Atmospheres Of Gas Giants Research Articles

Global climate modelling of Saturn’s atmosphere, Part V: Large-scale vortices

This paper presents an analysis of large-scale vortices in the atmospheres of gas giants, focusing on a detailed study conducted using the Saturn-DYNAMICO global climate model (GCM). Large-scale vortices, a prominent feature of gas giant atmospheres, play a critical role in their atmospheric dynamics. By employing three distinct methods – manual detection, machine learning via artificial neural networks (ANN), and dynamical detection using the Automated Eddy-Detection Algorithm (AMEDA) – we characterise the spatial, temporal, and dynamical properties of these vortices within the Saturn-DYNAMICO GCM. Our findings reveal a consistent production of vortices due to well-resolved eddy-to-mean flow interactions, exhibiting size and intensity distributions broadly in agreement with observational data. However, notable differences in vortex location, size, and concentration highlight the model’s limitations and suggest areas for further refinement. The analysis underscores the importance of zonal wind conditions in influencing vortex characteristics and suggests that more accurate modelling of giant planet vortices may require improved representation of moist convection and jet structure. This study not only provides insights into the dynamics of Saturn’s atmosphere as simulated by the GCM but also offers a framework for comparing vortex characteristics across observations and models of planetary atmospheres.

Accurate reference spectra of HD in an H2–He bath for planetary applications

Context. The hydrogen deuteride (HD) molecule is an important deuterium tracer in astrophysical studies. The atmospheres of gas giants are dominated by molecular hydrogen, and the simultaneous observation of H2 and HD lines provides reliable information on the D/H ratios on these planets. The reference spectroscopic parameters play a crucial role in such studies. Under the thermodynamic conditions encountered in these atmospheres, spectroscopic studies of HD require not only the knowledge of line intensities and positions but also accurate reference data on pressure-induced line shapes and shifts. Aims. Our aim is to provide accurate collision-induced line-shape parameters for HD lines that cover any thermodynamic conditions relevant to the atmospheres of giant planets, namely any relevant temperature, pressure, and perturbing gas composition (the H2–He mixture). Methods. We performed quantum-scattering calculations on our new, highly accurate ab initio potential energy surface (PES), and we used scattering S matrices obtained in this way to determine the collision-induced line-shape parameters. We used cavity ring-down spectroscopy to validate our theoretical methodology. Results. We report accurate collision-induced line-shape parameters for the pure rotational R(0), R(1), and R(2) lines, the most relevant HD lines for investigations of the atmospheres of the giant planets. Besides the basic Voigt-profile collisional parameters (i.e., the broadening and shift parameters), we also report their speed dependences and the complex Dicke parameter, which can influence the effective width and height of the HD lines up to almost a factor of 2 for giant planet conditions. The sub-percent-level accuracy reached in this work is a considerable improvement over previously available data. All the reported parameters (and their temperature dependences) are consistent with the HITRAN database format, hence allowing for the use of the HITRAN Application Programming Interface (HAPI) for generating the beyond-Voigt spectra of HD.

An atlas of resolved spectral features in the transmission spectrum of WASP-189 b with MAROON-X

Exoplanets in the ultra-hot Jupiter regime provide an excellent laboratory for testing the impact of stellar irradiation on the dynamics and chemical composition of gas giant atmospheres. In this study, we observed two transits of the ultra-hot Jupiter WASP-189 b with MAROON-X/Gemini-North to probe its high-altitude atmospheric layers, using strong absorption lines. We derived posterior probability distributions for the planetary and stellar parameters by calculating the stellar spectrum behind the planet at every orbital phase during the transit. This was used to correct the Rossiter–McLaughlin imprint on the transmission spectra. Using differential transmission spectroscopy, we detect strong absorption lines of Ca+, Ba+, Na, Hα, Mg, Fe, and Fe+, providing an unprecedented and detailed view of the atmospheric chemical composition. Ca+ absorption is particularly well suited for analysis through time-resolved narrow-band spectroscopy, owing to its transition lines formed in high-altitude layers. The spectral absorption lines show no significant blueshifts that would indicate high-altitude day-to-night winds, and further analysis is needed to investigate the implications for atmospheric dynamics. These high signal-to-noise observations provide a benchmark data set for testing high-resolution retrievals and the assumptions of atmospheric models. We also simulate observations of WASP-189 b with ANDES/ELT, and show that ANDES will be highly sensitive to the individual absorption lines of a myriad of elements and molecules, including TiO and CO.

