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, from ultra-hot Jupiters to temperate super-Earths. The next generation of space and ground based facilities, including current high-resolution instruments (e.g. ESPRESSO, Spirou, CHEOPS, IGRINS, 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.
This session will also address results on all aspects of plasma physics and interactions of solar and stellar wind interactions with planets and exoplanets.
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Oral and Poster presentations and abstracts
Water-rich planets should be ubiquitous in the universe. Among the current exoplanet populations, many of those worlds are subject to important irradiation from their host star. As a consequence, water-rich worlds display supercritical water layer surrounded by an extended steam atmosphere making them good candidates for matching the observed mass-radius distribution of sub-Neptunes . Here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (EoS) for water, and an atmospheric model that takes into account radiative transfer. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- or Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. We also provide mass-radius relationships for water-rich planets and their analytical expression. This allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. The possible existence of such planets is discussed in light of atmospheric loss processes, suggesting that some sub-Neptunes are the outcome of planets that lost their H/He reservoirs.
Figure 1. Mass-radius relationships produced by our model (green, yellow and red thick lines) , compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines) [3,4]. A few planets of the solar system, the GJ-9827 system and the TOI-178 system are shown as well [5,6].
 Mousis, O., Deleuil, M., Aguichine, A., et al. 2020, ApJL, 896, L22.
 Aguichine, A., Mousis, O., Deleuil, M., et al. 2021, accepted in ApJ.
 Zeng, L., Sasselov, D. D., & Jacobsen, S. B. 2016, ApJ, 819, 127.
 Brugger, B., Mousis, O., Deleuil, M., et al. 2017, ApJ, 850, 93.
 Kosiarek, M. R., Berardo, D. A., Crossfield, I. J. M., et al. 2021, AJ, 161, 47.
 Leleu, A., Alibert, Y., Hara, N. C., et al. 2021, A&A, 649, A26.
How to cite: Aguichine, A., Mousis, O., Deleuil, M., and Marcq, E.: Modeling the structure of irradiated ocean planets - implications for mass-radius relationships, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-27, https://doi.org/10.5194/epsc2021-27, 2021.
The increasing number of well characterised low-mass planets, combined with the valuable informations from stellar and planetary spectroscopy, opens the way to the modeling of planetary structures and compositions, which can be obtained with theoretical and numerical works. This approach gives a valuable insight to understand the formation of planetary systems in the low-mass range. We present a 1D planetary model where the interior is coupled with the atmosphere in radiative-convective equilibirum within a Bayesian retrieval scheme. In addition to a Fe core and a silicate mantle, we take into account water in all its possible phases, including steam and supercritical phases, which is necessary for systems with a wide range of stellar irradiations.
Our interior-atmosphere model calculates the compositional and atmospheric parameters, such as Fe and water content, surface pressures, scale heights and albedos. We analyse the multiplanetary systems K2-138 and TRAPPIST-1, which present six low-mass planets with different densities and irradiations. From the individual composition of their planets, we derive a similar trend for both systems: a global increase on the water content with increasing distance from the star in the inner region of the systems, while the planets in the outer region present a constant water mass fraction. This trend reveals the possible effects of migration, formation location and atmospheric mass loss during their formation history.
How to cite: Acuña, L., Deleuil, M., Mousis, O., López, T. A., Morel, T., Santerne, A., and Marcq, E.: Characterising the interior structures and atmospheres of multiplanetary systems., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-44, https://doi.org/10.5194/epsc2021-44, 2021.
Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub- Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of atmosphere-stripped exoplanets may thus constrain magma ocean dynamics.
How to cite: Lichtenberg, T.: Redox hysteresis of super-Earth exoplanets from magma ocean circulation , Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-131, https://doi.org/10.5194/epsc2021-131, 2021.
Liquid water is generally assumed to be the most important factor for the emergence of life, and so a major goal in exoplanet science is the search for planets with water oceans. On terrestrial planets, the silicate mantle is a large source of water, which can be outgassed into the atmosphere via volcanism. Outgassing is subject to a series of feedback processes between atmosphere and interior, which continually shape both atmospheric composition, pressure, and temperature, as well as interior dynamics. For example, water has a high solubility in surface lava, which can strongly limit its outgassing into the atmosphere even at low atmospheric pressures. In contrast, CO2 can be easily outgassed. This drives up the surface pressure and temperature, potentially preventing further water outgassing .
We present the results of an extensive parameter study, where we use a newly developed 1D numerical model to simulate the coupled evolution of the atmosphere and interior of terrestrial exoplanets up to 5 Earth masses around Sun-like stars, with internal structures ranging from Moon- to Mercury-like. The model accounts for the main mechanisms controlling the global-scale, long-term evolution of stagnant-lid rocky planets (i.e. bodies without plate tectonics), and it includes a large number of atmosphere-interior feedback processes, such as a CO2 weathering cycle, volcanic outgassing based on the pressure-dependent solubility of volatiles in surface lava, a water cycle between ocean and atmosphere, greenhouse heating, as well as the influence of a primordial H2 atmosphere, which can be lost through escape processes. While many atmosphere-interior feedback processes have been studied before in detail (e.g. [2, 3]), we present here a comprehensive model combining the important planetary processes across a wide range of terrestrial planets.
We find that a significant majority of high-density exoplanets (i.e. Mercury-like planets with large cores) are able to outgas and sustain water on their surface. In contrast, most planets with intermediate, Earth-like densities either transition into a runaway greenhouse regime due to strong CO2 outgassing, or retain part of their primordial atmosphere, which prevents water from being outgassed. This suggests that high-density planets could be the most promising targets when searching for suitable candidates for hosting liquid water. Furthermore, the degeneracy of the interior structures of high-density planets is limited compared to that of planets with Earth-like density, which further facilitates the characterization of these bodies, and our results predict largely uniform atmospheric compositions across the range of high-density planets, which could be verified by future spectroscopic measurements.
 Tosi, N. et al. The habitability of a stagnant-lid earth. A&A 605, A71 (2017).
 Noack, L., Rivoldini, A. & Van Hoolst, T. Volcanism and outgassing of stagnant-lid planets: Implications for the habitable zone. Physics of the Earth and Planetary Interiors 269, 40–57 (2017).
 Foley, B. J. & Smye, A. J. Carbon Cycling and Habitability of Earth-Sized Stagnant Lid Planets. Astrobiology 18, 873–896 (2018).
How to cite: Baumeister, P., Tosi, N., MacKenzie, J., and Grenfell, J. L.: Abundance of water oceans on high-density exoplanets from coupled interior-atmosphere modeling, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-270, https://doi.org/10.5194/epsc2021-270, 2021.
The vigour and style of mantle convection in tidally-locked super-Earths may be substantially different from Earth's regime where the surface temperature is spatially uniform and sufficiently cold to drive downwellings into the mantle.
The thermal phase curve for super-Earth LHS 3844b suggests a solid surface and lack of a substantial atmosphere. The dayside temperature is around 1040 K and the nightside temperature is around 0 K, which is unlike any temperature contrast observed at present day for planets in the Solar System. On the other hand, the thermal phase curve of super-Earth 55 Cnc e suggests much hotter temperatures with a nightside temperature around 1380 K and a substellar point temperature around 2700 K. The substellar point is also substantially shifted eastwards, which requires efficient energy circulation in the atmosphere.
Here, we use constraints from thermal phase curve observations to model the interior mantle flow. To constrain the surface temperature of 55 Cnc e, we use the results from general circulation models varying the atmospheric composition and optical depth.
Depending on how strong the surface temperature contrast is, this can lead to hemispheric tectonic regimes. Such a regime could influence a planet's atmosphere through interior-exterior coupling mechanisms (e.g. volcanic outgassing).
We run geodynamic simulations of the interior mantle flow using the mantle convection code StagYY. The models are fully compressible with an Arrhenius-type viscosity law where the mantle is modelled with an upper mantle, a perovskite-layer and a post-perovskite layer. The lithospheric strength is modelled through a plastic yielding criteria and the heating mode is either basal heating only or mixed heating (basal and internal heating).
For LHS 3844b we find that the surface temperature dichotomy can lead to a hemispheric tectonic regime depending on the strength of the lithosphere and the heating mode in the mantle. In a hemispheric tectonic regime, downwellings occur preferentially on one side and upwellings rise on the other side (Fig. A). We compare these results to the case of 55 Cnc e, where large parts of the surface could be molten. At first order we expect that a magma ocean could homogenise the temperatures at the interface between the magma ocean and the underlying solid mantle and therefore reduce the likelihood of hemispheric tectonics operating on 55 Cnc e (Fig. B).
For LHS 3844b, the contribution of the interior flux to the thermal phase curve is on the order of 15-30 K, and therefore below the detecting capabilities of current and near-future observations. However, for hemispheric tectonics, upwellings might lead to preferential melt generation and outgassing on one hemisphere that could manifest as a secondary signal in phase curve observations. Such signals could also be produced on hotter planets such as 55 Cnc e where parts of the surface are hot enough to melt.
How to cite: Meier, T. G., Bower, D. J., Lichtenberg, T., Tackley, P. J., and Demory, B.-O.: Exploring the convection in super-Earths: Comparing LHS 3844b with 55 Cnc e, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-500, https://doi.org/10.5194/epsc2021-500, 2021.
Earth has been the only known habitable world and thus used as a reference to understand habitability. The origin of life on Earth is not yet clearly understood, but known traces are up-to the Archean (∼ 3.5Ga, Ga-billion years). Earth had water and continents from the Hadean Earth (> 4.0Ga), which had different atmospheric conditions compared to the Archean Earth. Similarly, the current state and composition of atmosphere does not represent its future state. Climate changes are partly attributed to feedback mechanism between the internal processes and the atmosphere. And as such, each atmospheric state is depictive of an instance a long a trajectory path of a coupled evolution of Earth system. Venus was thought to be habitable until into the 1960s, when its surface was observed to be oven-hot with surface pressure a hundred times that of Earth. Why and when the evolutionary paths of Venus and Earth, which are similarly sized and should have similar internal compositions, started to diverge? Moreover, known exoplanets, planets and moons have very different geophysical characteristic from Earth. This implies exotic life might vary substantially from what we know. As a result, understanding evolution of rocky planets, that is their interior structure, atmospheres and climate regardless of their habitability is of great importance. In this work we study the relation between a rocky planet’s internal properties and its observable surface and atmosphere properties over time. We explore the different convection regimes (stagnant lid, episodic-lid and tectonic), studying the relation between a planet’s viscous state, its interior composition and structure. Focusing on the effects of mantle convection on volatile recycling processes such as CO2 outgassing that influence the atmospheric state and climatic conditions over time. The computed models are then used to compute observables, that ultimately can be tested with observations.
How to cite: Adhiambo, V., Root, B., and Desert, J.-M.: The interior-atmosphere coupling of rocky worlds, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-664, https://doi.org/10.5194/epsc2021-664, 2021.
