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).


Barstow J. K., Aigrain S., Irwin P. G. J., Sing D. K., 2017, ApJ, 834, 50

Barstow J. K., 2020, arxiv:2002.02945

Fisher C., Heng K., 2018, MNRAS, 481, 4698

Pinhas A., Madhusudhan N., Gandhi S., MacDonald R., 2019, MNRAS, 482, 1485

Sing D. K., et al., 2016, Nature, 529, 59

Tsiaras A., et al., 2018, AJ, 155, 156


How to cite: Barstow, J.: Unveiling cloudy exoplanets: the influence of cloud model choices on retrieval solutions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-132,, 2020.

Jasmina Blecic

The planetary multi-dimensional nature poses many challenges to their atmospheric modeling. However, as targets and data quality improve with the TESS and CHEOPS missions and soon to be launched JWST, PLATO and ARIEL missions, so too must our modeling approach if we would like to assess a truly 3D picture of planetary atmospheres. We present a physically-consistent GCM-motivated multi-dimensional temperature model, that utilizes the dominant dynamical property of short-period tidally-locked planets, the planetary jet, and accounts, for the first time, for the advection of energy around the planet. In our approach, we utilize a tractable set of parameters efficient enough to enable Bayesian analysis and return physical insights not yet retrieved for exoplanets. By fundamentally linking the planetary longitudes and retrieving spectra at all orbital phases simultaneously, we recover three essential properties of the planetary jet (phase offset, amplitude, and pressure where the jet is located) together with the self-consistent temperature structure. 


                                         Figure 1: Two examples of our parameterized advective temperature component at the equator.

How to cite: Blecic, J.: Physically-Consistent Multi-Dimensional Temperature Structure for Retrieval, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-890,, 2020.

Kai Hou Yip, Quentin Changeat, Nikolaos Nikolaou, Mario Morvan, Billy Edwards, and Ingo Waldmann

Deep learning algorithms are growing in popularity in the field of exoplanetary science due to their ability to model highly non-linear relations and solve interesting problems in a data-driven manner. Several works have attempted to perform fast retrieval of atmospheric parameters with the use of machine learning algorithms or deep neural networks (DNNs).  Yet, despite their high predictive power,  DNNs are also infamous for being `black boxes’. It is their apparent lack of explainability that makes the astrophysics community reluctant to adopt them. What are their predictions based on? How confident should we be in them? When are they wrong and how wrong can they be? In this work, we present a number of general evaluation methodologies that can be applied to any trained model and answer questions like these.  In particular, we train 3 different popular DNN architectures to retrieve atmospheric parameters from exoplanet spectra and show that all 3 achieve good predictive performance. We then present an extensive analysis of the predictions of DNNs, which can inform us —among other things — of the credibility limit for atmospheric parameters for a given instrument and model. Finally, we perform a sensitivity analysis to identify to which features of the spectrum the outcome of the retrieval is most sensitive. We conclude that for different molecules, the wavelength ranges to which the DNN’s predictions are most sensitive, indeed coincide with their characteristic absorption regions. The methodologies presented in this work help to improve the evaluation of DNNs and to grant interpretability to their predictions.

How to cite: Yip, K. H., Changeat, Q., Nikolaou, N., Morvan, M., Edwards, B., and Waldmann, I.: Peeking inside the Black Box: Interpreting Deep Learning Models for Exoplanet Atmospheric Retrievals, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-66,, 2020.

Ahmed Al-Refaie, Quentin Changeat, Olivia Venot, Ingo Waldmann, and Giovanna Tinetti


TauREx 3.1 is the next version of the open-source python retrieval framework TauREx 3[1], which is backward-compatible with the previous version but offers a swathe of improvements and optimizations to the overall architecture. This version upgrade includes support for k-tables, non-uniform priors, and H- opacities. The most major inclusion in this version of TauREx is the plugin system, which allows any developer to imbue TauREx 3 with new features without touching the main codebase. Plugins are installable additions that TauREx 3 will detect and automatically include in its Bayesian retrieval pipeline. They can be installed from PyPI through pip install or directly from a git repository. They can consist of collections of new chemistries, temperature profiles, contribution functions, stellar and planetary models, non-uniform prior functions, opacity formats, and forward models, to name a few. Anyone can host and develop them, and they are designed so that all are interoperable with each other. Presented are the CUDA and OpenCL plugins, which provide GPU accelerated forward models. Fastchem[2], GGchem[3], and disequilibrium[4] chemical plugins and petitRADTRANS[5] and phase curve forward model plugins. Presented are Forward models and retrievals that exploit the plugins



Exoplanetary atmospheres are multi-faceted physical phenomena that touch many scientific fields. Chemical modeling, cloud physics, fluid dynamics, orbital mechanics and molecular spectroscopy are some of the physical processes that need to be appropriately handled in a retrieval framework to characterize these complex environments correctly. With the upcoming JWST and Ariel telescope expected to bring a higher density of information, it is vital that the many codes and contributions of a wide variety of fields can be exploited for characterization.



TauREx 3 allowed for the inclusion of custom codes in the pipeline. TauREx 3.1 provides a means for which a developer can develop and distribute their custom codes through plugins. Plugins exploit the python packaging system to allow developers to make their codes installable and easily used in retrievals without modification of the main TauREx 3 codebase.  The installation is an essential aspect as this allows many FORTRAN and C++ codes to be automatically compiled or binaries distributed. TauREx will then automatically detect these plugins and integrate them into its retrieval pipeline. Plugins can provide replacements for all components in the TauREx 3 framework. For example, if a user wishes to use the GGchem chemistry code in atmospheric retrievals, they can simply write pip install taurex_ggchem, which will automatically download a precompiled GGchem library and its data files and install it alongside a new TauREx chemistry component. A user can then immediately include GGchem for both forward models and retrievals in input files or python scripts. A single plugin can consist of any number of new replacement atmospheric components and can make use of FORTRAN, C++, and python codes/libraries.



