Toward a multidimensional analysis of transmission spectroscopy. Part III: Modelling 2D effects in retrievals with TauREx

New-generation spectrographs dedicated to the study of exoplanetary atmospheres require a high accuracy in the atmospheric models to better interpret the input spectra. Thanks to space missions, the observed spectra will cover a large wavelength range from visible to mid-infrared with an higher precision compared to the old-generation instrumentation, revealing complex features coming from different regions of the atmosphere. For hot and ultra hot Jupiters (HJs and UHJs), the main source of complexity in the spectra comes from thermal and chemical differences between the day and the night sides. In this context, one-dimensional plane parallel retrieval models of atmospheres may not be suitable to extract the complexity of such spectra. In addition, Bayesian frameworks are computationally intensive and prevent us from using complete three-dimensional self-consistent models to retrieve exoplanetary atmospheres. We propose the TauREx 2D retrieval code, which uses two-dimensional atmospheric models as a good compromise between computational cost and model accuracy to better infer exoplanetary atmospheric characteristics for the hottest planets. TauREx 2D uses a 2D parametrization across the limb which computes the transmission spectrum from an exoplanetary atmosphere assuming azimuthal symmetry. It also includes a thermal dissociation model of various species. We demonstrate that, given an input observation, TauREx 2D mitigates the biases between the retrieved atmospheric parameters and the real atmospheric parameters. We also show that having a prior knowledge on the link between local temperature and composition is instrumental in inferring the temperature structure of the atmosphere. Finally, we apply such a model on a synthetic spectrum computed from a GCM simulation of WASP-121b and show how parameter biases can be removed when using two-dimensional forward models across the limb.Comment: 16 pages, 16 figures. Accepted for publication in Astronomy & Astrophysic

Hot Exoplanetary Atmospheres in 3D

Hot giant exoplanets are very exotic objects with no equivalent in the Solar System that allow us to study the behavior of atmospheres under extreme conditions. Their thermal and chemical day–night dichotomies associated with extreme wind dynamics make them intrinsically 3D objects. Thus, the common 1D assumption, relevant to study colder atmospheres, reaches its limits in order to be able to explain hot and ultra-hot atmospheres and their evolution in a consistent way. In this review, we highlight the importance of these 3D considerations and how they impact transit, eclipse and phase curve observations. We also analyze how the models must adapt in order to remain self-consistent, consistent with the observations and sufficiently accurate to avoid bias or errors. We particularly insist on the synergy between models and observations in order to be able to carry out atmospheric characterizations with data from the new generation of instruments that are currently in operation or will be in the near future

Effets de la structure tridimensionnelle des atmosphères d’exoplanètes chaudes sur les observations et les modèles d’inversion de données

