Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020

Oral presentations and abstracts


The field of extrasolar planets is one of the most rapidly changing areas of astrophysics and planetary science. Ground-based surveys and dedicated space missions have already discovered more than 4000 planets with many more detections expected in the near future. A key challenge is now the characterisation of their atmospheres in order to answer to the questions: what are these worlds actually like and what processes govern their formation and evolution?

To answer these questions, a broad range of skills and expertise are required, stretching from Solar System science to statistical astrophysics, from ground-based observations to spacecraft measurements, and atmospheric/interior/orbital modelling. The numerous studies conducted in the past twenty years have unveiled a large diversity of atmospheres. The next generation of space and ground based facilities (e.g. E-ELT, JWST, and ARIEL) will characterise this multifarious population in stunning detail and challenge our current understanding. Both theoretical works and experimental measurements are required to prepare for such a change of scale.

This session will focus on the atmospheric characterisation of exoplanets and the conveners welcome any abstract related to this subject.

Convener: Olivia Venot | Co-conveners: Monika Lendl, Giuseppe Morello, Vivien Parmentier, Ingo Waldmann

Session assets

Session summary

Chairperson: Olivia Venot, Giuseppe Morello, Ingo Waldmann, Monika Lendl, Vivien Parmentier
General studies / Missions
Vatsal Panwar, Jean-Michel Désert, Kamen Todorov, Jacob Bean, Catherine Huitson, Jonathan Fortney, Kevin Stevenson, and Marcel Bergmann

We present a comparative exoplanetology program of a broad sample of transiting gas giant exoplanet atmospheres using a multi-wavelength ground-based survey. The survey comprises optical and near-infrared spectrophotometric observations with Gemini/GMOS and Keck/MOSFIRE respectively. By observing transits and eclipses of an ensemble of close-in gas giants spanning a range of varying bulk and stellar host properties, and using a consistent methodology for modeling systematics and stellar activity, we put constraints on the presence and properties of clouds, alkali metals, and molecular absorbers in their atmospheres. Combining these results with observations from other observatories (TESS, HST, and Spitzer), we probe the overall properties of close-in giant exoplanet atmospheres, including their metallicity, using multiple tracers across the wide wavelength range. Characterizing the bulk chemical and physical properties of the whole sample helps to constrain the formation and evolution histories of these planets. We also discuss the opportunities of low-resolution spectroscopy observations of exoplanet atmospheres in the JWST era.

How to cite: Panwar, V., Désert, J.-M., Todorov, K., Bean, J., Huitson, C., Fortney, J., Stevenson, K., and Bergmann, M.: A comprehensive comparative exoplanetology program to probe atmospheric properties of close-in giant exoplanets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1117,, 2020.

Lorenzo V. Mugnai, Enzo Pascale, Quentin Changeat, Ahmed Al-Refaie, and Giovanna Tinetti

In the next decade the Ariel Space Telescope will provide the first statistical dataset of exoplanet spectra, performing spectroscopic observation of about 1000 exoplanets in the wavelength range 0.5→7.8 μm thanks to its Reconnaissance Survey. About one half of these 1000 targets will be then selected for more accurate observations with higher spectral resolution.

We present a novel metric to assess the information content of the Ariel Reconnaissance Survey low resolution transmission spectra. The proposed strategy will not only allow us to select candidate planets to be re-observed in Ariel higher resolution Tiers, but also to classify exoplanets by their atmospheric composition and to put the basis for the statistical analysis of such a large exoplanetary sample.

To test our metric we use Alfnoor, a new package combining the TauRex spectral modelling with the ArielRad payload performance model, to produce populations of hundreds of exoplanets matching those presented in the Ariel Mission Reference Sample. For each of the planets in the Ariel candidate targets list we create an atmosphere with a randomised quantity of H2O, CH4, CO2, NH3 and clouds. 

Our metric proves able to identify methane,  carbon  dioxide  and  water  rich  atmospheres in the cases of molecular abundances > 10−4 in mixing ratio,  but it shows its limits in separating water from ammonia. 

We compare our metric with four different Deep Learning algorithms, they show only ∼10% better performance in identifying the molecular content.

How to cite: Mugnai, L. V., Pascale, E., Changeat, Q., Al-Refaie, A., and Tinetti, G.: Alfnoor: assessing the information content of Ariel's low resolution spectra with planetary population studies., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-272,, 2020.

John Lee Grenfell, Mareike Godolt, Juan Cabrera, Ludmila Carone, Antonio Garcia Munoz, Daniel Kitzmann, Alexis M. S. Smith, and Heike Rauer

We assess broadband color filters for the two fast cameras on the PLAnetary Transits and Oscillations (PLATO) of stars space mission with respect to exoplanetary atmospheric characterization. We focus on Ultra Hot Jupiters and Hot Jupiters placed 25pc and 100pc away from the Earth and warm Super-Earths placed 10pc and 25pc away. Our analysis takes as input literature values for the difference in transit depth between the broadband lower (500-675nm) wavelength interval (hereafter referred to as ”blue“) and the upper (675-1125nm) broadband wavelength interval (hereafter referred to as ”red“) for transmission, occultation and phase curve analyses. Planets orbiting main sequence central stars with stellar classes F, G, K and M are investigated. We calculate the signal-to-noise ratio with respect to photon and instrument noise for detecting the difference in transit depth between the two spectral intervals. Results suggest that bulk atmospheric composition and planetary geometric albedos could be detected for (Ultra) Hot Jupiters up to ~100pc (~25pc) with strong (moderate) Rayleigh extinction. Phase curve information could be extracted for Ultra Hot Jupiters orbiting K and G dwarf stars up to 25pc away. For warm Super-Earths, basic atmospheric types (primary and water-dominated) and the presence of sub-micron hazes in the upper atmosphere could be distinguished for up to a handful of cases up to ~10pc (manuscript accepted in Experimental Astronomy).

