EXOA6

We recreate a Titan-like climate using an Earth-like global climate model (GCM) by varying a small set of planetary parameters. Understanding the range of possible climate states for Earth-like planets is important for interpreting exoplanet observations and Earth’s own climate history. We find that simply reducing the available water at the surface does not fully reproduce Titan-like conditions. This may indicate that there are many possible “in-between” states an Earth-like planet can have that span the gap between the Earth and Titan climate archetypes. We use three observationally motivated criteria to determine Titan-like conditions: 1) the peak in surface specific humidity is not at the equator, despite it having the warmest annual-mean temperatures (Ádámkovics et al. 2016); 2) the vertical profile of specific humidity in the equatorial column is nearly constant through the lower troposphere (Niemann et al. 2005); and 3) the relative humidity near the surface at the equator is significantly lower than saturation (lower than 60%; Niemann et al. 2005; Tokano et al. 2006). We first limit the available water by placing a continental land strip centered on the equator and varying its width. This mimics Titan’s dry tropics and wet poles, and could be similar to past continental arrangements in Earth’s history. Land strips alone allow some experiments to meet two Titan-like criteria, but none show the near-constant vertical profile of specific humidity. We take three of these land strip widths and vary the rotation period, starting with Earth’s rotation and moving towards Titan’s (16 Earth days). Slowing the rotation results in fewer experiments meeting any of the Titan-like criteria due to increased access to oceanic moisture from the widened Hadley Circulation. For the same three land strip widths and using Earth rotation, we vary the volatility of the condensable via a constant multiplied to the saturation vapor pressure. Titan’s condensable, methane, is more volatile under Titan’s surface conditions than water is on Earth, resulting in high specific humidities. By artificially increasing the saturation vapor pressure, we can approximate this effect without changing the properties of the condensable. Experiments with a volatility constant of 2.5 (the maximum used in this work) meet all three Titan-like criteria, demonstrating that an Earth-like planet can display Titan-like climatology by changing only a few physical parameters.

How to cite: McKinney, M. and Mitchell, J.: Dune, Waterworld, and Everything in-between: Creating a Titan-like Climate on an Earth-like Planet, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-742, https://doi.org/10.5194/epsc2022-742, 2022.

The runaway greenhouse effect [1-4] is a very interesting process for terrestrial planets, studied in particular to determine the inner limit of the Habitable Zone (HZ). This is also important to understand a possible evolution of terrestrial planets from temperate Earth-like planets to magma-ocean planets. This runway greenhouse transition is usually defined via the calculation of the asymptotic limit of thermal emission of the planet (OLR = Outgoing Longwave Radiation), also called Simpson-Nakajima limit. We have recently shown, using a 1D radiative-convective model, that a radiatively inactive gas such as nitrogen (N2) strongly modifies the OLR of the atmosphere [5] and can extend the inner edge of the HZ towards the host star [6]. We have also highlighted the importance of some physical processes sometimes considered as second order processes (e.g., collisional broadening of water lines).

In continuation of this work, we use a 3D global climate model, LMD-Generic, to study the runaway greenhouse for similar atmospheres. First, we explore the runaway evaporation in a temperature range that goes beyond every previous work which only studied up to the tipping point [7,8]. We aim to understand the contribution of the inherently three-dimensional processes (e.g. clouds and dynamics) to the evolution of the atmosphere. We find strong differences with 1D simulations but also with the usual climate pattern of temperate stable states. Second, we also explore the evolution of the atmosphere when the entire water ocean is evaporated, and the convergence on a post-runaway state. This allow us to have a complete overview of the runway transition by linking our results to previous studies of hot Earth-like planets [9].

References

[1] Komabayasi, M. 1967, Journal of the Meteorological Society of Japan. Ser. II

[2] Ingersoll, A. 1969, Journal of the Atmospheric Sciences

[3] Nakajima, S., Hayashi, Y.-Y., & Abe, Y. 1992, Journal of the Atmospheric Sciences

[4] Goldblatt, C. & Watson, A. J. 2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

[5] Chaverot G., Bolmont, E., Turbet, M., Leconte, J. 2021, Astronomy & Astrophysics

[6] Goldblatt, C., Robinson, T. D., Zahnle, K. J., & Crisp, D. 2013, Nature Geoscience

[7] Pop, M., Schmidt, H., Marotzke, J. 2016, Nature Communications

[8] Leconte, J., Forget, F., Charnay, B. et al., 2013, Nature

[9] Turbet, M., Bolmont, E., Chaverot, G., et al. 2021, Nature

How to cite: Chaverot, G., Bolmont, E., and Turbet, M.: First exploration of the entire runaway greenhouse transition with a 3D global climate model, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-883, https://doi.org/10.5194/epsc2022-883, 2022.

The population of Earth-sized exoplanets in short orbital periods of a few Earth days around small mass stars has continuously increased over the past years [1 - 3]. A fraction of these planets has stellar irradiation levels closer to Venus than the Earth, suggesting that a Venus-like Climate is more likely on those exoplanets [4]. At the same time, their small size, combined with a close-in orbit and small radius of the host star (relatively small star-planet size ratio), makes these worlds the best targets for follow-up atmospheric studies. Furthermore, when the planet transits the host star, such as in the case of TRAPPIST-1 planets, transmission spectra become available, potentially expanding the understanding of the planets’ atmospheric composition [5, 6].

The James Webb Space Telescope will advance the atmosphere and Climate characterisation of nearby rocky exoplanets, including TRAPPIST-1 c [7, 8]. The field will expand with the support of upcoming ground-based observatories and space telescopes, such as the ESA/Ariel mission, scheduled for launch in 2029. The interpretation of the observables produced by these missions: reflection, thermal emission, and transmission spectra will need support from dedicated models and theoretical studies of exoplanetary atmospheres. In particular, 3D Global Climate Models (GCMs) are critical for interpreting the observable signal’s modulations. They provide synthetic top-of-the-atmosphere fluxes that can be disk-integrated as a function of the orbital phase. The spatial and temporal variability of these fluxes reflects the atmospheric variability of the simulated temperature and wind fields and provides insight into the large-scale circulation.

In this work, we use the Generic-GCM to simulate a possible Venus-like atmosphere on TRAPPIST-1 c, considered a benchmark for highly-irradiated rocky exoplanets orbiting late-type M-dwarf stars. The Generic-GCM has been originally developed at Laboratoire de Météorologie Dynamique for exoplanet and paleoclimate studies [9 - 11], and has been continuously improved thanks to the efforts of several teams (e.g., LAB, Bordeaux; LESIA, Paris; Observatoire astronomique de l'Université de Genève). The model uses a 3D dynamical core, common to all terrestrial planets, a planet-specific physical part, and an up-to-date generalised radiative transfer routine for variable atmospheric compositions. To simulate a Venus-like atmosphere as a possible framework for the atmospheric conditions in TRAPPIST-1 c, we took a series of assumptions: synchronous rotation, zero obliquity and eccentricity, a Venus-like, carbon dioxide dominated atmosphere with 92-bar surface atmospheric pressure, and a radiatively-active global cover of Venus-type aerosols. The overarching goal is twofold: (1) to study the large-scale atmospheric circulation of rocky exoplanets with similar stellar irradiations to Venus; and (2) to address the observational prospects by producing phase curves (reflection and emission) and transmission spectra.