This work aims to determine the mass-radius rela-tionships of highly irradiated (500< Tirr<2000K)small planets (0.2<M<2.3M⊕) with water con-tents up to 5%. To do so, we coupled an internalmodel of small terrestrial planets (Brugger et al.,2017) to the atmosphere model elaborated by Marcqet al. (2017, 2019), following the approach depictedin Aguichine et al. (2021) and Mousis et al. (2020).
We show that these planets, even with smallwater contents, can become strongly inflated andproduce large radii for small masses.We alsoshow that strongly irradiated small planets cannotsustain their atmospheres due to the lack of hy-drostatic stability, implying they cannot preserveany hydrosphere. The temperature and the watermass fraction are the key parameters controllingthe extent of inflation and the thickness of thesupercritical layer. An important amount of wateralso leads to the contraction of the rocky interior.However, the composition of the rocky interioronly has a limited impact on the final mass-radiusrelationship, and barely impacts the behavior of thehydrosphere.
How to cite: Vivien, H., Aguichine, A., Mousis, O., Deleuil, M., and Marcq, E.: Mass-Radius relationships of small, highly irradiated exoplanets with small water mass fractions, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-249, https://doi.org/10.5194/epsc2021-249, 2021.
Ultra-hot Jupiters (UHJs; Teq ≥ 2500 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. Their continuum, which can be measured with space-facilities, can be mostly attributed to H- opacity, an indicator of metallicity. From the ground, the high spectral resolution emission spectra of UHJs contains thousands of lines of refractory (Fe, Ti, TiO, …) and volatile species (OH, CO, …), whose combined atmospheric abundances could track planet formation history in a unique way. In this talk, we take a deeper look to the optical emission spectrum of KELT-9b covering planetary phases 0.25 - 0.75 (i.e. between secondary eclipse and quadrature), and search for the effect of atmospheric dynamics and three-dimensionality of the planet atmosphere on the resolved line profiles, in the context of a consolidated statistical framework. We discuss the suitability of the traditionally adopted 1D models to interprete phase-resolved observations of ultra-hot Jupiters, and the potential of this kind of observations to probe their 3D atmospheric structure and dynamics. Ultimately, understanding which factors affect the line-shape in UHJs will also lead to more accurate and more precise abundance measurements, opening a new window on exoplanet formation and evolution.
How to cite: Pino, L., Brogi, M., Désert, J.-M., and Rauscher, E.: Searching for 3D effects in the optical, high spectral resolution emission spectrum of KELT-9b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-308, https://doi.org/10.5194/epsc2021-308, 2021.
Ultra-hot Jupiters are defined as giant planets with equilibrium temperatures larger than 2000 K. Most of them are found orbiting bright A-F stars, making them extremely suitable object to study their atmospheres using high-resolution spectroscopy.
TOI-1431b, also known as MASCARA-5b, a newly discovered planet with the temperature of 2375 K is a prefect example of ultra-hot Jupiter. We studied this object using three transit observations obtained with high-resolution spectrographs HARPS-N and EXPRES. Analysis of Rossiter-McLaughlin effect shows that the planet is in the polar orbit, which speaks about an interesting dynamical history, and perhaps indicating the presence of more than one planet in the early history of this system. Applying the cross-correlation and transmission spectroscopy method, we find no evidence of atoms and molecules in this planet. There results are at odds with the other studies of similar UHJs orbiting bright stars, where various species have been found.
How to cite: Stangret, M., Palle, E., Casasayas-Barris, N., and Oshagh, M.: Studies of the atmosphere of ultra-hot Jupiter TOI-1431b/MASCARA-5b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-511, https://doi.org/10.5194/epsc2021-511, 2021.
Ultra-hot Jupiters have dayside temperatures similar to those of M-dwarfs. While molecular absorption from the hydroxyl radical (OH) is easily observed in near-infrared spectra of M-dwarfs, it is often not considered when studying the atmospheres of (ultra-)hot Jupiters. We use high-resolution spectroscopic near-infrared observations of a transit of WASP-76b obtained using CARMENES to assess the presence of OH. After validating the OH line list, we generate model transit spectra of WASP-76b with petitRADTRANS. The data are corrected for telluric contamination and cross-correlated with the model spectra. After combining all cross-correlation functions from the transit, a detection map is constructed. OH is detected in the atmosphere of WASP-76b with a signal-to-noise ratio of 6.1. From a Markov Chain Monte Carlo retrieval we obtain Kp=234 km/s and a blueshift of 13.9 km/s. Considering the fast spin-rotation of the planet, the OH signal is best explained with the signal mainly originating from the evening terminator and the presence of a strong day- to nightside wind. The signal appears to be broad, with a full width at half maximum of 16.2 km/s. The retrieval results in a weak constraint on the temperature of 2420-3150 K at the pressure of the OH signal. Our results demonstrate that OH is readily observable in the transit spectra of ultra-hot Jupiters. Studying this molecule can give new insights in the molecular dissociation processes in the atmospheres of such planets.
How to cite: Landman, R., Sánchez-López, A., Mollière, P., Kesseli, A., Louca, A., and Snellen, I.: Detection of OH at the evening terminator of the ultra-hot Jupiter WASP-76b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-222, https://doi.org/10.5194/epsc2021-222, 2021.
Extreme temperature contrasts between the day and nightside of ultra-hot Jupiters (UHJ) result in significantly asymmetric atmospheres, with a region of extreme atmospheric expansion appearing over a small range of latitudes around the terminator. Over the course of a transit, WASP-76 b rotates by about 30° and hence temporal variations of the observable atmosphere could significantly affect the detectability of its constituents. Specifically, the trailing limb of this planet allows us to probe a significant portion of the inflated dayside, resulting in a higher atmospheric detectability. This geometric effect could mimic the observed time-variability of absorption signals due to condensation in the nightside of these planets, which has been recently reported for neutral iron in WASP-76 b. By studying molecules that are not expected to condense in the nightside of UHJs (~1000K), we can isolate the possible effect of different day and nightside scale heights. Here, we will analyze a stronger water vapor signal during the egress of the planet than at ingress, which cannot be explained by condensation and suggests that the extreme geometry of UHJ manifests itself as time-dependent absorption signals. Additionally, we report a redshifted HCN signature arising from the leading limb (i.e., observable in the first half of the transit and absent from the second half) and a weak evidence of ammonia using high-resolution observations of WASP-76 b with CARMENES.
How to cite: Sánchez López, A., Landman, R., Casasayas Barris, N., Kesseli, A., and Snellen, I.: Spatial characterization of the trailing and leading limbs of WASP-76b: Detection of H2O and HCN at high-resolution, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-563, https://doi.org/10.5194/epsc2021-563, 2021.
Currently, one of the most used techniques to study the atmosphere of the exoplanets is transmission spectroscopy by means of high-resolution facilities (R > 105). This methodology has led to the detection of several species in the atmosphere of exoplanets, showing that ultra-hot Jupiters (Teq > 2000 K) are one of the most intriguing exoplanets, possessing the richest atmospheres measured to date. Here, using two transit observations with the high-resolution spectrograph CARMENES, we study the atmosphere of one of the most famous ultra-hot Jupiters: WASP-76b. We take advantage of the redder wavelength coverage of CARMENES, in comparison with the facilities used in previous studies of this same planet, and focus our analysis on the CaII IRT triplet at 850nm and the metastable HeI triplet at 1083nm. In line with recent studies, we detect ionised calcium in the atmosphere of WASP-76b and, additionally, find possible evidence of HeI. We contextualise our findings with previous atmospheric studies of other ultra-hot Jupiters and, in particular, with those showing the presence of CaII and HeI absorption in their transmission spectrum. We show that this planet is a potential candidate for further follow up studies of the HeI lines using high-resolution spectrographs located at larger telescopes, such as CRIRES+.
How to cite: Casasayas-Barris, N., Orell-Miquel, J., Stangret, M., Nortmann, L., Yan, F., Palle, E., Snellen, I., Oshagh, M., and Sánchez-Lopez, A.: The atmosphere of WASP-76b seen with CARMENES: looking for CaII IRT and HeI, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-622, https://doi.org/10.5194/epsc2021-622, 2021.
Practically, we leverage the unique capabilities of Hubble Space Telescope Wide Field Camera 3 together with novel data analysis techniques to understand the nature of a set of exoplanets that reside under these extreme conditions. Ultimately, this project enable us to improve our understanding of exo-atmospheric processes and planet formation that ultimately shape the atmospheres of hot Jupiters that are observed today.
How to cite: Jacobs, B., Désert, J.-M., Barat, S., Line, M., and Pino, L.: Extreme exoplanets as a tool to understand trends in exoplanets atmospheres., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-775, https://doi.org/10.5194/epsc2021-775, 2021.
Exoplanet atmospheres are often treated as a single monolithic whole in transmission spectroscopy, while in reality they are dynamic and complex objects rich with inhomogeneities. We will show that using the technique of transit limb scanning it is possible to recover additional information on the spatial, chemical and velocity distributions of planet atmospheres that would otherwise have been lost.
We will present results of transit limb scanning applied to a variety of hot jupiters, in particular using high resolution data of the sodium absorption to recover the equatorial and polar wind speeds on several planets spanning the temperature regime, and a new model of the metastable helium outflow of WASP 107b, where we find strong evidence of an extended comet-like tail.
In each case we fit a variety of models with different atmosphere architecture in increasing complexity to the time resolved high resolution transmission spectra, using a Bayesian evidence approach to model comparison in order to find the model that best explained the data.
Mapping exoplanets will be the key to solving a number of theoretical issues, as atmospheric wind speed is governed by the level of drag in the atmosphere, which is not well constrained by theoretical models. Similarly, the shape of helium outflows on evaporating planets will be important to proper determinations of evaporation rate, which sculpts the shape of the entire planet population.
How to cite: Louden, T.: Mapping exoplanet atmospheres in high energy environments, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-726, https://doi.org/10.5194/epsc2021-726, 2021.
We investigate how radiatively driven heating and cooling in the upper atmosphere (at pressures below 1 bar) influences the interior temperature profile (at pressures between 1 to 700 bar) by means of dynamical heat transport. To achieve this goal, we perform fully coupled 3D-radiation-hydrodymamical models with the new full RT 3D climate model MITgcm/ExoRadPRT for WASP-43 b and HD209458 b. We show in our simulations under which conditions the interior temperature profile converges to a hot deep adiabat. Furthermore, we show if differences occur between the non inflated WASP-43 b and the inflated HD209458 b due to different flow structures at depth for similar irradiation.
How to cite: Schneider, A., Carone, L., Decin, L., and Jorgensen, U.: Connecting the atmosphere and the interior in extrasolar gas planets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-583, https://doi.org/10.5194/epsc2021-583, 2021.
