Exoplanet atmospheres

Abstract:

Introduction: Recent advances in observation with the JWST and high-resolution ground-based instruments have enabled the study of exoplanets to progress towards atmospheric characterisation, as opposed to merely detection. Hot and ultra-hot Jupiters remain among the best characterised and studied class of exoplanet, due to their large sizes and close orbits, however how the internal heating and resulting radius inflation of bloated ultra-hot Jupiters and related coupling to the internal magnetic field impacts their atmospheric circulation remains an open question. Moreover, the impact of atmospheric dynamics on observable properties can now be studied in detail. This study investigates the effect of varying both atmospheric drag and internal heat flux on the observable properties of WASP-76b, with comparisons made to JWST NIRSpec white-light phase curves. In addition, we perform a broader parameter sweep using the SPARC/MITgcm to investigate the influence of internal heating and inflated radii on the observable properties of hot and ultra-hot Jupiters.Methods: A suite of general circulation models are run, which solve the primitive equations of meteorology coupled to non-grey correlated-k radiative transfer with the SPARC/MITgcm [1]. The effect of Lorentz forces is represented by changing a spatially constant drag timescale , and for WASP-76b we consider two different internal heat fluxes for comparison, across the range of predicted values for hot and ultra-hot Jupiters [2]. We then will perform a broader parameter sweep, exploring the space of inflated-radii hot and ultra-hot Jupiters by covering a range of irradiation levels from zero-albedo full-redistribution equilibrium temperatures of 1000 – 3200K, again using the SPARC/MITgcm. This parameter space is inclusive of most inflated gas-giant planets, excluding KELT-9b, and will allow us to study the impact of internal heating on atmospheric circulation, with interior heating and evolution modelled using MESA [3]. We then use the gCMCRT radiative transfer code [4] to post-process the GCM results to produce simulated phase curves.Results: The key result from this study is shown in Figure 1, with simulated phase curves shown in comparison to Spitzer telescope data [5] at 3.6mm. We make the comparison to Spitzer data here as a placeholder for the comparison to JWST NIRSpec data, as the JWST data is not yet published. Figure 3 shows the impact of the interior heat flux on the internal temperature structure of WASP-76b. There is no observable difference between the interior heat flux scenarios. Figures 2 and 4 show characteristics of the atmospheric dynamics and temperature structure. Strong drag acts to suppress all winds throughout the atmosphere, as is expected, while intermediate drag removes the offset of the hot spot due to the suppression of the deep equatorial jet. There is a strong equatorial jet within the deep atmosphere, and the T-P profile implies that cloud species Al2O4 and Mg2SiO4 can form on the night-side and terminators of WASP-76b, and within its deep atmosphere.Conclusions: Spitzer data is best matched by a strong () drag case. There is no potentially observable difference between the hot interior flux and cold interior flux. The comparisons of these simulated phase curve to JWST NIRSpec white-light phase curves will help further constrain drag in the ultra-hot regime, which will be a useful point of comparison to other ultra-hot Jupiters. Other ultra-hot Jupiters with Spitzer phase-curves (WASP-18b [6], WASP-103b [7], WASP-121b [8]) also show high dayside-nightside temperature differences. This may imply that the drag mechanisms are similar in each planet in the ultra-hot regime (~2000-2500 K). New JWST NIRSpec/G395H phase-curve data (JWST GO proposal 5268) will also constrain metallicity, breaking the drag/metallicity degeneracy. The similarity in deep-atmosphere temperature shown by Figure 3 motivates the need for a parameter sweep where the temperature at the bottom boundary is varied, as opposed to an interior heat flux, in order to speed up convergence. Likewise, the T-P profile in Figure 4 motivates the need for longer simulation runs, as the model has not reached equilibrium within the deep atmosphere.References:[1] Showman, A.P. et al. (2009), The Astrophysical Journal, 699(1), pp. 564–584.[2] Thorngren, D. et al. (2019), ApJL (Vol. 884, Issue 1)[3] Jermyn, A.S. et al. (2023), The Astrophysical Journal Supplement Series, 265, p. 15.[4] Lee, E.K. et al. (2022), The Astrophysical Journal, 929(2), p. 180[5] May, E.M. et al. (2021), The Astronomical Journal, 162(4), p. 158.[6] Maxted, P.F. et al. (2012), Monthly Notices of the Royal Astronomical Society, 428(3), pp. 2645–2660[7] Kreidberg, L. et al. (2018), The Astronomical Journal, 156(1), p. 17[8] Davenport, B. et al. (2025),  Available at: https://arxiv.org/abs/2503.12521 (Accessed: 20 March 2025).