The TRAPPIST-1 c first 3D modelling results indicate a strong equatorial zonal superrotation jet responsible for the advection of warm air masses from the substellar region towards the nightside hemisphere. The thermal phase curves have different amplitudes and orbital phases of peak emission depending on whether they are: (i) carbon dioxide absorption bands (e.g., 14.99-16.21 μm in Figure 1 (a)); or (ii) part of the continuum (e.g. 11.43-12.50 μm, in Figure 1 (a)). The corresponding OLR and temperature fields suggest different spectral bands sound different atmospheric levels. The carbon dioxide absorption bands sound mesospheric levels (p ~ 1 mbar), while the continuum spectral bands sound the cloud top (p ~ 37 mbar) (see Figure 1 (b-e)). We will explore and expand these initial results in the context of the thermal structure and large-scale circulation of TRAPPIST-1 c. Furthermore, we will provide transmission spectra of TRAPPIST-1 c based on the outputs from our simulations with the Generic-GCM.

Additionally, we will provide a parametric study focused on the response of the thermal structure, large-scale atmospheric circulation and predicted observables to the variation of several parameters: surface gravity and radius following mass-radius relationships, planetary rotation rate (e.g., 1:1 versus 2:1 and 3:2 spin-orbit resonances), and instellation.

Figure 1. Relation between thermal phase curves, OLR and temperature fields and remote sensing of different TRAPPIST-1 c atmospheric levels. The two emission phase curves in panel (a) planet-to-star contrast as a function of the orbital phase, for an inclination 90º are: (i) 14.99-16.21 μm (solid red line); and (ii) 11.43-12.50 μm (solid blue line). The coloured arrows identify each phase curve peak emission's orbital phase and corresponding longitude, while the two head black arrows identify the amplitude of each phase curve. The green vertical dashed lines mark the orbital phases 0 and π, corresponding to eclipse and transit, respectively. Panels (b, c) represent the time-mean OLR fields in mW/m²/cm^-1 (latitude vs. longitude) for the two selected phase curves. The red/blue cross mark the longitudinal location of the maximum peak emission over the equator. Panels (d, e) represent the time-mean temperature fields in K at two different pressure levels: p ~ 1 mbar (mesosphere) and p ~ 37 mbar (cloud top level), respectively. A white star (purple dot) identifies the substellar (antistellar) point. A solid (dashed) black line represents the equator (prime meridian), while the terminators are represented in solid blue lines. Data in all panels are time-averaged for ten orbits of TRAPPIST-1 c.

References:

[1] Gillon et al. 2017. Nature. 542.

[2] Zeichmeister et al. 2019. A&A. 627.

[3] Faria et al. A&A. 658.

[4] Kane et al. 2018. ApJ. 869.

[5] Lincowski et al. 2018. ApJ. 867

[6] Morley et al 2017. ApJ. 850

[7] JWST Proposal 2589 – Atmospheric reconnaissance of the TRAPPIST-1 planets https://www.stsci.edu/jwst/phase2-public/2589.pdf

[8] JWST Proposal 2304 – Hot Take on a Cool World: Does Trappist-1c Have an Atmosphere?

https://www.stsci.edu/jwst/phase2-public/2304.pdf

[9] Forget & Leconte, 2014. Phil. Trans R. Soc. A372.

[10] Turbet et al. 2016. A&A. 596. A112.

[11] Wordsworth et al. 2011. ApJL. 733. L48.

Acknowledgments

This work is supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grants UIDB/04434/2020, UIDP/04434/2020, P-TUGA PTDC/FIS-AST/29942/2017

How to cite: Quirino, D., Gilli, G., Navarro, T., Turbet, M., Fauchez, T., Leconte, J., and Machado, P.: 3D Climate modelling of TRAPPIST-1 c with a Venus-like atmosphere and observational prospects, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1110, https://doi.org/10.5194/epsc2022-1110, 2022.

Water-rich planets should be ubiquitous in the universe, and could represent a notable fraction of the sub-Neptune population. Among the detected exoplanets that have been characterized as sub-Neptunes, many are subject to important irradiation from their host star. As a consequence, hydrospheres of such planets are not in condensed phase, but are rather in supercritical state, with steam atmospheres on top. Such irradiated ocean planets (IOP) are good candidates to explain the distribution of masses and radii in the sub-Neptune category of exoplanets [1]. 

Here, we present the IOP model that computes the structure of water-rich planets that have high irradiation temperatures. The IOP model [2] combines two models in a self-consistent way: one for the interior structure, and one for the steam atmosphere. The interior structure model [3] contains several refractory layers (iron core and rocky mantle), and on top of them an hydrosphere with an up to date equation of state (EOS) with a validity range that extends to the plasma regime. The atmosphere model [4] connects the top of the interior model with the host star by solving equations of radiative transfer.

Our model has been applied to the GJ 9827 system as a test case and indicates Earth- and Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. We also compute mass-radius relationships for IOP and their analytical expression, which can be found in [2]. This allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model.

Due to their high irradiation temperatures, sub-Neptunes are expected to be subject to strong atmospheric escape. This supports the idea that a massive hydrosphere could be the remnant of a complete loss of an H-He envelope. The stability of hydrospheres themselves is discussed as well [5].

Figure 1. Mass-radius relationships produced by our model (green, yellow and red thick lines) [2], compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines). A few planets of the solar system, the GJ-9827 system and the TOI-178 system are represented as well. Shaded regions correspond to important atmospheric loss by Jeans escape (H and H2O), or hydrodynamic escape.

[1] Mousis, O., Deleuil, M., Aguichine, A., et al. 2020, ApJL, 896, L22.
[2] Aguichine, A., Mousis, O., Deleuil, M., et al. 2021, ApJ, 914, 84A.
[3] Brugger, B., Mousis, O., Deleuil, M., et al. 2017, ApJ, 850, 93.
[4] Marcq, E., Baggio, L., Lefèvre, F., et al. 2019, Icarus, 319, 491M.
[5] Vivien, H., Aguichine, A., Mousis, O., et al. 2022, accepted in ApJ.

How to cite: Aguichine, A., Mousis, O., Deleuil, M., Marcq, E., and Vivien, H.: Interior structure and possible existence of irradiated ocean planets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-904, https://doi.org/10.5194/epsc2022-904, 2022.

The atmospheres of sub-Neptunes are expected to exhibit considerable chemical diversity, beyond what is anticipated for gas-giant exoplanets. Recently, in Guzman-Mesa et al 2022 we constructed self-consistent radiative transfer and equilibrium chemistry models to explore this chemical diversity. We use GJ 436 b as a case study to further study joint atmosphere-interior models. In particular, we constrain the properties of the interior and atmosphere of the planet based on the available Spitzer measurements. While it is possible to fit the emission spectrum of GJ 436 b using a high-metallicity model, we demonstrate that such an atmosphere is inconsistent with physically plausible interior structures. It remains the case that no existing study can adequately fit the 4.5-micron Spitzer secondary eclipse measurement, which is probably caused by chemical disequilibrium. In the light of the recently-launched JWST, we recommend that future analysis of emission and transmission spectra of sub-Neptune planets are carried out self-consistently using both the atmospheric and interior structure models.

How to cite: Guzmán Mesa, A.: Chemical diversity of the atmospheres and interiors of sub-Neptunes, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-25, https://doi.org/10.5194/epsc2022-25, 2022.

Theories of planet formation like core accretion mechanism  have been successful over the years in explaining the formation gas giant planets and even Neptune sized planets.  However, there are several open questions in the field of planet formation like the entropy of formation and its subsequent impact on the accretion process. Young planetary atmospheres that are freshly baked products of planet formation provide opportunities to test and constrain planet formation theories. Several such young planets like HR 8799 planets have been observed using direct imaging techniques.

