EXO3

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.

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.

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 [1].

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.

References:

[1] Tosi, N. et al. The habitability of a stagnant-lid earth. A&A 605, A71 (2017).

[2] 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).

[3] 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; T_eq ≥ 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 (T_eq > 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 [1] 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 [2] 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.

Introduction

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.

Conclusion

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.

References

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 F_XUV ~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 µ_P = 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 B_p=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 [1], [2], [3].

References

[1] Lampón, M., López-Puertas, M., Lara, L.M., et al. 2020, A&A, 636, A13
[2] Lampón, M., López-Puertas, M., Sanz-Forcada, J., et al. 2021, A&A, 647, A129
[3] 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.

1. Introduction
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.

2. Model
To study these mechanisms, the 3D non-hydrostatic dynamical CM1 is used coupled to a grey band radiative transfer [1]. 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 [2].

Figure 1: Initial vertical temperature profile (solid line) and condensation profile for the considered clouds (dotted line).

3. Results
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.

References
[1] Freedman, R. S., et al. The Astrophysical Journal SupplementSeries, 214(2):25. 2014.
[2] Tan, X. and Showman, A. P. The Astrophysical Journal, 874(2):111. 2019.
[3] Visscher, C., et al. The Astrophysical Journal, 716(2):1060–1075. 2010.
[4] Wakeford, H. R., et al. Monthly Notices of the Royal Astronomical Society, 464(4):4247–4254. 2014.
[5] Morley, C. V., et al. The Astrophysical Journal, 756(2):172. 2012.

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.

Abstract

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.

Introduction

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 (f_CH4), the optical thickness of the cloud (τ_c), 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 (r_eff). We also include the planet radius (R_p) as another model parameter. Through Mie theory, r_eff 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^[1]. 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)^[2] 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.

Results

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 R_p, 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^[3].

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^[4].

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^[5] 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.

References

[1] García Muñoz & Mills (2015), A&A, 573, A72
[2] Carrión-González et al. (2020), A&A, 640, A136
[3] Nayak et al. (2017), PASP, 129, 973
[4] Carrión-González et al. (2021), A&A, accepted
[5] 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 M_Jup) 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.

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.

Summary

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. [3] (a contribution to EPSC 2020), we retrieve the atmospheric structure and composition of thermal spectra of the Earth at various epochs [4]: 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.

Context

Temperate terrestrial exoplanets are predicted to be very abundant in our galaxy [5]. 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 [6] and LUVOIR [7] 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).

Methods

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 [9], 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 [10] 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. [3]. 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 [4]: 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. [3].

Results

As shown in Figures from 1 to 4, the simulated spectra of the Earth [3] 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 [3]). 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.

Context

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)).

Methods

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.

Results

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.

References

Quanz, S. P., et al., 2018, Proc. SPIE, 107011I

Bryson, S. et al., 2021, AJ, 161, 36. doi:10.3847/1538-3881/abc418

Quanz, S. P. et al., 2019, arXiv e-prints arXiv:1908.01316

Konrad, B. S., et al., 2020, European Planetary Science Congress

Mollière, P., et al., 2019, A&A, 627:A67

Feroz, F., et al., 2009, MNRAS, 398(4):1601–1614

Websites

[a] https://www.luvoirtelescope.org

[b] https://www.jpl.nasa.gov/habex/

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).

REFERENCES:

Baranov, Y. I. 2018, Journal of Molecular Spectroscopy, 345, 11

Baranov, Y. I., La erty, W. J., & Fraser, G. T. 2004, Journal of Molecular Spectroscopy, 228, 432

Clough, S. A., Kneizys, F. X., & Davies, R. W. 1989, Atmospheric Research, 23, 229

Clough, S. A., Shephard, M. W., Mlawer, E. J., et al. 2005, JQSRT, 91, 233

Deitrick, R., Mendonca, J. M., Schro enegger, U., et al. 2020, ApJS, 248, 30

Gordon, I. E., Rothman, L. S., Hill, C., et al. 2017, JQSRT, 203, 3

Grimm, S. L., & Heng, K. 2015, ApJ, 808, 182

Grimm, S. L., Malik, M., Kitzmann, D., et al. 2021, ApJS, 253, 30

Gruszka, M., & Borysow, A. 1997, Icarus, 129, 172

Malik, M., Kitzmann, D., Mendonca, J. M., et al. 2019, AJ, 157, 170

Malik, M., Grosheintz, L., Mendonca, J. M., et al. 2017, AJ, 153, 56

Mendonca, J. M., Grimm, S. L., Grosheintz, L., & Heng, K. 2016, ApJ, 829, 115

Mlawer, E. J., Payne, V. H., Moncet, J. L., et al. 2012, Philosophical Transactions of the Royal Society of London Series A, 370, 2520

