ 1214b both orbiting around M dwarf stars. These planets have interesting differences with respect to hot Jupiters. First, because the host M dwarf star is smaller and cooler than a solar-type star, the planet is less severely heated, resulting in planetary effective temperatures below 1000 K. It is interesting to note that transit spectra of GJ 436b indicates that its atmo-sphere is poor in methane [1, 2, 3], yet this species is predicted to be the major carbon reservoir at thermo-chemical equilibrium. Although such interpretation has been disputed [4], if the poor methane content of GJ 436b&#39;s atmosphere is real, there must be an impor-tant disequilibrium process, which so far has not been identified. A detailed chemical model by [5], consider-ing thermochemical kinetics, vertical mixing, and pho-tochemistry, concluded that CH 4 should be the major carbon-bearing molecule in GJ 436b&#39;s atmosphere un-der most plausible conditions. A second important difference with respect to hot Jupiters is that the lower mass of (sub-)Neptune plan-ets allows to expect an elemental atmospheric compo-sition significantly enriched in heavy elements, even an atmosphere not dominated by H and He but by CO 2 , H 2 O, or some other compounds [6]. In the case of GJ 1214b, its flat transmission spectrum indicates that the planet atmosphere either is hydrogen domi-nated but contains clouds or hazes, or consists mostly of water vapour [7, 8, 9, 10, 11, 12]. The possibility of a hydrogen dominated atmosphere for GJ 1214b has been explored through chemical modelling by [13], who found that methane would be the major carbon reservoir, just as the findings of [5]&#39;s model on the atmosphere of GJ 436b, and that photolysis of CH 4 , which could lead to the formation of hazes, would take place at heights substantially higher than required by the observations. The recent discovery of the transiting hot Uranus GJ 3470b [14] provides a new promising candidate for follow-up characterisation of its atmosphere and for a better understanding of the atmospheric chemistry of (sub-)Neptunes. Here we aim at studying its atmo-spheric composition through a chemical model which considers thermochemical kinetics, vertical mixing, and photochemistry. The chemical network has been adapted from combustion modelling and is described in [15]. The atmosphere model relies on some key input information such as the elemental composition, the vertical profile of temperature and eddy diffusion coefficient, and the stellar ultraviolet flux, which are badly constrained. In order to explore to some extent the sensitivity of the atmospheric chemical composi-tion to these uncertain parameters we have varied them around some standard choices and computed a grid of 17 models. In most cases, the CH 4 /CO ratio is above 1, as what is predicted by chemical equilibrium. But we found that when the metallicity increases (i.e. so-lar metallicity ×100) some models lead to a CH 4 /CO ratio under unity. We will present you these results, to-gether with the corresponding synthetic spectra. This result is very interesting because most of exoplanet at-mospheres observed so far seem to have CH 4 /CO ra-tio opposite from the equilibrium calculation, but no chemical model succeed to find the set of parameters that leads to this result. A very high metallicity seems to be a solution to explore as it is very likely for these atmospheres.
Most of exoplanets detected so far have atmospheric temperatures significantly higher than 300 K.... more Most of exoplanets detected so far have atmospheric temperatures significantly higher than 300 K. These exoplanets are often close to their star and thus receive an intense UV photons flux, triggering important pho-todissociation processes. However, the temperature dependency of VUV absorption cross sections, which are essential data to model photolyses in atmospheric models, are barely known. Thus, by lack of appropriate data, absorption cross sections at room temperature are used in photochemical models of extrasolar planets , leading to a non-measurable uncertainty. With the future space-or ground-based telescopes that will be developed in the coming years (JWST, E-ELT.. .) investigating these research fields becomes urgent [1]. In this context, we quantified the temperature dependency of the VUV absorption cross section of carbon dioxide (CO 2). We performed experimental measurements on the range (115-230 nm) between 150 and 800 K. The absorption cross section of CO 2 increases ...