This presentation focuses on the V1298 Tau system, which host multiple transiting planets and is estimated to be 23 Myr old, thus comparable to the HR 8799 planets. In this work we present transit observations of this system, including with HST/WFC3, and the interpretation of transmission spectra obtained for these planets using various atmospheric models.

Using these measurements, we explore different formation pathways for this planet system and present our findings in the context of mature planets as well as young directly imaged planets which have similar age but may have experience different formation and evolution pathways.

How to cite: Barat, S. and Desert, J.-M.: Constraining planet formation with atmospheric observations from the V1298 Tau planet system, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-583, https://doi.org/10.5194/epsc2022-583, 2022.

How to cite: Saba, A., Tsiaras, A., Morvan, M., Thompson, A., Changeat, Q., Edwards, B., Jolly, A., Waldmann, I., and Tinetti, G.: The transmission spectrum of WASP-17 b from the optical to the near-infrared wavelengths: combining STIS, WFC3 and IRAC datasets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-30, https://doi.org/10.5194/epsc2022-30, 2022.

The study of extra-solar planets, or simply, exoplanets,  planets outside our own Solar System, is fundamentally a grand quest to understand our place in the Universe. Discoveries in the last two decades have re-defined what we know about planets, and helped us comprehend the uniqueness of our very own Earth. In recent years, however, the focus has shifted from planet detection to planet characterisation, where key planetary properties are inferred from telescope observations using Monte Carlo-based methods. However, the efficiency of sampling-based methodologies is put under strain by the high-resolution observational data from next generation telescopes, such as the James Webb Space Telescope and the Ariel Space Mission. We propose to host a regular competition with the goal of identifying a reliable and scalable method to perform planetary characterisation. Depending on the chosen track, participants will provide either quartile estimates or the approximate distribution  of key planetary properties. They will have access to synthetic spectroscopic data generated from the official simulators for the ESA Ariel Space Mission. The aims of the competition are three-fold. 1) To offer a challenging application for comparing and advancing conditional density estimation methods. 2) To provide a valuable contribution towards reliable and efficient analysis of spectroscopic data, enabling astronomers to build a better picture of planetary demographics, and 3) To promote the interaction between ML and exoplanetary science.

The competition is open for all and is expected to run from July to October. We will provide a brief introduction to the competition, its aim and the different tracks available for participants. We will also be sharing preliminary results from the competition in this session.

How to cite: Yip, K. H., Changeat, Q., Morvan, M., Nikolaou, N., and Waldmann, I.: Ariel x NeurIPS Competition - Inferring Physical Properties of Exoplanets From Next-Generation Telescopes, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-133, https://doi.org/10.5194/epsc2022-133, 2022.

High-resolution (HR) transmission spectroscopy has been proven to be very effective in the detection of multiple molecular species in the atmospheres of extrasolar planets (Giacobbe et al., 2021). At HR, absorption bands of molecules are resolved into thousands of individual lines, so that species can be unambiguously identified by line matching (e.g. via cross-correlation) with planetary model templates, even though most of the single spectral lines are embedded in the photon noise.

The next challenge is to link the detection of molecular species to the chemical and physical properties of the exoplanet atmosphere. To this end, it is necessary to shift from the standard cross-correlation framework to a Bayesian log-likelihood Markov chain Monte Carlo framework, so as to infer fundamental properties such as the abundances of molecular species and the atmospheric pressure/temperature profile (Line et al., 2021). We present both the methodology and the first results on retrievals from transmission spectroscopy observations of warm/hot Jupiters carried out with the GIANO-B (R ~ 50000) near-infrared spectrograph by the GAPS (Global Architecture of Planetary System) consortium. From the derived volume mixing ratios of several molecules, we are able to derive the atmospheric C/H, O/H and C/O abundances, which are thought to be tracers of planet formation and migration scenarios.

How to cite: Giacobbe, P.: Retrieval of molecular abundances and temperature-pressure profiles with high-resolution transmission spectroscopy in the near-infrared., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1057, https://doi.org/10.5194/epsc2022-1057, 2022.

High-resolution (HR) ground-based spectrographs have drastically improved the investigation of exoplanet atmospheres. In this scenario the near-infrared (0.9-2.45 μm) HR (R /sim 50000) spectrograph GIANO-B mounted at the Nasmyth-B focus of the Telescopio Nazionale Galileo (TNG) telescope is playing an important role.

With the simultaneous detection of six molecules in the atmosphere of the Hot-Jupiter HD 209458b, we have recently demonstrated (Giacobbe+2021) that exoplanetary atmospheres can show a chemical richness previously unknown -as only a few molecules had been previously detected in an exoplanetary atmosphere.  Thus, the question of whether the complexity of HD 209458b’s atmosphere is unique or other exo-atmospheres can also show such a rich molecular composition arises spontaneously.

Here we report on transmission spectroscopy observations of two warm-giant planets, namely WASP-69b, and WASP-80b, gathered within the GAPS large program aimed at detecting atomic and molecular species in exoplanet atmospheres and possibly constraining the planetary C/O ratio, which is thought to be linked to planet migration and formation mechanisms.

We present the simultaneous detection of multiple molecules in the atmosphere of each of the investigated exoplanets -thus unveiling chemical richness also in warm Jupiters for the first time- and interpret the results in terms of possible scenarios of atmospheric composition (C/O ratio, metallicity). 

The analysis presented here, together with Giacobbe+ 2021, opens a new frontier in the characterization of exoplanetary atmospheres, and additional surprising discoveries are expected with both ground-based HR spectrographs, such as CRIRES+, SPIRou, and NIRPS, and the low-resolution (LR) spectrographs on board the JWST telescope.

How to cite: Guilluy, G., Carleo, I., Giacobbe, P., Sozzetti, A., and Bonomo, A.: The rich chemistry of two warm-giant planets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-325, https://doi.org/10.5194/epsc2022-325, 2022.

Context

High-resolution spectrographs provide an excellent opportunity for probing exoplanetary atmospheres, utilizing the transmission spectroscopy method (among others). This method allows us to explore deep into the atmosphere, detecting multiple atomic and molecular species. We can also study the atmospheric wind patterns by characterizing the line profile. So far, dozens of exoplanets, mainly hot Jupiters and warm Neptunes, have their atmosphere successfully observed with this method. Most studies so far have focussed on exoplanets showcasing easily detectable signatures (in particular, sodium); however, it is important, not to bias the sample of studied planets, to enquire about more challenging cases, which could feature different atmospheric conditions.

KELT-10b

Using the HARPS spectrograph, I will show my work on transmission spectroscopy of KELT-10b, a standard hot Jupiter-type planet, utilizing data from two transit nights. We used spectra from the HEARTS survey, which aims to study exoplanetary atmospheres using transmission spectroscopy with HARPS. I have been mainly focusing on the sodium lines and Balmer lines in the transmission spectrum of KELT-10b. Sodium has not been detected in KELT-10b with HARPS, although recently detected by UVES. I will discuss how high-quality non-detections can further strengthen our confidence in detected signals and how precise rectification of stellar effects is necessary for detections. Two photometric light curves have been observed complementary to the two transit night observations with HARPS. This allows us to monitor the star for potential stellar variation, and, by including the already public dataset, improve the ephemeris of this system.

Rossiter-McLaughlin effect

Since HARPS allows for precise observations of radial velocities, we analyzed the Rossiter-McLaughlin effect during the transits. We measured the obliquity and stellar projected equatorial velocity, finding the system to be aligned.