The hot Jupiter exoplanet population is extremely diverse, spanning more than an order of magnitude in instellation, gravity, rotation period and atmospheric metallicity. As a new era of high-quality exoplanet observation fast approaches, with the coming James Webb Space telescope and Ariel missions providing wide wavelength coverage and ground-based telescopes supplying high resolution data, hot Jupiters will continue to be the best targets for atmospheric characterisation. A hierarchy of atmospheric models, from 1D radiative transfer codes coupled with advanced chemical networks up to 3D GCMs with complex treatment for atmospheric dynamics, have been used to model these planets, often trading modelling complexity for computational speed and cost. Yet, most of these planets are tidally locked and their atmospheres are intrinsically 3D, so they cannot be fully understood with 1D or 2D models. For example, predictions for the water feature strength observed in the HST/WFC3 bandpass vary drastically between 1D and 3D models, see Figure 1. This is increasingly prevalent at higher temperatures where strong day-side temperature inversions caused by TiO/VO may result in the feature being observed more strongly in emission than 1D models currently predict.
Figure 1: Comparison between our 3D grid computed using the non-grey SPARC/MiTgcm, a 1D grid of models using the 1D radiativ/convectivee transfer code CHiMERA and observation data.
Calculated using the state-of-the-art non-grey global circulation model SPARC/MiTgcm, we here create the largest library of 3D hot Jupiter models yet. This consists of 150 models spanning a wide range of instellation, metallicity, gravity, rotation period and the presence of strong photo-absorbing molecules TiO and VO, with the view to additionally explore planetary radius and atmospheric drag in the future. In addition to systematically varying these parameters, we also vary them jointly, something which has not been incorporated in any previous studies to date. From these simulations, we analyse the atmospheric pressure-temperature profiles and dynamic flows to identify any resulting qualitative trends in the atmospheric properties. We also calculate secondary eclipse spectra, transit spectra and phase curves to investigate how the day/night heat redistribution and spectral properties vary with planetary parameters. From this analysis we observe huge variations in the atmospheric properties within the grid. For example, the redistribution factor, an expression of day to night heat redistribution, varies by up to a factor of two depending on the parameters in our grid, see Figure 2. This means that, when working in synergy, intrinsic planetary parameters may cause divergence from previously computed models by a factor greater than any other additional processes such as nightside clouds, chemistry or MHD effects. Additionally, degeneracies in these values for our grid parameters, for instance higher surface gravity models having similar redistribution factors to higher metallicity, low surface gravity, models, complicates the picture even further.
Ultimately, we will interpolate this grid of GCM simulations to compare specific predictions for our range of possible observed planets, and compare with observed and predicted trends in hot Jupiter observations.
Figure 2: Comparison of redistribution factor, defined as f= (Tday/Teq)4, between models in our grid. Here we show the effects of surface gravity and metallicity. A value of 1 on this plot equates to an idealised fully homogenous atmosphere and a value of 2.66 to a case with no day to night heat redistribution.
How to cite: Roth, A. and Parmentier, V.: Exploring Hot Jupiter Atmospheres with a Grid of 150 Parameterised Non-Grey GCM Simulations., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-744, https://doi.org/10.5194/epsc2021-744, 2021.
Photochemically produced hazes provide a possible explanation for aerosol features in the transmission spectra of many hot Jupiters, especially those with relatively low equilibrium temperatures. Recent simulations of photochemical hazes as passive tracers in a 3D general circulation model demonstrate that the distribution of hazes can be highly inhomogeneous, with horizontal abundance variations of over an order of magnitude. At the same time, one-dimensional radiative transfer models show that absorption and scattering by hazes can change the atmospheric temperature profile by several hundred Kelvin. The additional heating and cooling have the potential to significantly affect atmospheric circulation. In this talk, we present new GCM simulations of hot Jupiter HD 189733b that include radiative feedback from hazes. A focus will be on changes in the atmospheric temperature structure and circulation. We will then compare the 3D haze distribution from previous simulations with radiatively passive hazes to the new haze distribution in simulations that include haze radiative feedback. Finally, we predict transit spectra based on the simulations and compare them to observations.
How to cite: Steinrueck, M., Koskinen, T., Lavvas, P., Zhang, X., and Tan, X.: Simulating haze radiative feedback in general circulation models of hot Jupiters, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-419, https://doi.org/10.5194/epsc2021-419, 2021.
Wasp-15 b is an inflated hot Jupiter orbiting a bright host star. Its low density and consequent large atmospheric scale height make it an excellent candidate for atmospheric characterization using transmission spectroscopy. In fact, it has previously been observed with the FORS2 spectrograph on the VLT, but large systematics have so far prevented this data from being used. Here, we show that Gaussian Process modelling can remove systematic noise features with amplitudes up to that of the transit signal, allowing us to achieve a precision comparable to later data without the systematics. We present the first transmission spectrum of the atmosphere of Wasp-15 b and compare it to theoretical spectra to discuss the implications.
How to cite: Petit dit de la Roche, D., van den Ancker, M., and Miles Páez, P.: The first atmospheric characterisation of Wasp-15b with Gaussian Process modelling, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-693, https://doi.org/10.5194/epsc2021-693, 2021.
The hot Jupiter HD 80606b has an extremely eccentric orbit (e ~ 0.93). The stellar irradiation the planet received drastically increases by more than two orders of magnitude during the perihelion passage. The variation due to eccentric orbits provides unique opportunities to directly probe the dynamical, radiative, and chemical timescales. To understand the interplay between these processes, we set up a model framework to explore the atmospheric response. We first run three-dimensional general circulation models of HD 80606b using MITgcm  for various atmospheric metallicities and internal heat. Based on the hemispheric-averaged results from the GCM, we then time-step the 1D photochemical model VULCAN  along the orbits to investigate the compositional response in detail. The kinetics results show that efficient vertical mixing leads to deep quench levels of CO and CH4. Because of the depth of quench levels where the radiative timescale is long, the temperature variations have no effects on the quenching behavior. Instead, photolysis and the rapid heating in the upper stratosphere is the main driver of the time-dependent chemistry. We find a transient state of [CO]/[CH4] > 1 after the perihelion. Since the quenched abundances of CO and CH4 are independent of the orbital phase, the [CO]/[CH4] ratio can provide constraints on the metallicity and internal heat. In addition, we find a sequence of sulfur species initiated by the sudden thermal and photochemical forcing near perihelion, which can be potential signatures for the existence of sulfur on hot Jupiters.
Figure 1. Dayside averaged temperature as a function of time relative to perihelion from the 3D general circulation model, assuming solar metallicity and Tint =100 K. The white dotted line indicates perihelion and the black dotted lines enclose the period where the planet is in synchronous rotation.
Figure 2. The dayside-averaged CO mixing ratio as a function of time relative to perihelion (left), compared to the hypothetical scenario where the planet is fixed at each orbital location (right) to isolate the orbital effects.
How to cite: Tsai, S.-M., Steinrueck, M., Parmentier, V., Lewis, N., and Pierrehumbert, R.: Compositional Variations of the Highly Eccentric Planet HD 80606b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-684, https://doi.org/10.5194/epsc2021-684, 2021.
We present results from a set of cloud-free simulations of exoplanet atmospheres using a coupled three-dimensional (3D) hydrodynamics-radiation-chemistry model. We report in particular our investigation of the thermodynamic and chemical structure of the atmospheres of HAT-P-11b and WASP-17b and their comparison with the results for the atmospheres of HD 189733b and HD 209458b presented in Drummond et al. (2020). We found that the abundances of chemical species from simulations with interactive chemistry depart from their respective abundances computed at local chemical equilibrium, especially at higher latitudes. To understand this departure, we analysed the CH4-to-CO conversion pathways within the Venot et al. (2019) reduced chemical network used in our model using a chemical network analysis. We found that at steady state nine CH4-to-CO conversion pathways manifest in our 3D simulations with interactive chemistry, with different pathways dominating different parts of the atmosphere and their area of influence being determined by the vertical and horizontal advection and shifting between planets.
How to cite: Zamyatina, M., Hebrard, E., Mayne, N., and Drummond, B.: 3D simulations of warm and hot Jupiter atmospheres: the role of 3D mixing in shaping CH4-to-CO conversion pathways, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-573, https://doi.org/10.5194/epsc2021-573, 2021.
During the past few years, exoplanet atmospheric studies have grown tremendously. Detections of atomic and molecular species are reported from the ultraviolet to the infrared at low- and high-resolution for Earth-mass to Jupiter-mass planets and from temperate to ultra-hot worlds. Nowadays, ground-based high-resolution spectrographs are starting to produce groundbreaking results that inform us of the temperature structure and dynamics of exoplanet atmospheres.
A reference system for atmospheric studies: WASP-127b
WASP-127b (Lam et al. 2017) orbits a bright (V = 10.17) G5-type star with a period of 4.18 days. The host star is at the end of its main sequence phase with an age of ~10Gyr and radius of 1.30RS and has entered the sub-giant phase. Therefore, the planet might be going through an inflation process for the second time (Lopez & Fortney 2016), leading to its large radius (~1.31RJ). WASP-127b is a lukewarm (~600 times Earth irradiation) Saturn at the right mass border of the evaporation desert. Assuming a hydrogen-helium composition, its atmospheric scale height is about 2100 km. In this case, the signal in transmission for one scale height is around 420 ppm, potentially making this planet one of the best among those of its class to study exo-atmospheres through transmission spectroscopy.
Near-infrared low-resolution data obtained with the Hubble Space Telescope (Spake et al. 2020) have revealed the strongest water band amplitude in an exoplanet with a mean amplitude of about 800ppm. Moreover, the presence of clouds and hazes is necessary to explain the complete spectrum. Such planets with a high-amplitude water signature in the J-band are well placed to be studied from the ground with visible and NIR spectrographs, allowing the impact of hazes and clouds to be analyzed by measuring the water content at different wavelengths.
Observations of WASP-127b with ESPRESSO
ESPRESSO is a fiber-fed, ultra-stabilized high-resolution echelle spectrograph installed at Paranal. It can collect the light from each 8m Unit Telescope (UT) individually or the 4UTs simultaneously of the Very Large Telescope (VLT). Two transits of WASP-127b were obtained within the framework of the GTO consortium. We published our results in Allart et al. 2020, which includes the first measurement of spin-orbit alignment of this system revealing the peculiar orbital architecture of the system. The old star WASP-127 is a slow rotator while its planet has a misaligned retrograde orbit (Fig. 2). This is surprising as stars with Teff below 6250K are supposed to have aligned systems. An explanation could be that WASP-127b remained trapped in a Kozai resonance with an outer companion and only recently migrated close to its star.
A view on the atmosphere of WASP-127b
We used the ESPRESSO data to analyze the transmission spectrum of the exoplanet. Visible high-resolution datasets are known to reveal the exoplanet thermosphere through atomic species as the well-known sodium doublet. The WASP-127b transit datasets have revealed an excess of absorption of 0.34 +/- 0.04% at the expected position of the sodium doublet corresponding to a small extension over 7 scale heights. However, we do not detect the presence of other atomic species but we were able to set upper limits of only a few scale heights.