TauREx-CUDA and TauREx-OpenCL are plugins that, when installed, provide replacement forward models that take advantage of heterogeneous computing. These replacement forward models allow the optical depth calculation to execute on hardware accelerators such as Nvidia, AMD, and Intel GPUs to be easily exploited for a 25--50x speed up in both forward models and retrievals. 



The four plugins TauREx-ACE, TauREx-Fastchem, and TauREx-GGchem, are installable components that provide the ACE[6], Fastchem[2] and GGchem[3] equilibrium codes for use in both forward modeling and retrievals. These can be easily installed and used in Windows, Mac, and Linux through PyPi and provide their full capabilities for both forward modeling (Figure 1) and retrievals (Figure 2).  Also included is a new plugin for a photochemical kinetic solver[4] that provides disequilibrium chemistry with retrieval capabilities (Figure 3).



Figure 1. Plots of simulated JWST transmission spectra from different chemistry schemes.


Figure 2. Posteriors  of  ACE  (blue),  Fastchem  (red),  GGchem  (green)  and GGchem with condensation (orange)


Figure 3. Active molecular profiles using a photochemical kinetic solver[4] with retrieval sampling uncertainties.


Forward Model plugins

Plugins can include entirely new forward models. The TauREx-petitRADTRANS plugin that utilizes petitRADTRANS[5] code to compute the transmission and emission spectra. It demonstrates the interoperable nature of plugins. Running petitRADTRANS under the TauREx 3.1 framework gives it the ability to use all available chemistries, including ACE, Fastchem, GGchem, and disequilibrium codes, as well as retrievals utilizing nested sampling with non-uniform priors. The TauREx-phase plugin implements a phase curve forward model for retrievals and can exploit all plugins, including the equilibrium chemistry and CUDA, for self-consistent accelerated optimizations.



The plugin system in TauREx 3.1 aims to simplify the inclusion of new atmospheric parameters and external codes. TauREx 3.1 is available at or through PyPi. Each plugin is also available through both in the ucl-exoplanets GitHub page and PyPi.



[1] Ahmed F. Al-Refaie, Quentin Changeat, Ingo P. Waldmann, and Giovanna Tinetti. Taurex III: A fast, dynamic and extendable framework for retrievals, 2019.

[2] Joachim W Stock, Daniel Kitzmann, A Beate C Patzer, and Erwin Sedlmayr. FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres .Monthly Notices of the Royal Astronomical Society,479(1):865–874, 06 2018.

[3] Woitke, P., Helling, Ch., Hunter, G. H., Millard, J. D., Turner, G. E.,Worters, M., Blecic, J., and Stock, J. W. Equilibrium chemistry down to 100 k - impact of silicates and phyllosilicates on the carbon to oxygen ratio..A&A, 614:A1, 2018.

[4] Venot, O., Hebrard, E., Agundez, M., Dobrijevic, M., Selsis, F., Hersant,F., Iro, N., and Bounaceur, R. A chemical model for the atmosphere of hot jupiters. A&A, 546:A43, 2012.

[5] Molliere, P., Wardenier, J. P., van Boekel, R., Henning, Th., Molaverdikhani, K., and Snellen, I. A. G. petitRADTRANS - a python radiative transfer package for exoplanet characterization and retrieval.A&A, 627:A67, 2019.

[6] M. Agundez, O. Venot, N. Iro, F. Selsis, F. Hersant, E. Hebrard, and M. Do-brijevic. The impact of atmospheric circulation on the chemistry of the hotJupiter HD 209458b.A&A, 548:A73, Dec 2012.

How to cite: Al-Refaie, A., Changeat, Q., Venot, O., Waldmann, I., and Tinetti, G.: TauREx 3.1 - Extending atmospheric retrieval with plugins., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-669,, 2020.

Wilfrid Somogyi and Sergey Yurchenko

Molecular oxygen (O2) is of particular interest in exoplanetary observations not least of all as an important biosignature on habitable planets. The atmospheric absorption bands are well studied, but a complete and accurate, high-resolution linelist is yet to be produced. Owing to their symmetry, the commonly employed electric dipole approximation is not valid for homonuclear diatomic molecules, and their rovibrational spectra are instead dominated by higher order transitions moments. These higher-order moments, such as the electric quadrupole and magnetic dipole, give rise to transition linestrengths that are orders of magnitude weaker than typical electric dipole transitions. Although such transitions are observable for atmospheric path lengths, their weak nature makes laboratory measurements especially challenging. In this work we develop and apply ab initio computational techniques to produce an accurate electric quadrupole spectrum of molecular oxygen presented for use in atmospheric retrievals across a range of temperatures, and made available through the ExoMol database.

How to cite: Somogyi, W. and Yurchenko, S.: A High-Resolution Linelist for Molecular Oxygen, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-539,, 2020.

Ildar F. Shaikhislamov and Maxim L. Khodachenko

The aeronomy hydrodynamic simulation Salz et al. (2016) has shown that the warm Neptune GJ 3470b should have one of the largest mass loss rates due to its low mass, close orbit and relatively high activity of the host star. The Lyα observation of GJ 3470b reported in Bourrier et al. (2018) revealed large absorption depths of ~35 % in the blue wing [-94; -41] km/s of the line. Different to similar warm Neptune GJ 436b, significant absorption depth of ~23 % was detected also in the red wing [23; 76] km/s, as well as a relatively short transit duration of ~2 hours without any distinct early ingress and extended egress phases.

