This session aims to present recent progress in exoplanet atmosphere characterisation based on a combination of observation and modelling. The session focuses on cloud and gas-phase chemistry modelling, the modelling of magnetic coupling and charged particles in atmospheres and how these have and can be observed. Contributions working on the cross-over of solar system and exoplanet sciences are particularly welcomed.
This session is triggered by the upcoming PLATO launch at the end of 2026 and ongoing CHEOPS-PLATO synergies, including atmospheric characterization of hot to ultra-hot Jupiters facilitated by optical observations (secondary eclipse measurements/phasecurves) that are highly complementary to JWST observations in the infrared. The session will also discuss atmosphere interpretation activities on incorporating complex 3D modelling in their data interpretation. This session is further part of the PLATO WP activities for exoplanet gas giants.
Orals: Mon, 4 May, 16:15–18:00 | Room 0.94/95
We present a suite of General Circulation Models (GCMs) and interior evolution models of the ultra-hot Jupiter WASP-76b using the SPARC framework of ADAM (formerly the SPARC/MITgcm) and compare the results to recently obtained JWST NIRSpec/G395H phase-curve and emission data. The emission spectra of the planet is obtained on the dayside, nightside, and morning and evening limbs.
We vary a spatially independent atmospheric drag term; this crudely represents effects such as Ohmic dissipation, turbulent mixing, shocks, and hydrodynamic instabilities, suppressing the atmospheric flow within the atmosphere. We present five scenarios, varying from strong atmospheric drag to essentially drag free cases. We run models with and without the cloud species enstatite and corundum, which are allowed to circulate through the atmosphere and feed back into the radiative transfer calculations. We also account for the effect of hydrogen dissociation on the hot dayside of WASP-76b.
We use a grid of MESA models to predict heating strengths required to match the present-day radius. We find which heating strengths and depths are suitable to match the present-day radius of WASP-76b and use the output temperature profiles to fix the bottom atmosphere temperature for the GCM runs. We compare the evolution and resulting profiles of models with no core, models with a simple constant density heavy-element core, and models with a self-consistent compressible core.
We post-process the GCM outputs using the gCMCRT radiative transfer code. We find that the atmospheres with moderately strong drag and clouds provide the best fit to the James Webb phase-curve data. The need for strong drag aligns with results for other ultra-hot Jupiters (WASP-18b, WASP-103b, WASP-121b), from both Spitzer and JWST phase-curves.
We find that our simple drag treatment doesn’t capture the complexity of the circulation around the limbs of the planet. East-west asymmetries are clear in the JWST emission data, with the morning limb being ~200 PPM ‘hotter’ than the evening limb (in units Fp/Fs). The requirement of relatively strong atmospheric drag to match the phase curve data results in near-identical simulated emission spectra in our model limbs. This motivates further research to physically motivate the mechanisms causing atmospheric drag, such as magnetohydrodynamic effects.
We also vary the metallicity and C/O ratio, to better fit the emission spectra. We find that producing fits to the emission spectra requires careful consideration of the atmospheric composition.
We find that interior heating has little effect on the observational properties of the planet, with the main observational effects being from the varying atmospheric drag.
These results showcase the current state-of-the-art emission and phase-curve observations of WASP-76b, with comparisons to careful modelling efforts utilising a GCM with a high level of physical complexity.
How to cite: Allen, J., Komacek, T., Wardenier, J., and Coulombe, L.-P.: Circulation models, interior evolution, and James Webb observations of the ultra-hot Jupiter WASP-76b, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7842, https://doi.org/10.5194/egusphere-egu26-7842, 2026.
Ultra-hot Jupiters exhibit extreme day-to-night temperature contrasts exceeding 1000 K, driven by the competing effects of strong atmospheric winds, short radiative timescales, magnetic drag, and H₂ dissociation and recombination. Spectroscopic phase curves provide a uniquely powerful tool to probe these processes by mapping longitudinal temperature distributions and constraining planetary energy budgets across a range of atmospheric pressures.
We present results from a full-orbit phase-curve observation of the iconic ultra-hot Jupiter WASP-103b, obtained with JWST/NIRSpec-PRISM optical to near-infrared wavelengths in a single continuous visit. This observation provides an unprecedented view of a strongly tidally influenced exoplanet, enabling simultaneous constraints on atmospheric structure, dynamics, and composition as a function of orbital phase.