Effects of planetary day-night temperature gradients on He 1083 nm transit spectra

A notable fraction of helium observations probing the evaporating atmospheres of short-period gas giants at 1083 nm exhibit a blueshift during transit, which might be indicative of a day-to-night side flow. In this study, we explore the gas dynamic effects of day-to-night temperature contrasts on the escaping atmosphere of a tidally locked planet. Using a combination of 3D hydrodynamic simulations and radiative transfer post-processing, we modeled the transmission spectra of the metastable helium triplet. Our key findings are as follows: (1) Increasing the day-night anisotropy leads to a narrowing of the helium line and an increase in the blueshift of the line centroid of a few km s−1. (2) The velocity shift of the line depends on the line-forming altitude, with higher planetary mass-loss rates causing the line to form at higher altitudes, resulting in a more pronounced velocity shift. (3) A critical point of day-night anisotropy comes about when the blueshift saturates, due to turbulent flows generated by outflow material falling back onto the planet’s night side. (4) A strong stellar wind and the presence of turbulent flows may induce time variations in the velocity shift. Assuming that the day-night temperature gradient is the main cause of the observed blueshifts in the He-1083 nm triplet, the correlation between the velocity shift and day-night anisotropy provides an opportunity to constrain the temperature gradient of the line-forming region.

Coupling haze and cloud microphysics in WASP-39b’s atmosphere based on JWST observations

ABSTRACT We present a study on the coupling of haze and clouds in the atmosphere of WASP-39b. We developed a cloud microphysics model simulating the formation of Na2S and MgSiO3 condensates over photochemical hazes in gas giant atmospheres. We apply this model to WASP-39b, recently observed with the JWST to study how these heterogeneous components may affect the transit spectrum. We simulate both morning and evening terminators independently and average their transit spectra. While MgSiO3 formation has negligible impact on the spectrum, Na2S condensates produce grey opacities in the water band, in agreement with Hubble Space Telescope (HST) and JWST observations. Moreover, the formation of Na2S on the morning side depletes the atmosphere of its sodium content, decreasing the strength of the Na line. Combining morning and evening profiles results in a good fit of the Na observations. These nominal results assume a small Na2S/haze contact angle (5.7°). Using a larger value (61°) reduces the cloud density and opacity, but the effect on the Na profile and spectral line remains identical. In addition, the presence of haze in the upper atmosphere reproduces the ultraviolet (UV)-visible slope observed in the HST and Very Large Telescope data and contributes to the opacity between the water bands at wavelengths below 2 μm. The averaged spectra are rather insensitive to the variation of eddy diffusion and haze mass flux tested in this study, though the UV-visible slope, probing the haze layer above the clouds, is affected. Finally, our disequilibrium chemistry model, including photochemistry, reproduces the SO2 and CO2 absorption features observed.

Acoustic signatures of helium abundance in hydrogen for planetary science

The aim of this work is to model and measure the acoustic signatures of varying mixtures of helium, ortho-hydrogen, and para-hydrogen. In particular, we hope to demonstrate a sensor for helium abundance and hydrogen ortho:para ratio for planetary science missions to Saturn or Uranus. Gas composition as a function of depth is important for understanding atmospheric dynamics and planetary formation of the gas giants but is not well known. In the presence of molecular relaxation, sound speed and absorption in polyatomic gas mixtures become dispersive due to frequency-dependent heat capacities. This may potentially allow the identification of gas composition through relaxational acoustic spectroscopy. We compare theoretical predictions to measurements done in a pressure vessel up to a maximum pressure of 20 bar of relevance to gas giant atmospheres. Experiments for different gas mixtures at various pressures and temperatures are conducted using wide-bandwidth ultrasound between 20 kHz and 10 MHz. A technique is proposed to determine the ratio of hydrogen to helium using speed of sound and attenuation spectra. This approach may be further utilized to determine the ortho:para ratio. Challenges include providing sufficient bandwidth and adjusting for temperature, diffraction, and reflections. [Work supported from NASA Center Innovation Fund.]