Perrin, M. Y., & Hartmann, J. M. 1989, JQSRT, 42, 311

Quanz, S. P., Ottiger, M., Fontanet, E., et al. 2021, arXiv e-prints, arXiv:2101.07500

Rothman, L. S., Gordon, I. E., Barber, R. J., et al. 2010, JQSRT, 111, 2139

Silva, L., Vladilo, G., Murante, G., & Provenzale, A. 2017, MNRAS, 470, 2270

Tonkov, M. V., Filippov, N. N., Bertsev, V. V., et al. 1996, Applied Optics, 35, 4863

Vladilo, G., Silva, L., Murante, G., Filippi, L., & Provenzale, A. 2015, ApJ, 804, 50

Yang, J., Leconte, J., Wolf, E. T., et al. 2016, ApJ, 826, 222

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.

1.  Introduction

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 [1]. 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% [2].  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 [3] 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 [4] 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 [5] 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.

Acknowledgements

NC acknowledges the financial support of the European Research Council (ERC Starting Grant PRIMCHEM, Grant agreement no. 636829).

References

[1]  Liggins, P., Shorttle, O., Rimmer, P., 2020. Can volcanism build hydrogen-rich early atmospheres ? Earth and Planetary Science Letters 550

[2]  Fleury, B., Carrasco, N., Marcq, E., Vettier, L., Määttänen, A., 2015. The Astrophysical Journal Letters 807

[3]  Szopa, C., Cernogora, G., Boufendi, L., Correia, J., Coll, P., 2006. Planetary and Space Science 54

[4]  Gautier, T., Serigano, J., Bourgalais, J., Hörst, S.M., Trainer, M.G., 2020. Decomposition of electron ionization mass spectra for space application using a Monte-Carlo approach. Rapid Communications in Mass Spectrometry

[5]  Tsai, S-M., Lyons, J.R., Grosheintz, L, Rimmer, P.B., Kitzmann, D., Heng, K.,2017. VULCAN : An Open-Source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres. The Astrophysical Journal Supplement Series 228

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.

Abstract

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 [1].

In this work, we propose to use a 3D Global Climate Model (GCM) developed explicitly for exoplanets and paleoclimate studies [2] 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.

1.Introduction

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 [3]. 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 [4] established possible limits for both the habitable zone and the “Venus Zone” [1]. 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 [5]. 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 [6].

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 [2], or Proxima b [5].

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 [7]. 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.

3.Preliminary Results

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 [8]. 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.

Figure 2. Instantaneous temperature field for the cloud-top pressure level (p~0.02-bar) for TRAPPIST-1c, 300 orbits after the quasi-steady state was obtained. The sub-stellar point is represented by the white star.

Acknowledgments

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

References

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

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

[3] Hamano et al. 2013. Nature, 497, 607-610

[4] Kopparapu et al.2014. ApJL. 787.L29.

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

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

[7] Zeng et al.2016. ApJ. 819. 127.

[8] Garate-López & Lebonnois 2018 Icarus 314.

How to cite: Gilli, G., Quirino, D., Navarro, T., and Turbet, M.: Planetary parameters impact in the large-scale circulation of Venus-like exoplanetary atmospheres and observational prospects, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-354, https://doi.org/10.5194/epsc2021-354, 2021.

Transmission spectroscopy has been integral to the atmospheric characterisation of transiting exoplanets – constraining their chemical abundances and temperature profiles. However, transit spectra are often interpreted using 1D models of the atmosphere, and this can lead to biased inferences in retrievals. Especially on tidally locked planets, which have a permanently irradiated dayside and a permanently dark nightside, atmospheric variations along the line of sight can be substantial. In order to assess whether a 1D model suffices, or whether a 3D model is needed to interpret observational data, one requires an estimate of the planet’s opening angle. This is the angle subtended by the atmospheric region that contributes to the observation along the line of sight, as seen from the centre of the planet. In this talk, we show that the opening angles that have been computed in previous works are likely an overestimation of the true opening angles. This is because the maximum and minimum pressure probed by transit observations do not lie on the same transit chords. Using two different methods, we re-evaluate the opening angles for a large number of atmospheres with different scale heights and planetary radii. We also present a new analytical formula to estimate the more realistic size of the opening angle.