Transmission spectroscopy

Searching for sodium in the transmission spectroscopy has been unsuccessful, as KELT-10b is quite a faint target. However, due to the characteristics of the system, the effect of the Rossiter-McLaughlin effect is significant, possibly explaining the signature previously detected in UVES data.

How to cite: Steiner, M., Attia, O., Ehrenreich, D., and Bourrier, V.: Transmission spectroscopy of the aligned hot Jupiter KELT-10b using HARPS, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-411, https://doi.org/10.5194/epsc2022-411, 2022.

The CHEWIE survey (Clouds, Hazes and Elements vieWed on giant Exoplanets) aims to study the impact of the stellar environment on planet atmospheres and their aerosols at the day-night terminator through transmission spectra of planets in the Jupiter to Neptune mass range. It does this with ground-based, medium resolution observations between 330nm and 1100nm with the FORS2 instrument on the VLT. Our coverage of the optical wavelengths is complementary to upcoming JWST infrared observations. In this talk we present the first transmission spectrum of the survey, that of WASP-69b, a warm Saturn-mass planet with a puffed up atmosphere. We find that the spectrum shows the presence of aerosols and possible signs of sodium in the atmosphere, which is consistent with previous observations.

How to cite: Petit dit de la Roche, D. and Lendl, M.: A CHEWIE first bite: the transmission spectrum of WASP-69b, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-571, https://doi.org/10.5194/epsc2022-571, 2022.

1. Introduction

For exoplanets with T < ~1500 K, photochemistry can seriously affect the atmospheric gas-phase composition [1] — on the one hand by destructing major molecules such as carbon monoxide (CO), water (H₂O), or methane (CH₄) and on the other hand by enhancing the formation of more complex species such as acetylene (C₂H₂), hydrogen cyanide (HCN), heavier hydrocarbons or nitriles with more carbon atoms such as benzene (C₆H₆) [2, 3]. These disequilibrium processes have been considered when analyzing some observational data, highlighting that, in the case of highly irradiated exoplanets, photochemistry may be responsible for an observed chemical composition departing from the one predicted by thermochemical models [4, 5]. In addition, numerous observations suggest that aerosols are ubiquitous in a large variety of exoplanet atmospheres [6-8], including giant exoplanets. However, the nature (condensate clouds or photochemical hazes) of these aerosols and their properties remain largely unconstrained by these observations.

Laboratory experiments are important to advance our understanding of photochemical processes and aerosols properties in exoplanet atmospheres. In our previous studies, we investigated experimentally the influence of photochemistry on the composition and the formation of photochemical aerosols in hot giant exoplanet atmospheres with T > 1000 K and different C/O ratios [9, 10]. Here we will present the results of new laboratory experiments focusing on warm atmospheres (T < 1000 K), for which CH₄ is expected to be the main carbon carrier [3] instead of CO for the higher temperatures that we investigated previously. This particularity may be more favorable to a more efficient formation of hydrocarbons such as C₂H₂ or ethane (C₂H₆), making these planets good candidates to detect tracers of atmospheric photochemistry [3].

2. Material and Methods

To simulate the photochemistry and the formation of aerosols in warm giant exoplanet atmospheres, we used the Cell for Atmospheric and Aerosol Photochemistry Simulations of Exoplanets (CAAPSE) experimental setup [9]. A scheme of the setup is presented in Figure 1.

The cell was filled at room temperature with 15 mbar of either a H₂:CH₄:N₂ (99%:0.5%:0.5%) or H₂:CH₄:H₂O gas mixture with (98.4%:0.8%:0.8%). These compositions were chosen based on the main atmospheric constituents predicted for an exoplanet temperature of 500 K and a solar C/O ratio of 0.54 [3]. The gases were heated at 5 K minute^-1 to oven temperatures ranging from room temperature (~295 K) to 1073 K. After attaining the desired temperature, the gas mixture was irradiated with UV photons at 121.6 nm (Ly_α) and 140-160 nm using a hydrogen microwave discharge lamp separated from the cell by a MgF₂ window.

The evolution of the gas mixture composition was monitored using infrared spectroscopy in transmission.

3. Results and Discussions

We found that photochemistry led to significant modifications in the gas-phase composition resulting in the consumption of CH₄ and the formation of different photochemical products. The main hydrocarbon product is C₂H₆ in every studied condition while C₂H₂ and propane (C₃H₈) have also been detected in smaller amounts. In addition, we observed that the methane consumption efficiency and the hydrocarbon production yields vary significantly with the temperature. When the temperature increases, the methane consumption and the hydrocarbon production decrease. Finally, our results highlight that the production of hydrocarbons was more efficient in the experiments performed with the H₂:CH₄:N₂ gas mixture than in the ones made with the H₂:CH₄:H₂O gas mixture.

In the case of giant planet atmospheres with methane as the main carbon carrier, our results suggest that products of organic photochemistry, such as hydrocarbon molecules (C₂H₂, C₂H₆) and maybe photochemical organic aerosols, are more likely to be observed in planets with lower atmospheric temperatures and lower water amounts.

Acknowledgments

The research work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This work was supported by the NASA Exoplanet Research Program. B.F. thanks the Université Paris-Est Créteil (UPEC) for funding support (postdoctoral grant).

References

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9) Fleury, B., et al., Photochemistry in Hot H2-dominated Exoplanet Atmospheres. The Astrophysical Journal, 2019. 871(2).
10) Fleury, B., et al., Influence of C/O Ratio on Hot Jupiter Atmospheric Chemistry. The Astrophysical Journal, 2020. 899(2): p. 147.

How to cite: Fleury, B., Benilan, Y., Venot, O., Yang, J., Henderson, B., Swain, M., and Gudipati, M.: Experimental Investigation of the Photochemical Production of Hydrocarbons in Warm Giant Exoplanet Atmospheres, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-29, https://doi.org/10.5194/epsc2022-29, 2022.

Motivation

Photochemical hazes are expected to form in the atmospheres of many hot Jupiters, especially those with equilibrium temperatures near 1,200 K (like HD 189733b) and below. Heating and cooling from photochemical hazes can strongly impact temperature structure and atmospheric circulation but has previously been neglected in 3D general circulation models (GCMs) of hot Jupiters.

Methods

We present 3D simulations of hot Jupiter HD 189733b that include radiative feedback from photochemical hazes. Hazes were simulated as radiatively active tracers with a constant particle size of 3 nm. For the nominal simulations, a complex refractive index of soot was assumed. To examine how the results depend on the choice of the refractive index, we also performed additional simulations with a refractive index of Titan-type hazes.

Effect on atmospheric circulation

The response of atmospheric circulation to heating and cooling by hazes strongly depends on the assumed haze refractive index. For simulations with soot-like hazes, the equatorial jet broadens and slows down (Fig. 1, center panel). At low pressures, the day-to-night component of the flow strengthens. Vertical velocities increase. The horizontal haze mixing ratio distribution (Fig. 2) remains relatively similar to simulations without haze radiative feedback, with particularly high haze abundances near the morning terminator (as also seen in Steinrueck et al., 2021). For simulations with Titan-type hazes, the equatorial jet instead accelerates and extends to lower pressures (Fig. 1, right panel). This results in a substantially different 3D distribution of hazes, with hazes being most abundant at the dayside, the evening terminator and the equatorial region around the planet. This means that circulation, thermal structure, and haze distribution depend strongly on the assumed haze composition and optical properties.