We also undertake a thorough search for water vapor at visible wavelengths. To do so, we used the well-known cross-correlation function technique to average thousands of water lines in velocity space. To be as model-independent as possible, we applied binary masks containing the position of water lines at different temperatures and with an increasing number of lines. We showcased that such a technique is sensitive enough to retrieve planetary signals by doing an injection recovery test. Once applied to the transit datasets of WASP-127b, we were able to put a 3-sigma upper limit on the presence of water vapor at visible wavelengths of only 38ppm on the average depth of the 1600 strongest water lines at the equilibrium temperature. This upper limit corresponds to an atmospheric extension of only 0.08 scale height.
Combining low- and high-resolution spectroscopy
Based on this unique precision obtained with ESPRESSO, we explored the compatibility between ground-based high-resolution spectroscopy and space-based low-resolution spectroscopy. We computed a grid of models with different grey cloud-deck pressure based on the results of Spake et al. 2020 and using the pi-eta line-by-line radiative transfer code (Pino et al 2018). On one hand, models with grey cloud deck pressure ranging from 0.3 to 1 mbar are compatible with the HST datasets, while in another hand only models with pressure below 0.5 mbar are compatible with the ESPRESSO datasets. Therefore, by combining the low- and high-resolution datasets of WASP-127b, we can constrain the grey cloud pressure between 0.3 and 0.5 mbar.
We used two transits of WASP-127b obtained with ESPRESSO to acquire a thorough understanding of the orbital architecture of the system and the exoplanet atmosphere.
We propose a new framework to search for water vapor and other molecular species at high resolution. Despite the good data quality, we did not detect water vapor. However, we combined this result with a low-resolution detection of water at 1.3 microns to constrain the presence of clouds in the atmosphere of WASP-127b.
To conclude, we report for the first time that high-resolution visible data can be used to differentiate between cloudy and cloud-free exoplanets by measuring the water content and can also provide essential information on the cloud-deck pressure. The framework developed here to measure this water content will be applied to other exoplanets in the ESPRESSO GTO atmospheric survey and other surveys such as the NIRPS GTO atmospheric survey.
Allart R., Pino, L., Lovis, C. et al., 2020, A&A, 644, A155
Pino, L., Ehrenreich, D., Wyttenbach, A., et al. 2018, A&A, 612, A53
Spake, J. J., Sing, D. K., Wakeford, H. R., et al. 2020, MNRAS
How to cite: Allart, R. and the The ESPRESSO consortium: WASP-127b: a misaligned planet with a partly cloudy atmosphereand tenuous sodium signature seen by ESPRESSO, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-438, https://doi.org/10.5194/epsc2021-438, 2021.
Using the global 3D multi-fluid HD and its extension to MHD we simulated the measured HD209458b transit absorption depths at the FUV lines, and at the NIR line (10830 Å) of metastable helium HeI(23S) triplet, paying attention to possible change of the absorption profiles due to the presence of planetary intrinsic magnetic field. As continuation of our previous studies of HD209458b (Shaikhislamov et al. 2018, 2020), the inclusion of the HeI(23S) line into consideration and the comparison with corresponding measurements allows to constrain the helium abundance by He/H ~ 0.02, and stellar XUV flux at 1 a.u. by FXUV ~10 erg cm2 s-1 at 1 a.u. For the first time, we studied the influence of the planetary dipole magnetic field with a model which self-consistently describes the generation of the escaping upper atmospheric flow of a magnetized hot Jupiter, formation of magnetosphere and its interaction with the stellar wind. We simulated the absorption in the most of spectral lines for which measurements have been made. MHD simulations have shown that the planetary magnetic dipole moment µP = 0.61 of the Jovian value, which produces the magnetic field equatorial surface value of 1 G, profoundly changes the character of the escaping planetary upper atmosphere. The total mass loss rate in this case is reduced by 2 times, as compared to the non-magnetized planet. In particular, we see the formation of the dead- and the wind- zones around the planet with the different character of plasma motion there. The 3D MHD modelling also confirmed the previous 2D MHD simulations result of Khodachenko et al (2015) that the escaping PW forms a thin magnetodisk in the equatorial region around the planet. The significantly reduced velocity of PW at the low altitudes around the planet, and especially at the night side, results in the stronger photo-ionization of species and significantly lower densities of the corresponding absorbing elements. Altogether, the reduced velocities and lower densities result in significant decrease of the absorption at Lyα (HI), OI, and CII lines, though the absorption at HeI(23S) line remains nearly the same.
As it was shown in our previous papers, the dense and fast stellar wind, interacting with the escaping upper atmosphere of HD209458b, generates sufficient amount of Energetic Neutral Atoms (ENAs) to produce significant absorption in the high-velocity blue wing of the Lyα line. However, according to the performed 3D MHD modelling reported here, the planetary magnetic dipole field with the equatorial surface value of Bp=1 G prevents the formation of ENAs, especially in the trailing tail. This effect opens a possibility to constrain the range of planetary magnetic field values for the evaporating hot Jupiters and warm Neptunes in the stellar-planetary systems where sufficiently strong SW is expected.
The presented results fitted to the available measurements indicate that the magnetic field of HD209458b should be at least an order of magnitude less than that of the Jupiter. This conclusion agrees with the previous estimates, based on more simplified models (e.g., Kislyakova et al. 2014) and much less observational data, when only Lyα absorption was considered. We believe that the application of 3D MHD models simulating the escape of upper atmospheres of hot exoplanets and the related transits at the available for measurement spectral lines, sensitive to the dynamics of planetary plasma affected by the MF, opens a way for probing and quantifying of exoplanetary magnetic fields and sheds more light on their nature.
This work was supported by grant № 18-12-00080 of the Russian Science Foundation and grant № 075-15-2020-780 of the Russian Ministry of Education and Science.
Khodachenko, M.L., Shaikhislamov, I.F., Lammer, H., et al., 2015, ApJ, 813, 50.
Shaikhislamov, I. F., Khodachenko, M. L., Lammer, H., et al., 2018, ApJ, 866(1), 47.
Shaikhislamov, I. F., Khodachenko, M. L., Lammer, et al., 2020, MNRAS, 491(3), 3435-3447
How to cite: Shaikhislamov, I., Khodachenko, M., Miroshnichenko, I., Rumenskikh, M., and Berezutsky, A.: Magnetosphere of Hot Jupiter HD209458b and transit absorption in lines related to the upper atmosphere, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-88, https://doi.org/10.5194/epsc2021-88, 2021.
Hydrodynamic escape is the most efficient atmospheric mechanism of planetary mass loss and has a large impact on planetary evolution. However, the lack of observations remained this mechanism poorly understood. Therefore, new observations of the He I triplet at 10830 Å provide key information to advance hydrodynamic escape knowledge. In this work, we analyse the hydrodynamic escape of three exoplanets, HD209458 b, HD189733 b, and GJ 3470 b via an analysis of He triplet absorptions recently observed by the CARMENES high-resolution spectrograph, and their available Ly-alpha measurements, involving a 1D hydrodynamic model. We characterise the main upper atmospheric parameters, e.g., the temperature, the composition (H/He ratio), and the radial outflow velocity. We also study their hydrodynamic regime and show that HD209458 b is in the energy-limited regime, HD189733 b is in the recombination-limited regime, and GJ 3470 b is in the photon-limited regime. Details of this work can be found in , , .
 Lampón, M., López-Puertas, M., Lara, L.M., et al. 2020, A&A, 636, A13
 Lampón, M., López-Puertas, M., Sanz-Forcada, J., et al. 2021, A&A, 647, A129
 Lampón, M., López-Puertas, M., Czesla, S., et al. 2021, A&A, 648, L7
How to cite: Lampón, M., López-Puertas, M., Sánchez-López, A., Czesla, S., and Sanz-Forcada, J. and the CARMENES Consortium: Characterisation of the hydrodynamic atmospheric escape of HD 209458 b, HD 189733 b, and GJ 3470 b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-413, https://doi.org/10.5194/epsc2021-413, 2021.
The four planets of the HR8799 system provide a benchmark for directly imaged exoplanets. As these planets share a formation history, variations between the planet’s atmospheric properties - likely tracing their individual formation pathways - could provide insight into the details of the process of planet formation. In order explore these atmospheres and their evolution, we use new data obtained with the GRAVITY instrument at the VLTI as part of the ExoGRAVITY campaign, combined with data from SPHERE, GPI, CHARIS, ALES and OSIRIS in order to provide the best picture of the planetary atmospheres across a broad wavelength range. Using petitRADTRANS in a Bayesian retrieval framework, we compare a suite of state-of-the-art models applied to each of the targets in order to measure atmospheric properties such as metallicity, molecular abundances, and the C/O ratio, which is a well known tracer of the formation history. In this talk I will describe the data processing and modelling efforts which allow us to peer into the atmospheres of the HR8799 planets, and will outline the steps needed to tie the newly retrieved planetary properties to the formation history of the system.
How to cite: Nasedkin, E. and Molliere, P. and the ExoGRAVITY: A Systematic Characterization of the HR8799 System with GRAVITY, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-571, https://doi.org/10.5194/epsc2021-571, 2021.
Brown dwarfs are object between giant planets and star in term of mass, numerous observations suggest active meteorology. A near-infrared brightness variability is observed among L and T dwarfs. Several atmospheric dynamics have been proposed, but the mechanisms remain unclear. Clouds could also play an important role in shaping the thermal structure and spectral properties of these atmospheres via their opacity. In this study we propose to use a 3D convection resolving model couple to a grey-band radiative transfer and to a microphysical to study radiative cloud feedback over a large set of temperature, cloud composition and metallicity. The mechanism discussed in this study could play a role in the observed flux variability in brown dwarfs and is also applicable for directly imaged extrasolar giant planets.
To study these mechanisms, the 3D non-hydrostatic dynamical CM1 is used coupled to a grey band radiative transfer . An idealized cloud microphysical model was added, considering MgSiO3 , Fe, Al2O3 , CaTiO3 , Cr and MnS particles [3, 4, 5]. Particle settling is included. The effect of metallicity is taken into account. The clouds are radiatively active using Rosseland mean opacities. The cloud particles are considered spherical following a gaussian size distribution, with radius between 0.01 and 100 μm. The density of cloud particle is a free parameter. The model is initialized using temperature profile from a 1D model .
Figure 1: Initial vertical temperature profile (solid line) and condensation profile for the considered clouds (dotted line).
The model shows that the convective layer height increases in function of the temperature (Fig 2). An estimate of the vertical mixing is determined. With the inclusion of radiative property of the clouds, some feedback is observed. MgSiO3 , Fe and Al2O3 clouds tend to expend the convective layer altitude. This feedback is most visible at high temperature and depends on the clouds particle size. CaTiO3 , Cr and MnS have very low impact on the convective layer, due to a thin cloud layer and a low abundance.
Figure 2: Vertical profile of the mean potential temperature (K) for the different temperature cases considerate without clouds.
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How to cite: Lefèvre, M., Tan, X., Lee, E., and Pierrehumbert, R.: Cloud-convection feedback in brown dwarfs atmosphere, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-675, https://doi.org/10.5194/epsc2021-675, 2021.