How to cite: Wardenier, J. and Parmentier, V.: Are Opening Angles in Exoplanet Transmission Spectroscopy Overestimated?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-325, https://doi.org/10.5194/epsc2021-325, 2021.

Transmission spectroscopy provides us with information on the atmospheric properties at the limb, which is often intuitively assumed to be a narrow annulus around the planet. This is why all existing retrieval algorithms used so far to constrain the atmospheric composition from data rely either on i) a single 1D forward model, thus assuming a uniform limb or ii) a linear combination of 1D models to account for heterogeneities between different regions of the limb (e.g. east vs. west). Even full three-dimensional atmospheric models (GCMs) commonly use only the atmospheric
columns at the terminator to predict the observable transmission spectrum for a given simulation.

Here, we will present numerical experiment from hot Jupiters to ultra hot Jupiters which demonstrate that the region probed in transmission actually extends significantly toward the day and night sides of the planet and that, as a result, the real transmission spectrum computed from a GCM simulation with our fully 3D radiative transfer differs significantly from results obtained with the usual assumptions, especially for the hottest atmospheres. This comes from the fact that the terminator of hot, synchronously rotating planets is a region exhibiting sharp thermal and compositional gradients.

Fig 1: Sum up of the different geometry required in retrievals code to avoid biases according to the equilibrium temperature ofthe planet and the presence or the absence of optical absorber. 1D retrieval model appears to be correct for planets with equilibrium temperature lower than 1400 K when optical absorber (such as TiO, VO, Na, K, etc) are present in the atmosphere. They are howeverbiased above this limit where 2D retrieval code are mandatory.

Using realistic hot exo-atmospheres from GCM model SPARC/MIT, we will demonstrate how this effect can lead to strong biases is the temperature and abundances retrieved from actual data biases that will need to be addressed and corrected for if we want to be able to make robust inferences from future JWST and ARIEL data. We will determine a global limit where the biases due the 1D hypothesis of retrieval model start to be negligible. We have also established a hierarchy of the different 3D effects (vertical, horizontal along and/or across the limb) in order to be able to chosse the right tool to break down the biases (see Fig. 1).  We will finally present our new tool, a 2D version of TauREx, which is designed to unravel these biases.

How to cite: Pluriel, W., Leconte, J., Zingalès, T., Falco, A., and Parmentier, V.: Evolution of the biases in retrieved atmospheric composition of hot Jupiters, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-5, https://doi.org/10.5194/epsc2021-5, 2021.

How to cite: Zingales, T., Falco, A., Pluriel, W., and Leconte, J.: TauREx 2D: Modelling 2D effects in retrievals, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-6, https://doi.org/10.5194/epsc2021-6, 2021.

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

How to cite: Yip, K. H., Changeat, Q., Nikolaou, N., Morvan, M., Edwards, B., Waldmann, I., and Tinetti, G.: Peeking inside the Black Box: Interpreting Deep Learning Models for Exoplanet Atmospheric Retrievals, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-110, https://doi.org/10.5194/epsc2021-110, 2021.

How to cite: Ardevol Martinez, F., Min, M., Kamp, I., and Palmer, P. I.: Machine learning as an ultra-fast alternative to Bayesian retrievals, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-713, https://doi.org/10.5194/epsc2021-713, 2021.

As next generation observation facilities become available for the characterisation of Exoplanet atmospheres, the capacity to move beyond the assumption of molecules existing in local thermodynamic equilibrium becomes more pressing. While atmospheric retrieval of Exoplanet atmospheres has operated under this assumption, it is known that many effects within planetary atmospheres drive molecules away from this equilibrium - into a state of non-local thermodynamic equilibrium, or non-LTE.  Here we revisit the bi-temperature model for approximating non-LTE molecule populations which uses a two temperature parameterisation: distinct rotational and vibrational temperatures. Here the implementation of this model is used in the molecular cross section generation code Exocross (Yurchenko et al. 2018) to further explore the differences arising in forward modelled spectra due to molecules existing in non-LTE.