Gas Giant Simulations of Eddy‐Driven Jets Accompanied by Deep Meridional Circulation

AbstractJupiter's atmosphere comprises several dynamical regimes: the equatorial eastward flows and surrounding retrograde jets; the midlatitudes, with the eddy‐driven, alternating jet‐streams and meridional circulation cells; and the jet‐free turbulent polar region. Despite intensive research conducted on each of these dynamical regimes over the past decades, they remain only partially understood. Saturn's atmosphere also encompasses similar distinguishable regimes, but observational evidence for midlatitude deep meridional cells is lacking. Models offer a variety of explanations for each of these regions, but only a few are capable of simulating more than one of the regimes at once. This study presents new numerical simulations using a 3D deep anelastic model that can reproduce the equatorial flows as well as the midlatitudinal pattern of the mostly barotropic, alternating eddy‐driven jets and the meridional circulation cells accompanying them. These simulations are consistent with recent Juno mission gravity and microwave data. We find that the vertical eddy momentum fluxes are as important as the meridional eddy momentum fluxes, which drive the midlatitudinal circulation on Earth. In addition, we discuss the parameters controlling the number of midlatitudinal jets/cells, their extent, strength, and location. We identify the strong relationship between meridional circulation and the zonal jets in a deep convection setup, and analyze the mechanism responsible for their generation and maintenance. The analysis presented here provides another step in the ongoing pursuit of understanding the deep atmospheres of gas giants.

Experimental Investigation of the Photochemical Production of Hydrocarbons in Warm Gas Giant Exoplanet Atmospheres

In warm (equilibrium temperature <1000 K) gas giant exoplanet atmospheres, the observation of trace species in abundances deviating from thermochemical equilibrium predictions could be used as an indicator of disequilibrium chemical processes, such as photochemistry. To predict which compounds could be used as such tracers, it is therefore essential to study how photochemical processes affect their abundances. For this purpose, we investigated experimentally the efficiency of the photochemical formation of hydrocarbons in gas mixtures representative of warm gas giant atmospheres as a function of the gas temperature at millibar pressures. We find that, compared to thermal reactions alone, photochemistry efficiently promotes, under the studied conditions, the formation of hydrocarbons, with the detection of acetylene, ethane, and propane, as well as carbon monoxide. Therefore, our results confirm the importance of photochemistry in exoplanet atmospheres as a disequilibrium process. Ethane is the major hydrocarbon formed in our experiments, in apparent contradiction with the prediction by thermo-photochemical models that acetylene should be the main hydrocarbon product. We also observe an evolution of the hydrocarbon production efficiency as a function of the temperature, a behavior not reproduced by a 0D thermo-photochemical model. Additional studies are necessary to definitively understand the origin of the differences between the experimental and modeling results and to infer the importance of our results for understanding hydrocarbon formation in warm gas giant exoplanet atmospheres. Finally, our work demonstrates the importance of experimental studies together with modeling studies to accurately interpret, understand, and predict observations of exoplanet atmospheres.

Temperature–chemistry coupling in the evolution of gas giant atmospheres driven by stellar flares

ABSTRACT The effect of enhanced UV irradiation associated with stellar flares on the atmospheric composition and temperature of gas giant exoplanets was investigated. This was done using a 1D radiative-convective-chemical model with self-consistent feedback between the temperature and the non-equilibrium chemistry. It was found that flare-driven changes to chemical composition and temperature give rise to prolonged trends in evolution across a broad range of pressure levels and species. Allowing feedback between chemistry and temperature plays an important role in establishing the quiescent structure of these atmospheres, and determines their evolution due to flares. It was found that cooler planets are more susceptible to flares than warmer ones, seeing larger changes in composition and temperature, and that temperature–chemistry feedback modifies their evolution. Long-term exposure to flares changes the transmission spectra of gas giant atmospheres; these changes differed when the temperature structure was allowed to evolve self-consistently with the chemistry. Changes in spectral features due to the effects of flares on these atmospheres can be associated with changes in composition. The effects of flares on the atmospheres of sufficiently cool planets will impact observations made with JWST. It is necessary to use self-consistent models of temperature and chemistry in order to accurately capture the effects of flares on features in the transmission spectra of cooler gas giants, but this depends heavily on the radiation environment of the planet.