Abstract:

Over four decades have elapsed since the last in situ spectrophotometric observations of the Venusian atmosphere, specifically from the Venera 11 (1978) and Venera 13 and 14 (1982) missions. These missions recorded spectral data during their descent from approximately 62 km to the surface. Unfortunately, the original data were lost; however, a portion has been reconstructed by digitising the graphical outputs that were generated during the initial data processing phase of each of the three missions [1]. This reconstructed data is crucial as it remains the sole set of in situ spectrophotometric observations of Venus’s atmosphere and is likely to be so for the foreseeable future.While re-analysing the reconstructed Venera datasets, we identified several artefacts, errors and sources of noise, necessitating the implementation of some corrections and validation checks to isolate the most unaffected part of the reconstructed data. Then, using NEMESIS, a radiative transfer and retrieval tool [2], we conducted a series of retrievals to simultaneously fit the downward-going spectra at all altitudes. During this process, several parameters were retrieved. The first set of retrievals focused on the structure of the main cloud deck (MCD), which includes the cloud base altitude and abundance profiles of all four cloud modes. Previous corrections that were used to account for the effect of the unknown UV absorber did not result in good fits with the spectra shortward of 0.6 µm. Hence, we derived a new correction by retrieving the imaginary refractive index spectra of the Mode 1 particles.In the next phase, the MCD retrievals were used to update the model atmospheres for each of the missions. Then, the H2O volume mixing ratio profiles were retrieved and compared with the previous retrievals using the same data by [1] along with other remote sensing observations. The final retrieval phase concentrated on characterising particulate matter in the deep atmosphere. In [3], we outlined a methodology for retrieving a near-surface particulate layer using the reconstructed Venera 13 dataset. In this new work, we apply this methodology to encompass the Venera 11 and 14 datasets and compare the retrievals from the three datasets.This research thus provides a comprehensive overview of three distinct retrievals: 1) main cloud deck, 2) H2O, and 3) near-surface particulates using the reconstructed spectrophotometric data of Venera 11, 13, and 14.References: [1] Ignatiev, N. I., Moroz, V. I., Moshkin, B. E., Ekonomov, A. P., Gnedykh, V. I., Grigor’ev, A. V., and Khatuntsev, I. V. Cosmic Research 35(1), 1–14 (1997).[2] Irwin, P. G., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J., Tsang, C. C., Wilson, C. F., Calcutt, S. B., Nixon, C. A., and Parrish, P. D. Journal of Quantitative Spectroscopy and Radiative Transfer 109(6), 1136–1150 (2008).[3] Kulkarni, S. V., Irwin, P. G. J., Wilson, C. F., & Ignatiev, N. I. Journal of Geophysical Research: Planets, 130, e2024JE008728, (2025).

Abstract:

We present a re-analysis of archival data-cubes of Neptune obtained with the GEMINI Near-Infrared Integral Field Spectrometer (NIFS), aiming to refine constraints on the abundance of hydrogen sulphide (H₂S) in Neptune's atmosphere. To enhance spatial and spectral fidelity, we employ a modified CLEAN algorithm that effectively deconvolves the data while conserving flux. To mitigate observational and instrumental artifacts, we utilize Singular Spectrum Analysis (SSA) on single-wavelength images and apply Principal Component Analysis (PCA) across the full data-cube to suppress both random and systematic noise. Spectral retrievals are conducted using ArchNemesis, an optimal estimation inverse modeling tool. We retrieve vertical profiles at individual locations, and use Minnaert-corrected reflectivity functions across latitude bands to investigate latitudinal variability. Using the deconvolution and data analysis techniques, we are able to extract more scientific utility from legacy datasets and describe a template that can be repeated for similar datasets.

Abstract:

Clouds have broad significance in understanding the evolution and climate of planetary atmospheres. Moreover, the presence of clouds in the atmospheres of hot Jupiter exoplanets is supported both by direct spectral detections (Grant et al. 2023, Inglis et al. 2024), and observational trends, such as nightside brightness temperature (Beatty et al. 2019) and phase curve hot spot offsets (Bell et al. 2024), suggesting that an accurate understanding of clouds is needed, not only to understand the atmospheres of these planets, but to properly interpret observations. However, the properties of clouds are impacted by inherently coupled effects of circulation, radiation, and cloud microphysics. Full coupling of these processes remains computationally expensive, and as a result, current modeling schemes implement simplified cloud parametrizations that neglect one or more of these effects. Within this work, we implement a one-way indirect coupling of the cloud microphysical model 1D CARMA and MITgcm/DISORT, a general circulation model including double-grey radiative transfer, through including a novel particle size distribution that better represents the output of CARMA. We use pre-existing CARMA data for ultra-hot Jupiter TOI-1431b from Gao & Powell (2021), which has particle size distributions that are not well described by a log-normal distribution, with corundum in particular displaying distinctly bimodal behavior. We hypothesize the smaller particle size mode corresponds to nucleation, whereas the larger particle size has formed through condensational growth and coagulation. We present a particle size distribution function that can account for this wide range of distribution variability using two log-normals and two log-exponentials. We implement this particle size distribution for corundum within MITgcm/DISORT for ultra-hot Jupiter TOI-1431b, and compare this work to that of Komacek et al. (2022a), which includes a log-normal roughly corresponding with the larger particle size mode in our distribution. We present the results of this comparison, and discuss the impact of particle size distribution on properties of ultra-hot Jupiters.