Fig. 1: Zonal-mean zonal velocity in a simulation without haze radiative feedback (left), with soot-like hazes (center) and with Titan-type hazes (right). Black contours highlight the regions in which the zonal-mean zonal velocity is larger than 50% and 75% of its peak value within the simulation. The haze production rates are identical for both simulations with haze radiative feedback (2.5x10^-11 kg/m²/s).

Fig. 2.: Haze mass mixing ratio at the 0.1 mbar level in a simulation with soot-like hazes (left) and with Titan-type hazes (right). The substellar point is located at the center of each panel. Both simulations shown have a haze production rate of 2.5x10^-11 kg/m²/s at the substellar point.

Effect on temperature structure and emission spectra

In all simulations with haze radiative feedback, strong thermal inversions appear at low pressures on the dayside (Fig. 3). In the soot-like case, two distinct thermal inversions form, separated by a temperature minimum below the haze production region. This additional structure is not seen in 1D simulations. It is caused by upwelling on the dayside transporting air with low haze abundance upwards, resulting in a local minimum in the haze number density below the production region. Deeper regions of the atmosphere (p>100 mbar) cool compared to simulations without hazes.

The altered temperature structure leads to changes in emission spectra (Fig. 4): The amplitude of the near-infrared water features decreases in simulations with haze radiative feedback. At wavelengths > 4 µm, the emitted flux increases. Because thermal inversions caused by photochemical hazes peak at much lower pressures than the regions probed by existing low-resolution observations, current observations of HD 189733b neither confirm nor rule out such a temperature inversion.

 Fig. 3: Dayside temperature profiles, calculated using an average weighted by the cosine of the angle of incidence

Fig. 4: Dayside emission spectra. For comparison, blackbody spectra are shown as thin gray lines.

References:

Steinrueck, M. E., A. P. Showman, P. Lavvas, T. Koskinen, X. Tan, and X. Zhang (2021). MNRAS, 504(2), pp. 2783-2799. doi:10.1093/mnras/stab1053.

How to cite: Steinrueck, M., Koskinen, T., Parmentier, V., Lavvas, P., Tan, X., and Zhang, X.: Photochemical hazes dramatically alter temperature structure and atmospheric circulation in 3D simulations of hot Jupiters, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-763, https://doi.org/10.5194/epsc2022-763, 2022.

By measuring the geometric albedo of a planet, the reflectivity of its atmosphere can be determined. This constitutes a vital piece of information when trying to characterise the nature of the planetary atmosphere. The albedo of a planet can be determined by measuring the drop in observed stellar flux when the planet is occulted by its host star during secondary eclipse.

We present observations of secondary eclipses of the gas giants HD189733b and HD209458b at optical wavelengths performed by the Characterising Exoplanets Satellite (CHEOPS). As both planets have moderate temperatures, the thermal contribution to their eclipse depth in the optical is small, making our observations uniquely sensitive to the reflectivity of the planetary atmospheres. Our data thus allow precise measurements of the planets’ geometric albedos, which we will present here. We will further discuss our findings and their implications in terms of the planetary atmospheric composition and the possible presence of aerosols. Finally, we compare our results with those of similar studies and discuss the implications of our findings in the context of future observations characterising gas giant atmospheres. 

How to cite: Krenn, A., Lendl, M., and Brandeker, A.: CHEOPS Geometric albedo measurements of benchmark hot Jupiters, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-697, https://doi.org/10.5194/epsc2022-697, 2022.

We present a new GCM-motivated multidimensional temperature parameterization of hot-Jupiter atmospheres that self consistently models the entire planet in 3D, accounting for both radiative and advective phenomena. Analytic formulations for the radiative component of the energy budget are readily available but an analytic model for the advective component, characterized primarily by strong jets, has proven elusive. To address this, we utilize GCM models to decouple the two processes. Utilizing a subset of simulations with very large damping we effectively reproduce the analytic radiative solution, which can then be subtracted off the full results to isolate the advective component. We find this advective component is well modeled in pressure, latitude, and longitude by subdividing the atmosphere into longitudinal sections, with negative values on the dayside where the jet is removing energy, and positive values on the nightside where energy is deposited. The extent of this term in pressure defines the depth to which the jet penetrates into the atmosphere while the latitudinal extent defines the width. The framework is sufficiently flexible to recreate a wide variety of atmospheres, including oddballs like westward shifted offsets.

How to cite: Dobbs-Dixon, I.: GCM-Motivated Multidimensional Atmospheric Temperature Parameterization, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-787, https://doi.org/10.5194/epsc2022-787, 2022.

Transmission observations of transiting exoplanets allow us to constrain the composition of their atmospheres.  In particular, the GIANO-B high-resolution spectrograph can probe a wide range of the near-infrared spectrum with unprecedented detail (0.9--2.45 microns), being able to test for the presence of several molecular species such as H2O, CO, CO2, CH4, HCN, NH3, and C2H2. The simultaneous detection of multiple carbon-, oxygen-, and nitrogen-bearing species places direct constraints to infer which chemical processes shape the observed composition of a planetary atmosphere, allowing us to study them in an unprecedented manner.
Warm Jupiters, having equilibrium temperatures near the CO--CH4 equal-abundance boundary (~1000 K), have atmospheric compositions particularly sensitive to temperature, and are thus favorable for characterization. Here we will employ physically motivated models to explore the atmospheric condition and chemical processes of recent GIANO-B observations that show a rich chemistry in carbon, nitrogen, and oxygen species.  In particular we will contrast the impact of equilibrium/disequilibrium processes and variable C/O ratios, and their consequences on the planet observable spectra.

How to cite: Cubillos, P. E.: Probing Atmospheric Chemical Processes with Warm Jupiter Observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-405, https://doi.org/10.5194/epsc2022-405, 2022.

Ultra-hot Jupiters form a new class of exoplanets that tend to orbit hot early type stars in short periods, and may be heated to temperatures much greater than 2,000K on their day-sides. The extreme temperature dissociates all but the most strongly bound molecules and a significant fraction of the atomic gas may be thermally ionised. Under these circumstances, line absorption lines by metals and some molecules are dominant sources of short-wave opacity, causing strong thermal inversions. These inversions have consequences for atmospheric chemistry, as well as global circulation of gas and heat. Excitingly, due to the highly elevated temperatures, thermal inversion layers cause strong emission lines, that can be observed using high-resolution spectroscopy. This allows the chemical and thermal structure of the atmospheric to be constrained, in principle in three dimensions. 

Previous transit observations of the ultra-hot Jupiter WASP-121 b have revealed a rich spectrum of various metals, including iron and vanadium, but with a notable absence of titanium and titanium-oxide, which may be depleted due to condensation processes. In this talk I will present our recent observations of the emission spectrum of the planet’s dayside, which, beside showing a collection of emitting metals, provide strong direct evidence of the fate of titanium-bearing species on the cooler night-side of the planet (Fig. 1).

Fig. 1:

How to cite: Hoeijmakers, J., Kitzmann, D., Prinoth, B., Lee, E., Borsato, N., and Thorsbro, B.: Titanium chemistry in WASP-121 b revealed by high-resolution day-side spectroscopy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1134, https://doi.org/10.5194/epsc2022-1134, 2022.

Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. These “ultra-hot Jupiters” have atmospheres made of ions and dissociated molecules and feature strong day-to-night temperature gradients. Photometric observations of such planets at different orbital phases (e.g. transits, eclipses) provide insights on their atmospheric properties.

In this talk, we present the analysis of the photometric observations of WASP-189 acquired with the instrument CHEOPS, from which we derive constraints on the system architecture and the planetary atmosphere. We describe our implementation of a light curve model suited for asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. Our approach also includes modelling of the reflective and thermal components of the planetary flux, and precise timing of the transit and eclipse events by accounting for stellar oblateness and light-travel time. In addition, the model corrects for systematic noise typical for CHEOPS observations and features a Gaussian process to fit for stellar activity.