The Nancy Grace Roman Space Telescope, to be launched in 2025, will directly image exoplanets in reflected starlight for the first time. This observing technique will enable the study of a population of exoplanets whose atmospheres cannot be characterized with current techniques. Previous works have analysed the possible science outcome of reflected-starlight observations through atmospheric retrievals. These have shown that an accurate atmospheric characterization from a reflected-light spectrum will likely be hindered if the radius and the atmospheric properties (e.g. cloud properties) of the exoplanet are unknown a priori. In this work we study how different observing strategies can improve the atmospheric characterization in such cases. We conclude that combining measurements at different star-planet-observer phase angles (α) is a powerful strategy to better characterize the atmosphere of an exoplanet and constrain its radius.
Understanding how planetary and atmospheric properties affect the reflected-starlight spectra of exoplanets is a key to interpreting future direct-imaging observations. This may also help propose observing strategies to optimize the prospects for characterization of the planet. That understanding of the physical fundamentals of exoplanet remote sensing will be applicable to space missions such as the Roman Telescope, LUVOIR or HabEx.
Model and retrieval procedure
We assume a H2-He atmosphere with methane as the only absorbing species and a cloud layer. The atmospheric parameters that we consider in our model are: the methane abundance (fCH4), the optical thickness of the cloud (τc), the altitude at which the cloud top is located, the geometrical extension of the cloud, the single-scattering albedo (ω0) of the aerosols and their effective radius (reff). We also include the planet radius (Rp) as another model parameter. Through Mie theory, reff determines the aerosol scattering phase function which describes the interaction between the photons and the aerosols depending on the incident direction of the light.
For a grid of ~300,000 atmospheric configurations, we computed their reflected-starlight spectra (500-900 nm) at phase angles α=37º, 85º and 123º by means of a pre-existing multiple-scattering radiative transfer code. The spectral resolution is R~125-225, consistent with mission concepts like LUVOIR or HabEx. We simulated observations of three atmospheric configurations, labelled as cloud-free, thin-cloud and thick-cloud scenarios. These observations were simulated at each of the three phase angles considered by adding wavelength-independent noise. The signal-to-noise ratio was set to S/N=10 in all cases.
We used the MCMC retrieval method developed in Carrión-González et al. (2020) to run atmospheric retrievals for each of the single-phase simulated observations at α=37º, 85º and 123º. For that, we assumed no prior knowledge of any of the model parameters. Furthermore, we extended this retrieval method in order to run simultaneous retrievals of multiple observations at different phase angles.
We first ran single-phase retrievals (Fig. 1) at each phase angle and repeated this for the three cloud scenarios. We verify that no single-phase observation with S/N=10 allows us to distinguish between cloudy and cloud-free atmospheres. This is due to the parameter correlations between Rp, the cloud properties and the methane abundance. This consistent with the findings in Carrión-González et al. (2020) for α=0º. We also find that a single-phase observation at a large phase angle (123º) can constrain the planet radius with an error smaller than 35% in all of the cloud scenarios. Our findings are consistent with previous works carrying out single-phase retrievals of reflected-starlight spectra.
We also ran multi-phase retrievals to combine spectra obtained at different phase angles. We tested the combinations 37º+85º, 37+123º and 37º+85º+123º. For comparison, we also ran single-phase retrievals at α=37º with an increased signal-to-noise ratio of S/N=20. The adopted phase angles are within the ranges of observable conditions for the known exoplanets that will be detectable by LUVOIR and HabEx. Such ranges of α might also be observable for certain targets in an optimistic configuration of the Roman Telescope coronagraph.
We find that combining small (37º) and large (123º) phase angles is an effective strategy to break some of the aforementioned correlations between model parameters (Fig. 1). Both of the combinations (37+123º) and (37º+85º+123º) allow to distinguish between cloudy and cloud-free atmospheres in all cloud scenarios and accurately constrain most of the model parameters. Combining small (37º) and moderate (85º) phase angles fails to achieve this. Similarly, a single-phase retrieval at α=37º with S/N=20 also fails to break the parameter correlations.
The shape of the aerosol scattering phase function is found to affect the improvements in multi-phase retrievals. We verified that the improvements are smaller for more isotropic scattering phase functions. The cloud properties and their uncertainties hence play an important role in the retrievals. Indeed, we find that if the cloud properties are assumed known a priori, the retrieval results become overly optimistic. This is consistent with previous works adopting such assumptions and happens because less correlations between model parameters take place in the retrievals.
We therefore conclude that combining small and large phase angles is a generally effective observing strategy to accurately characterize exoplanets for which no prior information on the planet radius or cloud composition is available. This suggests that exoplanets with wide ranges of observable phase angles should be priority targets for reflected-starlight telescopes.
 García Muñoz & Mills (2015), A&A, 573, A72
 Carrión-González et al. (2020), A&A, 640, A136
 Nayak et al. (2017), PASP, 129, 973
 Carrión-González et al. (2021), A&A, accepted
 Damiano et al. (2020), AJ, 160, 206
How to cite: Carrión-González, Ó., García Muñoz, A., Santos, N. C., Cabrera, J., Csizmadia, S., and Rauer, H.: Reflected-starlight phase curves: an observing strategy to constrain the radius and atmospheric properties of directly imaged exoplanets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-694, https://doi.org/10.5194/epsc2021-694, 2021.
Spectroscopic characterization of imaged exoplanets and brown dwarfs is essential for understanding their atmospheres, formation, and evolution, but such work is challenged by the unavoidably simplified model atmospheres needed to interpret spectra. While most previous work has focused on single or at most a few objects, comparing a large collection of spectra to models can uncover trends in data-model inconsistencies needed to improve model predictions, thereby leading to robust properties from exoplanet and brown dwarf spectra. Therefore, we are conducting a systematic analysis of a valuable but underutilized resource: the numerous high-quality spectra of (directly imaged and free-floating) exoplanets and brown dwarfs already accumulated by the community.
Focusing on the cool-temperature end, we have constructed a Bayesian modeling framework using the new Sonora-Bobcat model atmospheres and have applied it to study near-infrared low-resolution spectra of >50 late-T imaged planets and brown dwarfs (≈600-1200K, ≈10-70 MJup) and infer their physical properties (effective temperature, surface gravity, metallicity, radii, mass). By virtue of having such a large sample of high-quality spectra, our analysis identifies the systematic offsets between observed and model spectra as a function of wavelength and physical properties to pinpoint specific shortcomings in model predictions. We have also found that the spectroscopically inferred metallicities, ages, and masses of our sample all considerably deviate from expectations, suggesting the physical and chemical assumptions made within these models need to be improved to fully interpret data. Our work has established a systematic validation of cloudless model atmospheres to date and we discuss extending such analysis to wider temperature and wavelength (e.g., JWST) ranges, as well as finding new planetary-mass and brown dwarf benchmarks, in order to validate ultracool model atmospheres over larger parameter space.
How to cite: Zhang, Z., Liu, M., Marley, M., Line, M., and Best, W.: Bayesian Spectroscopic Characterization of Directly Imaged Planets and Brown Dwarfs and Implications for Ultracool Model Atmospheres, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-818, https://doi.org/10.5194/epsc2021-818, 2021.
Within the Young Suns Exoplanet Survey (YSES) we are observing a homogeneous sample of 70 solar-mass members of the approximately 16 Myr-old Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association to search for sub-stellar companions.
High-contrast imaging observations with VLT/SPHERE/IRDIS revealed (i) a shadowed transition disk around Wray 15-788 that shows significant signs of ongoing planet formation and (ii) one of the lowest-mass companions imaged to date: YSES-2 b has a mass of 6.5 Jupiter masses and is orbiting its solar-mass primary at a separation of 110 au. Most intriguing, though, was (iii) the discovery of the first directly imaged multi-planet system around a Sun-like star. The detection of two gas-giant companions of 14±3 and 6±1 Jupiter masses that are orbiting YSES-1 (TYC 8998-760-1) at separations of 160 au and 320 au, respectively, provides important implications for the outer architecture of planetary systems and the underlying formation mechanisms.
In addition to the SPHERE observations, we identified further companions to our ‘Young Suns’ outside the instrument’s field of view in the third early data release of the Gaia mission. Based on parallaxes and proper motions provided in this catalogue, we detected eight additional sub-stellar companions at separations larger than 500 au amongst our sample.
By combining Gaia astrometry with the high-contrast imaging capabilities of SPHERE, our survey will provide a complete census of wide-orbit sub-stellar companions for a statistically highly significant sample of young, solar analogues. From the current results we derived a preliminary probability of 14.3±3.1% for our solar-type stars to host wide-orbit, sub-stellar companions. As follow-up observations of 45 YSES targets are still pending, this ratio can be interpreted as a lower limit, which is tentatively indicating a higher companion yield than previous surveys.
How to cite: Kenworthy, M., Bohn, A., Ginski, C., Reggiani, M., Meshkat, T., Mamajek, E., Pecaut, M., and Snik, F.: The Young Suns Exoplanet Survey: imaging infant planets around young, solar analogs, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-35, https://doi.org/10.5194/epsc2021-35, 2021.
Irradiated exoplanet atmospheres, with their hot day sides and eternally dark night sides, are intrinsically three-dimensional and highly dynamical. Vigourous atmospheric motions are expected to mix the atmosphere, reducing potential chemical variations with longitude. Day-side photochemistry, on the other hand, would enhance those variations. Both mixing and photochemistry drive the atmospheric chemistry out of equilibrium, and, as of yet, it is unclear to what degree both processes influence the composition of different exoplanet atmospheres.
We will present results from a grid of atmospheric disequilibrium chemistry models, incorporating vertical mixing, horizontal advection and photochemical reactions. Our grid spans a wide range of planetary temperatures (400 K – 2600 K), surface gravities, and rotation rates, so we will highlight the role that dynamical mixing and photochemistry play in each corner of the parameter space. We further focus on the compositional differences between the day- and night-side hemispheres that may arise, or be washed away, by disequilibrium chemistry processes. Finally, the influence of these processes on observations, such as transmission spectra, will be discussed. This work provides valuable constraints on the importance of disequilibrium chemistry, and the expected chemical diversity of exoplanets, with regards to upcoming space missions.
How to cite: Baeyens, R., Decin, L., Carone, L., Venot, O., Agúndez, M., and Mollière, P.: Exploring Disequilibrium Chemistry in Exoplanet Atmospheres with a Grid of Pseudo-2D Photochemical Models, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-46, https://doi.org/10.5194/epsc2021-46, 2021.