From the phase-resolved spectra, we measure wavelength-dependent hotspot offsets and quantify the planet’s heat redistribution efficiency, revealing the combined impact of extreme irradiation and short radiative timescales on the longitudinal temperature gradients. We will present the planet's emission spectra, probing the dayside and nightside atmospheric chemistry, and also the transmission spectrum constraining the terminator composition. Together, the data tests the predictions of chemical equilibrium and thermal structure models for ultra-hot Jupiters, including the survival of key molecular species at different longitudes.
Beyond atmospheric characterization, the phase-curve morphology of WASP-103b carries signatures of tidal deformation, providing important context for understanding how intense star–planet interactions shape both atmospheric dynamics and planetary evolution. The talk will discuss the power of JWST full-orbit spectroscopy to connect atmospheric circulation, chemistry, and tidal physics in extreme exoplanets and establish WASP-103b as a benchmark target for studies at the intersection of exoplanet atmospheres and interiors.
How to cite: Akinsanmi, B., Lendl, M., and Barros, S.: Unraveling the atmosphere of WASP-103b from its JWST/NIRSPec-Prism phasecurve, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10042, https://doi.org/10.5194/egusphere-egu26-10042, 2026.
Magnetic coupling between weakly ionized atmospheres and planetary magnetic fields is expected to influence the circulation of ultra-hot Jupiters, where dayside thermal ionization becomes important. Similar coupling processes are well established in the upper atmospheres of the Solar System gas giants, where interactions between the charged particles and neutrals control momentum and energy exchange. WASP-18 b, one of the best-studied ultra-hot Jupiters, exhibits a highly ionized dayside atmosphere extending deep enough to be strongly influenced by magnetic forces, making it an ideal laboratory to study magnetic drag in exoplanet atmospheres. Previous studies have shown that magnetic fields can exert a drag on the neutral gas component, but their impact on the atmospheric circulation remains poorly constrained.
We investigate the effect of inhomogeneous ionization on atmospheric dynamics by implementing an analytically derived parametrization of anisotropic magnetic drag, including Pedersen and Hall drag components, together with the associated frictional heating, into the 3D General Circulation Model ExoRad. The drag coefficients are computed from the local ionization fraction, dipolar magnetic field geometry, and collisional coupling between charged particles and neutrals, following the framework used to describe collisional coupling in Solar System gas giant atmospheres and ionospheres.
Our simulations demonstrate that anisotropic magnetic drag significantly modifies wind strength and direction in the upper atmosphere, reshaping the day–night circulation and generating asymmetric temperature patterns. In particular, anisotropic drag enhances the morning–evening terminator temperature contrast near the 0.1 bar level and produces two off-equatorial hotspot regions with reduced eastward displacement. The terminator regions are especially sensitive to how magnetic drag is parametrized. These results emphasize the importance of anisotropic magnetic drag and frictional heating for interpreting phase-curve and high-resolution spectroscopic observations and for constraining planetary magnetic field strengths.
How to cite: Blöcker, A., Carone, L., and Helling, C.: How Anisotropic Magnetic Drag Shapes the Atmospheric Circulation of WASP-18 b, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10046, https://doi.org/10.5194/egusphere-egu26-10046, 2026.
Taking advantage of CHEOPS' precision and flexible pointing strategy, we explored the variability of the atmosphere of KELT-1b. KELT-1b is a transiting brown dwarf (MP= 27MJ) orbiting very close to its host star (P=1.2 days), its orbit and high irradiation make it similar to an ultra-hot Jupiter. We combined occultation observations over 29 epochs with CHEOPS and three TESS sectors, together spanning over five years. We manage to obtain precise measurements of the brown dwarf's occultation depths over time. The individual occultations observed by CHEOPS reveal hints of atmospheric variability. In the TESS data, we also find a significant variation (>4 sifma) among the sectors. These results suggest time variability in the dayside of KELT-1b's atmosphere, potentially caused by a variability in cloud coverage."
How to cite: Baron, J., Deline, A., and Lendl, M.: Variability of KELT-1b’s dayside as seen by CHEOPS and TESS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23031, https://doi.org/10.5194/egusphere-egu26-23031, 2026.
In the era of JWST and upcoming space- and ground-based observatories (PLATO, ARIEL, ELT, and TMT), we will see an unprecedented surge in data, including phase curves and morning–evening asymmetry measurements. To understand the physical processes that govern the 3D structure of the observed exoplanet atmosphere, a state-of-the-art 3D climate model and cloud microphysics are required.