Aims. We investigate the atmospheric composition of the long period (P orb = 10 days), eccentric ... more Aims. We investigate the atmospheric composition of the long period (P orb = 10 days), eccentric exo-Saturn WASP-117b. WASP-117b could be in atmospheric temperature and chemistry similar to WASP-107b. In mass and radius WASP-117b is similar to WASP-39b, which allows a comparative study of these planets. Methods. We analyze a near-infrared transmission spectrum of WASP-117b taken with Hubble Space Telescope/WFC3 G141, which was reduced with two independent pipelines to ensure a robust detection of the 3σ-water spectrum. High resolution measurements were taken with VLT/ESPRESSO in the optical. Results. Using a 1D atmosphere model with isothermal temperature, uniform cloud deck and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity [Fe/H] = 2.58 +0.26 −0.37 and clear skies. The data are also consistent with a lower-metallicity composition [Fe/H] < 1.75 and a cloud deck between 10 −2.2 − 10 −5.1 bar, but with weaker Bayesian preference. We retrieve a low CH 4 abundance of < 10 −4 volume fraction within 1σ. We cannot constrain the temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH 4 with K zz ≥ 10 8 cm 2 /s. We report indications of Na and K in the VLT/ESPRESSO high resolution spectrum with substantial Bayesian evidence in combination with HST data.
arXiv: Earth and Planetary Astrophysics, 2019
We are now on a clear trajectory for improvements in exoplanet observations that will revolutioni... more We are now on a clear trajectory for improvements in exoplanet observations that will revolutionize our ability to characterize their atmospheric structure, composition, and circulation, from gas giants to rocky planets. However, exoplanet atmospheric models capable of interpreting the upcoming observations are often limited by insufficiencies in the laboratory and theoretical data that serve as critical inputs to atmospheric physical and chemical tools. Here we provide an up-to-date and condensed description of areas where laboratory and/or ab initio investigations could fill critical gaps in our ability to model exoplanet atmospheric opacities, clouds, and chemistry, building off a larger 2016 white paper, and endorsed by the NAS Exoplanet Science Strategy report. Now is the ideal time for progress in these areas, but this progress requires better access to, understanding of, and training in the production of spectroscopic data as well as a better insight into chemical reaction ki...
Experimental Astronomy
Using two-dimensional (2D) thermal structure models and pseudo-2D chemical kinetics models, we ex... more Using two-dimensional (2D) thermal structure models and pseudo-2D chemical kinetics models, we explore how atmospheric temperatures and composition change as a function of altitude and longitude within the equatorial regions of closein transiting Neptune-class exoplanets at different distances from their host stars. Our models predict that the day-night stratospheric temperature contrasts increase with increasing planetary effective temperatures T eff and that the atmospheric composition changes significantly with T eff. We find that horizontal transport-induced This work was supported by the National Aeronautics and Space Administration under grant number NNX16AC64G issued through the Exoplanets Research Program.
We present as ’proof of concept’ a 3D global circulation model for the fast rotating (Porb = 0.83... more We present as ’proof of concept’ a 3D global circulation model for the fast rotating (Porb = 0.835 days), high surface gravity (g = 47.4 m/s) hot Jupiter WASP-43b [1] with anomalous dynamics that at least partly breaks the ’superrotation paradigm’. We will discuss the difference between this model and a 3D model for HD 209458b, the dynamics of which is dominated by unperturbed superrotation. We will show that the anomalous dynamical effect can at the very least explain the reduced east-ward hot spot shift in hot Jupiters and naturally leads to very large day to night side temperature gradients. Our results suggest that we have to fundamentally question basic assumptions in 3D atmosphere modelling of exoplanets to explain observations of some hot to ultra-hot Jupiter atmospheres. Indeed, there are currently two exoplanets that outright question the paradigm that the hottest spot of a hot Jupiter is always eastward shifted due to superrotation: CoRoT-2b with an apparent westward shift...
Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retr... more Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retrievals. As the James Webb Space Telescope (JWST) and Ariel launch draw near, assessing the underlying biases and assumptions made when applying self-consistent chemistry into spectral retrievals is crucial. Here we use the flexibility of TauREx 3.1 to cross-compare three state of the art chemical equilibrium codes: ACE, FastChem and GGchem. We simulate JWST spectra for ACE, FastChem, GGchem and GGchem+condensation containing only C, H, O, N elements and spectra for FastChem, GGchem and GGchem+condensation with a more extensive range of elements giving seven simulated JWST spectra in total and then cross-retrieve giving a total of 49 retrievals. Our analysis demonstrates that like-for-like, all chemical codes retrieve the correct parameters to < 1% of the truth. However, retrievals, where the contained elements do not match the truth, parameters such as metallicity deviate by 20% while...
We will review the observations of species useful to constrain the O/H ratio in the interior of t... more We will review the observations of species useful to constrain the O/H ratio in the interior of the ice giants. We will apply a comprehensive thermochemical and diffusion model to the ice giants and derive constraints on their deep O/H ratios.