Thus, GJ 3470b appears to be the second hot exoplanet with a large hydrogen envelope extending far beyond the Roche lobe. Moreover, besides of the hydrogen related Lyα, also the absorption in line 10830 Å of metastable helium has been detected for this planet. Ninan et al. (2019) reported about 1% absorption averaged over the line width of 1.2 Å taking place mostly at the blue wing [-36; 9] km/s of the line. The simulation, based on 1D profiles of helium atoms and ions performed in Salz et al. (2016) assuming standard abundance He/H=0.1, yielded the column density of He(23S) atoms one order of magnitude larger than that inferred from the observations. Very recently new three transits at the 10830 Å line have been reported by Palle et al. (2020). The spectro-photometric light curve has been obtained, which shows that absorption by He(23S) atoms coincides with the expected ingress and egress times. The spectrally resolved absorption at transit shows the depth of 1.5% around the line center restricted by the interval [-30; 20] km/s, while the half width interval is [-22; 10] km/s.

In the present paper we use a 3D global hydrodynamic multifluid code which allows fully self-consistent calculation of the formation of the escaping planetary wind (PW) of hot exoplanets and its interaction with the stellar wind (SW). Previously we employed this code to interpret the Lyα absorption at GJ 436b Khodachenko et al. (2019) and the absorption in HI, OI, CII, SiIII resonant lines at hot Jupiter HD209458b Shaikhislamov et al. (2020). For the GJ 3470b, we calculate the absorption in both, Lyα and He 10830 Å lines. A number of simulation runs with different modelling parameter sets has been performed, assuming slow and fast SW conditions and using the estimated XUV and Lya fluxes of the star.

The obtained results show that, similar to findings in Khodachenko et al. (2019) regarding GJ436b, the Lyα transit for GJ3470b is produced by ENAs formed in course of the interaction between the escaping PW and surrounding SW. As in the case of our previous studies of HD20458b and GJ436b, the role of the radiation pressure has been found to be insignificant. The simulation runs with different modelling parameter sets revealed that the observed fast decay of the Lyα absorption in the egress part of the transit light-curve can be the result of sufficiently high ram pressure of fast SW, which rapidly blows away from the orbital line the trailing tail of escaping planetary atmospheric material. The applied model is able to reproduce, within the measurements error margins, the 10% Lyα absorption at the red-shifted velocities of about 80 km/s, as well as 20% absorption, averaged over the whole red wing of the line. The red-shifted Lyα absorption is produced in the shocked region by ENAs, which have sufficiently high velocity dispersion to provide absorption in the blue and red parts of the line. The best fit parameters of the SW correspond in the temperature and velocity to the fast Solar wind and imply for the parent star of GJ3470b the total mass loss rate of 0.1 of the Solar value, which is compatible with the smaller than the Sun size of the star.

Similarly to 1D modeling of Ninan et al. (2019) and Palle et al. (2020), we found that He(23S) atoms produced by GJ3470b outflow extend to the distances of at least 10 planet radii. To fit the He(23S) absorption at the same parameters, as those derived to fit the Lyα absorption, the helium abundance in the upper atmosphere of GJ3470b should be He/H≈0.015, i.e. about an order of magnitude lower than the Solar value. At the same time, a good agreement of the simulated absorption profile with the measurements was found.

The comparative study of various pumping and depopulation processes of He(23S) state has shown that the interpretation of the measured absorption in 10830 Å line can be quite intricate, because in different regions of the escaping planetary material, as well as in the shocked region, different processes are responsible for the production of absorbing agent. Altogether, the performed 3D self-consistent multi-fluid simulations of the expanding and escaping upper atmosphere of GJ3470b and the related spectral absorption features and transit light-curves have shown that the available observational data can be relatively well interpreted within the range of reasonable values of physically justifiable parameters related with the planetary atmospheric composition, stellar XUV flux and SW plasma flow.




This work was supported by grant № 18-12-00080 of the Russian Science Foundation. Parallel computing simulations, key for this study, have been performed at Computation Center of Novosibirsk State University and SB RAS Siberian Supercomputer Center.



Bourrier V. et al. (2018). A&A, 620, A147

Khodachenko M. L. et al. (2019). ApJ, 885(1), 67

Ninan J. P. et al. (2019). preprint arXiv:1910.02070

Palle E. et al. (2020). A&A, 638, A61

Salz M. et al. (2016). A&A, 586, A75

Shaikhislamov I. F. et al (2020). MNRAS, 491(3), 3435

How to cite: Shaikhislamov, I. F. and Khodachenko, M. L.: Global 3D hydrodynamic modeling of GJ3470b and transit absorption in Lyα and He 10830 A lines, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-147,, 2020.

Doriann Blain, Benjamin Charnay, and Bruno Bézard

The atmospheric composition of exoplanets with masses between 2 and 10 M⊕ is poorly known. In that regard, the sub-Neptune K2-18b offers a valuable opportunity for the characterisation of such atmospheres under Earth-like stellar irradiation. Previous analyses of its transmission spectrum from the Kepler, Hubble and Spitzer space telescopes data using both retrieval algorithms and forward-modelling suggest the presence H2O, as well as a low amount of CH4 in a H2–He atmosphere.

We present here simulations of the atmosphere of K2-18 b using Exo-REM, our self-consistent 1D atmospheric model — recently adapted for transiting, high-metallicity giant exoplanets — to study the atmosphere of K2-18b. We compared the transmission spectra computed by our model with the above-mentionned data (0.4 to 5 μm) to infer the planet atmospheric composition assuming a H2–He dominated atmosphere. We investigated the effect of irradiation, eddy diffusion coefficient, internal source, clouds, C/O ratio and metallicity on the atmospheric structure and transit spectrum. 
We will put an emphasis of the relative contributions of the various absorbers to the transmission spectrum. We will show that our simulations favor atmospheric metallicities from 100 to 200 times solar. We will also discuss the possibility of a CH4-depleted atmosphere and of liquid H2O cloud formation.

How to cite: Blain, D., Charnay, B., and Bézard, B.: 1D atmospheric modelling of K2-18b, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-245,, 2020.