In this work, we couple ExoRad (a 3D climate model) with the DRIFT (cloud microphysics model), in which clouds (self-consistently generated) are used as a new non-grey opacity source in ExoRad, incorporating both heating and cooling effects. As cloud properties are intrinsically linked to the thermodynamic state and vice versa, we recalculate the cloud properties using the updated thermodynamic structure of the atmosphere and iterate between the DRIFT and the ExoRad, which quickly converges in a few iterations.
We apply this method to WASP-107b, an inflated warm gas giant with an equilibrium temperature of 770 K and an abnormally high interior temperature. WASP-107 b has been observed to host silicon clouds, morning–evening asymmetry, and disequilibrium chemical species (CH4 and SO2), linked to atmospheric dynamics. We run the model for several metallicity levels, ranging from solar to 40 times solar metallicity, based on the observed constraints.
We find that clouds have a significant impact on the overall thermal structure in all model runs. The presence of clouds makes the planet's atmosphere hotter in the infrared photosphere, producing a weak thermal inversion. The coupling among zonal wind jet, thermal structure and cloud microphysics processes is required to reproduce the observed 150–200 K temperature difference between the morning and evening terminators. We also observe the thermodynamic trends in the metallicity space, which includes the zonal wind jet, day-night and morning-evening temperature differences, and vertical wind structure.
How to cite: Soni, V., Carone, L., Helling, C., Goodis Gordon, K., and Rohit Bangera, N.: Coupled 3D climate and cloud microphysics model for WASP-107 b , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15705, https://doi.org/10.5194/egusphere-egu26-15705, 2026.
Grant et al (2023) recently detected an 8.6 micron absorption in the atmosphere of the exoplanet WASP-17b using the James Webb Space Telescope (JWST), an infrared feature proposed to be caused by the presence of ~10nm radius “Quartz Cloud” droplets. WASP-17b is a so-called “hot Jupiter” exoplanet: its upper atmosphere has a temperature of 1250 K and pressure of 10-3 bar. Such conditions are below the melting point of quartz but also within the region of the silica phase diagram where β-tridymite should be the most stable phase.
In this work, the vibrational densities of states of silica nanoparticles (quartz, β-tridymite and amorphous silica) have been calculated using both traditional force field molecular dynamics (Heinz et al 2013) and extended tight binding (Bannwarth et al 2019) methods, showing generally good agreement with the JWST data. The degree of hydrogenation of dangling Si-O bonds is found to affect the absorption wavelength (and therefore the overlap with the planetary spectrum) more significantly than the phase of the nanoparticles, confirming solid Silica is likely present in the WASP-17b atmosphere, but is not necessarily quartz.
Under the assumption that such "droplets” form through a nucleation and growth mechanism akin to that of terrestrial aerosol, atomistic simulations were conducted using the new generation neural network potential MACE-MH-1 (Batatia et al 2025). Both molecular SiO2 nucleation and the proposed oxidation of silicon monoxide by water were studied. We report a novel exoplanetary aerosol formation mechanism, involving clusters that initially form as polymeric chains with tetrahedral arrangements of Silica units, before transitioning to larger interconnected rings as they grow.
References
David Grant et al, The Astrophysical Journal Letters, 2023, 956, L29
Hendrik Heinz et al, Langmuir, 2013, 29(6), 1754
Christoph Bannwarth et al , J. Chem. Theory Comput., 2019, 15(3), 1652
Ilyes Batatia et al, arXiv, 2025, 2510.25380
How to cite: Ingram, S., Chen, Y., and Vehkamaki, H.: Probing the Formation Mechanisms and Vibrational Spectra of Silicate Cloud Particles on WASP-17b using Molecular Simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9272, https://doi.org/10.5194/egusphere-egu26-9272, 2026.
How to cite: Rohit Bangera, N., Carone, L., Lecoq-Molinos, H., Soni, V., Woitke, P., Rimmer, P., and Helling, C.: Tracing gas-giant global and local atmospheric processes through photo-kinetic chemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7790, https://doi.org/10.5194/egusphere-egu26-7790, 2026.
