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

1) Moses, J.I., Chemical kinetics on extrasolar planets. Philos Trans A Math Phys Eng Sci, 2014. 372(2014): p. 20130073.
2) Moses, J.I., et al., Chemical Consequences of the C/O Ratio on Hot Jupiters: Examples from WASP-12b, CoRoT-2b, XO-1b, and. The Astrophysical Journal, 2013. 763(1): p. 25.
3) Venot, O., et al., New chemical scheme for studying carbon-rich exoplanet atmospheres. A&A, 2015. 577: p. A33.
4) Knutson, H.A., et al., 3.6 and 4.5 μm Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b. The Astrophysical Journal, 2012. 754(1): p. 22.
5) Roudier, G.M., et al., Disequilibrium Chemistry in Exoplanet Atmospheres Observed with the Hubble Space Telescope. The Astronomical Journal, 2021. 162(2): p. 37.
6) Sing, D.K., et al., A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion. Nature, 2016. 529(7584): p. 59-62.
7) Knutson, H.A., et al., A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b. Nature, 2014. 505(7481): p. 66.
8) Kreidberg, L., et al., Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b. Nature, 2014. 505(7481): p. 69-72.
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.