Bulletin of the American Astronomical Society, 2019
We have developed a photo-thermo-chemical model adapted to the study of the hot terrestrial atmos... more We have developed a photo-thermo-chemical model adapted to the study of the hot terrestrial atmospheres. Such a model is essential to interpret future observations and to predict the composition of hot extrasolar terrestrial planets. It is also important to understand the formation and the evolution of some of their key atmospheric species. We investigate here the effect of an increase of the temperature on the predicted abundances of some of these key species, such as ozone O3 and carbon dioxide CO2.
We have created a new model to study the atmosphere of exoplanets. Derivated from a car engine co... more We have created a new model to study the atmosphere of exoplanets. Derivated from a car engine combustion model, it is particularly adapted to the high temperature chemistry occuring in the atmosphere of hot Jupiters. Such a model appears essential to interpret recent and future observations, predict the composition and understand the formation and evolution of these planetary bodies. Preliminary results of a 1D thermo-photochemical model for HD 209458b are presented.
The Astronomical Journal
We present the analysis of the hot-Jupiter KELT-7 b using transmission and emission spectroscopy ... more We present the analysis of the hot-Jupiter KELT-7 b using transmission and emission spectroscopy from the Hubble Space Telescope, both taken with the Wide Field Camera 3. Our study uncovers a rich transmission spectrum that is consistent with a cloud-free atmosphere and suggests the presence of H 2 O and H −. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature-pressure profile, collision induced absorption, and H −. KELT-7 b had also been studied with other space-based instruments and we explore the effects of introducing these additional data sets. Further observations with Hubble, or the next generation of space-based telescopes, are needed to allow for the optical opacity source in transmission to be confirmed and for molecular features to be disentangled in emission. Unified Astronomy Thesaurus concepts: Transmission spectroscopy (2133); Exoplanet atmospheres (487); Astronomy data analysis (1858)
We have developed a new model to study the atmospheres of exoplanets, adapted to the high tempera... more We have developed a new model to study the atmospheres of exoplanets, adapted to the high temperature and conditions of the atmospheres of hot Jupiters. Such a model appears essential to interpret recent and future observations, predict the composition and understand the formation and evolution of these planetary bodies. Results of a 1D thermo-photochemical model for HD 209458b are presented. An important problem of photochemical model is the lack of high temperature photochemical data. In order to improve this situation, we have begun a campaign of measurement of VUV absorption cross section at high temperature for H2O, CO2, CH4 and CO. We will present the influence of these new experimental data on the thermo-photochemical model.
Oxygen-rich deep interiors of the Giant Planets cannot explain the discovery of H2O and CO2 in th... more Oxygen-rich deep interiors of the Giant Planets cannot explain the discovery of H2O and CO2 in the stratospheres of the Giant Planets by Feuchtgruber et al. (1997) because these species are trapped by condensation around their tropopause levels (except CO2 in Jupiter and Saturn). Therefore, several sources in the direct or far environment of the Giant Planets have been proposed: icy rings and/or satellites, interplanetary dust particles and large comet impacts. CO does not condense at the tropopauses of Giant Planets, so that oxygen-rich interiors are a valid source. An internal component has indeed been observed in the vertical profile of CO in Jupiter (Bezard et al., 2002) and in Neptune (Lellouch et al., 2005), while an upper limit has been set on its magnitude by for Saturn (Cavalie et al., 2009). In addition to interiors, large comets seem to be the dominant external source, as shown by various studies: Bezard et al. (2002) for Jupiter, Cavalie et al. (2010) for Saturn and Lell...
We have developed a new model to study the atmosphere of exoplanets adapted to the characteristic... more We have developed a new model to study the atmosphere of exoplanets adapted to the characteristics of the atmospheres of hot Jupiters and hot Neptunes. Such a model appears essential to interpret recent and future observations, to predict the composition and to understand the formation and the evolution of these planetary bodies. As the chemistry of nitrogen compounds is not well constrained, we investigated several sub-networks for nitrogen-bearing species and investigate their impact on the predicted abundances and spectra of HD 189733b. We present these results. An important problem of photochemical models is the lack of high temperature photochemical data. In order to improve this situation, we have begun a campaign of measurement of VUV absorption cross section at high temperature for H2O, CO2 and NH3. We will present the influence of these new experimental data on the thermo-photochemical model.
arXiv: Earth and Planetary Astrophysics, 2014
We developed a 1D photo-thermochemical model to study the atmosphere of warm exoplanets. The chem... more We developed a 1D photo-thermochemical model to study the atmosphere of warm exoplanets. The chemical scheme used in this model is completely new in planetology and has been constructed in collaboration with specialists of combustion. It has been validated as a whole through experiments on a large range of temperature (300 - 2500 K) and pressure (1 mbar - 100 bar), allowing to study a wide variety of exoplanets. We have used this chemical model to study the atmosphere of two warm Neptunes, GJ3470b and GJ436b, and the influence of different parameters (vertical mixing, metallicity, temperature, . . . ) on their chemical composition. We present here the results obtained in these studies.