The inflated radii observed in hundreds of Hot Jupiters (HJs) represents a long-standing open issue, with Ohmic dissipation derived from atmospheric magnetic induction being one of the most promising mechanisms for a quantitative explanation. Using the evolutionary code MESA, we simulate the evolution of irradiated giant planets, spanning the observed range of masses and equilibrium temperatures. We incorporate Ohmic dissipation, accounting for atmospheric induction and realistic profiles of electrical conductivity, and, for the first time, we study how it couples with the dynamo-generated internal field, which is assumed to scale as the internal heat flux as in fully convective stars and Solar planets. We find that, contrarily to the widespread expectations of large magnetic fields in HJs, Ohmic dissipation can partially suppress convection and keep the dynamo-generated magnetic fields at Jovian-like values maximum (few gauss). This has consequence in terms of measurability of atmospheric wind velocities, which depend on the magnetic drag. This talk is based on Viganò et al. 2025, A&A.
How to cite: Viganò, D.: Inflated Hot Jupiters have Jovian-like magnetic fields: predictions from long-term evolutionary models with atmospherically-induced Ohmic dissipation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3294, https://doi.org/10.5194/egusphere-egu26-3294, 2026.
The James Webb Space Telescope is opening a new window into the atmospheres of sub‑Neptunes, a class of planets where magma oceans may play a central role in shaping their atmospheric composition. At the magma ocean-envelope boundary (MEB; pressures >10 kbar), gas behaviour departs strongly from ideality, yet the consequences of real‑gas effects for chemical equilibria remain poorly quantified.
We model coupled magma-gas and gas-gas equilibrium chemistry for TOI‑421b, a hot sub‑Neptune, using real‑gas equations of state in the H–He–C–N–O–Si system. Our results show that H and N are the most soluble species in magma, followed by He and C. Using new real gas fits to experimental SiH₄ data, we find that SiH₄ dominates the MEB composition for a fully molten mantle at solar metallicity, but CH₄ becomes favoured at 100× solar. Reducing the mantle melt fraction suppresses both Si transfer from the magma ocean and the solubility of H and He, producing more H₂‑ and He‑rich envelopes.
Extending equilibrium chemistry through the observable atmosphere (1 mbar-100 bar), we find that Si‑bearing condensate clouds efficiently remove Si‑bearing gases, though SiH₄ remains a key species when solar‑metallicity gas is accreted. Both the SiH₄/CH₄ ratio and the Si/C ratio increase with mantle melt fraction and decrease with gas metallicity.
These trends identify the competition between SiH₄ and CH₄ as a diagnostic of both metallicity and the presence of magma oceans on sub‑Neptunes with equilibrium temperatures below 1000 K. Conversely, H₂‑ and He‑rich atmospheres that are SiH₄‑poor yet CH₄‑bearing may suggest a limited or absent role for magma oceans.
How to cite: Hakim, K., Bower, D. J., Seidler, F., and Sossi, P.: Silane/Methane Ratio as a Magma Ocean Signature of Sub-Neptunes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20536, https://doi.org/10.5194/egusphere-egu26-20536, 2026.
The unique properties of Hot Jupiters (HJs) have motivated extensive research efforts focusing on their detection, characterization, and theoretical modeling. However, observations and models must develop hand in hand to unravel the complex interplay of physical processes such as atmospheric winds, radiative transfer, and chemistry. Those shape and constrain observable properties including radius inflation, hotspot offsets, day–night brightness contrasts, Doppler-shifted spectral lines, and potentially radio emission associated with magnetic fields.
Magnetic effects are expected to become increasingly important with rising equilibrium temperature, as electrical conductivity increases steeply due to alkali metal ionization. Under these conditions, magnetic coupling between atmospheric flows and the planetary magnetic field becomes unavoidable. However, most existing models of magnetized Hot Jupiter atmospheres are either tailored to individual benchmark planets or rely on simplified magnetic prescriptions, such as linear drag or kinematic induction, despite the inherently nonlinear nature of magnetic field generation and saturation. While such approaches may be adequate for weakly conducting atmospheres, they cannot capture magnetic field amplification, Lorentz-force feedback, or the transition to magnetically dominated regimes.
To test these expectations in a self-consistent framework, we exploit a fully nonlinear magnetohydrodynamic (MHD) model that treats Hot Jupiter atmospheres as an anelastic fluid with homogeneous electrical conductivity in a stably stratified spherical shell. The system is subject to rotation, permanent dayside irradiation, and an imposed deep-interior dipolar magnetic field. We systematically explore models spanning equilibrium temperatures from 1000 to 3000 K by increasing the electrical conductivity accordingly.