From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189 b, R_p = 1.600^+0.017_-0.016 R_J, with a precision of 1%, and the true orbital obliquity of the planetary system Ψ_p = 89.6 ± 1.2 deg, which is fully consistent with a polar orbit. The phase curve does not feature any significant hotspot offset (-7 ± 17 deg) and we robustly constrain its amplitude from the eclipse depth δ_ecl = 96.5^+4.5_-5.0 ppm. This value provides an upper limit on the geometric albedo of WASP-189 b: A_g < 0.48. We find that thermal emission only is marginally consistent (at 1.6 σ) with such an eclipse providing hints that the atmosphere either has extremely low Bond albedo and heat redistribution efficiency or is quite reflective. Finally, we attribute the photometric variability detected in the data to the star and its rotation, which can be explained by either superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope.

Based on the derived system architecture, we predict the eclipse depth in the upcoming TESS observations to be up to ∼ 165 ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbands might help disentangle between reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment J₂ (oblateness). This effect can be directly quantified by a variation of the impact parameter.

How to cite: Deline, A. and the CHEOPS consortium: The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-513, https://doi.org/10.5194/epsc2022-513, 2022.

How to cite: Dyrek, A., Ducrot, E., and Lagage, P.-O.: Entering the realm of transiting exoplanets with JWST/MIRI observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1009, https://doi.org/10.5194/epsc2022-1009, 2022.

Here we present a study of non-local thermodynamic equilibrium (LTE) effects on the exoplanetary spectra of a collection of molecules that are key in the investigation of exoplanet atmospheres: water, methane, carbon monoxide, and titanium oxide. These molecules are chosen as examples of different spectral ranges (infrared and ultraviolet), molecular types (diatomics and polyatomics), and spectral types (electronic and rovibrational); the importance of different vibrational bands in forming distinct non-LTE spectral features is investigated. Most notably, such key spectral signatures for distinguishing between the LTE and non-LTE cases include: for CH₄ the 3.15 μm band region; for H₂O the 2.0 and 2.7 μm band regions; for TiO, a strong variation in intensity in the bands between 0.5 and 0.75 μm; and a sole CO signature between 5 and 6 μm. The analysis is based on the ExoMol cross-sections and takes advantage of the extensive vibrational assignment of these molecular line lists in the ExoMol data base. We examine LTE and non-LTE cross-sections under conditions consistent with those on WASP-12b and WASP-76b using the empirically motivated bi-temperature Treanor model.

An example variation between the LTE case and Non-LTE case with our approach can be seen here for an important Methane band shown at high resolution and low pressure:

How to cite: Wright, S., Waldmann, I., and Yurchenko, S.: Non-local thermal equilibrium spectra of atmospheric molecules for exoplanets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-248, https://doi.org/10.5194/epsc2022-248, 2022.

What makes the study of exoplanetary atmospheres so hard is the extraction of its tiny signal from observations, usually dominated by telluric absorption, stellar spectrum and instrumental noise. The High-Resolution Spectroscopy has emerged as one of the leading techniques for detecting atomic and molecular species (Birkby, 2018), but although it is particularly robust against contaminant absorption in the Earth’s atmosphere, the non-stationary stellar spectrum — in the form of either Doppler shift or distortion of the line profile during planetary transits —  creates a non-negligible source of noise that can alter or even prevent the detection. Recently, significant improvements have been achieved by using 3D, radiative hydrodynamical (RHD) simulations for the star and Global Circulation Models (GCM) for the planet (e.g., Chiavassa&Brogi 2019, Flowers et al. 2019). However, these numerical simulations have been computed independently so far, while acquired spectra are the result of the natural coupling at each phase along the planet's orbit. With my work, I aim at generating emission spectra of G, F, and K-type stars and Hot Jupiters and couple them at any phase of the orbit. I will present the unprecedented precise synthetic emission spectra obtained with the upgraded 3D radiative transfer code Optim3D (Chiavassa et al. 2009), showing the impact that they have on the detection of a sample of molecules (e.g., CO, H2O, CO2, CH4) for a grid of mock observations (Maimone&Chiavassa, in prep.). This approach is expected to be particularly advantageous to improve the detectability of those molecules that are present in both the atmospheres and form in the same region of the spectrum, resulting in mixed and overlapped spectral lines. 

How to cite: Maimone, M. C., Chiavassa, A., Leconte, J., and Brogi, M.: Coupling 3D Simulations to Study Stellar and Planetary Atmospheres, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-34, https://doi.org/10.5194/epsc2022-34, 2022.

Introduction

The large diversity of planetary worlds has been firmly established, since the discovery of the first exoplanet in 1995. Some planets have the size of Jupiter and orbit at very close distances from their host star, making them “Hot Jupiter” with atmospheric temperatures as high as 2000 K. To understand how such diversity can be, we need more information about the physical and chemical characteristics of those planets. This is one of the main goals of the JWST mission and will be the main objective of the Ariel mission. The observations of these telescopes will be interpreted thanks to photo/thermochemical kinetics models, that calculate the atmospheric abundance profiles. Such models need input data like UV absorption cross sections of gases and, unfortunately most of them are badly constrained at high temperatures.

Experimental setup

To overcome this lack of knowledge in the temperature dependency of VUV absorption cross-sections, we have developed a new experiment at LISA to measure VUV absorption cross-sections of important molecules for atmospheric chemistry of warm exoplanets, such as CO, C₂H₂, NH₃ or HCN. The experimental setup is composed of a quartz cell inside an oven that can reach temperatures up to 1173K, a VUV monochromator with a deuterium lamp to produce the flux and a photomultiplier. With this experiment, we will be able to systematically determine the temperature variations of gas absorption cross-sections in the 110-300 nm wavelength domain.

Spectroscopic study

During the test of the spectroscopic platform, we have studied the absorption cross-section of CO in the A¹Π-X¹Σ⁺ transition between 68 000 and 78 000 cm^-1 (128 to 147 nm), at different temperatures between 300 and 800 K, thanks to experimental data acquired on the synchrotron facility SOLEIL. This work led us derive a new line list of the rovibrational transitions with 3≤v’≤10 et v”=0, 1. In addition, this line list was then used to determine the temperature of gas inside the oven. Indeed, one of the uncertainties occurring in this kind of laboratory measurements remains the determination of the temperature of gas inside the oven. It was the case when our group has determined some years ago the absorption cross-sections of CO₂ at high temperatures [1][2]. Here, our study shows that CO can be used as a direct temperature probe of the gas inside our oven. Finally, the obtained line list will be made available to the community for astrophysical studies (Poveda et al. in prep.).

Atmospheric model

These new data will be implemented in 1D kinetic models to simulate the composition of warm and hot exoplanets atmospheres. We use the ATMO code [3] coupled to a chemical scheme to describe the reactions occurring inside the atmosphere [4]. First, the code calculates the chemical composition at thermodynamic equilibrium. Then, stellar irradiation is introduced and the chemical composition is computed as a function of time, according to the continuity equation (1), to obtain the chemical composition of the atmosphere at steady state, with photochemical reactions and vertical mixing.

            (1)

Summary and Conclusions

In order to improve our knowledge of hot exoplanets’ atmospheres, we have developed a new VUV spectroscopic platform at LISA. We have started to perform measurements on absorption cross-sections of CO and C₂H₂ at different temperatures, and thanks to spectroscopic studies we are able to analyse these data. The first study was made on CO and this led us to draw up a new line list of the rovibrational transitions of CO in the VUV field. At the end, this line list will be made available to the community for astrophysical study.