How to cite: Grenfell, J. L., Godolt, M., Cabrera, J., Carone, L., Garcia Munoz, A., Kitzmann, D., Smith, A. M. S., and Rauer, H.: Atmospheric Characterization via Broadband Color Filters on the PLAnetary Transits and Oscillations of stars (PLATO) Mission, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-40,, 2020.

Daniel Sebastian, Michael Gillon, Elsa Ducrot, Francisco J. Pozuelos, and Lionel J. Garcia and the SPECULOOS science team
One of the most promising roads for detailed analysis of temperate Earth-sized exoplanets is their detection in transit of small stars. If close enough, upcoming giant telescopes like ELT or JWST will make possible their thorough atmospheric characterisation. In this context, the TRAPPIST-1 planets form an unique benchmark system that has gathered broad interest in and out of the scientific community.

The SPECULOOS survey is a transit-search survey, targeting a volume-limited (40 pc) sample of ultracool dwarf stars (spectral type M7 and later). The survey is powered by a global network of dedicated robotic 1 m telescopes, and its strategy leverages on the synergy with TESS for its brighter and earlier targets. Given its detection potential, once completed, it will not only provide targets for atmospheric characterisation, but will also deliver robust constraints on the structure of planetary systems of ultracool dwarf stars. 
In this talk, I will detail the SPECULOOS target selection process, including new ultracool dwarf candidates, and introduce to its observing strategy.


How to cite: Sebastian, D., Gillon, M., Ducrot, E., Pozuelos, F. J., and Garcia, L. J. and the SPECULOOS science team: The SPECULOOS Project: New targets to hunt planets of Ultra-cool dwarfs. , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-337,, 2020.

Monika Lendl

The Characterizing Exoplanets Satellite (CHEOPS) is the first ESA space mission dedicated primarily to the study of exoplanetary systems. The satellite, carrying a 30cm photometric telescope, has been launched successfully in December 2019 and has seen first light in January 2020. Throughout it's nominal mission of 3.5 years, it will perform ultra-high precision photometry of bright stars know to host extrasolar planets. Next to searching for transits of planets known from radial velocities and measuring precise radii of known transiting planets, CHEOPS will dedicate approximately 25% of its observing time to characterizing exoplanet atmospheres. 

In this talk, I will describe the CHEOPS space mission, summarize its scientific program and detail how we will use CHEOPS to probe exoplanet atmospheres, such as optical-light occultations and planetary phase curves. After introducing the mission, I will give an update on it's current status, performances and show first results. I will conclude by discussing synergies with other facilities, both ground- and space-based, and illustrate how together they will advance our global understanding of planetary atmospheres.

How to cite: Lendl, M.: The Characterizing Exoplanet Satellite (CHEOPS): news and first results, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1121,, 2020.

Guillaume Gronoff, Phil Arras, Suleiman Baraka, Jared M Bell, Gael Cessateur, Ofer Cohen, Shannon M Curry, Jeremy J Drake, Meredith Elrod, Justin Erwin, Katherine Garcia-Sage, Cecilia Garraffo, Nicholas G Heavens, Kylie Lovato, Romain Maggiolo, Chris D Parkinson, Cyril Simon Wedlund, Dan R Weimer, and William B Moore

The recent discoveries of telluric exoplanets in the habitable zone of different stars have led to questioning the nature of their atmosphere, which is required to determine their habitability. Atmospheric escape is one of the challenging problems to be solved: simply adapting what is currently observed in the solar system is doomed to fail due to the large variations in the conditions encountered around other stars. A better strategy is to review the different processes that shaped planetary atmospheres and to evaluate their importance depending upon the stellar conditions. This approach allowed us to show that processes like ion-pickup were a more important way to lose atmosphere at Mars in the past. 

We reviewed the different escape mechanisms and their magnitude in function of the different conditions. This led us to discover discrepancies in the current literature concerning problems such as the Xenon paradox or the importance of a magnetic field in protecting an atmosphere.
This shows that one should be very careful before claiming the presence of an atmosphere on planets in the habitable zone of their M-dwarfs: new criteria such as the Alfven surface location with respect to the planet should be taken into account a-priori.
Overall, the habitability of a planet should not be claimed only on by its location in the habitable zone but also after careful analysis of the interaction between its atmosphere and its parent star [Gronoff et al. 2020]. 


 Gronoff, G., Arras, P., Baraka, S., Bell, J. M., Cessateur, G., Cohen, O., et al. ( 2020). Atmospheric Escape Processes and Planetary Atmospheric Evolution. Journal of Geophysical Research: Space Physics, 125, e2019JA027639. 

How to cite: Gronoff, G., Arras, P., Baraka, S., Bell, J. M., Cessateur, G., Cohen, O., Curry, S. M., Drake, J. J., Elrod, M., Erwin, J., Garcia-Sage, K., Garraffo, C., Heavens, N. G., Lovato, K., Maggiolo, R., Parkinson, C. D., Simon Wedlund, C., Weimer, D. R., and Moore, W. B.: Atmospheric Escape Processes and Planetary Atmospheric Evolution: from misconceptions to challenges, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-32,, 2020.

Miriam Rengel, Ansgar Reiners, David Cont, Cyril Gapp, Jessica Khaimova, Luisa M. Lara, Denis Shulyak, and Fei Yan

In the framework of the Priority Programme “Exploring the Diversity of Extrasolar Planets” (SPP 1992) of the German Research Foundation (DFG) we carried out the project “The key physical-chemical processes determining the Composition and Temperature of (exo)planetary atmospheres”. Characterizing the atmospheres of extrasolar planets is a new frontier in exoplanetary science, is dependent on observations and interpretation toolkits. The project intends addressing a key question in current exoplanetary atmospheric research: what are and how do the key chemical and physical processes determine the atmospheric composition and temperature of exoplanets?