Exoplanets with size between the Earth and Neptune (1-4R⊕) do not have any equivalent in our Solar System and remain challenging to characterize. Yet, there are ubiquitous in the Galaxy and Fulton et al. (2017) showed that their distribution (number of planets per star vs radius) is bimodal highlighting a gap in the number of planets around 1.7R⊕. Planets with a radius below 1.7R⊕ are thought to be mostly rocky planets, and called Super-Earth, above this limit planets are most likely made of gas and called Sub-Neptune. We made use of the available data from the Hubble Space Telescope in Near-Infrared (HST WFC3 G141) and gathered 18 transmission spectra of planets with size below 6 R⊕ to study the transition between rocky and gaseous planets. First, we used TauREx3 (Al-Refaie et al. 2019), a Bayesian retrieval code, to rule out atmospheric scenarios. We proved that a primary clear atmosphere dominated by Hydrogen and Helium is rejected with more than 3σ for a large majority of planets in the sample. Then, we measured the amplitude of the spectra in the water absorption band (around 1.4μm) and compared observational values to simulated ones using a self-consistent modeling code ExoREM (Baudino et al. 2015; Charnay et al. 2018). We explored the connection between the water absorption amplitudes and the temperature by setting the stellar and planetary parameters to those of HD 3167 c (2.7 R⊕, 8.33 M⊕) and trying different metallicities (1, 10, 100 and 1000 x solar), cloud compositions and temperatures (300-1200K).
How to cite: Gressier, A., Marcq, E., Beaulieu, J.-P., and Charnay, B.: HST WFC3 G141 data analysis: exploring the transition from Super-Earth to Sub-Neptune, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-194, https://doi.org/10.5194/epsc2021-194, 2021.
We quantify the potential of a mid-infrared space-based mission like LIFE (Large Interferometer for Exoplanets) [1, 2] to detect atmospheric signatures of life in the spectrum of a terrestrial planet at various stages of its evolution. We use a Bayesian retrieval framework to simulate observations obtained through LIFE. Using the minimal requirements for the spectral resolution, the signal to noise ratio, and the wavelength range for LIFE, as discussed in Konrad et al.  (a contribution to EPSC 2020), we retrieve the atmospheric structure and composition of thermal spectra of the Earth at various epochs : modern day, the Neoproterozoic Oxygenation Event (NOE, 0.8 billion years ago), the Great Oxygenation Event (GOE, 2.0 billion years ago), and a prebiotic Earth (3.9 billion years ago).
These simulations determine in more detail the potential of the LIFE space mission. They also further constrain the technical requirements of the mission, as well as determining the robustness of the analyses routines.
Temperate terrestrial exoplanets are predicted to be very abundant in our galaxy . Such planets are the preferred targets to study when searching for life in the universe.
The only way to characterize a terrestrial exoplanet in the context of its habitability is by studying its atmosphere. Atmospheric spectra are strictly linked to the chemical composition, the temperature structure of the atmosphere, the presence of clouds, the emission and scattering from the surface, as well as many other processes.
With the current instruments, it’s hard to find planets that are similar to the Earth in the habitable zone around their stars. Because of the lack of observational data, we rely on theoretical spectra of terrestrial exoplanets to develop analysis pipelines that could be most effective for the characterisation of such targets. In addition to that, a theoretical approach can be used to determine the technical requirements for future missions, in order to be able to detect the most relevant atmospheric signatures.
Space missions that aim at characterizing terrestrial exoplanets have been proposed, e.g. HabEx  and LUVOIR  which focus on the reflected (visible and near-infrared) portion of the planetary spectrum, and LIFE [1, 2], the Large Interferometer for Exoplanets, which will characterize terrestrial planets in the thermal (mid-infrared), emitted portion of the planetary spectrum.
Using nulling interferometry, LIFE will allow us to further constrain the bulk parameters and the surface conditions of a few dozens of terrestrial planets, as well as to gather information about their atmospheric structure and composition. The current status of this project, as well as the summary of all the submitted contributions, is discussed in more detail in Angerhausen et al. (2021, this conference).
Bayesian retrieval routines are, so far, the key to a statistically significant analysis of an atmospheric spectrum. These have been successfully used in other astrophysical contexts, as well as similar atmospheric analyses of Jovian exoplanets [see e.g. 8].
The Bayesian retrieval routine that is currently used is composed by two modules:
- the forward model petitRADTRANS , which applies the radiative transfer equation to produce theoretical spectra given a set of parameters (pressure-temperature structure, chemical abundances, bulk parameters,…);
- the parameter estimation module, which applies the Bayesian Inference Nested Sampling method  to assess the goodness of the theoretical spectrum when compared to the observed spectrum.
We validated the routine with an Earth twin orbiting a Sun-like star at 10 pc distance from the observer, as presented in Konrad et al. . In our previous work, we used petitRADTRANS both to produce the input spectrum and as forward model for the Bayesian routine. While still being useful to determine the minimum requirements of the LIFE Mission with respect to resolution, signal to noise ratio and wavelength range, this approach is very simplified and prone to bias.
In this work, to better assess the robustness of the routine with different input spectra, we use instead simulated spectra of the Earth at various stages of its evolution calculated by Rugheimer & Kaltenegger : a prebiotic Earth (at 3.9 billion years ago, or Ga), the Earth during the Great Oxygenation Event at 2.0 Ga and the Neoproterozoic Oxygenation Event at 0.8 Ga, and the modern Earth. We consider both cloudfree and cloudy atmospheres.
We simulate observations obtained with LIFE by using its simulator LIFESim (Ottiger et al., in prep.), assuming these four scenarios and considering an Earth-sized on a 1 AU orbit around a Sun-like star at 10 pc distance. LIFESim allows to calculate the wavelength-dependent S/N considering the major astrophysical and instrumental noise sources (e.g. stellar leakage, local zodiacal dust, exozodiacal dust).
We consider a spectral resolution of 50, a signal to noise ratio of 10, and a wavelength range of 4-18.5 micron, which are the minimum requirements for LIFE as discussed in Konrad et al. .
As shown in Figures from 1 to 4, the simulated spectra of the Earth  in the various epochs appear very different. The presence of a 60% global cloud cover also has an impact on the shape of the spectrum.
Branching out from the modern Earth-twin scenario is therefore essential to understand to what extent LIFE would be able to differentiate between the various evolutionary stages of a terrestrial planet, both before and after the appearance of life on the surface.
Retrieval runs are currently ongoing. Some preliminary results can be seen in Figure 5, which shows the retrieved spectra of a cloudfree prebiotic Earth planet and of a cloudfree modern Earth, compared to the input spectra (from ). The retrieval suite appears able to reproduce the main features of the spectrum, with subsequent insight on the atmospheric compositions and structures.
A thorough analysis of these retrievals will be discussed in more detail and presented in this conference.
How to cite: Alei, E., Konrad, B., Mollière, P., Quanz, S., and Angerhausen, D. and the LIFE Collaboration: Diagnostic potential of the mid-infrared space interferometer LIFE for studying Earth analogues, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-340, https://doi.org/10.5194/epsc2021-340, 2021.
Current knowledge suggests that temperate terrestrial exoplanets commonly occur in our galaxy (Bryson et al., 2021). One long-term goal of exoplanet research is to characterize the atmospheres of a sizable sample of temperate planets. Such measurements will add to our knowledge of the diversity of worlds in our galaxy, which is a driving force behind this effort, and they will enable the discovery of habitable worlds.
The sensitivity of currently planned space- and ground-based observatories will unlikely allow for the characterization of a large number of temperate exoplanet atmospheres. Concepts for future missions (e.g. NASA's LUVOIR [a] and HabEx [b]), capable of characterizing exoplanet atmospheres in reflected light (optical and near-infrared (NIR) range), have been proposed. Complementary to these efforts, the LIFE mission introduced in Quanz et al. (2018) (see also Angerhausen et al. (2021, this conference) for a general overview) is a proposed space-based nulling interferometer which measures the mid-infrared (MIR) thermal emission of exoplanets.
The MIR regime is particularly powerful, since it provides probes for atmospheric molecules not accessible in the optical or NIR (e.g. the biosignatures CH4 and N2O). Furthermore, MIR emission observations, in contrast to optical and NIR observations, allow us to probe the temperature structure, radius and surface conditions on exoplanets (Quanz et al., 2019; Konrad et al. in prep.). Previous work has focussed on constraining technical requirements for LIFE via retrievals of cloud-free Earth-twin MIR spectra (Konrad et al., 2020; Konrad et al. in prep.). We now generalize these estimates by looking beyond the cloud-free Earth-twin. Specifically we consider Venus (this submission) and Earth’s evolution through time (Alei et al. (2021, this conference)).
Our approach is based on the Bayesian retrieval of simulated mock observations with LIFE for a Venus-twin exoplanet around a sun-like star located at 10 pc. We generate Venus’ emission spectrum using the 1D radiative transfer tool petitRADTRANS (Mollière et al. 2019). The model takes the planetary radius and mass, the pressure-temperature (PT) profile, the atmospheric composition and cloud properties as input. We parametrize Venus’ PT profile via a 3rd order polynomial and consider line and collision-induced absorption by H2O, CO2, and CO as well as absorption and emission contributions from Venus’ opaque H2SO4 clouds.
With LIFESim(Ottiger et al. in prep.), we simulate the wavelength-dependent SNR expected for observations with LIFE for a Venus-twin. LIFESim considers noise contributions from stellar leakage, local zodiacal dust, and exozodiacal dust.
Our retrieval mechanism is built upon the Multinest algorithm (Feroz et al., 2009). Using the LIFESim noise estimate as uncertainty on the Venus spectrum, we retrieve for the mass and radius, the PT profile, the surface pressure, the molecular abundances and the cloud parameters. By covering a range of different wavelength ranges (3-20 μm, 6-17 μm), spectral resolutions (R = 20, 35, 50, 100) and signal to noise ratios (S/N = 5, 10, 15, 20), we obtain estimates for the technical requirements LIFE needs to meet to:
- Differentiate between a Venus- and an Earth-twin.
- Find evidence for clouds in Venus’ atmosphere.
- Accurately characterize structure and composition of Venus’ atmosphere.
This approach will show whether the previously determined technical requirements for LIFE (Konrad et al., in prep.) are sufficient. Many similar MIR retrieval studies have been performed for Earth-like exoplanets. However, to the best of our knowledge, no MIR retrieval studies exist for a Venus-like planet.
In Figures 1 and 2, we provide first preliminary results, as a proof of concept from testing our approach for retrieving cloudy MIR spectra with our retrieval framework. We used a Venus-twin spectrum (range = 3 - 20 μm, R = 50, SNR = 20) assuming a distance of 10 pc from the Sun as input for this retrieval run. Please note, that for these retrieval validation runs, we only consider the planet’s photon noise and not yet additional noise sources.
Figure 1 shows the spectrum corresponding to the retrieved parameters in relation to the input spectrum. From this plot we see that our retrieval provides a good fit to the input spectrum. Figure 2 shows that the PT profile parameters are well retrieved for the upper atmosphere of Venus. Due to the opaque cloud layer in Venus’ atmosphere at approx. 0.1 bar, the surface temperature and surface pressure are no longer retrievable (as can be seen from the cut in the green uncertainty at 0.1 bar). Instead we interpret the retrieved “surface” pressure as the pressure at which Venus’ cloudy atmosphere becomes opaque.
With these first retrieval runs we demonstrate that our retrieval suite produces reliable results for cloudy atmospheres. Further studies are currently carried out and will be presented at the conference. Furthermore, we will address the points listed above and discuss how results from cloudy retrievals could be safely interpreted.