Now we include an exploration of non-LTE in the the optical with the additional consideration of Titanium Oxide (TiO) - this diatomic exhibits bands of accentuated intensity when in non-LTE. This can be seen in the figure shown here - forward model examples for TiO in the atmosphere of WASP-76b with 3 transit observations simulated for JWST's NIRSpec instrument set to use its G140H grating. Here the divergence between spectra for the LTE and non-LTE cases can be seen to be particularly pronounced around 0.85 micron. 

In addition we show that the bi-temperature paramterisation is tractable for atmospheric retrieval. Here modifications were made to the publicly available atmospheric retrieval code TauREx 3 to include the additional temperature degree of freedom and non-LTE cross section data were generated using the Exocross code. This enables us to demonstrate the retrieval of both rotational and vibrational temperature parameters from JWST data simulated with under 10 transits.

How to cite: Wright, S. and Yurchenko, S.: Towards non-LTE retrieval of molecules in Exoplanet atmospheres, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-48, https://doi.org/10.5194/epsc2021-48, 2021.

We present a novel code that converts the widely-used wavelength-dependent opacities of gaseous species into Rosseland and Planck mean opacities (RPMs). RAPOC (Rosseland and Planck Opacity Converter) is a straightforward and efficient Python code that makes use of ExoMol and DACE data as well as any other user-defined data, provided that it is within the correct format. Furthermore, RAPOC has the useful ability of rapidly interpolating between discrete data points, therefore allowing for a complete incorporation in atmospheric models. 

Whereas RPMs should not be used as a replacement for more rigorous opacity analyses, they have certain benefits. For example, RPMs  allow  one  to  use  Grey  or  semi-Grey  models  when  analysing  gaseous environments;  which  are  simpler,  have  exact  solutions,  and  can  be  used  as benchmarks  for  more  rigorous  approaches. By incorporating the pressure and temperature dependence of RPMs, RAPOC provides a more complex treatment of the mean opacities than what is sometimes used within the literature, notably assuming constant values or adopting simple analytic formulations.  We report  examples  of RAPOC opacities  that  are  incorporated  into  a  semi-Grey  model  to produce the temperature profile of HD 209458 b that is then compared to the realisations of the more rigorous POSEIDON code.

The RAPOC code will provide the exoplanetary community a new tool for atmospheric modelling. For a quick installation in one's machinery, the “pip install rapoc” command can be used.

How to cite: Mugnai, L. V. and Modirrousta-Galian, D.: Rapoc: the Rosseland and Planck opacity converter. A user-friendly and fast opacity program for Python, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-108, https://doi.org/10.5194/epsc2021-108, 2021.

The study of exoplanets atmospheres is one of the most intriguing challenges in the exoplanet field nowadays and the High Resolution Spectroscopy (HRS) has recently emerged as one of the leading methods for detecting atomic and molecular species in their atmospheres (e.g., Birkby, 2018). While this technique is particularly robust against contaminant absorption in the Earth’s atmosphere, the non-stationary stellar spectrum, in the form of either Doppler shift or distortion of the line profile during planetary transits, creates a non-negligible source of noise that can alter or even prevent detection. In the last years, it has become computationally possible to simulate the stellar surface convection that, in the end, allows to correctly reproduce asymmetric and blue-shifted spectral lines due to the granulation pattern of the stellar disk, which is a very important source of uncertainties (Chiavassa & Brogi, 2019). In the context of HRS and on the planet hand side, only recently multidimensional models have been used to detect the weak planet signal in the spectrum (e.g., Flowers et al. 2019).

However, these numerical simulations have been computed independently for star and planet so far, while acquired spectra are the result of the natural coupling at each phase along the planet orbit. A next step forward is needed: coupling stellar and planetary 3D models dynamics during the transit.

I will present the unprecedented precise synthetic spectra obtained with the upgraded 3D radiative transfer code Optim3D (Chiavassa et al. 2009). Optim3D takes as inputs the state-of-art 3D RHD stellar simulations (Stagger code, Nordlund et al. 2009, Magic et al. 2013) and the 3D Global Climate Models (SPARC/MITgcms, Showman et al. 2009, Parmentier et al. 2021) for stars and planets respectively, coupling them at any phase along the planet orbit. I will show the impact of this new approach on the detection of molecules by cross-correlating our spectra with HRS observations (e.g., Snellen et al 2010 and Brogi et al. 2016). This approach is particularly advantageous for those molecular species that are present in both the atmospheres and form in the same region of the spectrum, resulting in mixed and overlapped spectral lines (e.g. CO and H2O, crucial to constrain the C/O ratio). Moreover, the use of 3D models provides us with information about the dynamics processes at play, such as stellar convection and planetary winds.