Here we will review key novel results and scientific achievements obtained with emphasis on:

(1) A feasibility study on retrieving the vertical temperature distribution and abundances from ground-based high-resolution spectroscopy in the near-infrared, test case: VLT/CRIRES+.

(2) Studies of some mechanisms/effects on spectra, composition and temperature: atmospheric chemistry and dynamic under intensive

irradiation, clouds/hazes effect on the transmission spectrum of mildly irradiated exoplanets, and kinetics-related disequilibrium processes.

(3) A look to the composition of the atmosphere of Jupiter, an archetype of gas giants,  as seen by Herschel/PACS.

How to cite: Rengel, M., Reiners, A., Cont, D., Gapp, C., Khaimova, J., Lara, L. M., Shulyak, D., and Yan, F.: Investigating physical and chemical mechanisms in planetary atmospheres and their impacts on the observables, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-563,, 2020.

Luis Welbanks, Nikku Madhusudhan, Nicole F. Allard, Ivan Hubeny, Fernand Spiegelman, and Thierry Leininger

Atmospheric compositions can provide powerful diagnostics of formation and migration histories of planetary systems. In this talk, I will present the results of our latest survey of atmospheric compositions focused on atmospheric abundances of H2O, Na, and K. We employ a sample of 19 exoplanets spanning from cool mini-Neptunes to hot Jupiters, with equilibrium temperatures between ~300 and 2700 K. We employ the latest transmission spectra, new H2 broadened opacities of Na and K, and homogeneous Bayesian retrievals. We confirm detections of H2O in 14 planets and detections of Na and K in 6 planets each. Among our sample, we find a mass-metallicity trend of increasing H2O abundances with decreasing mass, spanning generally substellar values for gas giants and stellar/superstellar for Neptunes and mini-Neptunes. However, the overall trend in H2O abundances, is significantly lower than the mass-metallicity relation for carbon in the solar system giant planets and similar predictions for exoplanets. On the other hand, the Na and K abundances for the gas giants are stellar or superstellar, consistent with each other, and generally consistent with the solar system metallicity trend. The H2O abundances in hot gas giants are likely due to low oxygen abundances relative to other elements rather than low overall metallicities, and provide new constraints on their formation mechanisms. Our results show that the differing trends in the abundances of species argue against the use of chemical equilibrium models with metallicity as one free parameter in atmospheric retrievals, as different elements can be differently enhanced.

How to cite: Welbanks, L., Madhusudhan, N., Allard, N. F., Hubeny, I., Spiegelman, F., and Leininger, T.: Mass-Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H2O, Na, and K, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-168,, 2020.

Ultra-Hot Jupiters
Joost Wardenier, Vivien Parmentier, and Graham Lee
Ultra-hot Jupiters are tidally-locked gas giants with two chemical regimes: on the scorching dayside molecular species are dissociated and metals are ionised, while the permanent nightside is cool enough for cloud formation to occur. This means that the abundances of particular chemical species, such as iron, will exhibit a sharp gradient across the terminator region, which can be probed by transmission spectroscopy. We present a state-of-the-art 3D Monte-Carlo radiative transfer framework, adapted from Lee et al. (2017, 2019), that allows for the 3D modelling of high-resolution spectra of ultra-hot Jupiters. We use this tool to post-process the output of the SPARC/MITgcm global circulation model, with the aim to better understand how inhomogeneous chemistry, clouds and Doppler shifts due to atmospheric dynamics impact the appearance of a transit spectrum and its cross-correlation signal.
In this talk, we apply our model to the transit of WASP-76b, for which Ehrenreich et al. (2020) recently presented a time-varying iron signature at high spectral resolution. The observation suggests that iron condenses on the nightside of the planet. We show that different parts of the limb lead to very different cross-correlation signals and we show that the relative contributions from the east and west limb change during the transit, resulting in a time-varying cross-correlation signal. Finally, we explore different atmospheric scenarios for WASP-76b and we demonstrate that the occurrence of iron condensation, combined with the specific time-varying geometry during the transit, can quantitatively reproduce the Ehrenreich et al. (2020) result.

How to cite: Wardenier, J., Parmentier, V., and Lee, G.: Modelling high-resolution transmission spectra of the ultra-hot jupiter wasp-76b with 3D Monte-Carlo radiative transfer, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1118,, 2020.

Billy Edwards, Quentin Changeat, William Pluriel, Niall Whiteford, Kai Hou Yip, Robin Baeyens, Jake Taylor, Angelos Tsiaras, Ahmed Al-Refaie, Ingo Waldmann, and Jean-Philippe Beaulieu

The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) has been widely used for transmission and emission spectroscopy of exoplanet atmospheres, identifying the main molecular constituents, detecting the presence of clouds and probing their thermal structure. Hubble observations of the emission spectra of a number of ultra-hot Jupiters have led to somewhat surprising results. Initially, these very hot planets were predicted to have inverted temperature pressure profiles due to strong optical absorption by TiO/VO in the upper atmospheres. However, observations of their emission spectra have been inconclusive on their thermal structure and composition. While some datasets show rich spectral features, others can be fit with simple blackbody models.