Moist Convection in the Giant Planet Atmospheres

The outer planets of our Solar System display a myriad of interesting cloud features, of different colors and sizes. The differences between the types of observed clouds suggest a complex interplay between the dynamics and chemistry at play in these atmospheres. Particularly, the stark difference between the banded structures of Jupiter and Saturn vs. the sporadic clouds on the ice giants highlights the varieties in dynamic, chemical and thermal processes that shape these atmospheres. Since the early explorations of these planets by spacecrafts, such as Voyager and Voyager 2, there are many outstanding questions about the long-term stability of the observed features. One hypothesis is that the internal heat generated during the formation of these planets is transported to the upper atmosphere through latent heat release from convecting clouds (i.e., moist convection). In this review, we present evidence of moist convective activity in the gas giant atmospheres of our Solar System from remote sensing data, both from ground- and space-based observations. We detail the processes that drive moist convective activity, both in terms of the dynamics as well as the microphysical processes that shape the resulting clouds. Finally, we also discuss the effects of moist convection on shaping the large-scale dynamics (such as jet structures on these planets).

Impact of stellar flares on the chemical composition and transmission spectra of gaseous exoplanets orbiting M dwarfs

Context. Stellar flares of active M dwarfs can affect the atmospheric composition of close-orbiting gas giants, and can result in time-dependent transmission spectra. Aims. We aim to examine the impact of a variety of flares, differing in energy, duration, and occurrence frequency, on the composition and transmission spectra of close-orbiting, tidally locked gaseous planets with climates dominated by equatorial superrotation. Methods. We used a series of pseudo-2D photo- and thermochemical kinetics models, which take advection by the equatorial jet stream into account, to simulate the neutral molecular composition of a gaseous planet (Teff = 800 K) that orbits a M dwarf during artificially constructed flare events. We then computed transmission spectra for the evening and morning limb. Results. We find that the upper regions (i.e. below 10 μbar) of the dayside and evening limb are heavily depleted in CH4 and NH3 up to several days after a flare event with a total radiative energy of 2 × 1033 erg. Molar fractions of C2H2 and HCN are enhanced up to a factor three on the nightside and morning limb after day-to-nightside advection of photodissociated CH4 and NH3. Methane depletion reduces transit depths by 100–300 parts per million (ppm) on the evening limb and C2H2 production increases the 14 μm feature up to 350 ppm on the morning limb. We find that repeated flaring drives the atmosphere to a composition that differs from its pre-flare distribution and that this translates to a permanent modification of the transmission spectrum. Conclusions. We show that single high-energy flares can affect the atmospheres of close-orbiting gas giants up to several days after the flare event, during which their transmission spectra are altered by several hundred ppm. Repeated flaring has important implications for future retrieval analyses of exoplanets around active stars, as the atmospheric composition and resulting spectral signatures substantially differ from models that do not include flaring.

Line mixing study of carbon monoxide near [formula omitted] broadened by nitrogen, helium, and hydrogen