Markus Scheucher, Fabian Wunderlich, John Lee Grenfell, and Heike Rauer

The atmospheres of small, potentially rocky exoplanets are expected to cover a diverse range in composition and mass. Studying such objects therefore requires flexible and wide-ranging modeling capabilities. We present here our newly developed, flexible radiative transfer module, REDFOX, validated for the Solar system planets Earth, Venus and Mars, as well as steam atmospheres. REDFOX is a k-distribution model using the correlated-k approach with random overlap method for the calculation of opacities used in the δ-two-stream approximation for radiative transfer. Opacity contributions from Rayleigh scattering, UV / visible cross sections and continua can be added selectively.

With the improved capabilities of our new model, we calculate various atmospheric scenarios for K2-18b, a super-Earth / sub-Neptune with ∼8 M⊕ orbiting in the temperate zone around an M-star, with recently observed H2O spectral features in the infrared. We model Earth-like, Venus-like, as well as H2-He primary atmospheres of different Solar metallicity and show resulting climates and spectral characteristics, compared to observed data. Our results suggest that K2-18b has an H2-He atmosphere with limited amounts of H2O and CH4. Results do not support the possibility of K2-18b having a water reservoir directly exposed to the atmosphere, which would reduce atmospheric scale heights, hence too the amplitudes of spectral features inconsistent with the observations. We also performed tests for H2-He atmospheres up to 50 times Solar metallicity, all compatible with the observations.

How to cite: Scheucher, M., Wunderlich, F., Grenfell, J. L., and Rauer, H.: Consistently Simulating a Wide Range of Atmospheric Scenarios for K2-18b with a Flexible Radiative Transfer Module, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-634,, 2020.

Jasmine MacKenzie, Philipp Baumeister, Mareike Godolt, John Lee Grenfell, and Nicola Tosi

Ever since the discovery of sub-Neptunes, exoplanets with masses < 20 M⊕ and radii < 4 R⊕, they have presented a distinct challenge in the exoplanet modelling community. When plotted on a mass-radius diagram, their bulk densities lie in a range spanning from that of pure iron to less than water. Such bulk densities are not necessarily indicative of the interior structure within, and when characterized using interior models the results are often varied in their morphology and highly degenerate. 


A semi-grey pressure-temperature profile approximation for an atmosphere is a popular choice in Interior-Atmosphere modelling as could allow us to estimate the radius contribution of an atmosphere as well as a full radiative transfer line-by-line model, but without the computational cost of a full 1-D radiative convective climate-chemistry model. Since the parameter space is large, thousands of interior-atmosphere model runs are required in order to quantify the potential degeneracies. Nevertheless, while the semi-grey approximation treats the problem in a more simplified manner than other more robust methods, which allows for faster analytical calculations, there are still underdetermined factors which make choosing the most appropriate value difficult without more data (e.g. atmospheric spectra and profiles). 


In this talk I will explore the impact of the different ways one chooses the value of one factor, the mean-opacity (𝜅). As this is a function of the stellar and planetary radiation wavelengths, it has an effect on not only the atmospheric and planetary profiles, but also the range of characterization solutions and their degeneracies therein. To highlight these differences, I will be focussing on two real-world test cases: GJ 1214 b and K2-18 b, at two different atmospheric compositions (1x and 50x solar metallicity). By comparing the atmosphere profiles and the range of solutions from interior modelling, both within the parameter range and to values in literature, we will quantify the impact on planetary characterization and develop a more systematic method for future models.

How to cite: MacKenzie, J., Baumeister, P., Godolt, M., Grenfell, J. L., and Tosi, N.: Investigating the Influence of Mean-Opacity (𝜅) Values on Interior-Atmosphere Modelling, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1078,, 2020.

Rocky Planets
Fabian Wunderlich, Markus Scheucher, Mareike Godolt, John Lee Grenfell, Franz Schreier, P. Christian Schneider, David J. Wilson, Alejandro Sánchez López, Manuel López Puertas, and Heike Rauer

The TRAPPIST-1 system is one of the most prominent targets for characterizing the atmospheres of terrestrial planets in the near future. We model potential atmospheres of planet e, which lies well in the habitable zone of the star and could hold liquid water. However, during the extended pre-main sequence phase of TRAPPIST-1, the planets may have experienced extreme water loss, leading to a desiccated mantle. 
We simulate dry and wet atmospheres of TRAPPIST-1 e using a newly developed photochemical model for planetary atmospheres, coupled to a radiative-convective model then calculate theoretical spectra to determine how distinguishable these scenarios could be. 
The resulting atmospheric composition is used to compute cloud-free transmission spectra. From this we calculate the detectability of molecular features using the Extremely Large Telescope (ELT) and the James Webb Space Telescope (JWST).


1. Introduction

The nearby terrestrial planet TRAPPIST-1 e, orbiting the cool host star TRAPPIST-1, offers the opportunity for studying its atmosphere with next generation telescopes. 
The stellar luminosity evolution of such cools stars is quite different to that of e.g. the Sun. 
In particular the active pre-main sequence phase of the star can be extended and the stellar Ultra Violet (UV) radiation is high for about a billion years [1]. 
This could lead to a runaway greenhouse state on an ocean-bearing terrestrial planet and a loss of substantial amounts of planetary water vapour before the star enters the main sequence phase [2]. This study aims to determine whether it is feasible to distinguish between wet and dry surface conditions of TRAPPIST-1 e from atmospheric observations using low resolution spectroscopy with the JWST and high resolution cross-correlation spectroscopy with the ELT.