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How to cite: Konrad, B. S., Alei, E., Angerhausen, D., and Quanz, S. P. and the LIFE collaboration: Atmospheric Retrieval of Cloudy Venus-Twin Exoplanets in the Context of the LIFE Mission, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-578, https://doi.org/10.5194/epsc2021-578, 2021.
The next generation of astronomical facilities will be able to retrieve exoplanetary atmospheric spectra in increasing quantity and of increasing quality. Radiative transfer (RT) models of these atmospheres is essential both for interpreting observational data and for linking these data to the planetary physical state with the aid of dedicated climate models. So far, a large effort has been placed in modelling the atmospheres of giant planets, which are the most easily accessible to observations. Now times are ripe to extend these studies to treat the relatively thin atmospheres of terrestrial-type exoplanets, which are the most likely targets for the search of atmospheric biomarkers.
Here we present a procedure to perform radiative transfer calculations for terrestrial-type exoplanets with temperate physical conditions (Simonetti et al. in preparation). The procedure is based on HELIOS and HELIOS-K, which are novel, flexible and publicly available codes developed by the University of Bern (Grimm & Heng, 2015; Malik et al., 2017, 2019; Grimm et al., 2021) as a part of the Exoclime Simulation Platform (ESP) repository. These codes make full use of the computing power of Graphics Processing Units (GPUs, colloquially known as graphics cards) being therefore much faster (up to one order of magnitude, see Grimm et al. 2021) than other similar codes and are integrated with a variety of molecular and atomic line repositories such as HITRAN (Gordon et al., 2017), HITEMP (Rothman et al., 2010) and Kurucz. Until now, HELIOS has been mostly applied to study Jupiter-like planets. The main features of the procedure that we have implemented for the treatment of rocky, habitable planets can be summarized as follows.
First, we added the treatment of the continuum absorption features of a variety of gases, in particular H2O (Clough et al., 1989; Mlawer et al., 2012) and CO2 (Gruszka & Borysow, 1997; Baranov et al., 2004; Baranov, 2018). These continua strongly contribute to the overall opacity of Earth-like atmospheres and cannot be neglected. Second, we paid special attention to the sub-Lorentzian profile of CO2 absorption lines, testing the effects of different recipes (Perrin & Hartmann, 1989; Tonkov et al., 1996). Third, we considered different hypotheses regarding the convective lapse rate of the troposphere. On these basis we: (i) tested the robustness of HELIOS and HELIOS-K against changes in model variables and (ii) compared them with other codes already published and used in the same context (e.g. LBLRTM Clough et al., 2005), as done by Yang et al. (2016).
One of the main goals of this work is to provide a new and fast radiative transfer treatment for the ESTM, an energy balance climate model with upgraded treatment of the vertical and horizontal energy transport Vladilo et al. (2015). The ESTM is extremely flexible and allows for a rapid exploration of the planetary and atmospheric parameter space, providing us the ability to map quantitative indices of habitability on these parameters (Silva et al., 2017). The flexibility of both HELIOS and ESTM will allow us to test a wide variety of atmospheric compositions, which have applications in the study both of exoplanets and of ancient Earth and Mars. Moreover, the HELIOS procedure adapted to terrestrial-type atmospheres can be used to generate synthetic TOA fluxes useful to link the conditions at the planet's surface with quantities that will become observable with future generations of instruments, such as secondary eclipse spectra and direct IR emission spectra from terrestrial-type exoplanets (see e.g. Quanz et al., 2021). Finally, the output of the same procedure can be applied to other codes in the ESP repository, such as the THOR GCM (Mendonca et al., 2016; Deitrick et al., 2020).
Figure 1 shows the TOA albedo obtained for three different stellar spectral classes for different values of surface temperature and stellar zenith angle, for an atmosphere of 1 bar of CO2 and a relative H2O humidity of 100%, as obtained by HELIOS using the procedure presented in Simonetti et al. (in preparation). The surface albedo was set to 0.15.
Figure 2 shows the relation between OLR and surface temperature for different radiative transfer models for an Earth-like atmosphere composed by N2, O2, 360 ppmv of CO2, 1.8 ppmv of CH4 and a temperature-dependent quantity of H2O (relative humidity equal to 100%). The thick red curve labelled "HELIOS" has been obtained with the novel procedure presented in Simonetti et al. (in preparation). The data relative to the other curves have been taken from Yang et al. (2016).
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How to cite: Simonetti, P., Vladilo, G., Malik, M., Silva, L., Ivanovski, S., Maris, M., Murante, G., Biasiotti, L., Bisesi, E., and Monai, S.: Terrestrial-type planetary atmospheres with HELIOS, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-819, https://doi.org/10.5194/epsc2021-819, 2021.
How to cite: Noack, L.: How does volcanic outgassing differ on geological time scales between planets with and without plate tectonics?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-832, https://doi.org/10.5194/epsc2021-832, 2021.
Sub-Neptunes (Rp~1.25-4 REarth) remain the most commonly detected exoplanets to date. However, it remains difficult for observations to tell whether these intermediate-sized exoplanets have surfaces and where their surfaces are located. Here we propose that the abundances of trace species in the visible atmospheres of these sub-Neptunes can be used as proxies for determining the existence of surfaces and approximate surface conditions. As an example, we used a state-of-the-art photochemical model to simulate the atmospheric evolution of K2-18b and investigate its final steady-state composition with surfaces located at different pressures levels (Psurf). We find the surface location has a significant impact on the atmospheric abundances of trace species, making them deviate significantly from their thermochemical equilibrium and “no-surface” conditions. This result arises primarily because the pressure-temperature conditions at the surface determine whether photochemically-produced species can be recycled back to their favored thermochemical-equilibrium forms and transported back to the upper atmosphere. For an assumed H2-rich atmosphere for K2-18b, we identify seven chemical species that are most sensitive to the existence of surfaces: ammonia (NH3), methane (CH4), hydrogen cyanide (HCN), acetylene (C2H2), ethane (C2H6), carbon monoxide (CO), and carbon dioxide (CO2). The ratio between the observed and the no-surface abundances of these species, can help distinguish the existence of a shallow surface (Psurf < 10 bar), an intermediate surface (10 bar < Psurf < 100 bar), and a deep surface (Psurf > 100 bar). This framework can be applied together with future observations to other sub-Neptunes of interest.
Figure 1: Selected criteria and a flowchart of possible steps to identify the existence of the surface and the surface pressure for a hydrogen-dominated exoplanet with properties similar to K2-18b.
How to cite: Yu, X., Moses, J., Fortney, J., and Zhang, X.: How to identify exoplanet surfaces using atmospheric trace species in hydrogen-dominated atmospheres, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-184, https://doi.org/10.5194/epsc2021-184, 2021.
Hydrogen emisssion by degassing magma is likely to have a significant impact on the H2 mixing ratio in early atmospheres of terrestrial planets depending on the surface pressure, volcanic flux and oxygen fugacity of the magma . This process can account for the presence of a few percent of hydrogen in the early atmospheres of terrestrial exoplanets.
The formation of water using a N2-CO2-H2 mixture was identified in a previous experimental study focusing on the early Earth with nitrogen as a dominant gas and an initial H2 mixing ratio fixed at 4% . We now explore various amounts of hydrogen in the mixture to cover the unknown parameters regarding surface emission and to highlight the role played by hydrogen in the chemistry of these exoplanetary atmospheres.
2. Experimental method
The PAMPRE (french for “aerosol production in microgravity using a reactive plasma”) experimental setup  is a plasma reactor used to simulate the photochemistry at low pressure (around 1 hPa) in planetary atmospheres. The CO2-N2-H2 mixture is injected in the reactor with various N2 to H2 abundance ratio and a fixed abundance of 70% for carbon dioxide. The molecular hydrogen mixing ratio is varied from 5% down to 0.5% in volume. The gas phase in the PAMPRE reactor is analyzed using a quadrupole mass spectrometer (Hiden Analyticals) to identify the species formed once the plasma is turned on.
3. Experimental results
Figure 1. Production of water and oxygen with 0.5% H2
Figure 2. Production of water and oxygen with 5% H2
The significant oxygen production associated to a hydrogen ratio of 0.5% is reduced drastically when increasing the hydrogen mixing ratio by a factor of 10. The formation of oxygen via the HOx cycle well known in the case of Mars becomes secondary when the hydrogen mixing ratio increases. As a result, the production rate of the OH radical formed by (1) increases.
O(1D) + H2 --> OH + H (1)
The radical OH then reacts by (2) and (3) which explains the significant formation of water with an initial hydrogen mixing ratio of 5%.
H2 + OH --> H2O + H (2)
2 OH --> H2O + O (3)
These new experiments put forward the presence of a hydrogen mixing ratio threshold over which the formation of water dominates the formation of oxygen. Two regimes can therefore be identified : O2-dominant production regime at low amounts of H2 and H2O-dominant production regime at higher amounts of H2.
4. Conclusions and perspectives
For terrestrial exoplanets known to be in the habitable zone of their host star, the present study shows that molecular hydrogen in the atmosphere is critical to characterize their habitability as this particular molecule leads to an important formation of water in oxydized conditions. It is also shown that based on the hydrogen abundance in the atmosphere, two regimes can be identified and this particular process suggests that high amounts of hydrogen could lead to a significant abundance of water in these atmospheres even without liquid water at the surface. Quantification of relative concentrations using quadrupole mass spectrometry by a recently developped tool  is in progress and would allow to quantify the H2 mixing ratio which seperates the two regimes in our experimental conditions. Based on these experimental results, the impact of this process is now being studied using the chemical kinetics model VULCAN  taking into account vertical mixing and using a known star spectrum. The predictions obtained from the model will be used to predict future observations of these specific environments in the frame of JWST and ARIEL space missions.
NC acknowledges the financial support of the European Research Council (ERC Starting Grant PRIMCHEM, Grant agreement no. 636829).
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How to cite: Drant, T., Carrasco, N., Perrin, Z., Vettier, L., Gautier, T., Tsai, S.-M., and Heng, K.: Molecular hydrogen in oxidized atmospheres of terrestrial exoplanets : Implications for water and oxygen formation , Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-503, https://doi.org/10.5194/epsc2021-503, 2021.
K2-141 b is a transiting, small (1.5 RE) Ultra-Short-Period (USP) planet orbiting its star every 6.7 hours discovered by the Kepler space telescope. The planet’s high surface temperature of more than 2000 K makes it an excellent target for atmospheric studies by the observation of its thermal emission. We present 65 hours of continuous photometric observations of K2-141 b collected with Spitzer’s IRAC Channel 2 at 4.5 microns spanning 10 full phases of the orbit. Our best fit model of the Spitzer data shows no significant offset of the thermal hotspot and is inconsistent with the observed offset of the well-studied USP planet 55 Cnc e at a 3.7 sigma level. We measure an eclipse depth of 142 +/- 40 ppm and an amplitude variation of 120 +/- 40 ppm in the infrared. The joint analysis of the observations collected in the two photometric bands favors a non-zero geometric albedo with Ag = 0.26 +/- 0.07 and a tentative temperature gradient. With a dayside temperature of 2141 -361 +352 K and a night-side temperature of 1077 -623 +473 K we also find no evidence of heat redistribution on the planet. We compare the observations to a 1D rock vapor model and a 1D circulation toy model and argue that the data are best explained by a thin rock vapor atmosphere with a thermal inversion.