References

[1] High-temperature measurements of VUV-absorption cross sections of CO2 and their application to exoplanets, O.Venot et al., Astronomy & Astrophysics, 2013.

[2] VVV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres, O.Venot et al., Astronomy & Astrophysics, 2018.

[3] Fingering convection and cloudless models for cool brown dwarf atmospheres, P.Tremblin et al., The Astrophysical Journal Letters, 804:L17 (6pp), 2015 May.

[4] New chemical scheme for giant planet thermochemistry, O.Venot et al., Astronomy & Astrophysics, 2020.

How to cite: Poveda, M., Bénilan, Y., Fleury, B., Jolly, A., Tremblin, P., and Venot, O.: High temperature VUV cross-section measurements for the study of hot exoplanets’ atmospheres: new line list and temperature dependance of A1Π-X1Σ+ CO transition, 3 ≤v’ ≤ 10 and v” = 0, 1, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1157, https://doi.org/10.5194/epsc2022-1157, 2022.

Spectroscopic studies of exoplanetary atmospheres by the next generation space missions, such as the James Webb Space Telescope (JWST) and Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL), will rely on spectroscopic data available at mid-infrared and visible/infrared wavelengths for the bulk of already detected or expected molecules.  While in gas giants the main perturbers are hydrogen (H₂) and helium (He), due to the large variety of exoplanet atmospheres to be probed, a whole range of other broadeners are also of interest, including carbon dioxide (CO₂), nitrogen (N₂), oxygen (O₂), water vapor (H₂O), carbon monoxide (CO), nitric monoxide (NO), methane (CH₄) and ammonia (NH₃). Moreover, because of the elevated temperatures encountered, not only “exotic” molecules but also molecular ions have to be considered as optically active species.

Several spectroscopic databases (e.g., HITRAN [1], GEISA [2], ExoMol [3], TheoReTS [4] and MoLList [5]) provide extensive line lists of positions and intensities of isolated spectral transitions, some of which contain many billions of lines.  However, the associated pressure-broadening and shift parameters, as well as their temperature dependences, remain poorly determined or completely missing (see Figure). In addition, due to the specific conditions of hot atmospheres and chemical reactions which lead to the formation of spectroscopically active species, laboratory studies are extremely scarce in both infrared/microwave (IR/MW) and visible/ultraviolet(UV) regions. Therefore, there is a huge demand for robust theoretical approaches and estimates that could provide line-shape parameters for a large range of excitations covering wide ranges of temperatures and pressures and large variety of perturbers.

Figure: Availability of line broadening parameters in spectroscopic databases: missing (white), limited coverage (light green) and good coverage (dark green).

In this work, we introduce recipes for getting reasonable estimates of pressure line-broadening parameters and their temperature dependences for IR/MW (vibrotational) and UV (vibronic) transitions for molecules relevant to exoplanetary atmospheres including “exotic” neutral and ionic species (such as NO⁺, HCO⁺, H₃O⁺, HeH⁺ and H₃⁺, NH₄⁺).

The existing classical, quantum-mechanical and semi-classical theoretical approaches to collisional line-broadening and shifting used for the IR/MW region require pre-computed reliable potential-energy surfaces and CPU-costly calculations for each collisional pair. Here we suggest a simple theoretical expression requiring a minimal set of input parameters (kinetic molecular properties and the character of the leading term in the intermolecular interaction potential) [6]. Good consistency with available measurements over the temperature range 200-3000 K is demonstrated for NO and OH colliding with rare-gas atoms and non-polar molecules. Not only active neutral molecules but also molecular ions such as NO⁺, HCO⁺, H₃O⁺, HeH⁺ (which have permanent dipole moments) and H₃⁺, NH₄⁺ (with only transition dipole moments) can be treated by this approach.

In addition to the recipe for getting estimates, for the IR/MW region we consider traditional semiclassical calculation methods combined with accurate variational wavefunctions for large-scale calculations: a new program for computing line widths and shifts, based on the use of ExoMol ro-vibrational wavefunctions to compute the key (reduced) matrix elements. Given the large number of molecules, transitions, broadeners and range of temperatures required, we also explore the use of machine learng methods trained on data for selected systems to compute comprehensive and very large rotation-vibration and rovibronic pressure-broadening parameters.

For the UV region, where the lack of the line-shape data is especially critical, more accurate models, motivated by the known effect of the strongly dominating adiabatic collisions and based on the Fourier-integral/phase-shift theory, are introduced to take account of real molecular trajectories and very different interaction potentials of the active molecule in the initial and final states. Examples of applications for line lists from the ExoMol database are given.

The theoretical models presented will be incorporated into an updated ExoMol diet [7] to provide default line-broadening parameters when none are available from other sources and will be used to develop stand-alone approaches for automatic, large-scale production of collisional widths/shifts for line lists containing billions of transitions for molecules of interest for atmospheres of exoplanets.

References

[1] I.E. Gordon, L.S. Rothman, R.J. Hargreaves et al., J. Quant. Spectrosc. Radiat. Transfer 277, 107949 (2022)

[2] N. Jacquinet-Husson et al., J. Mol. Spectrosc. 327, 31 (2016)

[3] J. Tennyson, S.N. Yurchenko, A. F. Al-Refaie et al., J. Quant. Spectrosc. Radiat. Transfer 255, 107228 (2020)

[4] A.V. Nikitin, Y.L. Babikov, V. G. Tyuterev, J. Mol. Spectrosc. 327, 138 (2016)

[5] P.F. Bernath, J. Quant. Spectrosc. Radiat. Transfer 240, 106687 (2020)

[6] J. Buldyreva, S.N. Yurchenko, J. Tennyson, RASTI 2022 (under revision)

[7] E.J. Barton et al., J. Quant. Spectrosc. Radiat. Transfer 203, 490 (2017)

How to cite: Buldyreva, J., Yurchenko, S., Guest, E., Sokolov, A., and Tennyson, J.: Provision of high-definition pressure-broadening data for spectroscopic studies of exoplanetary atmospheres: ExoMol Diet 1.2, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1171, https://doi.org/10.5194/epsc2022-1171, 2022.

Molecular features in the spectra of exoplanet atmospheres are diagnostics for the physical and chemical conditions present and are essential elements in understanding planet formation and evolution. The Planetary Spectrum Generator contains all of the elements required these spectra. Aside from the modulations by the atmosphere, this includes stellar fluxes, geometrical considerations, as well as telescope and detector characteristics to assess the noise level of the observations. Molecular contributions in atmospheric emission or transmission spectra, are calculated using molecular energy levels, transition strengths, and line broadening parameters. Combining spectroscopic information from several databases is required to enable accurate calculations across the parameter space where exoplanetary atmospheres are found. 

Over the recent years, we have collected line broadening parameters, state and transitions energies, and line intensities from HITRAN, HITEMP and ExoMol to enable the calculation of absorption spectra in all types of environments, ranging from N₂-broadened such as the Earth, to CO₂-broadened Mars, and hydrogen/helium broadened hot-Jupiters and brown dwarfs. The combination of databases allows calculations of molecular absorption at high temperatures and at high energies (i.e., into the near-infrared and visible).