Abstract:

Titan’s substantial atmosphere is primarily composed of molecular nitrogen (N2) and methane (CH4), which are dissociated by solar UV photons and subsequently generate a vast chemical network of trace gases. The composition of Titan’s atmosphere is markedly different than that of Saturn, including both the complex molecular inventory and the hitherto measured isotopic ratios – including that of nitrogen (14N/15N). Atmospheric and interior evolution models (e.g., Mandt et al., 2014) indicate that the atmospheres of Saturn and Titan did not form in the same manner or from the same constituents, and that Titan’s atmospheric N2 may have originated from its interior as NH3. The evolution of 14N/15N in Titan’s atmosphere over time does not result in a value comparable to that measured on Saturn and instead is closer to cometary values; this indicates that the origin of Titan’s atmosphere appears to be from protosolar planetesimals enriched in ammonia and not from the sub-Saturnian nebula. However, selective isotopic fractionation of molecular species in Titan’s atmosphere complicates this picture, as the isotopic ratios may vary as a function of altitude (Figure 1). To further constrain the evolution of Titan’s atmosphere – and indeed, its origin – isotopic ratios must be measured throughout its atmosphere, instead of being interpreted from bulk values likely only representative of the stratosphere.While the measurement of Titan’s 14N/15N in N2 (167.7; Niemann et al. 2010) places it firmly below the lower limit derived for Saturn (~350; Fletcher et al., 2014), Titan’s atmospheric nitriles (e.g., HCN, HC3N, CH3CN) are further enriched in 15N, resulting in ratios closer to 70 (Molter et al., 2016; Cordiner et al., 2018; Nosowitz et al., 2025). The variation in nitrogen isotopic ratios between the nitriles and N2 is thought to be the result of higher photolytic efficiency of 15N14N compared to N2 in the upper atmosphere (~900 km), resulting in increased 15N incorporated into nitrogen-bearing species (Liang et al., 2007; Dobrijevic & Loison, 2018; Vuitton et al., 2019). As these species are advected to lower altitudes, the nitrogen isotope ratio may vary vertically (Figure 1, red and black profiles), but previous measurements have only presented bulk atmospheric isotope ratios primarily representing Titan’s stratosphere (Figure 1, blue lines).Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have allowed for the derivation of vertical abundance profiles of Titan’s trace atmospheric species and measurements of N, D, and O-bearing isotopologues (Molter et al., 2016; Serigano et al., 2016; Cordiner et al., 2018; Thelen et al., 2019; Nosowitz et al., 2025). However, vertical isotopic ratio profiles have yet to be derived. Here, we utilize observations acquired with ALMA in July 2022 containing high sensitivity measurements of the HC15N J=4–3 transition at 344.2 GHz (~ 0.87 mm) to investigate vertical variations in the 14N/15N of Titan’s HCN. We compare the results of the vertical 14N/15N profile to those predicted by photochemical models to determine the impact of the isotopic-selective photodissociation of nitrogen-bearing molecular species in Titan’s atmosphere, and the impact of the Saturnian and space environments that vary between model implementations.Figure 1. 14N/15N profile for HCN predicted by photochemical models from Vuitton et al. (2019; black line) and Dobrijevic & Loison (2018; red line). Blue colored bars in the lower atmosphere represent previous HCN nitrogen isotope ratios from Cassini, Herschel, and ground-based (sub)millimeter observations (see Molter et al., 2016, and references therein). Measurements are offset vertically for clarity, and all refer to HC14N/HC15N measurements for the bulk stratosphere.References:Cordiner et al., 2018, The Astrophysical Journal Letters, 859, L15.Dobrijevic & Loison, 2018, Icarus, 307, 371.Fletcher et al., 2014, Icarus, 238, 170.Liang et al., 2007, The Astrophysical Journal Letters, 644, L115.Mandt et al. 2014, The Astrophysical Journal Letters, 788, L24.Molter et al., 2016, The Astronomical Journal, 152, 42.Niemann et al., 2010, Journal of Geophysical Research, 115, E12006.Nosowitz et al., 2025, The Planetary Science Journal, 6, 107.Serigano et al., 2016, The Astrophysical Journal Letters, 821, L8.Thelen et al., 2019, The Astronomical Journal, 157, 219.Vuitton et al., 2019, Icarus, 324, 120.