Our simulations confirm that for temperatures up to about 1400 K, electromagnetic effects are negligible and atmospheric dynamics are dominated by a strong, axisymmetric prograde equatorial jet with peak velocities of several km/s. In this hydrodynamic regime, the longitudinal position of the brightness maximum may lie either east or west of the substellar point. For temperatures between roughly 1400 and 1900 K -nearly half of the known Hot Jupiter population- magnetic induction becomes significant. Bending and stretching of the internal field generate a predominantly azimuthal atmospheric magnetic field that can exceed the internal field strength by up to an order of magnitude, leading to a substantial reduction of flow amplitudes, particularly in the zonal direction. At even higher temperatures, corresponding to the Ultra-Hot Jupiter regime, magnetic induction in the atmosphere becomes sufficiently efficient to even drive a self-sustained stratospheric dynamo. Under these conditions, the flow and magnetic field are small-scale and time-dependent. Moreover, the magnetic field becomes independent of both the internal magnetic field and the electrical conductivity.
By systematically exploring a wide range of temperatures and thus electrical conductivities, our results can be related to observable quantities, such as day-to-night side brightness difference, hot spot advection for IR photometry or Doppler shift and line broadening for transmission spectroscopy and might provide a physically sound basis for interpreting current and future observations.
How to cite: Dietrich, W. and Wicht, J.: MHD Models of Hot Jupiter atmospheres, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11841, https://doi.org/10.5194/egusphere-egu26-11841, 2026.
55 Cnc e is the first rocky exoplanet for which strong evidence of a thick, volatile atmosphere exists (Hu+2024). The atmosphere of this hot super-Earth shows sub-weekly variability in emission (Demory+2016, Meier-Valdez+2023, Patel+2024). Among the multiple suggested scenarios ausing this variability is an outgassing – cloud formation cycle (Loftus+2024). We investigate, whether lava worlds could host such variable, cloudy atmospheres utilizing a 1D, time independent approach. We constuct a pipeline which combines radiative transfer with equilibrium chemistry, a cloud formation model and outgassing of the magma. We run this setup for a selection of atmospheric compositions and surface pressures for the purpose of our investigation and estimate the duration of each stage in the cycle from the physical processes involved. In this poster I present the results of our study, focusing on the spectral variability on cloudy lava worlds and their timescales.
How to cite: Janssen, L., Miguel, Y., Min, M., and Zilinskas, M.: Clouds can induce variability of lava worlds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2969, https://doi.org/10.5194/egusphere-egu26-2969, 2026.
Current space missions including CHEOPS and JWST, as well as upcoming missions such as PLATO, will help diagnose cloud properties and global climate regimes on gas giant exoplanets with unprecedented detail and in 3D. One key target of interest is WASP-107b, a warm (~750 K) cloudy transiting planet with a Neptune-like mass but a Jupiter-like radius, suggesting an unusually large, inflated atmosphere. A wide range of observations (i.e., with HST and JWST, including limb transmission spectra) are available for this planet covering the optical to infrared wavelengths (~0.8 – 12 μm). With these observations, spectroscopic features due to H2O, CH4, CO, CO2, SO2, and NH3, as well as a 200 K temperature difference between the morning and evening terminators, have been detected. Understanding the chemistry and horizontal temperature variations on WASP-107b requires constraints on the kinetic gas-phase chemistry (e.g., CH4) and photochemistry (e.g., SO2) as well as the planet’s interior temperature. Thus, a full 3D cloudy atmosphere model is needed with coherent observational constraints.
In this work, an iterative coupling between the ExoRad 3D global circulation model (GCM), which produces 3D temperature and gas abundance profiles assuming chemical equilibrium, with a kinetic cloud formation model (DRIFT) is used. The latter takes into account nucleation, surface growth, gravitational settling, mixing, element conservation, and equilibrium gas-phase chemistry in the whole computational volume.
Our iterative 3D GCM-cloud framework required approximately 5 iterations to provide the best fit to the observations. The results suggest that the iterative modeling approach reproduces the observed evening to morning limb temperature differences of 200 K, highlighting how clouds shape the 3D thermodynamics of the planet and are thus vital to properly interpret the chemical abundances of planetary atmospheres. Further, iron-free clouds with a reduced cloud mass load in the upper atmosphere that contains small cloud condensation nuclei are inferred. Depleted levels of CH4 along with increased abundances of SO2 and NH3 compared to equilibrium chemistry provide evidence of disequilibrium chemical processes. Finally, detailed analysis of the 4.3 μm CO2 feature allowed us to place constraints on the atmospheric metallicity of WASP-107b, where current estimates range from 10 – 43x solar metallicity.