Nowdays, we are able to discover more and more exoplanets, and even more important we can observe their atmospheres and we are starting to get information on their physical, dynamic and, chemical properties. With the new generation of space telescopes such as the JWST or Ariel, we will be able to observe spectral features that are now unobservable. However, during transit observations, the geometric structure of the atmospheres, and in particular the day to night dichotomy of hot and ultra hot Jupiters, affects the transmission spectrum and generates biases in the interpretations of retrieval outputs analysis.The aim of my thesis is to study the effects of the three-dimensional structure of exoplanet atmospheres, and in particular the hottest ones, in order to determine the importance and the origin of these biases to allow a better analysis of the spectral data. I set up a numerical experiment simulating observations of hot Jupiters where I control the entire observational chain, from the atmosphere's simulation to the retrieval. In addition, I analyzed observations of Kelt-7 b, a hot Jupiter, from the Hubble Space Telescope, to link my numerical analysis to real data.My work has shown that the particular structure of the hottest Jupiters significantly affects observations, implying significant biases in the results of 1D retrieval models. Although these models are valid over a large range of planets, I have demonstrated that for the hottest exoplanets, they are unable to find the abundances of species. I succeeded in quantifying these biases and in understanding their origins, hence an improvement in the interpretation of future results from 1D retrieval models. Furthermore, I conclude that it is necessary to develop 2D retrieval models to try to resolve these biases.Nous sommes aujourd'hui en mesure non seulement de découvrir de plus en plus d'exoplanètes, mais aussi d'observer leurs atmosphères afin d'obtenir des informations sur leurs propriétés physiques, dynamiques et chimiques. Avec la nouvelle génération de télescopes spatiaux tels que le JWST ou Ariel, nous serons en mesure d'observer des caractéristiques spectrales aujourd'hui non-observables. Cependant, lors des observations en transits, la structure géométrique des atmosphères, et notamment la dichotomie jour--nuit des Jupiters chauds et ultra chauds, affecte le spectre en transmission et génère des biais dans l'interprétation des modèles d'inversion de données.Ma thèse se concentre sur l'étude des effets de la structure tridimensionnelle des atmosphères d'exoplanètes, en particulier des plus chaudes d'entre elles. Le but est de déterminer leurs importances et leurs origines pour permettre une meilleure analyse des données spectrales. Pour y parvenir, j'ai mis en place une expérience numérique simulant des observations de Jupiters chauds où je contrôle l'ensemble de la chaîne observationnelle, de la génération de l'atmosphère à l'inversion de données. En complément, j'ai analysé des observations du télescope spatial Hubble de Kelt-7 b, un Jupiter chaud, pour lier mes analyses numériques à des données réelles.Mes travaux ont montré que la structure particulière des Jupiters les plus chauds affecte significativement les données d'observations, impliquant des biais importants dans les résultats des modèles d'inversion de données 1D. Bien que ces modèles restent valables sur une large gamme de planètes, j'ai démontré que pour les exoplanètes les plus chaudes, ils sont intrinsèquement incapables de trouver l'abondance des espèces. Je suis parvenu à quantifier ces biais et à comprendre leurs origines, apportant une amélioration à l'avenir des interprétations faites à partir des modèles 1D. Par ailleurs, je conclue qu'il est nécessaire de développer en parallèle des modèles 2D pour tenter de résoudre ces biais

Effects of the three-dimensional structure of hot exoplanet atmospheres on observations and retrieval models

Nous sommes aujourd'hui en mesure non seulement de découvrir de plus en plus d'exoplanètes, mais aussi d'observer leurs atmosphères afin d'obtenir des informations sur leurs propriétés physiques, dynamiques et chimiques. Avec la nouvelle génération de télescopes spatiaux tels que le JWST ou Ariel, nous serons en mesure d'observer des caractéristiques spectrales aujourd'hui non-observables. Cependant, lors des observations en transits, la structure géométrique des atmosphères, et notamment la dichotomie jour--nuit des Jupiters chauds et ultra chauds, affecte le spectre en transmission et génère des biais dans l'interprétation des modèles d'inversion de données.Ma thèse se concentre sur l'étude des effets de la structure tridimensionnelle des atmosphères d'exoplanètes, en particulier des plus chaudes d'entre elles. Le but est de déterminer leurs importances et leurs origines pour permettre une meilleure analyse des données spectrales. Pour y parvenir, j'ai mis en place une expérience numérique simulant des observations de Jupiters chauds où je contrôle l'ensemble de la chaîne observationnelle, de la génération de l'atmosphère à l'inversion de données. En complément, j'ai analysé des observations du télescope spatial Hubble de Kelt-7 b, un Jupiter chaud, pour lier mes analyses numériques à des données réelles.Mes travaux ont montré que la structure particulière des Jupiters les plus chauds affecte significativement les données d'observations, impliquant des biais importants dans les résultats des modèles d'inversion de données 1D. Bien que ces modèles restent valables sur une large gamme de planètes, j'ai démontré que pour les exoplanètes les plus chaudes, ils sont intrinsèquement incapables de trouver l'abondance des espèces. Je suis parvenu à quantifier ces biais et à comprendre leurs origines, apportant une amélioration à l'avenir des interprétations faites à partir des modèles 1D. Par ailleurs, je conclue qu'il est nécessaire de développer en parallèle des modèles 2D pour tenter de résoudre ces biais.Nowdays, we are able to discover more and more exoplanets, and even more important we can observe their atmospheres and we are starting to get information on their physical, dynamic and, chemical properties. With the new generation of space telescopes such as the JWST or Ariel, we will be able to observe spectral features that are now unobservable. However, during transit observations, the geometric structure of the atmospheres, and in particular the day to night dichotomy of hot and ultra hot Jupiters, affects the transmission spectrum and generates biases in the interpretations of retrieval outputs analysis.The aim of my thesis is to study the effects of the three-dimensional structure of exoplanet atmospheres, and in particular the hottest ones, in order to determine the importance and the origin of these biases to allow a better analysis of the spectral data. I set up a numerical experiment simulating observations of hot Jupiters where I control the entire observational chain, from the atmosphere's simulation to the retrieval. In addition, I analyzed observations of Kelt-7 b, a hot Jupiter, from the Hubble Space Telescope, to link my numerical analysis to real data.My work has shown that the particular structure of the hottest Jupiters significantly affects observations, implying significant biases in the results of 1D retrieval models. Although these models are valid over a large range of planets, I have demonstrated that for the hottest exoplanets, they are unable to find the abundances of species. I succeeded in quantifying these biases and in understanding their origins, hence an improvement in the interpretation of future results from 1D retrieval models. Furthermore, I conclude that it is necessary to develop 2D retrieval models to try to resolve these biases