We will present the analysis of Hubble WFC3 transmission and emission spectra for two ultra-hot Jupiters: WASP-76 b and KELT-7 b. In each case, the data was reduced and fitted using the open-source codes Iraclis and Taurex3. Previous studies of the WFC3 transmission spectra of WASP-76 b found hints of TiO and VO or non-grey clouds. Accounting for a fainter stellar companion to WASP-76, we reanalyse this data and show that removing the effects of this background star changes the slope of the spectrum, resulting in these visible absorbers no longer being detected, removing the need for a non-grey cloud model to adequately fit the data but maintaining the strong water feature previously seen. However, our analysis of the emission spectrum suggests the presence of titanium oxide (TiO) and an atmospheric thermal inversion. Meanwhile, our study of KELT-7 b uncovers a rich transmission spectrum which suggests the presence of water and H-. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature-pressure profile, collision induced absorption (CIA) and H-. 

These finding bring new insights into the nature of this intriguing class of planets but more data is required to fully understand them and thus we will also present the anticipated results of further characterisation.

How to cite: Edwards, B., Changeat, Q., Pluriel, W., Whiteford, N., Yip, K. H., Baeyens, R., Taylor, J., Tsiaras, A., Al-Refaie, A., Waldmann, I., and Beaulieu, J.-P.: Characterising Two Ultra-Hot Jupiters with the Hubble Space Telescope, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-657,, 2020.

Aurélien Wyttenbach, Paul Mollière, David Ehrenreich, Heather Cegla, Vincent Bourrier, Christophe Lovis, Lorenzo Pino, Romain Allart, Julia Seidel, Jens Hoeijmakers, Louise Nielsen, Baptiste Lavie, Francesco Pepe, Xavier Bonfils, and Ignas Snellen

Atmospheric escape rate is a key parameter to measure in order to understand the evolution of exoplanets. In this presentation, we will show that the Balmer series, observed with high-resolution transmission spectroscopy, is a precise probe to measure exoplanet evaporation, especially for ultra hot Jupiters orbiting early-type star. These hot gaseous giant exoplanets (such as KELT-9 b) are presumed to have an atmosphere dominated by neutral and ionized atomic species. In particular, hydrogen Balmer lines have been detected in some of their upper atmospheres, suggesting that hydrogen is filling the planetary Roche lobe and escaping from these planets. Here, we will present new significant absorptions of the Balmer series in the KELT-9b atmosphere obtained with HARPS-N. The precise line shapes of the Hα, Hβ, and Hγ absorptions allow us to put constraints on the thermospheric temperature. Moreover, the mass loss rate, and the excited hydrogen population of KELT-9 b are also constrained, thanks to a retrieval analysis performed with a new atmospheric model (the PAWN model). We retrieved a thermospheric temperature of T = 13 200+800-720 K and a mass loss rate of log10(MLR) = 10^(12.8+-0.3) g/s when the atmosphere was assumed to be in hydrodynamical expansion and in local thermodynamic equilibrium (LTE). Since the thermospheres of hot Jupiters are not expected to be in LTE, we explored atmospheric structures with non-Boltzmann equilibrium for the population of the excited hydrogen. We do not find strong statistical evidence in favor of a departure from LTE. However, our non-LTE scenario suggests that a departure from the Boltzmann equilibrium may not be sufficient to explain the retrieved low number densities of the excited hydrogen. In non-LTE, Saha equilibrium departure via photo-ionization, is also likely to be necessary to explain the data.

How to cite: Wyttenbach, A., Mollière, P., Ehrenreich, D., Cegla, H., Bourrier, V., Lovis, C., Pino, L., Allart, R., Seidel, J., Hoeijmakers, J., Nielsen, L., Lavie, B., Pepe, F., Bonfils, X., and Snellen, I.: Measuring and modeling the Balmer series in hot gaseous giant exoplanets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-115,, 2020.

Lorenzo Pino, Jean-Michel Désert, Matteo Brogi, Valerio Nascimbeni, Aldo Stefano Bonomo, Michael Line, and Antonio Maggio

Ultra-hot Jupiters (Teq ≥ 2,500 K) are the hottest gaseous giants known. They emerged as ideal laboratories to test theories of atmospheric structure and its link to planet formation. Indeed, because of their high temperatures, (1) they likely host atmospheres in chemical equilibrium and (2) clouds do not form in their day-side. Thousands of lines of refractory elements such as iron, normally inaccessible in planets, can be studied through high spectral resolution emission spectroscopy, providing a first look into the chemistry of refractory elements in exoplanets. In this talk we report the detection of neutral iron in the day-side emission spectrum of KELT-9b (Tday ~ 4,000  K), the first detection of an atomic species in the emission spectrum of an exoplanet, obtained with HARPS-N optical data gathered in the framework of the GAPS collaboration. Our detection unambiguously indicates the presence of a thermal inversion in the atmosphere of the planet. We also present a new technique to extract planetary parameters from the cross-correlation function in a statistically sound framework, which makes possible the combination with information from the planetary continuum that can be obtained with complementary space facilities. This is a crucial step towards the measurement of metal abundances in exoplanets, a quantity that can be compared to predictions of planet formation theories. In the near future, our technique will be extended to cooler exoplanets. In the era of EELTs and JWST, this kind of measurements could ultimately open a new window on exoplanet formation and evolution.

How to cite: Pino, L., Désert, J.-M., Brogi, M., Nascimbeni, V., Bonomo, A. S., Line, M., and Maggio, A.: Metals in the day-side of ultra-hot Jupiter atmospheres: a key test for planetary formation, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-812,, 2020.

Monika Stangret, Núria Casasayas-Barris, Enric Palle, Fei Yan, Alejandro Sánchez-López, and Manuel López-Puertas

Thanks to the different Doppler velocities of the Earth, the host star and the planet using high-resolution spectroscopy we are able to detect and characterise exoplanetary atmospheres. Exoplanetary signal is buried in the residual noise, however by preforming cross-correlation of atmospheric transmission model and hundreds of atmospheric lines the signal can be increase. Studying the atmospheres of ultra-hot Jupiters, objects with the temperature higher than 2200K which orbit close to their host stars, gives us great laboratory to study chemistry of the exoplanets. MASCARA-2b also known as KELT-20b with the temperature of 2230 K is a perfect example of ultra hot Jupiter. We studied this object using three transit observations obtained with HARPS-North. Using cross-correlation method we detected strong absorption of Fe I and FeII, which agrees with theoretical models. Additionally, because of the fast rotation of the star, the crosscorrelation residuals show strong Rossiter-MacLaughlin effect.