How to cite: Maimone, M. C., Chiavassa, A., Leconte, J., and Brogi, M.: A Full Characterisation of Stars and Planets through High Resolution Spectroscopy and 3D Simulations., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-72, https://doi.org/10.5194/epsc2021-72, 2021.

The evolution of the atmospheres of low and intermediate-mass planets is strongly connected to the physical properties of their host stars. The types and the past activities of planet-hosting stars can, therefore, affect the overall planetary population. We perform a comparative study of sub-Neptune-like planets orbiting stars of different masses and different evolutionary histories. As a model of atmospheric evolution, we employ our own framework combining planetary evolution in MESA with a realistic prescription of the escape of hydrogen-dominated atmospheres. We discuss general patterns of the evolved population as a function of planetary and stellar parameters. The final populations look qualitatively similar in terms of the atmospheres' survival around different stars, but quantitatively different, with this difference accentuated for planets orbiting more massive stars. We will discuss the potential input from different atmospheric escape mechanisms in shaping these populations.

How to cite: Kubyshkina, D. and Vidotto, A.: How does the mass and activity history of the host star affect the population of low-mass planets?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-652, https://doi.org/10.5194/epsc2021-652, 2021.

The vast majority of the detected exoplanets orbit in less than a month around their star, in extreme conditions unmet in the Solar System. The demographics of these close-in planets exhibit a striking feature: the lack of Neptune-size worlds on very short orbits, also dubbed the "Neptunian desert", which challenges our understanding of planetary formation and evolution. Two classes of mechanisms thought to play a predominant role in shaping the desert are orbital migration, which brings such planets close to their star, and atmospheric escape under the resulting increased irradiation. Yet, their relative roles remain poorly assessed, in part because we lack numerical models that couple the two processes with high precision and on secular timescales.

To address this need, we developed a state-of-the-art model, the JADE code, which allows to self-consistently simulate the complete lifetime of a planet around its host star. On the dynamical side, the most impactful processes for close-in planets are implemented. The three-dimensional evolution of the orbit is modeled under stellar and planetary tidal forces, a relativistic correction, and the action of a distant perturbing body. On the atmospheric side, the vertical structure of the atmosphere is integrated over time based on its thermodynamical properties, composition, inner heating, and the evolving stellar irradiation, which results, in particular, in high-energy-induced photo-evaporation.

We bench-marked the JADE code on the intriguing case of GJ436 b, an evaporating Neptune at the fringes of the desert whose eccentric and misaligned orbit despite an advanced age is still a puzzle. We showed that its exciting properties can be naturally explained by a strong interplay between eventful orbital and atmospheric histories. Particularly, a hidden companion on a wide orbit is able to trigger a Kozai—Lidov resonance, trapping the inner planet in high-eccentricity cycles for secular periods of time. During this resonance phase, the atmosphere pulsates in tune with the Kozai—Lidov cycles, which leads to stronger tides and an earlier migration than predicted from pure dynamical simulations. Nonetheless, the planet still starts to evaporate upon migrating billions of years after its formation, refining the paradigm that mass loss is dominant in the early age of close-in planets.

Precise measurements of orbital and atmospheric tracers are crucial to constrain our models. Our joined approach to the understanding of past dynamical and atmospheric history, combined with the servicing of next-generation instruments, offers the best chance to shed light on the origins of the desert and the processes that forge the close-in planet population.

Article:

“The JADE code: Coupling secular exoplanetary dynamics and photo-evaporation”

O. Attia, V. Bourrier, P. Eggenberger, C. Mordasini, H. Beust, D. Ehrenreich

March 2021

Astronomy & Astrophysics, Volume 647, id.A40

DOI: 10.1051/0004-6361/202039452

Figure 1: Illustration of how the JADE code works. The evolution of the inner planet’s orbit as well as its atmospheric structure is monitored. The figure depicts the configuration of the system at two different secular time steps. It illustrates a typical case where the inner orbit shrank, circularized, and changed inclination, and where the envelope substantially eroded.