Effects of the three-dimensional structure of hot exoplanet atmospheres on observations and retrieval models

Nous sommes aujourd'hui en mesure non seulement de découvrir de plus en plus d'exoplanètes, mais aussi d'observer leurs atmosphères afin d'obtenir des informations sur leurs propriétés physiques, dynamiques et chimiques. Avec la nouvelle génération de télescopes spatiaux tels que le JWST ou Ariel, nous serons en mesure d'observer des caractéristiques spectrales aujourd'hui non-observables. Cependant, lors des observations en transits, la structure géométrique des atmosphères, et notamment la dichotomie jour--nuit des Jupiters chauds et ultra chauds, affecte le spectre en transmission et génère des biais dans l'interprétation des modèles d'inversion de données.Ma thèse se concentre sur l'étude des effets de la structure tridimensionnelle des atmosphères d'exoplanètes, en particulier des plus chaudes d'entre elles. Le but est de déterminer leurs importances et leurs origines pour permettre une meilleure analyse des données spectrales. Pour y parvenir, j'ai mis en place une expérience numérique simulant des observations de Jupiters chauds où je contrôle l'ensemble de la chaîne observationnelle, de la génération de l'atmosphère à l'inversion de données. En complément, j'ai analysé des observations du télescope spatial Hubble de Kelt-7 b, un Jupiter chaud, pour lier mes analyses numériques à des données réelles.Mes travaux ont montré que la structure particulière des Jupiters les plus chauds affecte significativement les données d'observations, impliquant des biais importants dans les résultats des modèles d'inversion de données 1D. Bien que ces modèles restent valables sur une large gamme de planètes, j'ai démontré que pour les exoplanètes les plus chaudes, ils sont intrinsèquement incapables de trouver l'abondance des espèces. Je suis parvenu à quantifier ces biais et à comprendre leurs origines, apportant une amélioration à l'avenir des interprétations faites à partir des modèles 1D. Par ailleurs, je conclue qu'il est nécessaire de développer en parallèle des modèles 2D pour tenter de résoudre ces biais.Nowdays, we are able to discover more and more exoplanets, and even more important we can observe their atmospheres and we are starting to get information on their physical, dynamic and, chemical properties. With the new generation of space telescopes such as the JWST or Ariel, we will be able to observe spectral features that are now unobservable. However, during transit observations, the geometric structure of the atmospheres, and in particular the day to night dichotomy of hot and ultra hot Jupiters, affects the transmission spectrum and generates biases in the interpretations of retrieval outputs analysis.The aim of my thesis is to study the effects of the three-dimensional structure of exoplanet atmospheres, and in particular the hottest ones, in order to determine the importance and the origin of these biases to allow a better analysis of the spectral data. I set up a numerical experiment simulating observations of hot Jupiters where I control the entire observational chain, from the atmosphere's simulation to the retrieval. In addition, I analyzed observations of Kelt-7 b, a hot Jupiter, from the Hubble Space Telescope, to link my numerical analysis to real data.My work has shown that the particular structure of the hottest Jupiters significantly affects observations, implying significant biases in the results of 1D retrieval models. Although these models are valid over a large range of planets, I have demonstrated that for the hottest exoplanets, they are unable to find the abundances of species. I succeeded in quantifying these biases and in understanding their origins, hence an improvement in the interpretation of future results from 1D retrieval models. Furthermore, I conclude that it is necessary to develop 2D retrieval models to try to resolve these biases