At the time when the existence of nearly 2000 exoplanets have been confirmed, it is known that a ... more At the time when the existence of nearly 2000 exoplanets have been confirmed, it is known that a wide variety of elemental chemical composition exists, that is to say different metallicities and C/N/O/H ratios [1, 2, 3, 4]. Atmospheres with a high C/O ratio (above 1) are expected to contains an important quantity of hydrocarbons, including heavy molecules (with more than 2 carbon atoms). To study correctly these kind of atmospheres, a chemical scheme adapted to this composition is necessary. In this context, we have implemented a new chemical scheme than can describe the kinetics of species with up to 6 carbon atoms (C6 scheme). This chemical scheme is totally new in planetology because it has been developed with specialists of combustion and validated through experiments on a wide range of temperature (300 2500 K) and pressure (0.01-100 bar). This large range of validation allow us to study a broad variety of atmospheres. To determine in which studies this enhanced chemical scheme ...
Coronagraphic imaging and direct spectroscopy of young planets with the James Webb Space Telescop... more Coronagraphic imaging and direct spectroscopy of young planets with the James Webb Space Telescope (JWST) will add new insights into our understanding of the formation and evolution of exoplanets. This White Paper focuses on how JWST will add to our knowledge of young giant planets located at orbits beyond a few AU for the closest stars and a few 10s of AU for more distant ones. Companion White Papers concentrate on the study of mature planets via transit spectroscopy (White Paper by Greene et al.) and on the connection between exoplanets and planets within our own solar system (White Paper by Lunine et al.)
ABSTRACT Transit spectra have recently allowed to characterise the atmosphere of smaller planets ... more ABSTRACT Transit spectra have recently allowed to characterise the atmosphere of smaller planets than hot Jupiters, i.e. (sub-)Neptune size planets. For instance, the Neptune size planet GJ 436b and the mini Neptune or super-Earth GJ 1214b both orbiting around M dwarf stars. These planets have interesting differences with respect to hot Jupiters. First, because the host M dwarf star is smaller and cooler than a solar-type star, the planet is less severely heated, resulting in planetary effective temperatures below 1000 K. It is interesting to note that transit spectra of GJ 436b indicates that its atmo-sphere is poor in methane [1, 2, 3], yet this species is predicted to be the major carbon reservoir at thermo-chemical equilibrium. Although such interpretation has been disputed [4], if the poor methane content of GJ 436b&#39;s atmosphere is real, there must be an impor-tant disequilibrium process, which so far has not been identified. A detailed chemical model by [5], consider-ing thermochemical kinetics, vertical mixing, and pho-tochemistry, concluded that CH 4 should be the major carbon-bearing molecule in GJ 436b&#39;s atmosphere un-der most plausible conditions. A second important difference with respect to hot Jupiters is that the lower mass of (sub-)Neptune plan-ets allows to expect an elemental atmospheric compo-sition significantly enriched in heavy elements, even an atmosphere not dominated by H and He but by CO 2 , H 2 O, or some other compounds [6]. In the case of GJ 1214b, its flat transmission spectrum indicates that the planet atmosphere either is hydrogen domi-nated but contains clouds or hazes, or consists mostly of water vapour [7, 8, 9, 10, 11, 12]. The possibility of a hydrogen dominated atmosphere for GJ 1214b has been explored through chemical modelling by [13], who found that methane would be the major carbon reservoir, just as the findings of [5]&#39;s model on the atmosphere of GJ 436b, and that photolysis of CH 4 , which could lead to the formation of hazes, would take place at heights substantially higher than required by the observations. The recent discovery of the transiting hot Uranus GJ 3470b [14] provides a new promising candidate for follow-up characterisation of its atmosphere and for a better understanding of the atmospheric chemistry of (sub-)Neptunes. Here we aim at studying its atmo-spheric composition through a chemical model which considers thermochemical kinetics, vertical mixing, and photochemistry. The chemical network has been adapted from combustion modelling and is described in [15]. The atmosphere model relies on some key input information such as the elemental composition, the vertical profile of temperature and eddy diffusion coefficient, and the stellar ultraviolet flux, which are badly constrained. In order to explore to some extent the sensitivity of the atmospheric chemical composi-tion to these uncertain parameters we have varied them around some standard choices and computed a grid of 17 models. In most cases, the CH 4 /CO ratio is above 1, as what is predicted by chemical equilibrium. But we found that when the metallicity increases (i.e. so-lar metallicity ×100) some models lead to a CH 4 /CO ratio under unity. We will present you these results, to-gether with the corresponding synthetic spectra. This result is very interesting because most of exoplanet at-mospheres observed so far seem to have CH 4 /CO ra-tio opposite from the equilibrium calculation, but no chemical model succeed to find the set of parameters that leads to this result. A very high metallicity seems to be a solution to explore as it is very likely for these atmospheres.