We present quantitative, broadband absorbance measurements of the fundamental rovibrational band of carbon monoxide (CO) between 1965 and 2230 cm−1 in bath gases of nitrogen (N2), helium (He), and hydrogen (H2). These measurements are then compared to two constructed models capable of reproducing the effects of line mixing present in our measured results. The static cell measurements were taken using a narrow-linewidth, broad-scan external-cavity quantum-cascade laser at pressures of 15–35 atm and temperatures of 293, 453 (CO/H2) and 802 K (CO/N2, CO/He). Our first line mixing approach, based on the modified exponential gap (MEG) law with a fitted inter-branch factor, shows improved agreement with the measured spectra across different pressures and broadening partners relative to purely Lorentzian models. At the elevated temperatures, similar agreement is observed; however, a mismatch is present between extrapolated HITRAN broadening parameters and those observed in the measured spectra. This is likely due to the known deficiency of the single power law over large temperature ranges, and hence a minor scaling of the line-by-line temperature-dependence exponents is incorporated that is supported by previous studies in the literature. Our second, more empirical line mixing approach involves extracting MEG line mixing parameters through a direct fit to the measured spectra. The Direct Fit method bypasses the need for known line shape parameters and produces even stronger agreement with measured data, with a CO/H2 root-mean-square error of 0.4% at the highest-number-density condition of 293 K and 35 atm. The line mixing models presented and discussed will be useful for interpreting future satellite and telescope observations of CO from deeper, higher-number-density layers of exoplanetary gas-giant atmospheres, consisting of mainly H2 and He.

H2, He, and CO2 Pressure-induced Parameters for the HITRAN Database. II. Line Lists of CO2, N2O, CO, SO2, OH, OCS, H2CO, HCN, PH3, H2S, and GeH4

In recent years, extended efforts have been made to increase the potential for modeling and interpreting the spectra of planetary atmospheres using the HITRAN database. A significant objective is to provide broadening parameters due to the ambient pressure of He, H2, and CO2 gases. Since hydrogen and helium are the main constituents in the atmospheres of gas giants, and carbon dioxide dominates the atmospheres of many rocky planets, these spectroscopic data are essential for radiative transfer models dedicated to planetary atmospheres. In HITRAN2016, the He-, H2- and CO2-broadening parameters and their temperature dependencies, and in some cases pressure-induced shifts, were added to the line lists of CO, SO2, NH3, HF, HCl, OCS, and C2H2. This work describes a further expansion introduced in the HITRAN2020 edition. In particular, relevant data for the line lists of CO2, N2O, OH, H2CO, HCN, PH3, H2S, and GeH4 were added, while those for CO, SO2, and OCS were revised. The new data are based on the semiempirical models constructed on available and validated experimental measurements and theoretical predictions. These models strongly depend on the extent and quality of the available data. The paper explains how to use the online interface or the HITRAN Application Programming Interface (HAPI) to retrieve these data from the database. Examples of calculating a molecule’s spectra in a mixture of buffer-gases using HAPI are also provided. We also provide a set of Python codes allowing one to populate any line list of corresponding molecules with relevant broadening parameters.

Mineral snowflakes on exoplanets and brown dwarfs

Context. Brown dwarfs and exoplanets provide unique atmospheric regimes that hold information about their formation routes and evolutionary states. Cloud particles form through nucleation, condensation, evaporation, and collisions, which affect the distribution of cloud particles in size and throughout these atmospheres. Cloud modelling plays a decisive role in understanding these regimes. Aims. Modelling mineral cloud particle formation in the atmospheres of brown dwarfs and exoplanets is a key element in preparing for missions and instruments like CRIRES+, JWST, and ARIEL, as well as possible polarimetry missions like PolStar. The aim is to support the increasingly detailed observations that demand greater understanding of the microphysical cloud processes. Methods. We extend our kinetic cloud formation model that treats nucleation, condensation, evaporation, and settling of mixed material cloud particles to consistently model cloud particle-particle collisions. The new hybrid code Hybrid moments (Ls) and Size (HyLandS) is then applied to a grid of Drift-Phoenix (Tgas, pgas) profiles. Effective medium theory and Mie theory are used to investigate the optical properties. Results. Turbulence proves to be the main driving process of particle-particle collisions, with collisions becoming the dominant process in the lower atmosphere (p &gt; 10−4 bar) at the cloud base. Particle-particle collisions produce one of three outcomes for brown dwarf and gas-giant atmospheres: fragmenting atmospheres (log10(g[cms−2])=3.0) coagulating atmospheres (log10(g)=5.0), Teff ≤1800K) or condensational growth dominated atmospheres (log10(g) = 5.0, Teff &gt; 1800 K). Cloud particle opacity slope at optical wavelengths (Hubble) is increased with fragmentation, as are the silicate features at JWST NIRSpec, JWST MIRI, and ARIEL AIRS wavelengths. Conclusions. The hybrid moment-bin method HyLandS demonstrates the feasibility of combining a moment and a bin method for cloud modelling, whilst assuring element conservation. It provides a powerful and fast tool for capturing general trends of particle collisions, consistently with other microphysical growth processes. Collisions are an important process in exoplanet and brown dwarf atmospheres, but cannot be assumed to be hit-and-stick only. The spectral effects of cloud particle collisions in both optical and mid-infrared wavelengths complicate inferences of cloud particle size and material composition from observational data.