Figure 2: Possible interplay between secular dynamics and atmospheric evolution of GJ436 b, as unveiled by the JADE code. Top: a Kozai—Lidov resonance induced by a distant perturber generates large eccentricity oscillations. Middle: the periodic rise in eccentricity translates into shorter mean planet–star distance and higher stellar irradiation. This causes the atmosphere to heat up and pulsate in tune with Kozai—Lidov cycles (blue), as opposed to the case where this dynamical feedback is not taken into account (orange). Bottom: the increases in radius lead to stronger tidal effects and thus a faster migration (blue), as compared to the case where the atmosphere is not modeled (orange).

How to cite: Attia, O. and Bourrier, V.: Coupling the Atmospheric and Dynamical Evolution of Close-in Exoplanets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-575, https://doi.org/10.5194/epsc2021-575, 2021.

1) Introduction

If an Earth-like planet with a large amount of water is drifted towards its host star, the surface temperature increases, which leads the atmosphere to enter a catastrophic runaway greenhouse state [1-4]. Studying this runaway greenhouse effect allows to better determine the runaway greenhouse insolation threshold and therefore the inner edge of the habitable zone (HZ).

Some studies [5-7] have shown that radiatively inactive background gases - such as N₂ - can increase the Outgoing Longwave Radiation (OLR) and delay the onset of the runaway greenhouse. In other words, the OLR may “overshoot” the Simpson-Nakajima limit [4]. Consequently the inner edge of the HZ is moved closer to the star [8-11] and the planet is further from a catastrophic runaway greenhouse feedback. Explanations for this overshoot include the modification of the scale height of the atmosphere [7] or the coupled effect of the pressure broadening and a lapse rate close to a dry lapse rate [12]. However, there is still no consensus so far in the literature on whether an OLR overshoot is expected or not and what are the responsible mechanisms.

2) Method

First, we did multiple sensitivity tests to constrain the most important physical processes and parameterizations involved in 1D climate models by using a suite of models available in the literature [13-16]. This allows us to build a new hybrid 1D radiative-convective model named PyRADS-Conv1D to produce reference curves of the OLR relative to the surface temperature for H2O+N2 atmospheres (Fig. 1) to solve the question of the potential overshoot.

This sensitivity study, and particularly the understanding of the relevant processes involved in such atmospheres, are useful knowledge to produce accurate 3D simulations using a Global Climate Model (GCM). Therefore we are doing simulations with the LMD-Generic model for different theoretical study cases: a waterworld and a planet with Earth’s continents. Unique features of the LMD-Generic allow to explore the onset of the runaway greenhouse, even in situations where water is not a trace gas.

3) Results

By using the PyRADS-Conv1D model [17], we propose reference OLR curves relative to the surface temperature for different nitrogen pressures (Fig. 1). We confirm the occurrence of an overshoot of the OLR regarding the Simpson-Nakajima limit. We explain also that the non usual transition between a nitrogen dominated and a water dominated atmosphere challenges the modeling by making important usually second order processes. For example, neglecting the transition from the foreign to the self pressure broadening of the center of the water absorption lines leads to the suppression the overshoot [17]. PyRADS-Conv1D is based on the line-by-line radiative transfer method from PyRADS [7] but we built an accurate correlated-k table able to reproduce line-by-line results (exo_k curves on Fig. 1). This table is suitable for 3D GCM studies.

Finally we show through preliminary results from the LMD-Generic model (Fig. 2) that a GCM provides the same tendency than 1D models with a strong decrease of the OLR when the surface temperature increases, even without the radiative effect of the clouds. These results may be helpful to better understand the runaway greenhouse effect and thus the possible future of the Earth. We will explain in details during the presentation our results from 3D simulations for the different considered study cases assuming an H₂O-dominated atmosphere.

Figure 1: OLR relative to the surface temperature for different nitrogen pressures. PyRADS-Conv1D is our reference 1D model. Exo_k [15] is an accurate 1D model used to test the correlated-k table built for this work.

Figure 2: OLR relative to the surface temperature with (blue curve) or without (green curve) the radiative effect of the clouds, using the 3D LMD-Generic model. Here we assume 1 bar of nitrogen.