Most of exoplanets detected so far have atmospheric temperatures significantly higher than 300 K.... more Most of exoplanets detected so far have atmospheric temperatures significantly higher than 300 K. These exoplanets are often close to their star and thus receive an intense UV photons flux, triggering important pho-todissociation processes. However, the temperature dependency of VUV absorption cross sections, which are essential data to model photolyses in atmospheric models, are barely known. Thus, by lack of appropriate data, absorption cross sections at room temperature are used in photochemical models of extrasolar planets , leading to a non-measurable uncertainty. With the future space-or ground-based telescopes that will be developed in the coming years (JWST, E-ELT.. .) investigating these research fields becomes urgent [1]. In this context, we quantified the temperature dependency of the VUV absorption cross section of carbon dioxide (CO 2). We performed experimental measurements on the range (115-230 nm) between 150 and 800 K. The absorption cross section of CO 2 increases ...
Aims. We investigate the atmospheric composition of the long period (P orb = 10 days), eccentric ... more Aims. We investigate the atmospheric composition of the long period (P orb = 10 days), eccentric exo-Saturn WASP-117b. WASP-117b could be in atmospheric temperature and chemistry similar to WASP-107b. In mass and radius WASP-117b is similar to WASP-39b, which allows a comparative study of these planets. Methods. We analyze a near-infrared transmission spectrum of WASP-117b taken with Hubble Space Telescope/WFC3 G141, which was reduced with two independent pipelines to ensure a robust detection of the 3σ-water spectrum. High resolution measurements were taken with VLT/ESPRESSO in the optical. Results. Using a 1D atmosphere model with isothermal temperature, uniform cloud deck and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity [Fe/H] = 2.58 +0.26 −0.37 and clear skies. The data are also consistent with a lower-metallicity composition [Fe/H] < 1.75 and a cloud deck between 10 −2.2 − 10 −5.1 bar, but with weaker Bayesian preference. We retrieve a low CH 4 abundance of < 10 −4 volume fraction within 1σ. We cannot constrain the temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH 4 with K zz ≥ 10 8 cm 2 /s. We report indications of Na and K in the VLT/ESPRESSO high resolution spectrum with substantial Bayesian evidence in combination with HST data.
arXiv: Earth and Planetary Astrophysics, 2019
We are now on a clear trajectory for improvements in exoplanet observations that will revolutioni... more We are now on a clear trajectory for improvements in exoplanet observations that will revolutionize our ability to characterize their atmospheric structure, composition, and circulation, from gas giants to rocky planets. However, exoplanet atmospheric models capable of interpreting the upcoming observations are often limited by insufficiencies in the laboratory and theoretical data that serve as critical inputs to atmospheric physical and chemical tools. Here we provide an up-to-date and condensed description of areas where laboratory and/or ab initio investigations could fill critical gaps in our ability to model exoplanet atmospheric opacities, clouds, and chemistry, building off a larger 2016 white paper, and endorsed by the NAS Exoplanet Science Strategy report. Now is the ideal time for progress in these areas, but this progress requires better access to, understanding of, and training in the production of spectroscopic data as well as a better insight into chemical reaction ki...
Experimental Astronomy
Using two-dimensional (2D) thermal structure models and pseudo-2D chemical kinetics models, we ex... more Using two-dimensional (2D) thermal structure models and pseudo-2D chemical kinetics models, we explore how atmospheric temperatures and composition change as a function of altitude and longitude within the equatorial regions of closein transiting Neptune-class exoplanets at different distances from their host stars. Our models predict that the day-night stratospheric temperature contrasts increase with increasing planetary effective temperatures T eff and that the atmospheric composition changes significantly with T eff. We find that horizontal transport-induced This work was supported by the National Aeronautics and Space Administration under grant number NNX16AC64G issued through the Exoplanets Research Program.