How to cite: Goodis Gordon, K., Soni, V., Carone, L., Bangera, N., and Helling, C.: Linking Models to Observations: Unlocking the 3D Climate Structure of WASP-107b, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10442, https://doi.org/10.5194/egusphere-egu26-10442, 2026.
The Galaxy’s most common planetary systems consist of several Earth- to Neptune-sized planets on compact orbits, yet the young (10–30 Myr) star V1298 Tau hosts an unusual compact system of four large planets (≈5–10 Earth radii) arranged in a chain of near-mean-motion resonances that generate transit-timing variations of several hours. This system provides a rare opportunity to jointly investigate early dynamical, interior, and atmospheric evolution. We present new CHEOPS observations of the three innermost planets, delivering high-precision radius measurements that significantly improve constraints on their bulk densities and internal structures. Combined with recent mass estimates from transit-timing variations, we test whether the system formed in a resonant chain and subsequently evolved through tidal migration. We find that the planets are currently too far from exact commensurabilities for tidal dissipation to have driven them out of resonance, disfavouring a primordial full resonant chain. Accounting for post-formation planetary contraction further modifies the rate and direction of tidal migration, reducing the likelihood of resonance capture and suggesting formation with period ratios already below resonance. We also present complementary Hubble and JWST observations that reveal an extended hydrogen–rich atmosphere, with unexpectedly low metallicity for V1298 Tau b and a lack of methane, pointing to strong atmospheric mixing. Evolution models suggest substantial atmospheric loss over the next gigayear, potentially transforming the planet into a Neptune-sized world. V1298 Tau thus offers a benchmark for linking dynamical history with atmospheric and interior evolution, a synergy that will be greatly expanded by the large sample of young planets expected from ESA’s forthcoming PLATO mission.
How to cite: Shivkumar, H.: Tracing the dynamical, interior, and atmospheric evolution of the young V1298 Tau planetary system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18710, https://doi.org/10.5194/egusphere-egu26-18710, 2026.
Whether a planet's volcanic gas is oxidising or reducing is inherited from redox conditions in the planet's mantle. It is often presumed that reactions between iron species control mantle oxygen fugacity. However, iron alone need not be the sole dictator of how oxidising the interior of a planet is. Carbon is a powerful redox element, with great potential to feed back upon the mantle redox state as it melts. Despite Earth being carbon-poor, it has been proposed that the oxygen fugacity of Earth's upper mantle is in part controlled by carbon (Holloway et al., 1992; Stagno et al., 2013); a slightly-higher volatile endowment could make carbon-powered geochemistry inescapable. Indeed, a number of known rocky exoplanets are predicted to have formed with carbon contents greater than Earth (Bergin et al., 2023). We offer a framework for how carbon is transported from solid planetary interior to atmosphere, tracking redox couplings between carbon and iron. We also incorporate a coupled 1D energy- and mass-balance model to provide first-order predictions of the rate of volcanism. We show that carbon-iron redox coupling would maintain interior oxygen fugacity in a narrow range: more reducing than Earth magma, but not reducing enough to prevent CO2 outgassing entirely.
How to cite: Guimond, C. M., Shorttle, O., and Pierrehumbert, R.: Redox processes of slightly-carbon-rich rocky planets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20810, https://doi.org/10.5194/egusphere-egu26-20810, 2026.
How to cite: Gacesa, M. and Bop, C.: Quantum-mechanical H/D-CO₂ collisions and their impact on atmospheric escape and evolution of CO₂-rich planets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23082, https://doi.org/10.5194/egusphere-egu26-23082, 2026.
Sub-Neptunes are the most common type of exoplanets in the Galaxy, yet our own solar system does not have one. These worlds sit between Earth and Neptune in size, and their diversity makes them prime targets for understanding planetary habitability with upcoming missions such as the Habitable Worlds Observatory (HWO).
Two competing formation pathways have been proposed. In the gas-dwarf scenario, sub-Neptunes form in-situ, accumulating puffy H/He atmospheres that subsequently evolve through intense mass loss, cooling, and contraction. Alternatively, they could form farther out as volatile-rich worlds that migrate inward. Distinguishing between these scenarios requires answering several fundamental questions:
- What is the atmospheric composition of sub-Neptunes?