2. Methods

We use the 1D climate-photochemistry model 1D-TERRA [3, 4] in order to simulate the climate and photochemical response from wet and dry surface conditions. The TRAPPIST-1 input spectrum is taken from [5].
For wet conditions we assume a relative humidity of 80% and calculate dry as well as wet deposition for all species considered in the model. We consider in total three scenarios. The first two scenarios assume a liquid ocean at the surface. Scenario 1 is a dead case with only volcanic fluxes. Scenario 2 is an alive case with volcanic and Earth-like biogenic fluxes. Scenarios 3 is without a surface ocean using a relative humidity of 1%, no wet deposition and weaker dry deposition for CO and O2 compared to the wet scenarios 1 and 2. For all scenarios we then simulate N2 atmospheres with different amounts of CO2 ranging from 0.001 bar to 1 bar.

The simulated atmospheric composition and temperature profiles are used to predict potential transmission spectra of TRAPPIST-1~e. These spectra are then used to estimate the number of transits required to detect molecular features with JWST NIRSpec and ELT HIRES.


3. Results

For dry CO2-rich atmospheres a significant amount of O2 and O3 is produced abiotically [6, 7], due to the
low FUV/NUV ratio of TRAPPIST-1 [8]. However, the abundances of abiotic O2 and O3 are one order of magnitude lower than in those
runs with biogenic emissions. A detection of O2 or O3 will be challenging with JWST NIRSpec or ELT HIRES (see Fig. 1).

Figure 1: Number of transits required to reach a S/N of 5 for CO2 at 4.3 µm, O3 at 9.6 µm, CO at 2.35 µm and H2O at 1.4 µm with JWST NIRSpec (upper and middle panel) and CH4 from 2.1 to 2.5 µm and O2 from 1.24 to 1.3 µm with ELT HIRES (lower panel) in the atmosphere of TRAPPIST-1 e. Full filled bars: required number of transits is below or equal 30. Semi transparent bars: required number of transits is larger than 30. Figure from [4].


CO can be an indirect marker of an ocean, having concentrations enhanced by ~100 times on an ocean-less world with a CO2-rich atmosphere (see also [9, 10, 11]).
The detection of CO in the K-band might be feasible with JWST NIRSpec and ELT HIRES for dry surface conditions and CO2 partial pressure above 0.01 bar by co-adding several tens of transits.  

Significant amounts of CH4 are only present in the simulated atmospheres with Earth-like biogenic flux. It has been shown that for planets around cool host stars, weaker destruction of CH4 leads to stronger spectral features of CH4 compared to the Earth around the Sun [12]. 
About 30 transit observation in the K-band are needed to detect CH4 with ELT HIRES for the wet & alive case. 

In conclusion, the three scenarios considered for TRAPPIST-1 e might be distinguishable by combining ~30 transit observations with JWST NIRSpec and ELT HIRES in the K-band. The alive scenario, assuming Earth-like biogenic emissions, could be identified by the detection of CH4. The non-detection of CO would suggest the existence of a surface ocean. In turn, the detection of CO would suggest dry surface conditions (see more details in [4]).



[1] Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42.

[2] Luger, R., & Barnes, R. 2015, AsBio, 15, 119.

[3] Scheucher, M., Wunderlich, F., Grenfell, J. L., et al. accepted, ApJ.

[4] Wunderlich, F., Scheucher, M., Godolt, M., et al. accepted, ApJ.

[5] Wilson, D. J., Froning, C. S., Duvvuri, G. M., et al. submitted, ApJ.

[6] Selsis, F., Despois, D., & Parisot, J.-P. 2002, A&A, 388, 985.

[7] Harman, C. E., Schwieterman, E. W., Schottelkotte, J. C., & Kasting, J. F. 2015, ApJ, 812, 137.

[8] Tian, F., France, K., Linsky, J. L., Mauas, P. J., & Vieytes, M. C. 2014, EPSL, 385, 22.

[9] Gao, P., Hu, R., Robinson, T. D., Li, C., & Yung, Y. L. 2015, ApJ, 806, 249.

[10] Schwieterman, E. W., Reinhard, C. T., Olson, S. L., et al. 2019, ApJ, 874, 9.

[11] Hu, R., Peterson, L., & Wolf, E. T. 2020, ApJ, 888, 122.

[12] Wunderlich, F., Godolt, M., Grenfell, J. L., et al. 2019, A&A, 624, A49.

How to cite: Wunderlich, F., Scheucher, M., Godolt, M., Grenfell, J. L., Schreier, F., Schneider, P. C., Wilson, D. J., Sánchez López, A., López Puertas, M., and Rauer, H.: Characterization of the atmosphere of TRAPPIST-1 e with JWST and ELT, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-692,, 2020.

Tue Giang Nguyen, Nicolas Cowan, Agnibha Banerjee, and John Moores


Lava planets orbit close enough to their star that parts of their surface are molten. Temperatures on the dayside are often hot enough to vaporise rocks, which create a thin mineral vapour atmosphere. Lava planets are currently one of the best targets to observe rocky worlds outside the solar system.

We simulate the steady-state vapour-pressure driven flow of the recently discovered exoplanet K2-141b via a 1D hydrodynamical model. This model produces the atmospheric pressure, temperature, and wind velocity as well as evaporation and condensation rates. We then infer the magma ocean circulation required for mass balance and simulate how our results would affect photometric and spectroscopic observation.


The hydrodynamical model that we used was first developed by Ingersoll et al. (1985) to model the thin atmosphere of Io. The model was subsequently adapted by Castan and Menou (2011) to model lava planets such as Kepler 10-b and 55 Cnc-e. Although greatly idealized, these calculations are robust to the supersonic winds and atmospheric collapse that result from the extreme day-to-night temperature contrast.

Before introducing the system of equations that makes up the 1D model, it is important to list the assumptions and limitations of our idealized case. First, we assume a hydrostatically bound atmosphere that is thin enough to not absorb any radiation. Second, we assume a turbulent and well-mixed atmosphere, which leads to a vertically constant wind profile. Third, we assume only a single constituent which allows us to ignore chemical processes that greatly complicates our problem. Another idealization is the neglect of the planet’s rotation, which allows for symmetry about the subsolar/antisolar axis making the problem 1D.