How to cite: Stangret, M., Casasayas-Barris, N., Palle, E., Yan, F., Sánchez-López, A., and López-Puertas, M.: Fe I and Fe II in the atmosphere of Ultra-hot Jupiter MASCARA-2b, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1089,, 2020.

Hot Jupiters
Nour Skaf

We would like to present the atmospheric characterisation of three large, gaseous planets: WASP-127b, WASP-79b and WASP-62b. We analysed spectroscopic data obtained with the G141 grism (1.088 - 1.68 um) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) using the Iraclis pipeline and the TauREx3 retrieval code, both of which are publicly available. For WASP-127b, which is the least dense planet discovered so far and is located in the short-period Neptune desert, our retrieval results found strong water absorption corresponding to an abundance of log(H$_2$O) = -2.71$^{+0.78}_{-1.05}$, and absorption compatible with an iron hydride abundance of log(FeH)=$-5.25^{+0.88}_{-1.10}$, with an extended cloudy atmosphere.
We also detected water vapour in the atmospheres of WASP-79b and WASP-62b, with best-fit models indicating the presence of iron hydride, too.
We used the Atmospheric Detectability Index (ADI) as well as Bayesian log evidence to quantify the strength of the detection and compared our results to the hot Jupiter population study by Tsiaras et al 2018.
While all the planets studied here are suitable targets for characterisation with upcoming facilities such as the James Webb Space Telescope (JWST) and Ariel, WASP-127b is of particular interest due to its low density, and a thorough atmospheric study would develop our understanding of planet formation and migration. 

How to cite: Skaf, N.: Characterising the Hot Jupiters WASP-127\,b, WASP-79\,b and WASP-62\,b with HST, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-834,, 2020.

Lara Anisman, Billy Edwards, Quentin Changeat, Olivia Venot, Ahmed Al-Refaie, Angelos Tsiaras, and Giovanna Tinetti

We present spectral analysis of the transiting Saturn-mass planet WASP-117 b, observed with the G141 grism of the Hubble Space Telescope’s Wide Field Camera 3 (WFC3).  We reduce and fit the extracted spectrum from the raw transmission data using the open-source software Iraclis before performing a fully Bayesian retrieval using the publicly available analysis suite TauREx 3.0. We detect water vapour alongside a layer of fully opaque cloud, with an ADI of 2.30, retrieving a terminator temperature of Tterm =833+260-156 K. Due to the eccentric orbit of WASP-117 b, it is likely that chemical and mixing timescales oscillate throughout orbit due to the changing temperature, possibly allowing hotter chemistry to remain visible as the planet begins transit, despite the proximity of its point of ingress to apastron. We present simulated spectra of the planet as would be observed by the future space missions Ariel and JWST and show that, despite not being able to probe such chemistry with current HST data, these observatories should make it possible in the not too distant future.

How to cite: Anisman, L., Edwards, B., Changeat, Q., Venot, O., Al-Refaie, A., Tsiaras, A., and Tinetti, G.: WASP-117 b: An Eccentric hot-Saturn as a Future Complex Chemistry Laboratory, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-107,, 2020.

Leonardo A. dos Santos, David Ehrenreich, Vincent Bourrier, Romain Allart, George King, Monika Lendl, Christophe Lovis, Steve Margheim, Jorge Meléndez, Julia V. Seidel, and Sérgio G. Sousa

Large-scale exoplanet search surveys have shown evidence that atmospheric escape is a ubiquitous process that shapes the evolution and demographics of planets. However, we lack a detailed understanding of this process because very few exoplanets discovered to date could be probed for signatures of atmospheric escape. Recently, the metastable helium triplet at 1.083 μm has been shown to be a viable window for the presence of He-rich escaping envelopes around short-period exoplanets. Our objective is to use, for the first time, the Phoenix spectrograph to search for helium in the upper atmosphere of the inflated hot Jupiter WASP-127 b. We observed one transit and reduced the data manually since there is no pipeline available. We did not find a significant in-transit absorption signal indicative of the presence of helium around WASP-127 b, and set a 90% confidence upper limit for excess absorption at 0.87% in a 0.75 Å passband covering the He triplet. Given the large scale height of this planet, the lack of a detectable feature is likely due to unfavorable photoionization conditions to populate the metastable He I triplet. This conclusion is supported by the inferred low coronal and chromospheric activity of the host star and the old age of the system, which result in a relatively mild high-energy environment around the planet.

How to cite: dos Santos, L. A., Ehrenreich, D., Bourrier, V., Allart, R., King, G., Lendl, M., Lovis, C., Margheim, S., Meléndez, J., Seidel, J. V., and Sousa, S. G.: Search for helium in the upper atmosphere of the hot Jupiter WASP-127 b using Phoenix/Gemini, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-253,, 2020.

Julia Seidel, David Ehrenreich, Vincent Bourrier, Lorenzo Pino, Aurelien Wyttenbach, Romain Allart, Baptiste Lavie, Dany Mounzer, and Christophe Lovis

The sodium doublet is one of the most powerful probes of exoplanet atmospheric properties when observed in transmission spectroscopy during transits. Recent high-spectral resolution observations of the sodium doublet in hot gas giants allowed us to resolve the line shape, opening the way for extracting atmospheric properties using line-profile fitting.