Modeling the albedo of Earth-like magma ocean planets with H₂O-CO₂ atmospheres

During accretion, the young rocky planets are so hot that they become endowed with a magma ocean. From that moment, the mantle convective thermal flux control the cooling of the planet and an atmosphere is created by outgassing. This atmosphere will then play a key role during this cooling phase. Studying this cooling phase in details is a necessary step to explain the great diversity of the observed telluric planets and especially to assess the presence of surface liquid water. We used here a radiative-convective 1D atmospheric model (H2O, CO2) to study the impact of the Bond albedo on the evolution of magma ocean planets. We derived from this model the thermal emission spectrum and the spectral reflectance of these planets, from which we calculated their Bond albedos. Compared to Marcq et al. (2017), the model now includes a new module to compute the Rayleigh scattering, and state of the art CO2 and H2O gaseous opacities data in the visible and infrared spectral ranges. We show that the Bond albedo of these planets depends on their surface temperature and results from a competition between Rayleigh scattering from the gases and Mie scattering from the clouds. The colder the surface temperature is, the thicker the clouds are, and the higher the Bond albedo is. We also evidence that the relative abundances of CO2 and H2O in the atmosphere strongly impact the Bond albedo. The Bond albedo is higher for atmospheres dominated by the CO2, better Rayleigh scatterer than H2O. Finally, we provide the community with an empirical formula for the Bond albedo that could be useful for future studies of magma ocean planets

Strong biases in retrieved atmospheric composition caused by day–night chemical heterogeneities

Most planets currently amenable to transit spectroscopy are close enough to their host stars to exhibit a relatively strong day to night temperature gradient. For hot planets this leads to a chemical composition dichotomy between the two hemispheres. In the extreme case of ultra-hot Jupiters, some species, such as molecular hydrogen and water, are strongly dissociated on the day side while others, such as carbon monoxide, are not. However, most current retrieval algorithms rely on 1D forward models that are unable to reproduce this effect. We thus investigate how the 3D structure of the atmosphere biases the abundances retrieved using commonly used algorithms. We study the case of Wasp-121b as a prototypical ultra-hot Jupiter. We use the simulations of this planet performed with the Substellar and Planetary Atmospheric Radiation and Circulation global climate model and generate transmission spectra that fully account for the 3D structure of the atmosphere with Pytmosph3R. These spectra are then analyzed using the TauREx retrieval code. We find that the ultra-hot Jupiter transmission spectra exhibit muted H2O features that originate on the night side where the temperature, hence the scale-height, is smaller than on the day side. However, the spectral features of molecules present on the day side are boosted by both its high temperature and low mean molecular weight. As a result, the retrieved parameters are strongly biased compared to the ground truth. In particular the [CO]/[H2O] is overestimated by one to three orders of magnitude. This must be kept in mind when using the retrieval analysis to infer the C/O of a planet’s atmosphere. We also discuss whether indicators can allow us to infer the 3D structure of an observed atmosphere. Finally, we show that Wide Field Camera 3 from Hubble Space Telescope transmission data of Wasp-121b are compatible with the day–night thermal and compositional dichotomy predicted by models