- How do young and mature sub-Neptune atmospheres compare with each other?
- How diverse are sub-Neptunes immediately after formation?
- What physical processes govern early evolution and on what timescales?
For the first time, JWST allows us to unravel the atmospheric composition of these mysterious sub-Neptunes with unprecedented precision. In this talk, I will present new JWST results for both young (<100 Myr) and mature (~Gyr) sub-Neptunes, compare their atmospheric compositions across age, temperature, and stellar irradiation, and discuss emerging patterns that hint at their origins. I will connect these insights to formation pathways and early evolutionary mechanisms, and conclude with the key open questions that will define the next decade of observations and modeling as we work towards understanding the most common planets in our Galaxy.
How to cite: Barat, S.: Time-Lapse of Exoplanets: Watching Sub-Neptunes Evolve with JWST, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22092, https://doi.org/10.5194/egusphere-egu26-22092, 2026.
The outer edge of the habitable zone (HZ) around M-dwarfs can host planets with atmospheres rich in CO2 (or other greenhouse gases), a prerequisite for liquid surface water to be present. This study investigates the climate state of such CO2-rich atmospheres on synchronously rotating Proxima Centauri b-like aquaplanets.
We use the NASA GISS ROCKE-3D version 2 General Circulation Model (GCM). ROCKE-3D has been validated against other terrestrial exoplanetary GCMs in the THAI project, and is one of the few exoplanetary GCMs that includes a dynamic ocean component. This dynamic ocean allows for a physically-based calculation of the ocean heat transport, which is especially important in the outer HZ. We performed simulations for 3 configurations with 1 bar atmospheres ranging between 40% CO2 - 60% N2 to 99% CO2 - 1% N2. The importance of ocean heat transport in these configurations is demonstrated through surface energy budget considerations.
Our results reveal two main features:
At the permanent nightside, two persistent bands of sea ice stripes encompass the entire planetary nightside across all CO2 mixing ratios tested. These ice stripes modulate lower atmospheric climate and circulation which is separated from the upper atmosphere by a temperature inversion. An emphasis lies on their modulation of the hydrological cycle, both near the surface, through energy fluxes, and aloft, through cloud formation.
At the substellar region (global dayside) a “trident” pattern, which may be described as an extension to the commonly observed surface “lobster” pattern, emerges. Its spatial distribution is modulated by the sea ice stripes through “drying” and “blocking” effects sensitive to the partial pressure of CO2. We provide explanations of connections and influences between the two patterns.
These features are visible and different from N2-dominated aquaplanets in top-of-atmosphere radiative fluxes and may thereby be used to constrain surface features and planetary climate in future observations of CO2 -rich aquaplanets.
How to cite: Snöink, J., Way, M. J., Tsigaridis, K., and Daskalakis, N.: Sea ice stripes on CO2-rich aquaplanets with ROCKE-3D, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1175, https://doi.org/10.5194/egusphere-egu26-1175, 2026.
Future observations of rocky exoplanets are expected to enable the characterisation of their atmospheric compositions. This is expected to reveal a much larger diversity of atmospheric compositions than those known from our solar system. Although constraints on the abundances of atmospheric species might be possible, they will remain very challenging for rocky exoplanets. Therefore, the characterisation of exoplanetary atmospheres will rely on the theoretical understanding of potential atmospheric types and their observational differences. In addition to the implications on the atmosphere, these atmospheric types also function as a window into the surface conditions of the investigated planet.
During this presentation I will present our modelling approach on the connection between different atmospheric types, defined by their gas and cloud composition, and their corresponding surfaces. Our results are generated from a surface-atmosphere model which builds the atmosphere from bottom-to-top and includes cloud condensation.
Our investigations of various sets of elemental abundances based on different rock compositions reveal the diversity of atmospheric compositions, which form distinct atmospheric types. One of the most indicative links from the atmosphere to the surface conditions can be found in the chemistry of the sulphur species. While the sulphur cloud condensates of H2S and H2SO4 only form for planets with high surface pressures and/or temperatures, the sulphur-bearing condensates at the planetary surface (including especially FeS, FeS2, and CaSO4) are directly linked to the atmospheric types.
I will present model transmission spectra based on these atmospheric compositions, which show that the atmospheric composition can be constrained to a specific atmospheric type. Although it will remain challenging to obtain sufficient observations, these could in principle constrain the planetary surface mineralogy.