Using the MERC code (Seidel et al. 2020a), a retrieval tool to determine temperature-pressure profiles and high-altitude winds in exoplanet thermospheres, we have studied the curiously broadened sodium signatures of various hot Jupiters. We have updated the MERC code to a quasi 3D treatment of the atmosphere (Seidel et al. 2020c, in prep.) and analysed three hot Jupiters, spanning a wide range of this class of exoplanets (see figure). Using the sodium signature of three examples - WASP-76b (a highly irradiated ultra-hot Jupiter, Seidel et al. 2019), KELT-11b (a puffy hot Jupiter, Mounzer et al. 2020, in prep.), and lastly HD189733b (one of the most studied hot Jupiters to date, Wyttenbach et al. 2015) - we explore possible trends in the atmospheric structure of hot Jupiters.

We will first introduce the new quasi 3D retrieval of MERC, and proceed to show that high-velocity winds in the thermosphere are one possible explanation of the broadened sodium features seen in hot Jupiters. We plan to highlight various caveats and present likely origin scenarios for the observed wind patterns. We will then put these results in the context of past studies using global circulation models (GCMs) on hot Jupiters.

How to cite: Seidel, J., Ehrenreich, D., Bourrier, V., Pino, L., Wyttenbach, A., Allart, R., Lavie, B., Mounzer, D., and Lovis, C.: Wind of Change: Atmospheric wind retrieval and its implications for hot Jupiters, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-273,, 2020.

Maria Steinrueck, Adam Showman, Panayotis Lavvas, Tommi Koskinen, Xi Zhang, and Xianyu Tan


The transmission spectra of many hot Jupiters show signatures of high-altitude aerosols [e.g., 1,2]. One hypothesized formation mechanism for these aerosols is that photochemical processes generate hazes on the dayside. All previous studies of photochemical hazes on tidally locked giant planets used one-dimensional models [e.g., 3,4]. However, one-dimensional models have to make strongly simplifying assumptions about the strength of vertical mixing. Furthermore, they ignore that the strong day-night contrast on hot Jupiters and atmospheric circulation can lead to inhomogeneous aerosol distributions. For condensate clouds, it has been shown that inhomogeneous aerosol distributions are to be expected [5-7] and can lead to biases in the interpretation of observations [e.g., 8]. The same is likely to be true for photochemical hazes. Further, it has been suggested differences between the morning and evening terminator in ingress and egress transmission spectra could provide a diagnostic for distinguishing between condensate clouds and photochemical hazes [9]. Three-dimensional general circulation models (GCMs) are needed to study how atmospheric circulation shapes the distribution of photochemical hazes to guide future observations and models.


We present simulations of hot Jupiter HD 189733b using the MITgcm [10]. We use passive tracers representing photochemical hazes to study how hazes are transported by atmospheric circulation. Haze particles in our model have a constant size and are spherical.


The results show that the haze mass mixing ratio varies horizontally by at least an order of magnitude for all particle sizes considered and over the entire simulated pressure range. Depending on the particle size, the resulting 3D haze distribution falls into one of two regimes: small (<30 nm) and large (>30 nm) particles.

For small particles (< 30 nm), the timescale for gravitational settling is longer than the timescale for horizontal and vertical advection. The 3D distribution is thus controlled by advection and looks similar for all particle sizes in this regime. At low pressures, small particle hazes accumulate on the night side in two large midlatitude vortices centered east of the antistellar point (Fig. 1). Because the night side vortices span across the morning terminator, there are higher mass mixing ratios at the morning terminator compared to the evening terminator.

For large particles (>30 nm), the 3D haze distribution is strongly influenced by settling. At very low pressures, where the settling timescale is much shorter than the advection timescale, the horizontal pattern closely mirrors the haze production function. At somewhat higher pressures, where both timescales are within an order of magnitude from each other, hazes are concentrated on the dayside and the hemisphere east of the substellar point (Fig. 2). This results in higher mass mixing ratios at the evening terminator compared to the morning terminator. Because the distribution of hazes is dependent on where in the atmosphere these timescales become equal, the 3D size distributions look much less similar between different particle sizes within this regime compared to the small particle regime.

At pressures > 1 mbar, the advection time scale is shorter than the settling time scale for all particle sizes considered in our simulations. In this region, the equatorial jet dominates the atmospheric circulation and hazes of all sizes develop a more banded pattern (Fig. 3). Differences between morning and evening terminator become smaller in this pressure range.

Our model does not include particle growth and thus does not make predictions about the particle size distribution. To estimate whether terminator differences could be observable, we tried using a constant particle size as well as a size distribution from a 1D microphysics model [3]. In either case, one obtains a relatively small difference in transit depth between leading and trailing limb (Fig. 4). We note that the simulated spectral slope at short wavelengths is too flat to match the observational data. There could be multiple factors explaining why our model does not reproduce the slope of the data, including that a fully coupled three-dimensional microphysics and circulation model might be needed to reproduce the observational data. Furthermore, part of the slope could arise from unaccounted star spots. Another possibility is that mixing from small-scale turbulence not resolved by the GCM could be much more important than expected. In that case, the haze mass mixing ratio would decline more rapidly with increasing pressure, resulting in a steeper spectral slope.


[1] Pont, F., Sing, D. K., Gibson, N. P., et al.: The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations, Monthly Notices of the Royal Astronomical Society, 432, 4, 2917-2944, 2013.

[2] Sing, D. K., Fortney, J. J., Nikolov, N., et al.: A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion, Nature, 529, 7584, 59-62, 2016.

[3] Lavvas, P. and Koskinen, T.: Aerosol Properties of the Atmospheres of Extrasolar Giant Planets, The Astrophysical Journal, 847, 1, 32, 2017.