Signature of the atmospheric asymmetries of hot and ultra-hot Jupiters in light curves

International audienceWith the new generation of space telescopes such as the James Webb Space Telescope (JWST), it is possible to better characterize the atmospheres of exoplanets. The atmospheres of Hot and ultra-hot Jupiters are highly heterogeneous and asymmetrical. The difference between the temperatures on the day and night sides is especially extreme in the case of ultra-hot Jupiters. We introduce a new tool to compute synthetic light curves from 3D general circulation model (GCM) simulations, developed in the Pytmosph3R framework. We show how rotation induces a variation in the flux during the transit that is a source of information on the chemical and thermal distribution of the atmosphere. We find that the day–night gradient linked to ultra-hot Jupiters has an effect close to stellar limb darkening, but opposite to tidal deformation. We confirm the impact of the atmospheric and chemical distribution on variations in the central transit time, though the variations found are smaller than those in available observational data, which could indicate that the east–west asymmetries are underestimated, due to the chemistry or clouds

Toward a multidimensional analysis of transmission spectroscopy: I. Computation of transmission spectra using a 1D, 2D, or 3D atmosphere structure

International audienceConsidering the relatively high precision that will be reached by future observatories, it has recently become clear that one dimensional (1D) atmospheric models, in which the atmospheric temperature and composition of a planet are considered to vary only in the vertical, will be unable to represent exoplanetary transmission spectra with a sufficient accuracy. This is particularly true for warm to (ultra-) hot exoplanets because the atmosphere is unable to redistribute all the energy deposited on the dayside, creating a strong thermal and often compositional dichotomy on the planet. This situation is exacerbated by transmission spectroscopy, which probes the terminator region. This is the most heterogeneous region of the atmosphere. However, if being able to compute transmission spectra from 3D atmospheric structures (from a global climate model, e.g.) is necessary to predict realistic observables, it is too computationally expensive to be used in a data inversion framework. For this reason, there is a need for a medium-complexity 2D approach that captures the most salient features of the 3D model in a sufficiently fast implementation. With this in mind, we present a new open-source documented version of Pytmosph3R that handles the computation of transmission spectra for atmospheres with up to three spatial dimensions and can account for time variability. Taking the example of an ultrahot Jupiter, we illustrate how the changing orientation of the planet during the transit can allow us to probe the horizontal variations in the atmosphere. We further implement our algorithm in TauREx to allow the community to perform 2D retrievals. We describe our extensive cross-validation benchmarks and discuss the accuracy and numerical performance of each model

Early Evolution of Super-Earths: From Magma Ocean to Temperate Surface Conditions

Recent discoveries of potentially temperate rocky planets motivate the better characterization of their surface conditions to predict where life could be detected in the universe. Early habitability of rocky planets is determined by the cooling and solidification of the magma ocean (MO) stage. Indeed, the initial volatile content in the MO and the distance from the host star appear to play key-roles in the solidification of the MO, the extraction of the atmosphere, the existence of clouds and the formation (or not) of a primitive water ocean. However, the atmospheric properties strongly influence the planetary albedo, and therefore the amount of sunlight reaching the planet surface. This in turn acts on the cooling rate of the planet and its atmosphere degassing. Using a coupled 1-D MO-atmosphere model, we systematically studied how the feedback between albedo, atmospheric composition, planetary surface temperature and clouds, influences the formation of a water ocean at the end of the initial rapid cooling stage of the planet. Here we extend this approach to different MO scenarios for super-Earths (ratio of planetary to core radius, volatile delivery) and discuss their potential habitability at the end of the rapid cooling stage