A re-analysis of equilibrium chemistry in five hot Jupiters

Studying chemistry and chemical composition is fundamental to go back to formation history of planetary systems. We propose here to have another look at five targets to better determine their composition and the chemical mechanisms that take place in their atmospheres. We present a re-analysis of five Hot Jupiters, combining multiple instruments and using Bayesian retrieval methods. We compare different combinations of molecules present in the simulated atmosphere, different chemistry types as well as different clouds parametrization. As a consequence of recent studies questioning the detection of Na and K in the atmosphere of HD 209458b as being potentially contaminated by stellar lines when present, we study the impact on other retrieval parameters of misinterpreting the presence of these alkali species. We use spatially scanned observations from the grisms G102 and G141 of the WFC3 on HST, with a wavelength coverage of $\sim$0.8 to $\sim$1.7 microns. We analyse these data with the publicly available Iraclis pipeline. We added to our datasets STIS observations to increase our wavelength coverage from $\sim$0.4 to $\sim$1.7 microns. We then performed a Bayesian retrieval analysis with the open-source TauREx using a nested sampling algorithm. We explore the influence of including Na and K on the retrieval of the molecules from the atmosphere. Our data re-analysis and Bayesian retrieval are consistent with previous studies but we find small differences in the retrieved parameters. After all, Na and K has no significant impact on the properties of the planet atmospheres. Therefore, we present here our new best-fit models, taking into account molecular abundances varying freely and equilibrium chemistry. This work is a preparation for a future addition of more sophisticated representation of chemistry taking into account disequilibrium effects such as vertical mixing and photochemistry.Comment: 19 pages, 14 figure

Exploring the Ability of Hubble Space Telescope WFC3 G141 to Uncover Trends in Populations of Exoplanet Atmospheres through a Homogeneous Transmission Survey of 70 Gaseous Planets

We present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble’s Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. Among these, we use Bayesian hierarchical modeling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet’s mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass–metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H− opacity. We suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the Hubble Space Telescope’s WFC3 G141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. We set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the JWST, Twinkle, and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection

Characterizing a World Within the Hot-Neptune Desert: Transit Observations of LTT 9779 b with the Hubble Space Telescope/WFC3

We present an atmospheric analysis of LTT 9779 b, a rare planet situated in the hot-Neptune desert, that has been observed with Hubble Space Telescope (HST)/WFC3 with G102 and G141. The combined transmission spectrum, which covers 0.8–1.6 μm, shows a gradual increase in transit depth with wavelength. Our preferred atmospheric model shows evidence for H2O, CO2, and FeH with a significance of 3.1σ, 2.4σ, and 2.1σ, respectively. In an attempt to constrain the rate of atmospheric escape for this planet, we search for the 1.083 μm helium line in the G102 data but find no evidence of excess absorption that would indicate an escaping atmosphere using this tracer. We refine the orbital ephemerides of LTT 9779 b using our HST data and observations from TESS, searching for evidence of orbital decay or apsidal precession, which are not found. The phase-curve observation of LTT 9779 b with JWST NIRISS should provide deeper insights into the atmosphere of this planet and the expected atmospheric escape might be detected with further observations concentrated on other tracers such as Lyα

JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b

Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12 $\rm{\mu}$m. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 $\rm{\mu}$m, and detailed atmospheric modeling and retrievals identify this feature as SiO$_2$(s) (quartz) clouds. The SiO$_2$(s) clouds model is preferred at 3.5-4.2$\sigma$ versus a cloud-free model and at 2.6$\sigma$ versus a generic aerosol prescription. We find the SiO$_2$(s) clouds are comprised of small ${\sim}0.01$ $\rm{\mu}$m particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H$_2$O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).Comment: 19 pages, 7 figures, accepted for publication in ApJ

Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution

Impact des aérosols sur la transmission optique par satellite

Publication étudianteInternational audienceOptronic sensors on board satellites are used for remote sensing and telecommunications, but are submitted to meteorological conditions and among them cloud cover and aerosols. Aerosol presence in the field of view could be one of the key factor limiting performances of these sensors. The goal of this study is to predict optical transmission of a satellite’s sensor due to aerosols with a Monte Carlo method. Geometrical and optical properties required to build the model are obtained from CloudAerosol Lidar with Orthogonal Polarization (CALIOP) measurements. Atmospheric scenes containing aerosols are generated and transmission spectra are obtained along the line-of-sight of a virtual satellite. To evaluate the impact of aerosols on the optical link, we computed the probability that the transmittance along the LOS is higher than a given threshold. Different areas are selected and relevant satellites configurations are investigated: geostationary, Low-Earth-Orbit, nadir view angle, or tilted view. Results’ discussion points out the impact of climates and environments but also the importance of the satellite instruments angle of view in the optical transmission between ground stations and satellites.Les capteurs optroniques embarqués à bord des satellites sont utilisés pour la télédétection et les télécommunications, mais sont soumis aux conditions météorologiques et parmi elles, la couverture nuageuse et les aérosols. La présence d'aérosols sur la ligne de visée pourrait être l'un des facteurs clés limitant les performances de ces capteurs. L'objectif de cette étude est de prédire la transmission optique entre un satellite et le sol en présence d'aérosols avec une méthode de Monte Carlo. Les propriétés géométriques et optiques des aérosols nécessaires à la construction du modèle sont obtenues à partir des données du Lidar Caliop (Cloud-Aerosol Lidar with Orthogonal Polarization). Des scènes atmosphériques contenant des aérosols sont générées et la transmission est obtenue le long de la ligne de visée d'un satellite virtuel. Pour évaluer l'impact des aérosols sur la liaison optique, nous avons calculé la probabilité que la transmission le long de la LDV soit supérieure à un seuil donné. Différentes régions sont sélectionnées et les configurations satellites pertinentes sont étudiées : géostationnaire, orbite terrestre basse (LEO), vue nadir ou oblique. La discussion sur les résultats met en évidence l'impact des climats et des environnements, mais aussi l'importance de l'angle de vue des satellites sur la qualité de la transmission optique entre les stations au sol et les satellites