Using HITRAN to model opacities for planetary atmospheres: test case of microwave spectra of NH3, SO2, and PH3

ABSTRACT The latest version of the HITRAN molecular spectroscopic data base, HITRAN2020, has recently been released featuring many updates, including line-by-line broadening parameters (and their temperature dependence) appropriate for the dominant constituents of planetary atmospheres. In this work, line shape codes suitable for calculating microwave spectra have been implemented within the HITRAN Application Programming Interface (HAPI). These new additions allow for spectroscopic calculations of microwave absorbing species pertinent to current and future studies of the atmospheres of Jupiter and Venus, and more generally for the atmospheres of gas giants and rocky planets. The inversion spectrum of the NH3 molecule broadened by H2, He, and H2O dominates the microwave region of Jupiter, whereas for Venus, accurate spectroscopic data of SO2 broadened by CO2 are necessary in order to determine its significance, if any, on the reported detection of PH3 in the Venusian upper cloud deck. Comparisons have been made to available microwave laboratory opacities and the following results illustrate that HITRAN data can be used in conjunction with HAPI to reproduce the existing experimental measurements and provide reliable calculation of planetary opacities. Users should be mindful regarding selection of appropriate parameters in HITRAN and selecting suitable line shape functions in HAPI, depending on the spectral region, target molecular species, as well as ambient chemical and thermodynamic conditions.

Super stellar abundances of alkali metals suggest significant migration for hot Jupiters

ABSTRACT We investigate the origin of the measured overabundance of alkali metals in the atmospheres of hot gas giants, relative to both their host stars and their atmospheric water abundances. We show that formation exterior to the water snow line followed by inward disc-driven migration results in excess accretion of oxygen-poor, refractory-rich material from within the snow-line. This naturally leads to enrichment of alkali metals in the planetary atmosphere relative to the bulk composition of its host star but relative abundances of water that are similar to the stellar host. These relative abundances cannot be explained by in situ formation which places the refractory elements in the planetary deep interior rather than the atmosphere. We therefore suggest that the measured compositions of the atmospheres of hot Jupiters are consistent with significant migration for at least a subset of hot gas giants. Our model makes robust predictions about atmospheric composition that can be confirmed with future data from JWST and Ariel.

Calculation of rovibrational eigenstates of H3+ using ScalIT

H 3 + is a key player in molecular astrophysics, appearing in the interstellar medium and in the atmospheres of gas giants. It also plays an important role in star formation, and it has also been detected in supernova remnants. In theoretical chemistry, H3+ has long been a benchmark polyatomic system for high-level electronic-structure computations, as well as for quantum dynamics studies. In this work, exact quantum dynamical calculations are carried out for H3+, using the ScalIT suite of parallel codes, applied to two spectroscopically accurate potential energy surfaces. Specifically, rovibrational energy levels and wavefunctions are computed and labeled. Sixty vibrational states (for J = 0) are first determined, and then, rotational excitations for each of these “vibrational parent” states are computed up to total angular momentum J = 46, which is the highest value for which bound states of this molecule exist (D0 ∼ 35 000 cm−1). For these calculations, a very tight basis set convergence of a few 10−4 cm−1 (or less) has been achieved for almost all the computed energy levels. Where comparisons can be made, our results are found to agree well with earlier calculations and experimental data.