[4] Ohno, K. and Kawashima, Y.: Super-Rayleigh Slopes in Transmission Spectra of Exoplanets Generated by Photochemical Haze, The Astrophysical Journal Letters, 895, 2, L47, 2020.

[5] Parmentier, V., Showman, A. P. and Lian, Y.: 3D mixing in hot Jupiters atmospheres I . Application to the day / night cold trap in HD 209458b, Astronomy & Astrophysics, 558, A91, 2013.

[6] Lee, G., Dobbs-Dixon, I., Helling, Ch., et al.: Dynamic mineral clouds on HD 189733b. I. 3D RHD with kinetic, non-equilibrium cloud formation, Astronomy & Astrophysics, 594, A48, 2016.

[7] Lines, S., Mayne, N. J., Boutle, I. A., et al.: Simulating the cloudy atmospheres of HD 209458 b and HD 189733 b with the 3D Met Office Unified Model, Astronomy & Astrophysics, 615, A97, 2018.

[8] Line, M. and Parmentier, V.: The Influence of Nonuniform Cloud Cover on Transit Transmission Spectra, The Astrophysical Journal, 820, 1, 78, 2016.

[9] Kempton E. M. R., Bean J. L., Parmentier V.: An Observational Diagnostic for Distinguishing between Clouds and Haze in Hot Exoplanet Atmospheres, The Astrophysical Journal, 845, 2, L20, 2017.

[10] Adcroft A., Campin J.-M., Hill C., Marshall J.: Implementation of an Atmosphere Ocean General Circulation Model on the Expanded Spherical Cube, Monthly WeatherReview, 132, 2845, 2004.

How to cite: Steinrueck, M., Showman, A., Lavvas, P., Koskinen, T., Zhang, X., and Tan, X.: Three-dimensional Simulations of Photochemical Hazes in the Atmosphere of Hot Jupiter HD 189733b, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-768,, 2020.

Paul Mollière and the ExoGRAVITY team and collaborators

Young gas giant planets still glow hot from formation, sometimes even showing signs of active accretion. Studying the atmospheres of these directly imaged planets may help placing constraints on how they formed, which may also shed light on the formation process of the planetary systems they reside in. In general, this may be achieved by connecting atmospheric to planetary composition, and planetary composition to planet formation. In my talk I will present our work that investigates the first step of this process, namely constraining the atmospheric abundances of gas giant exoplanets via free retrievals of GRAVITY, SPHERE and GPI observations. Free retrievals work by parameterizing the atmospheric structure as much as possible when calculating spectra, thereby allowing the data to constrain the atmosphere’s state. This relaxes the need for a model to fulfill given assumptions which may not accurately describe the atmospheric physics, due to modeling uncertainties and oversimplifications. At the same time caution is required because unphysical atmospheric models can potentially lead to excellent fits to spectroscopic observations. I will show why including clouds and scattering is crucial for the analysis of directly imaged planets, what the effects of using inappropriate cloud models are, and outline the next steps to develop this analysis method further.

How to cite: Mollière, P. and the ExoGRAVITY team and collaborators: Retrieving the atmospheric properties of directly imaged planets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-131,, 2020.

Denis Shulyak, Miriam Rengel, Luisa Lara, and Nina Nemec

Thanks to the advances in modern instrumentation we learned about many exoplanets that spawn a wide range of masses and composition. Studying their atmospheres  provides insight into planetary diversity, origin, evolution, dynamics, and habitability. Present and future observing facilities will address these important topics in very detail by using more precise observations, high-resolution spectroscopy, improved analysis methods, etc. In this contribution we focus on the analysis of temperature and  disequilibrium chemical processes in hot Jupiter atmospheres. In particular, we investigate the impact of photochemistry and vertical transport processes on mixing ratio  profiles and on the simulated spectra of a hot Jupiters that orbits stars of various spectral types. We additionally address the impact of stellar activity that should be present in all stars with convective envelopes. Finally, we estimate the characterization of these processes using space and ground-based observations that will be carried out with near-future instruments and missions. 


How to cite: Shulyak, D., Rengel, M., Lara, L., and Nemec, N.: Studying physics and chemistry in atmospheres of hot Jupiters from future ground-based and space facilities, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-236,, 2020.

Jake Taylor, Vivien Parmentier, Michael Line, Graham Lee, Patrick Irwin, and Suzanne Aigrain

Observational studies of exoplanets show that many of them contain some form of cloud coverage. The current modelling techniques used in emission to account for the clouds tend to require prior knowledge of the cloud condensing species as well as not considering the scattering caused by the clouds. We explore the effects that scattering has on the emission spectra by modelling a suite of hot Jupiter atmospheres with varying cloud single scattering albedos and temperature profiles. We examine from simple isothermal cases to more complex thermal structures and physically driven cloud modelling. We show that scattering can produce spectral signatures in the emission spectrum even for isothermal atmospheres. We identify the problems that arise from fitting JWST spectra when the spectral shape is dominated by the scattering from the clouds. Finally, we propose a novel method of fitting the single scattering albedo of the cloud in emission retrievals, this technique does not require any prior knowledge of the cloud chemical or physical properties. We show that this technique can retrieve the wavelength dependent shape of the single scattering albedo while accurately modelling the chemistry in the atmosphere.  






How to cite: Taylor, J., Parmentier, V., Line, M., Lee, G., Irwin, P., and Aigrain, S.: The Impact of Scattering Clouds when Studying Exoplanet Emission Spectra with JWST, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-69,, 2020.