Population study: Exploring the transition from Super-Earth to Sub-Neptune with a Hubble transmission survey

International audienceExoplanets with size between the Earth and Neptune (1-4R⊕) do not have any equivalent in our Solar System and remain challenging to characterize. Yet, there are ubiquitous in the Galaxy and their distribution -number of planets per star vs radius- is bimodal highlighting a gap in the number of planets around 1.7R⊕, also known as the radius valley. Planets with a radius below 1.7R⊕ are thought to be rocky planets, and called Super-Earth, above this limit planets are most likely made of gas and called Sub-Neptune. We made use of the available data from the Hubble Space Telescope in Near-Infrared -using the Wide Field Camera 3 Grism 141- and gathered 25 transmission spectra of planets with size below 6 R⊕ to study the transition between rocky and gaseous planets. We retrieved each spectrum homogeneously with an atmospheric Bayesian code, TauREx 3.0. While it is still difficult to differentiate between a primary cloudy and a secondary atmosphere, we proved that a primary clear atmosphere dominated by hydrogen and helium is rejected with high confidence for a large majority of planets in the sample. The detectability of intermediate-size planets in the Near infrared is linked to the amplitude of the water feature around 1.4 microns and, thus, we build a new metric to assess the size of this absorption. Using this metric, we studied the cloudiness of warm Sub-Neptune and compared observational values to simulated ones. We explored the correlation between the 1.4 micron's feature amplitude and the temperature by constructing a grid in irradiation, metallicity and cloudiness using Exo-REM, a self-consistent radiative, convective model. We showed that photochemical hazes created by the photodissociation of methane in the high atmosphere of warm Sub-Neptune are likely required to explain the observations of flat transmission spectra in the Near infrared

Population study: Exploring the transition from Super-Earth to Sub-Neptune with a Hubble transmission survey

International audienceExoplanets with size between the Earth and Neptune (1-4R⊕) do not have any equivalent in our Solar System and remain challenging to characterize. Yet, there are ubiquitous in the Galaxy and their distribution -number of planets per star vs radius- is bimodal highlighting a gap in the number of planets around 1.7R⊕, also known as the radius valley. Planets with a radius below 1.7R⊕ are thought to be rocky planets, and called Super-Earth, above this limit planets are most likely made of gas and called Sub-Neptune. We made use of the available data from the Hubble Space Telescope in Near-Infrared -using the Wide Field Camera 3 Grism 141- and gathered 25 transmission spectra of planets with size below 6 R⊕ to study the transition between rocky and gaseous planets. We retrieved each spectrum homogeneously with an atmospheric Bayesian code, TauREx 3.0. While it is still difficult to differentiate between a primary cloudy and a secondary atmosphere, we proved that a primary clear atmosphere dominated by hydrogen and helium is rejected with high confidence for a large majority of planets in the sample. The detectability of intermediate-size planets in the Near infrared is linked to the amplitude of the water feature around 1.4 microns and, thus, we build a new metric to assess the size of this absorption. Using this metric, we studied the cloudiness of warm Sub-Neptune and compared observational values to simulated ones. We explored the correlation between the 1.4 micron's feature amplitude and the temperature by constructing a grid in irradiation, metallicity and cloudiness using Exo-REM, a self-consistent radiative, convective model. We showed that photochemical hazes created by the photodissociation of methane in the high atmosphere of warm Sub-Neptune are likely required to explain the observations of flat transmission spectra in the Near infrared

HST WFC3 G141 data analysis: exploring the transition from Super-Earth to Sub-Neptune

International audienc

Population study: Exploring the transition from Super-Earth to Sub-Neptune with a Hubble transmission survey

International audienceExoplanets with size between the Earth and Neptune (1-4R⊕) do not have any equivalent in our Solar System and remain challenging to characterize. Yet, there are ubiquitous in the Galaxy and their distribution -number of planets per star vs radius- is bimodal highlighting a gap in the number of planets around 1.7R⊕, also known as the radius valley. Planets with a radius below 1.7R⊕ are thought to be rocky planets, and called Super-Earth, above this limit planets are most likely made of gas and called Sub-Neptune. We made use of the available data from the Hubble Space Telescope in Near-Infrared -using the Wide Field Camera 3 Grism 141- and gathered 25 transmission spectra of planets with size below 6 R⊕ to study the transition between rocky and gaseous planets. We retrieved each spectrum homogeneously with an atmospheric Bayesian code, TauREx 3.0. While it is still difficult to differentiate between a primary cloudy and a secondary atmosphere, we proved that a primary clear atmosphere dominated by hydrogen and helium is rejected with high confidence for a large majority of planets in the sample. The detectability of intermediate-size planets in the Near infrared is linked to the amplitude of the water feature around 1.4 microns and, thus, we build a new metric to assess the size of this absorption. Using this metric, we studied the cloudiness of warm Sub-Neptune and compared observational values to simulated ones. We explored the correlation between the 1.4 micron's feature amplitude and the temperature by constructing a grid in irradiation, metallicity and cloudiness using Exo-REM, a self-consistent radiative, convective model. We showed that photochemical hazes created by the photodissociation of methane in the high atmosphere of warm Sub-Neptune are likely required to explain the observations of flat transmission spectra in the Near infrared