The system of equations below describes the conservation of mass (1), momentum (2), and energy (3) which are solved for state variable pressure, P, temperature, T, and wind velocity, V; P and T are evaluated at the top of the turbulent boundary layer. The angular distance from the subsolar point, θ is the only independent variable.

In equation (1)-(3), the important flux variables are E, the surface mass flux, τ , the surface drag, and Q, the surface energy flux. Detailed derivation along with calculations of the surface fluxes can be found in Ingersoll et al. (1985).


We simulate the atmosphere of K2-141b for atmospheric constituent SiO2 (due to abundance) or Na (due to volatility). The solution strongly depends on the saturated vapour pressure relation with temperature which is provided by Schaefer and Fegley (2009). Figures (1) and (2) below show the state variables solution for SiO2 and Na atmospheres, respectively.

Figure 1: solution to SiO2 atmosphere. Top panel: atmospheric boundary-layer pressure (left) and scale height (right). Middle panel: wind velocity (left) and Mach number (right). Bottom panel: atmospheric and surface temperature.

Figure 2: solution to Na atmosphere. The format is exactly the same as Fig. (1).

Since Na is much more volatile than SiO2, the Na atmosphere is much thicker, as expected. The Na atmosphere also extends further than SiO2 atmosphere. However, the SiO2 atmosphere retains heat better which makes it much warmer than its Na counterpart.

If we presume a pure SiO2 atmosphere, then we can infer the magma ocean circulation that balances out the mass transport by the atmosphere. The inferred ocean circulation depends on the ocean depth and the horizontal mass transport. The magma ocean depth can be approximated by first assuming a vertically constant temperature profile for the surface and determine the pressure at which liquid SiO2 change phase. The horizontal mass flux transported by the atmosphere can be approximated by integrating the precipitation rate. The figure below shows the magma ocean properties for the SiO2 case.

Figure 3. Left: velocity of magma ocean return flow. Negative values denote mass flow towards the subsolar point. Right: ocean depth.

We do the same analysis for the Na case where the ocean is set to have the same Na to SiO2 ratio as the Bulk Silicate Earth composition. This yields an ocean velocity that is 104 times the speed of the SiO2 case. This suggests that maintaining mass balance for SiO2 is much easier than for Na.

We do the same analysis for the Na case where the ocean is set to have the same Na to SiO2 ratio as the Bulk Silicate Earth composition. This yields an ocean velocity that is 104 times the speed of the SiO2 case. This suggests that the slow return flow may prohibit a steady-state Na atmosphere.

To simulate observations of K2-141b’s atmosphere, we calculate the radiative flux emitted at a given wavelength corresponding to spectral features of SiO2 and Na. We then integrate the flux of the visible hemisphere of K2-141b to obtain its orbital phase curve.

Figure 4. Top panel: predicted phase curve of K2-141b for a Na atmosphere (black lines) or for a SiO2 atmosphere (purple lines). The chosen wavelengths are near spectral features of SiO2 at 3.4 m and of Na at 589 nm. Bottom: Disk-integrated planetary brightness temperature for the two scenarios.


Idealized 1D models provide important insights for future observations of K2-141b and likewise of many other lava planets. Our results show that the atmosphere will fully condense before reaching the nightside for both cases. We also show that a steady-state Na atmosphere is difficult to achieve given the slow return flow through a SiO2 ocean. Finally, the thinner and hotter SiO2 atmosphere may be easier to observe due to its greater terminator at the limb of the planet as seen during transit.


We would like to thank R. Pierrehumbert for his guidance. This work was made possible by the Natural Science and Engineering Research Council (NSERC) of Canada’s Collaborative Research and Training Experience (CREATE) Program for Technology for Exo-planetary Sciences (TEPS).


Castan and Menou, 2011, APJ, 743, L36

Ingersoll, Summers, and Schlipf, 1985, Icarus, 64, 375

Schaefer and Fegley, 2009, APJ, 703, L113

How to cite: Nguyen, T. G., Cowan, N., Banerjee, A., and Moores, J.: Modelling the atmosphere of lava planet K2-141b: implications for photometry and spectroscopy, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-500,, 2020.

Ilai Guendelman and Yohai Kaspi

The insolation a planet receives from its parent star is the main engine of the climate and depends on the planet's orbital configuration. Planets with non-zero obliquity and eccentricity experience seasonal insolation variations. As a result, the climate exhibits a seasonal cycle, with its strength depending on the orbital configuration and atmospheric characteristics. In this study, using an idealized general circulation model, we examine the climate response to changes in eccentricity for both zero and non-zero obliquity planets. In the zero obliquity case, a comparison between the seasonal response to changes in eccentricity and perpetual changes in the solar constant shows that the seasonal response strongly depends on the orbital period and radiative timescale. More specifically, using a simple energy balance model, we show the importance of the latitudinal structure of the radiative timescale in the climate response. We also show that the response strongly depends on the atmospheric moisture content. The combination of an eccentric orbit with non-zero obliquity is complex, as the insolation also depends on the perihelion position. Although the detailed response of the climate to variations in eccentricity, obliquity, and perihelion is involved, the circulation is constrained mainly by the thermal Rossby number and the maximum temperature latitude. Finally, we discuss the importance of different planetary parameters that affect the climate response to orbital configuration variations.

How to cite: Guendelman, I. and Kaspi, Y.: Atmospheric dynamics on terrestrial planets with eccentric orbits, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-191,, 2020.