Planetary Mass and Metallicity Derived Directly from Transmission Spectroscopy
Subhanjoy Mohanty and James Owen
Retrieval Techniques / Methods
Óscar Carrión-González, Antonio García Muñoz, Juan Cabrera, Szilárd Csizmadia, Nuno C. Santos, and Heike Rauer


Direct-imaging observations of exoplanets in reflected starlight are expected to be available this decade. This will improve our knowledge about cold and temperate exoplanets and their atmospheres. Current theoretical efforts related to such planets aim to understand the effects that planet and atmospheric properties have on the spectra to be measured. This will help predict the science outcome of direct-imaging missions and identify the key needs for models used in the interpretarion of future measurements. In this work, we have investigated the information contained in reflected-light exoplanetary spectra and the role played by the planet radius in the atmospheric characterization.


Long-period exoplanets are a population that remains substantially unexplored because of the biases introduced by the technology currently available. These planets have small transit probabilities due to their large orbital distances and hence the direct-imaging technique will be key to analyse their atmospheres. Space missions such as NGRST (formerly WFIRST), LUVOIR or HabEx will allow us to study this population of long-period exoplanets, providing a more complete picture of exoplanet diversity.


We set up an atmospheric model with hydrogen and helium as the main components. We include methane, in a volume-mixing-ratio fCH4, as the only absorbing gaseous species. We add a cloud layer, described by its optical thickness (τc), its geometrical extension and the position of the cloud top. The aerosols are modelled by their single-scattering albedo and their effective radius, which determines the scattering phase function through Mie theory. This model is motivated by previous modelling of the atmospheres of Solar System gas giants. Apart from the six atmospheric parameters, we include the planet radius (Rp) as another model parameter. We apply our analysis to a particular target, Barnard's Star b candidate super-Earth[1], although our conclusions are generally planet-independent.


We built a grid of ~300,000 synthetic reflected-light spectra for a range of possible atmospheric configurations. The spectra were computed at phase angle α=0º (that is, with the exoplanet fully illuminated). The wavelength interval under study is 500-900 nm and the spectral resolution, R~125-225. The multiple-scattering radiative-transfer problem was solved with a previously validated code[2].

Observations were simulated by adding wavelength-independent noise at S/N=10. Three atmospheric configurations were considered to simulate observations and carry out retrievals: a cloud-free one (τc=0.05), one with a thin-cloud (τc=1.0) and one with a thick-cloud (τc=20.0). We developed an MCMC-based retrieval package achieving a continuous sampling of the parameter space by interpolating within the pre-computed grid of spectra.

The retrievals were carried out for cases where the planet radius was either known (and hence there were only 6 free parameters) or completely unconstrained (7 free parameters). We also analysed intermediate scenarios in which estimates of Rp with different uncertainties were assumed.


The retrievals of atmospheric properties degrade as the uncertainties in the value of Rp increase. Indeed, the correlations between model parameters triggered by adding Rp as a free parameter make it challenging to distinguish between cloudy- and cloud-free atmospheres. Fig. 1 shows that, even if the atmosphere contains a thick-cloud, the evidence for the cloud disappears as the uncertainties in Rp grow. When the planet radius is a priori unconstrained, the retrieval of τc shows a nearly-flat posterior probability distribution. This indicates that the evidence is equal for both thick clouds or cloud-free atmospheres. On the other hand, if Rp is known we can generally distinguish between cloudy or cloud-free atmospheres in all of the scenarios analysed in this work. The retrieval results for other parameters such as the methane abundance also improve if the planet radius is known.

Fig. 1 also shows that a priori estimates on the value of Rp improve the retrievals. This result encourages the development of synergies between direct-imaging and other techniques in order to reduce the uncertainties in the mass and radius of long-period exoplanets.

Besides, we find that, if Rp is completely unconstrained, direct-imaging observations can constrain its value to within a factor of ~2 for all the cases explored. This might help start addressing the bulk composition of an exoplanet.

Several works have addressed the possible science return of future direct-imaging observations[3]-[5]. Since the exoplanets observed in direct-imaging will generally lack a measurement of Rp, we conclude that this parameter will play an important role in the retrievals and therefore should be included in this type of retrieval exercises.


[1] Ribas et al. (2018), Nature, 563, 365
[2] García Muñoz & Mills (2015), A&A, 573, A72
[3] Lupu et al. (2016), AJ, 152, 217
[4] Nayak et al. (2017), PASP, 129, 973
[5] Damiano & Hu (2019), AJ, 159, 175


How to cite: Carrión-González, Ó., García Muñoz, A., Cabrera, J., Csizmadia, S., Santos, N. C., and Rauer, H.: Directly imaged exoplanets in reflected starlight. The importance of knowing the planet radius, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-674,, 2020.

Joanna Barstow

A substantial fraction of transiting exoplanets have some form of aerosol present in their atmospheres. Transit spectroscopy, especially of hot Jupiters, has provided evidence for this, in the form of steep downward slopes from blue to red in the optical part of the spectrum, and muted gas absorption features throughout. Studies analysing the atmospheres of these planets must therefore consider the presence of aerosol.

However, clouds and hazes are complex, and the transit spectra that are currently available allow us to constrain only limited properties of cloud and haze. Retrieval models – fast, parametric radiative transfer models coupled with an inversion algorithm – are typically used to analyse transit spectra, but these rely on minimising the number of variables to ensure rapid convergence. Optimising aerosol parameters to maximise constraints on cloud structure, whilst avoiding overfitting, is therefore a necessary step.

In this presentation, I investigate a range of aerosol parameterisations from the literature (Figure 1), and examine their effects on retrievals from transmission spectra of hot Jupiters HD 189733b (Figure 2) and HD 209458b. Regardless of the parameterisation used, results qualitatively agree for the cloud/haze itself, and using multiple approaches provides a more holistic picture. The retrieved H2O abundance is also robust to assumptions about aerosols. Additionally, strong evidence emerges that aerosol on HD 209458b covers less than half of the terminator region, but the situation for HD 189733b is less clear (Barstow 2020).