How to cite: Zieba, S., Zilinskas, M., Kreidberg, L., Cowan, N., Nguyen, G., Miguel, Y., Pierrehumbert, R., Lupu, R., Dang, L., Hammond, M., Malavolta, L., and Carone, L.: Optical and Infrared Phase Curves of the Lava Planet K2-141 b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-476, https://doi.org/10.5194/epsc2021-476, 2021.
We present a study on the spatially scanned spectroscopic observations of the transit of GJ 1132 b, a warm (~500 K) Super-Earth (1.13 Re) that was obtained with the G141 grism (1.125 - 1.650 micron) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We used the publicly available Iraclis pipeline to extract the planetary transmission spectra from the five visits and produce a precise transmission spectrum. We analysed the spectrum using the TauREx3 atmospheric retrieval code with which we show that the measurements do not contain molecular signatures in the investigated wavelength range and are best-fit with a flat-line model. Our results suggest that the planet does not have a clear primordial, hydrogen-dominated atmosphere. Instead, GJ 1132 b could have a cloudy hydrogen-dominated envelope, a very enriched secondary atmosphere, be airless, or have a tenuous atmosphere that has not been detected. Due to the narrow wavelength coverage of WFC3, these scenarios cannot be distinguished yet but the James Webb Space Telescope may be capable of detecting atmospheric features, although several observations may be required to provide useful constraints
How to cite: Mugnai, L. V., Modirrousta-Galian, D., and Edwards, B. and the ARES V team: ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-191, https://doi.org/10.5194/epsc2021-191, 2021.
Hot rocky exoplanets present us with the unique opportunity to give us insights into their interiors through the characterization of their atmospheres. With the upcoming launch of the JWST and ARIEL ushering in a new era of exoplanet observations, this topic is becoming more relevant than ever.
A crucial element in this work is the accurate modeling of the interaction between planetary atmospheres and their magma oceans. The key question here being: What is the atmospheric composition of a hot rocky exoplanet for a given magma ocean composition? One pressing issue one must face when answering this question is the inclusion of volatile species (such as H2, H2O, CO2, etc.). Currently, hot rocky exoplanets are often assumed to be entirely depleted of volatile species, or simplified models are applied in which but a few species in both the melt and the atmosphere are taken into account.
In this presentation we will show our ongoing work on including volatiles species in the modeling of magma ocean-atmosphere interactions on hot rocky exoplanets. The successful development of this method and subsequent comparisons to observations would allow us to start characterising rocky exoplanet compositions which could lead to new insights for formation models. Furthermore, it would also allow us to model the effects of transient magma oceans though to be present on young earth analogs. Deepening our understanding of how such processes influence the conditions present during later evolutionary stages could give us new insights in the evolution of the earth and the conditions necessary to sustain life.
How to cite: Van Buchem, C., Miguel, Y., and Van Westrenen, W.: Modeling volatile species in magma ocean-atmosphere interactions on hot rockyexoplanets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-687, https://doi.org/10.5194/epsc2021-687, 2021.
Launched on 18 December 2019, CHEOPS (CHaracterising ExOPlanet Satellite) is the first exoplanet mission dedicated to the search for transits of exoplanets by means of ultrahigh precision photometry of bright stars already known to host planets. It is the first S-(small) class mission in ESA’s Cosmic Vision 2015-2025, and a partnership between Switzerland and ESA, with important contributions from 10 other member states.
CHEOPS will provide the unique capability of determining accurate radii for a subset of planets in the super-Earth to Neptune mass range, for which masses have already been estimated from ground- based spectroscopic surveys. It will also provide precision radii for new planets discovered by ground- and space-based transit surveys, including TESS. By combining known masses with CHEOPS sizes, it will be possible to determine accurate densities for these smaller planets, providing key insight into their composition and internal structure. By identifying transiting exoplanets with high potential for in-depth characterisation – e.g. those that are potentially rocky and have thin atmospheres - CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres.
In this poster we detail how the Community can access CHEOPS, with emphasis on the ESA-run Guest Observers Programme and the Annual Announcement of Opportunity for observing time Year 3 of CHEOPS, which is foreseen to come out in Quarter 4 2021.
How to cite: Isaak, K. and Lüftinger, T.: Community Access to CHEOPS, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-842, https://doi.org/10.5194/epsc2021-842, 2021.
In order to determine the extent to which a global magnetic field is required for a planet to be habitable at its surface, expertise is required from diverse communities, some of which have diverged from each other over the past several decades. For example, modelers and observers of the terrestrial magnetosphere have limited overlap and interaction with modelers and observers of unmagnetized planets or the giant planets in our solar system. There is relatively limited interaction between any of the above communities and those who study exoplanets, though efforts are increasing to bridge the solar system and exoplanet communities.
We describe a NASA Heliophysics DRIVE Science Center selected to answer the central question of this session: “Do Habitable Worlds Require Magnetic Fields”. This Center, named MACH (Magnetic Fields, Atmospheres, and the Connection to Habitability) includes scientists who study atmospheric escape from Earth, unmagnetized planets, and exoplanets. Over the next several years MACH will construct a framework that enables the evaluation of atmospheric loss from an arbitrary rocky planet, given information about the planet and its host star. The MACH Center hosted a community-wide workshop in June 2021 centered around this topic, and is seeking to grow their interactions with interested scientists from relevant disciplines.
How to cite: Brain, D., Peterson, W., Cohen, O., Cravens, T., France, K., Futaana, Y., Glocer, A., Holmström, M., Kistler, L., Ma, Y., Peticolas, L., Ramstad, R., Seki, K., Strangeway, R., and Vidotto, A.: Magnetic Fields, Atmospheres, and the Connection to Habitability (MACH) – Using Team Science to determine how magnetic fields influence habitability, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-410, https://doi.org/10.5194/epsc2021-410, 2021.
In the perspective of detecting and characterizing more and more close-in-orbit hot terrestrial exoplanets transiting nearby M-dwarf stars (e.g., best Earth-size targets for observational studies), the atmosphere of our "sister" planet Venus is one of the most relevant cases to address observational prospects. The detection of Venus-like atmospheres at various orbital periods and planetary masses will create a picture of where the divergence between Earth and Venus originates .
In this work, we propose to use a 3D Global Climate Model (GCM) developed explicitly for exoplanets and paleoclimate studies  to simulate the atmospheres of a possible class of Venus-like exoplanets i.e., rocky, highly irradiated exoplanets orbiting M-dwarf stars. The objectives are twofold: 1) to study the impact of changing specific planetary parameters, e.g., planetary radius and gravity, in the large-scale atmospheric circulation; and 2) to reproduce synthetic emission and reflected phase curves capable of addressing observational prospects.
In the Solar System, Venus and the Earth are examples of two rocky planets with similar radii and mass values and possibly a similar bulk composition . Nonetheless, the two planets also represent a scenario of divergent climate evolution. Thus, in terms of mass and radius parameters, Venus and Earth would be astrophysically indistinguishable in the event we would be observing them as exoplanets.
Several modelling studies  established possible limits for both the habitable zone and the “Venus Zone” . These 1D modelling studies offered a first approximation for the future differentiation between Earth-like and Venus-like exoplanet populations. Nonetheless, the complete characterisation and differentiation between these two populations can only be currently accomplished with dedicated 3D GCMs, which can reproduce the sort of climate feedbacks that ultimately constraint surface habitability conditions . The diversity of planetary climates is expected to be significant given 1) the variety of planetary atmospheres on the rocky worlds of our Solar System 2) the diversity of the planetary parameters for the exoplanets observed so far. Thus, predicting the actual climate for a specific planet represents a challenging task .
A new Era for characterising rocky exoplanet atmosphere will be opened by the James Webb Space Telescope (JWST), foreseen to be launched in 2021 and continued by the ESA mission ARIEL scheduled for launch in 2029. In addition, a new generation of instruments is being developed, including a whole set of new high-resolution spectrographs for the Very Large Telescopes (VLT) and Extremely Large Telescopes (ELT).
2.GCM Modelling of Venus analogues
We propose using the Generic GCM firstly developed at the Laboratoire de Meteorologie Dynamique (hereinafter LMD G-GCM) to simulate Venus-like exoplanetary atmospheres and climate response to a realistic set of planetary parameters. We will also provide synthetic observables, reflected and emission phase curves, which are inherently 3D, to support the characterisation of the population of Venus-like exoplanets in the future.
The LMD G-GCM uses a 3D dynamical core, common to all terrestrial planets, and a planet-specific physical core. It includes an up-to-date generalised radiative transfer for variable gaseous atmospheric compositions made of various cocktails of CO2, N2, and H2O, O2, CO, using the correlated-k method. Processes such as the radiative effect of clouds or Rayleigh scattering are considered. For instance, it has successfully been used to simulate the climate of other exoplanets like the cold super-earth Gliese 581d, a tidally-locked exoplanet like Gliese 581c/HD85512b , or Proxima b .
In this work, the LMD G-GCM is adapted to study close-in Venus-like exoplanets orbiting M-dwarf stars. The work is focused on the response of large-scale atmospheric circulation to critical parameters: radius, gravity, surface atmospheric pressure, solid-body rotation rate. For the latter, we will be selecting two likely modes, 1:1 and 3:2 spin-orbit resonances. Each parameter will be changed while keeping the others fixed. Combinations of realistic parameter variations will be selected according to specific mass-radius relationships . This will allow for the characterisation of temperature and wind fields at different pressure levels, particularly at and above the classical Venus top cloud layer.
To address the impact from simulating hot, dense atmospheres typical for Venus-like exoplanets, we run the LMD G-GCM using the planetary parameters of exoplanet TRAPPIST-1c as a framework for a possible Venus-like exoplanet. Synchronous rotation, with no obliquity and eccentricity, were assumed, together with a Venus-like atmosphere, with 92-bar surface pressure, and similar chemical composition with radiatively active Venus-type clouds, UV absorbers, and meridional variation of the cloud structure . Quasi-convergence of temperature is achieved for the whole atmosphere after 15000 orbits (See Fig.1).
Using the last orbit, the quasi-steady state obtained will be taken as the initial state to run simulations varying the parameters space, allowing the study of atmospheric variables (See Fig.2). In addition, top-of-the-atmosphere longitude-latitude maps of outgoing fluxes computed by the LMD G-GCM will be used to produce phase curves and interpret possible variations due to atmospheric dynamics (e.g., superrotation, jets, waves).
Figure 1. Temperature profile (solid black line) for the quasi-steady state, used as a reference input for future simulations. The initial profile (thin blue line) is obtained after running the model for 300 days for a Venus-like planet orbiting a Sun-like star.