Athanasia Nikolaou, Lorenzo Mugnai, Oliver Herbort, Enzo Pascale, and Peter Woitke

   Early during their formation the planets capture an amount of atmosphere from the protoplanetary disk (Ikoma et al. 2018, Odert et al. 2018, Lammer et al. 2020, Kimura and Ikoma 2020). An additional proportion of their atmosphere is provided during the magma ocean stage by interior degassing. The latter mechanism is assumed to be the main provider of the final atmospheric mass. Its composition is compromised by the source silicate mineral and its chemical characterization (Gaillard and Scaillet 2014, Herbort et al. 2020).
   Numerous studies support the degassing of the oxidized gas species H2O and CO2 as main contributions from the magma ocean phase (Abe and Matsui 1988, Abe 1993, Elkins-Tanton 2008, Schaefer et al. 2012, Lebrun et al. 2013, Lupu et al. 2014, Gaillard and Scaillet 2014, Salvador et al. 2017, Nikolaou et al. 2019). Previous work has also shown that H2O, in particular, plays a crucial role (Hamano et al. 2013, Katyal et al. 2019, Turbet et al. 2019) in thermal blanketing. H2O possibly leads to “long-term” (Hamano et al 2013) or “conditionally continuous” (Nikolaou et al. 2019) magma oceans that effectively cease to cool. Water also ties directly to the availability of hydrogen that drives hydrodynamic escape (Airapetian et al. 2017, Lammer et al. 2018). CO2 factors into both above processes, as well (Wordsworth and Pierrehumbert 2013, Odert et al. 2018). Constraining the H2O and CO2 abundances early after formation is indispensible to the planet’s thermal evolution and extensive modeling effort has been devoted to it. Their constraint would in particular help revisit which magma ocean types among transient-conditionally continuous-permanent (Nikolaou et al. 2019) are detectable in future exoplanetary missions (ARIEL, Tinetti et al. 2018; PLATO, Rauer et al. 2014).

   In this work we focus on the combination of degassed and disk-captured atmosphere under the assumption of chemical equilibrium. Using simulations from the 1D Convective Ocean of Magma Radiative Atmosphere and Degassing model (Nikolaou et al. 2019) we obtain the thermal evolution and degassing tracks of a rocky planet. In order to evaluate the chemical abundances under equilibrium conditions we employ the thermodynamical model GGchem (Woitke et al. 2018).
   We explore the atmospheric conditions during the lifetime of a magma ocean under varying mineral compositions and protoplanetary disk contributions. We discuss the results in the context of the likely magma ocean types.
A.N. and P.W. wish to thank the Erwin Schrödinger International Institute for Mathematics and Physics (ESI) of the University of Vienna, Thematic Programme on “Astrophysical Origins: Pathways from Star Formation to Habitable Planets” 2019, which enabled this collaboration.

How to cite: Nikolaou, A., Mugnai, L., Herbort, O., Pascale, E., and Woitke, P.: Characteristics of an hybrid atmosphere with disk-captured and degassing contributions over a rocky planet’s magma ocean. A modeling approach., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-937,, 2020.

Nisha Katyal, Gianluigi Ortenzi, John Lee Grenfell, Lena Noack, Frank Sohl, Mareike Godolt, Antonio García Muñoz, Franz Schreier, and Heike Rauer

The magma ocean is a critical phase determining how Earth's atmosphere developed into habitability. However there are major uncertainties in the role of key processes such as outgassing from the planetary interior and escape to space which determine subsequent atmospheric evolution.  We investigate the impact of outgassing of species and escape of H2 for different mantle redox states upon the composition and evolution of the atmosphere for the magma ocean period. We include an important new atmosphere-interior coupling namely the redox evolution of the mantle which strongly affects the outgassing of species. We simulate volatile outgassing and chemical speciation at the surface for various redox states of the mantle by employing a C-H-O based chemical speciation model combined with an interior outgassing model.
We then apply a Line-By-Line radiative transfer model (GARLIC) to study the remote appearance of the planet in terms of the thermal infrared emission and transmission. Finally, we use a diffusion-limited and energy-driven  escape model for calculating the loss of H2 from the atmosphere. We obtain that the outgoing longwave radiation and effective height of the atmosphere are potentially influenced by the redox state of the mantle and the volatile outgassing from the magma ocean. An atmosphere above a reduced mantle consisting of light H2 emits larger outgoing radiation to space and has a larger effective height compared with heavier, oxidized atmospheres consisting of H2O and CO2 lying above an oxidized mantle. We simulate responses in the nature and composition of the atmosphere over the magma ocean period. Results also suggest that outgassing rates of H2 can be a factor of x10 larger than those of diffusive H2 escape rate during this period. We evaluate the mass-loss timescale of H2 via escape of the primary outgassed H2 atmosphere to be within few tens of Myr. Our work presents useful input to guide future studies such as those discussing exoplanetary interior composition and its possible links with atmospheric composition that might be estimated from observed infrared spectra (via retrieval) by future planned missions such as ELT, ARIEL and JWST etc.

How to cite: Katyal, N., Ortenzi, G., Grenfell, J. L., Noack, L., Sohl, F., Godolt, M., García Muñoz, A., Schreier, F., and Rauer, H.: Effect of mantle oxidation state and escape upon the evolution of Earth's magma ocean atmosphere, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-729,, 2020.

Kristina Kislyakova and Lena Noack

We investigate possible driving mechanisms of volcanic activity on large rocky super-Earths with masses exceeding four Earth masses. Due to high pressures in the mantles of these planets, melting in deep mantle layers can be suppressed, even if the energy release due to tidal heating and radioactive decay is substantial in these areas of the mantles. We investigate if a newly identified heating mechanism, namely induction heating by the star’s magnetic field, can drive volcanic activity on these planets due to its unusual heating pattern close to the planet’s surface, which leads to heat production in the very upper part of the mantle. In this region the pressure is not yet high enough to preclude the melt formation. We use a model for induction heating we developed and apply it to the super-Earth HD 3167b, which has a mass of approximately seven Earth masses. We calculate induction heating in the planet’s interiors assuming an electrical conductivity profile of a hot rocky planet and a moderate stellar magnetic field typical of an old inactive star, which one can expect for HD 3167. Then, we use a mantle convection code (CHIC) to simulate the evolution of volcanic outgassing with time.