How to cite: Herbort, O. and Sereinig, L.: Constraining the planetary surface by detections of distinct atmospheric types of rocky exoplanet atmospheres, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10226, https://doi.org/10.5194/egusphere-egu26-10226, 2026.
Cloud formation modeling is a crucial frontier in understanding atmospheric compositions, dynamics, and potential habitability (i.e., biosignature) of exoplanets. It is pivotal in determining which gas species may be observable in exoplanet spectra. The formation of cloud particles is determined by the local gas temperature, gas density, and the local gas composition, and hence, traces the local thermodynamic conditions. The relevant cloud properties include mean particle size, cloud particle number density, material volume fractions, and depleted element abundances for the elements that participate in the cloud formation process, which are required for solving the radiative transfer. These cloud properties are computed along one-dimensional local gas pressure-temperature profiles obtained from a three-dimensional general circulation model (GCM). The computation of these cloud properties involves solving a complex time-dependent reaction-diffusion equation, which is computationally expensive. Additionally, increasing the vertical resolution of the one-dimensional profiles can add more computational burden while solving the reaction-diffusion equation. To overcome such computational expenses, we present an alternative approach based on machine learning (ML). This work develops a neural network regressor that learns the relationship between the input parameters, local gas pressure–temperature profiles, global planetary temperature, effective temperature, latitude, and longitude, and the output cloud properties (e.g., mean particle size and cloud particle number density) in a transformed latent space. Due to the inhomogeneous representation of cloud properties, the neural network regressor comprises multiple branches, each dedicated to a specific property. Each branch employs a specialized neural network to extract latent features for the corresponding output, while latent features are also created from the input parameters. A fully connected network then maps the latent input to latent output features. We apply this ML framework on a GCM grid comprising 60 inflated hot Jupiters orbiting A, F, G, K, and M-type host stars, modelled using ExoRad.The Preliminary results are promising, showing high prediction accuracy for cloud properties at lower global temperatures. At higher global temperatures, increased prediction errors are expected, reflecting the greater complexity of cloud formation in these regimes.
How to cite: Reza, A., Zalenska, Z., Carone, L., and Helling, C.: Learning to Predict Clouds: A Neural Network Model for Predicting Exoplanetary Cloud Formation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18570, https://doi.org/10.5194/egusphere-egu26-18570, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 4
EGU26-21494 | ECS | Posters virtual | VPS28
Molecular and Crystalline Structures in a Highly Irradiated Protoplanetary Disk in NGC 6357Thu, 07 May, 14:15–14:18 (CEST) vPoster spot 4
Understanding star and planet formation in extreme environments is crucial for uncovering the origins of our solar system. While most knowledge comes from nearby, isolated regions such as Taurus and Lupus, over half of all stars and planetary systems form in environments exposed to strong far-ultraviolet (FUV) radiation emitted by massive OB stars, with energies below the Lyman limit (E <13.6 eV).
NGC 6357—a young (~1–1.6 Myr), massive star-forming complex located 1690 pc away and hosting over 20 O-type stars—provides a unique opportunity to study the effects of FUV radiation on protoplanetary disks. This is the focus of the XUE (eXtreme UV Environments) collaboration.
Here, we present results from XUE2, a disk in the Pismis 24 cluster, based on spectra from JWST/MIRI and VLT/FORS2, complemented by photometric data. We first characterize the central star through spectrophotometric fitting, a fundamental step since protoplanetary disks are shaped by their host stars.
To evaluate the potential for rocky planet formation, we conduct a molecular and mineralogical analysis of the disk. We identify CO and CO₂ and report a tentative detection of CH₃⁺, key molecules for organic chemistry. Additionally, we identify predominantly amorphous silicates, as well as crystalline species such as enstatite and forsterite—molecules and minerals also observed in disks exposed to lower irradiation levels.
These findings offer new insights into the composition of inner disk regions under strong FUV irradiation, helping to constrain the formation conditions of rocky planets in massive clusters—an essential contribution to understanding the origins of the diverse exoplanets observed today.
How to cite: Lemus Nemocon, M. A., Ramírez-Tannus, M. C., and Higuera Garzón, M. A.: Molecular and Crystalline Structures in a Highly Irradiated Protoplanetary Disk in NGC 6357, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21494, https://doi.org/10.5194/egusphere-egu26-21494, 2026.