Time-resolved Rotational Velocities in the Upper Atmosphere of WASP-33 b*

Abstract While steady empirical progress has been made in understanding the structure and composition of hot-planet atmospheres, direct measurements of velocity signatures, including winds, rotation, and jets, have lagged behind. Quantifying atmospheric dynamics of hot planets is critical for a complete understanding of their atmospheres, and such measurements may even illuminate other planetary properties, such as magnetic field strengths. In this manuscript we present the first detection of the Balmer lines Hα and Hβ in the atmosphere of the ultra-hot Jupiter WASP-33 b. Using atmospheric models that include the effects of atmospheric dynamics, we show that the shape of the average Balmer line transmission spectrum is consistent with rotational velocities in the planet’s thermosphere of km s−1. We also measure a low-significance day- to nightside velocity shift of km s−1 in the transmission spectrum, which is naturally explained by a global wind across the planet’s terminator. In a separate analysis the time-resolved velocity centroids of individual transmission spectra show unambiguous evidence of rotation, with a best-fit velocity of km s−1, consistent with the value of v rot derived from the shape of the average Balmer line transmission spectrum. Our observations and analysis confirm the power of time-resolved transmission spectra with a high signal-to-noise ratio to measure the velocity structures in exoplanet atmospheres. The high rotational and wind velocities we measure highlight the need for more detailed 3D global climate simulations of the rarefied upper atmospheres of ultra-hot gas giants.

Chemical Evolution in a Protoplanetary Disk within Planet Carved Gaps and Dust Rings

Abstract Recent surveys of protoplanetary disks show that substructure in dust thermal continuum emission maps is common in protoplanetary disks. These substructures, most prominently rings and gaps, shape and change the chemical and physical conditions of the disk, along with the dust size distributions. In this work, we use a thermochemical code to focus on the chemical evolution that is occurring within the gas-depleted gap and the dust-rich ring often observed behind it. The compositions of these spatial locations are of great import, as the gas and ice-coated grains will end up being part of the atmospheres of gas giants and/or the seeds of rocky planets. Our models show that the dust temperature at the midplane of the gap increases, enough to produce local sublimation of key volatiles and pushing the molecular layer closer to the midplane, while it decreases in the dust-rich ring, causing a higher volatile deposition onto the dust grain surfaces. Further, the ring itself presents a freeze-out trap for volatiles in local flows powered by forming planets, becoming a site of localized volatile enhancement. Within the gas-depleted gap, the line emission depends on several different parameters, such as the depth of the gap in surface density, the location of the dust substructure, and the abundance of common gas tracers, such as CO. In order to break this uncertainty between abundance and surface density, other methods, such as disk kinematics, become necessary to constrain the disk structure and its chemical evolution.

Deep model simulation of polar vortices in gas giant atmospheres

ABSTRACTThe Cassini and Juno probes have revealed large coherent cyclonic vortices in the polar regions of Saturn and Jupiter, a dramatic contrast from the east–west banded jet structure seen at lower latitudes. Debate has centred on whether the jets are shallow, or extend to greater depths in the planetary envelope. Recent experiments and observations have demonstrated the relevance of deep convection models to a successful explanation of jet structure, and cyclonic coherent vortices away from the polar regions have been simulated recently including an additional stratified shallow layer. Here we present new convective models able to produce long-lived polar vortices. Using simulation parameters relevant for giant planet atmospheres we find flow regimes of geostrophic turbulence (GT) in agreement with rotating convection theory. The formation of large-scale coherent structures occurs via 3D upscale energy transfers. Our simulations generate polar characteristics qualitatively similar to those seen by Juno and Cassini: They match the structure of cyclonic vortices seen on Jupiter; or can account for the existence of a strong polar vortex extending downwards to lower latitudes with a marked spiral morphology, and the hexagonal pattern seen on Saturn. Our findings indicate that these vortices can be generated deep in the planetary interior. A transition differentiating these two polar flows regimes is described, interpreted in terms of force balances and compared with shallow atmospheric models characterizing polar vortex dynamics in giant planets. In addition, heat transport properties are investigated, confirming recent scaling laws obtained with reduced models of GT.