Fig. 1. Total outgassing of CO2 , CO, H2O, and H2 from HD 3167b assuming the magnetic field of the star of 0, 1, and 5 G. Induction heating leads to a much earlier onset of volcanism on the planet and increases the outgassing by several tens of bar. The mantle viscosity is 10 times the mantle viscosity of the Earth.

According to our results, in most cases volcanic outgassing on HD 3167b is not very significant in the absence of induction heating, however, including this heating mechanism changes the picture and leads to a substantial increase in the outgassing from the planet’s mantle. Evolution of volcanic outgassing is illustrated in Fig. 1. Induction heating also leads to a much earlier onset of volcanic activity on this planet. This result shows that induction heating combined with a high surface temperature is capable of driving volcanism on massive super-Earths, which has very important observational implications.

How to cite: Kislyakova, K. and Noack, L.: Interior heating by stellar magnetic fields as a driver of volcanic activity on massive rocky planets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-852,, 2020.

Kaustubh Hakim, Dan J. Bower, Meng Tian, Russell Deitrick, Pierre Auclair-Desrotour, Daniel Kitzmann, Caroline Dorn, Klaus Mezger, and Kevin Heng

In the decade of JWST, ELT, TMT, PLATO, ARIEL and other specialized telescopes, observations of carbon dioxide in terrestrial exoplanet atmospheres are possible. The amount of carbon dioxide in the atmosphere of a tectonically active planet such as Earth is regulated by the carbonate-silicate cycle (long-term carbon cycle). Silicate weathering provides essential negative feedback to maintain temperate climates on Earth over billions of years. In this study, we model the chemistry of rock-water interaction for different silicate rocks and minerals applicable to both continental and seafloor weathering. We find that weathering rates depend mainly on the partial pressure of carbon dioxide, surface temperature and lithology, and other factors are secondary. This approach allows possessing a theoretical method to determine both continental and seafloor weathering rates on temperate exoplanets that depend little on present-day Earth calibrations. Our study gives a strong control over the connection between atmospheric observables and the carbon cycle. The ultimate goal is to provide an abiotic library of geological false positives of biosignatures.

How to cite: Hakim, K., Bower, D. J., Tian, M., Deitrick, R., Auclair-Desrotour, P., Kitzmann, D., Dorn, C., Mezger, K., and Heng, K.: The Role of Lithology in Silicate Weathering and CO2 Regulation on Rocky Exoplanets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-58,, 2020.

Effect of Environment
Colin Johnstone

The magnetic activity of stars is a crucially important factor influencing planet formation processes and the subsequent evolution of planetary atmospheres. Understanding how stellar activity evolves for stars with different masses is crucially important for understanding the effects of stellar winds and radiation at X-ray and ultraviolet wavelengths on the erosion of circumstellar disks and planetary atmospheres. I will present a new and comprehensive description of the rotational evolution of stars and the resulting evolution of X-ray and ultraviolet emission for F, G, K, and M dwarfs. I will demonstrate the importance of the star's initial rotation rate on the subsequent activity evolution and clarify common misunderstandings regarding the dependence on stellar mass, including the common belief that M dwarfs are more XUV active than G dwarfs. I will show why these results are important for the evolution of planetary atmospheres.

How to cite: Johnstone, C.: Activity evolution for F, G, K, and M dwarfs and the importance for planetary atmospheres, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-830,, 2020.

Donna Rodgers-Lee, Aline Vidotto, Andrew Taylor, Paul Rimmer, and Turlough Downes

Cosmic rays may have contributed to the start of life on Earth. Cosmic rays also influence and contribute to atmospheric electrical circuits, cloud cover and biological mutation rates which are important for the characterisation of exoplanetary systems. The flux of Galactic cosmic rays present at the time when life is thought to have begun on the young Earth or in other young exoplanetary systems is largely determined by the properties of the stellar wind. 

The spectrum of Galactic cosmic rays that we observe at Earth is modulated, or suppressed, by the magnetised solar wind and thus differs from the local interstellar spectrum observed by Voyager 1 and 2 outside of the solar system. Upon reaching 1au, Galactic cosmic rays subsequently interact with the Earth’s magnetosphere and some of their energy is deposited in the upper atmosphere. The properties of the solar wind, such as the magnetic field strength and velocity profile, evolve with time. Generally, young solar-type stars are very magnetically active and are therefore thought to drive stronger stellar winds. 

Here I will present our recent results which simulate the propagation of Galactic cosmic rays through the heliosphere to the location of Earth as a function of the Sun's life, from 600 Myr to 6 Gyr, in the Sun’s future. I will specifically focus on the flux of Galactic cosmic rays present at the time when life is thought to have started on Earth (~1 Gyr). I will show that the intensity of Galactic cosmic rays which reached the young Earth, by interacting with the solar wind, would have been greatly reduced in comparison to the present day intensity. I will also discuss the effect that the Sun being a slow/fast rotator would have had on the flux of cosmic rays reaching Earth at early times in the solar system's life.

Despite the importance of Galactic cosmic rays, their chemical signature in the atmospheres’ of young Earth-like exoplanets may not be observable with instruments in the near future. On the other hand, it may instead be possible to detect their chemical signature by observing young warm Jupiters. Thus, I will also discuss the HR 2562b exoplanetary system as a candidate for observing the chemical signature of Galactic cosmic rays in a young exoplanetary atmosphere with upcoming missions such as JWST.

How to cite: Rodgers-Lee, D., Vidotto, A., Taylor, A., Rimmer, P., and Downes, T.: The Galactic cosmic ray intensity at the evolving Earth and young exoplanets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-818,, 2020.