In our previous work [Kofman and Villanueva 2021], the ExoMol line lists of H₂O and HDO were ingested. The need of using more the more complete theoretical databases was demonstrated in high-temperature exoplanet atmospheres, as well as in the detectability of HDO, which absorbs in an absorbance minimum of H₂O. Figure 1 shows the absorbance of water at 880 K. Absorption was calculated using both HITRAN and the variational Pokazatel/VTT databases at the natural abundances of the isotopes. Note that the HDO absorbance maximum coincides with a minimum in H₂O, which is a region where HITRAN is relatively incomplete for higher temperatures.  

In atmospheres where water has a significant presence an important component of the absorbance is the water continuum, described by the MT_CKD formalism. Although not as strong as the typical ro-vibrational features, the continuum adds a significant amount of opacity between the main features, which is especially relevant when considering that this is where one often searches for other molecules. We show that the opacity can be well described using typical collision induced absorption parameterization and demonstrate its importance. Figure 1 shows the contrast ratio of GJ 1214b transiting in front of its host star, with MT_CKD-based H₂O-H₂O collisional induced absorption neglected/included. For this simulation, the atmosphere consists of 83% He, 16% H2, 670 ppm H₂O, and 485 ppm CH₄.

In this talk, in addition to the cases described above, we will highlight where in the parameters space of exoplanet atmospheres the new additions are particularly relevant. We will look at warm transiting exoplanets, water worlds, and hot-Jupiters at high-resolution using cross-correlation studies.

How to cite: kofman, V., Villanueva, G., Fauchez, T., Liuzzi, G., Faggi, S., and Stone, S.: Combining spectral databases to simulate molecular absorption in diverse exoplanetary atmospheres, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-619, https://doi.org/10.5194/epsc2022-619, 2022.

In the last 15 years, significant progress has been made in the field of atmospheric characterisation of exoplanets, utilising the most advanced instruments both on the ground and in space. Today, we are entering an era of very exiting prospects for the field of exoplanet characterisation. The James Webb Space Telescope (JWST) has been successfully launched, deployed and aligned, while ESA’s M4 mission, Ariel, has been adopted and is planned to fly in 2029.

This era will be characterised by the large volume of data that will be delivered from the new observatories. In my talk I will discuss the challenges we have to face in order to analyse the large data volume expected in the next decade. I will discuss the lessons learnt in the past years using the Wide Field Camera 3 on HST - the most successful instrument for exoplanet characterisation - and I will present a next-generation pipeline for the analysis of exoplanet spectroscopic observations, together with the first implementation on JWST data.

How to cite: Tsiaras, A.: From HST to JWST - New tools to analyse exoplanet spectrocopic observations from space, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-979, https://doi.org/10.5194/epsc2022-979, 2022.

Current endeavours in exoplanet characterisation rely on atmospheric retrieval to quantify crucial physical properties of remote exoplanets from observations. However, the scalability and efficiency of the technique are under strain with increasing spectroscopic resolution and forward model complexity. The situation becomes more acute with the recent launch of the James Webb Space Telescope and other upcoming missions. Recent advances in Machine Learning provide optimisation-based Variational Inference as an alternative approach to perform approximate Bayesian Posterior Inference. In this investigation we combined Normalising Flow-based neural network with our newly developed differentiable forward model, Diff-tau, to perform Bayesian Inference in the context of atmospheric retrieval. We demonstrated, with examples from real and simulated spectroscopic data, several advantages of our proposed framework: 1.) Our neural network does not require a large library of spectra, all it takes is a single observation 2.) It is able to produce distributions similar to sampling-based retrieval and 3.) It requires much less forward model computation to converge. Our proposed framework contribute towards the latest development of a neural-powered atmospheric retrieval.  Its flexibility and speed hold the potential to complement sampling-based approaches in large and complex data sets in the future.

How to cite: Yip, K. H., Changeat, Q., Al-Refaie, A., and Waldmann, I.: An Alternative Approach to Sampling: Retrieving Exoplanetary Spectra with Variational Inference and Normalising Flow, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-31, https://doi.org/10.5194/epsc2022-31, 2022.

Ground-based high-resolution spectroscopic observations of exoplanet atmosphere is a rapidly-evolving field with already significant successes, mainly in species detection using a cross-correlation approach. Since a few years new techniques are developed to tackle down the obstacles to not only detect species, but also retrieve abundances and other properties (e.g the temperature profile), a deed that was so far essentially reserved to low-resolution (R ~100) observations. 
The Mid-infrared Extremely Large Telescope (ELT) Imager and Spectrograph (METIS) features a high-resolution (resolving power of ~100,000) spectrograph in the L- and M-bands (2.90 to 5.30 $\mu$m). For exoplanet atmospheric characterisation, this instrument will represent a major leap forward. It will enable the observation of fainter and smaller objects and will drastically improve the quality of data from brighter objects due to the dependence of the Signal-to-Noise Ratio in the background-limited regime on the square of the telescope diameter. At these wavelengths the obscuring effects of hazes and/or clouds are much reduced.

We present here realistic simulated observations of several exoplanets of interest with METIS. We notably included telluric lines, and time-dependent airmass and Doppler shift of the planet spectra relative to the instrument. We also included realistic noise and uncertainties from the METIS dedicated radiometric code. We performed Bayesian analysis (using PyMultiNest) of these observations with a newly developed extension of petitRADTRANS, our atmospheric modelling software. We investigated which species could be retrieved, and how well, on these selected targets. We will also discuss the detection and abundance retrieving of trace species and isotopologues, as well as the retrieving of other key atmospheric properties. Finally, we will briefly introduce the new and robust atmospheric retrieval framework we developed for petitRADTRANS, which we tested on existing high-resolution data.

How to cite: Blain, D., Sánchez López, A., van Boekel, R., and Mollière, P.: ELT-METIS: estimating the constraining power of high-resolution exoplanet spectra with Bayesian inference, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-484, https://doi.org/10.5194/epsc2022-484, 2022.

Ground-based high-resolution spectroscopy allows us to probe the chemical composition and atmospheric dynamics of hot jupiters through the Cross-Correlation Function method. This requires however careful data processing and development of analysis tools in order to extract such a faint exoplanetary signal from the overwhelming telluric and stellar contributions. With a high spectral resolution power of 70,000 and a large continuous spectral range between 0.9 and 2.5 microns, the near-infrared spectro-polarimeter SPIRou on the CFHT is a powerful instrument for exoplanet atmosphere characterization since its first light in 2018. I will present our analysis of SPIRou primary transit observations of some short-period exoplanets. Preliminary results regarding the detection of the metastable He triplet and molecules in the hot jupiters HD 189733b and HD 20458b, the warm neptunes GJ 3470b and Au Mic b, the mini neptune GJ 1214b, the hot neptune WASP-127b, and the warm saturn WASP-69b, will be presented.

Figure 1: Cross correlation between observed and synthetic spectra of HD189733b (expressed in S/N ratio) calculated over a grid of velocity parameters Kp (radial velocity semi-amplitude) and V₀ (additional Doppler shift of atmospheric lines at mid-transit). The correlation is maximum at the expected position in this parameter space [1]. The model spectra include water vapor as the only molecular absorber.

References :

[1] Boucher, A., Darveau-Bernier, A., Pelletier, S., Lafrenière, D., Artigau, E., et al., (2021). Characterizing Exoplanetary Atmospheres at High Resolution with SPIRou: Detection of Water on HD 189733 b. The Astronomical Journal, American Astronomical Society, 162 (6), pp.233.

How to cite: Masson, A., Vinatier, S., Bezard, B., and Team, A.: Characterizing exoplanetary atmospheres with SPIRou, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-446, https://doi.org/10.5194/epsc2022-446, 2022.