References

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

[2] Ingersoll, A. 1969

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

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

[5] Goldblatt, C., Claire, M. W., Lenton, T. M., et al. 2009, Nature Geoscience

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

[7] Koll, D. D. B. & Cronin, T. W. 2019, The Astrophysical Journal

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

[9] Kopparapu, R. k., Ramirez, R., Kasting, J. F., et al. 2013, The Astrophysical Journal

[10] Ramirez, R. M. 2020, Monthly Notices of the Royal Astronomical Society

[11] Zhang, Y. & Yang, J. 2020, The Astrophysical Journal

[12] Pierrehumbert, R. T. 2010, Principles of planetary climate (Cambridge ; New York: Cambridge University Press)

[13] Koll, D. D. B. & Cronin, T. W. 2018, Proceedings of the National Academy of Sciences

[14] Turbet, M., Ehrenreich, D., Lovis, C. et al. 2019, Astronomy & Astrophysics

[15] Leconte, J. 2021, Astronomy & Astrophysics

[16] Marcq, E., Salvador, A., Massol, H. et al. 2017, Journal of Geophysical Research

[17] Chaverot et al. 2021, In prep.

How to cite: Chaverot, G., Bolmont, E., and Turbet, M.: How background gases can delay the onset of the runaway greenhouse? Insights from 1D and 3D modeling., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-759, https://doi.org/10.5194/epsc2021-759, 2021.

Galactic cosmic rays are important for exoplanetary atmospheres. They can contribute to the formation of hazes, prebiotic molecules and atmospheric electrical circuits. A number of so-called fingerprint ions, such as oxonium, have been identified from chemical modelling which are thought to be signatures of ionisation by energetic particles, such as Galactic cosmic rays. These fingerprint ions may be observed in exoplanetary atmospheres with upcoming JWST observations.

I will discuss our recent results that model the propagation of Galactic cosmic rays through the stellar winds of a number of nearby solar-type stars. Our sample comprises of 5 well-observed solar-type stars that we have constructed well-constrained stellar wind models for. This allows us to calculate the transport of Galactic cosmic rays through these systems. I will present our results of the Galactic cosmic ray fluxes that reach (a) the habitable zone and (b) the location of known exoplanets. The systems show a variety of behaviour and I will discuss the most promising systems for upcoming JWST observations. 

How to cite: Rodgers-Lee, D., Vidotto, A., and Mesquita, A.: Charting nearby stellar systems: The intensity of Galactic cosmic rays for a sample of solar-type stars, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-600, https://doi.org/10.5194/epsc2021-600, 2021.

Observations of exoplanets used to characterize the chemistry and dynamics of atmospheres have developed considerably throughout the years. Nonetheless, it remains a difficult task to give a full and detailed description using solely observations. With future space missions such as JWST and ARIEL, both expected to be launched within this decade, it becomes even more crucial to be able to fully explain and predict the underlying chemistry and physics involved. In this research, we focus on modeling star-planet interactions by using synthetic flare spectra to predict chemical tracers for future missions. We make use of a chemical kinetics code that includes synthetic time-dependent stellar spectra and thermal atmospheric escape to simulate the atmospheres of known exoplanets. Using a radiative transfer model we then retrieve emission spectra. This ongoing study is focused on various known planetary systems of which the stellar spectrum has been obtained by the (mega-)MUSCLES collaboration. Preliminary results on these systems show that stellar flares and thermal escape can have a significant effect on the chemistry in atmospheres. 

How to cite: Louca, A., Miguel, Y., and Tsai, S.-M.: The impact of time-dependent stellar activity on the atmospheric chemistry and observability of exoplanets, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-685, https://doi.org/10.5194/epsc2021-685, 2021.

Electromagnetic Star-Planet Interaction is a phenomenon that occurs when a planet is sufficiently close to its host star that Alfvén waves propagate to the star and can leave an imprint on the star. The resulting structure is called Alfvén wing. Stars also often have open field-line structures due to the influence of the stellar wind. In these open field line regions, two planets can share the same set of field lines at the same time. Therefore, it is possible that Alfvén wings interact with each other and cause a time-variability in the signal. We call this process wing-wing interaction. To understand wing-wing interaction further, we apply a three dimensional, fully time-dependent, magnetohydrodynamic model. There, we simulate two planets that generate star-planet interaction and eventually undergo wing-wing interaction. We present the temporal evolution of the Alfvén wings and of the Poynting flux. From these results, we can estimate how wing-wing interaction could appear in observations. 

How to cite: Fischer, C. and Saur, J.: Wing-wing Interaction - When Exoplanets interact with each other, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-827, https://doi.org/10.5194/epsc2021-827, 2021.