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The existence of organic matter presenting a high molecular diversity in extraterrestrial environments is well documented. To understand the origin of this organic diversity, laboratory experiments were developed and showed that irradiation and thermal alteration of simple molecules such as methanol, water, and ammonia in conditions mimicking astrophysical ice environments. Ices containing water, methanol, and ammonia (H2O: MeOH: NH3) photolyzed and monitored by infrared spectroscopy, while the organic matter formed at room temperature was analyzed in situ with infrared spectroscopy and ex situ with high-resolution mass spectrometry. Those ices irradiated at 77 K and 10−8 mbar shows a significant organic molecular diversity: residual organic compounds contain up to 78 C, 188 H, 123 N, and 37 O. Most of them contains all four CHNO atoms (76–86 per cent), followed by CHO (11–17 per cent), and CHN compounds (5–6 per cent). CHNO and CHO compounds are more aliphatic (34–53 per cent), while CHN compounds are mostly condensed aromatics (83–90 per cent). In this work, our objective is to investigate impacts of environment on this organic molecular diversity by focusing on three parameters: photon dose, pressure, and heating rate during the warming process. Analyses of the residue formed showed that the heating rate and pressure weakly alter the abundance of the final organic material, while the irradiation rate reduced its abundance at high photon doses by a factor of 8. These results give insights on the impact of icy environment conditions in the evolution of astrophysical organic matter. [ABSTRACT FROM AUTHOR]

Head-on giant impacts (collisions between planet-sized bodies) are frequently used to study the planet formation process as they present an extreme configuration where the two colliding bodies are greatly disturbed. With limited computing resources, focusing on these extreme impacts eases the burden of exploring a large parameter space. Results from head-on impacts are often then extended to study oblique impacts with angle corrections or used as initial conditions for other calculations, for example, the evolution of ejected debris. In this study, we conduct a detailed investigation of the thermodynamic and energy budget evolution of high-energy head-on giant impacts, entering the catastrophic impacts regime, for target masses between 0.001 and 12 M |$_{{\oplus }}$|⁠. We demonstrate the complex interplay of gravitational forces, shock dynamics, and thermodynamic processing in head-on impacts at high energy. Our study illustrates that frequent interactions of core material with the liquid side of the vapour curve could have cumulative effects on the post-collision remnants, leading to fragmentary disintegration occurring at lower impact energy. This results in the mass of the largest remnant diverging significantly from previously developed scaling laws. These findings suggest two key considerations: (1) head-on planetary collisions for different target masses do not behave similarly, so caution is needed when applying scaling laws across a broad parameter space; and (2) an accurate model of the liquid-vapour phase boundary is essential for modelling giant impacts. Our findings highlight the need for careful consideration of impact configurations in planetary formation studies, as head-on impacts involve a complex interplay between thermodynamic processing, shocks, gravitational forces, and other factors. [ABSTRACT FROM AUTHOR]

Water ice plays a crucial role throughout the different stages of planetary evolution and is abundant in the Universe. However, its presence and nature in debris discs of exoplanetary systems are not yet strongly established observationally. In this study, we quantify and discuss the impact of ice parameters such as volume fraction |${\mathcal {F}}_{\rm ice}$|⁠ , blow-out grain size, size distribution, and its phase on the observational appearance of debris discs, considering the diverse nature of these systems around stellar spectral types ranging from A to M. Our findings reveal that the prominent ice features at approximately 2.7 and 3.3  μ m depend on both the water ice fraction |${\mathcal {F}}_{\rm ice}$| and the scattering angle, with backscattering geometries yielding the most prominent signatures. When the phase function is considered and data are not background limited, strong forward and backward scattering (near edge-on discs) are expected to yield the strongest detections in images/spectra for A or F-type stars, while scattering angle matters less for later type stars. The Fresnel peak at 3.1  μ m serves as a viable discriminant for the transitional phase (crystalline/amorphous), while simultaneously constraining the water ice temperature. For JWST imaging, we find that the F 356 W and F 444 W filter combination is most effective for constraining the grain size distribution, while the F 356 W and F 277 W filter combination provides better constraints on the ice fraction |${\mathcal {F}}_{\rm ice}$| in debris discs. However, degeneracy between the grain size distribution and ice fraction when using photometric flux ratios means that obtaining robust constraints will likely require more than two filters, or spectroscopic data. [ABSTRACT FROM AUTHOR]

Particle–particle and particle–gas processes significantly impact planetary precursors such as dust aggregates and planetesimals. We investigate gas permeability (⁠|$\kappa$|⁠) in 12 granular samples, mimicking planetesimal dust regoliths. Using parabolic flights, this study assesses how gravitational compression – and lack thereof – influences gas permeation, impacting the equilibrium state of low-gravity objects. Transitioning between micro- and hyper-gravity induces granular sedimentation dynamics, revealing collective dust–grain aerodynamics. Our experiments measure |$\kappa$| across Knudsen number (Kn) ranges, reflecting transitional flow. Using mass and momentum conservation, we derive |$\kappa$| and calculate pressure gradients within the granular matrix. Key findings: (i) As confinement pressure increases with gravitational load and mass flow, |$\kappa$| and average pore space decrease. This implies that a planetesimal's unique dust-compaction history limits subsurface volatile outflows. (ii) The derived pressure gradient enables tensile strength determination for asteroid regolith simulants with cohesion. This offers a unique approach to studying dust-layer properties when suspended in confinement pressures comparable to the equilibrium state on planetesimals surfaces, which will be valuable for modelling their collisional evolution. (iii) We observe a dynamical flow symmetry breaking when granular material moves against the pressure gradient. This occurs even at low Reynolds numbers, suggesting that Stokes numbers for drifting dust aggregates near the Stokes–Epstein transition require a drag force modification based on permeability. [ABSTRACT FROM AUTHOR]

Context. When retrieving exoplanet atmospheric characteristics from spectroscopic observations, parameter estimation results strongly depend on the chosen forward model. In the era of the James Webb Space Telescope (JWST) and other next-generation facilities, the increased signal-to-noise ratio (S/N), wavelength coverage, and spectral resolution of observations warrant closer investigations into factors that could inadvertently bias the results of these retrievals. Aims. We aim to investigate the impact of utilising multi-point pressure–temperature (p–T) profiles of varying complexity on the retrieval of synthetically generated hot-Jupiter transmission spectra modelled after state-of-the-art observations of the hot Jupiter WASP-39 b with JWST. Methods. We performed homogenised atmospheric retrievals with the TauREx retrieval framework on a sample of synthetically generated transmission spectra, accounting for varying cases of underlying p–T profiles, cloud-top pressures, and expected noise levels. These retrievals are performed using a fixed-pressure multi-point p–T prescription with increasing complexity, ranging from isothermal to an eleven-point profile. We evaluated the performance of the retrievals based on the Bayesian model evidence, and the accuracy of the retrievals was compared to the known input parameters. Results. We find that performing atmospheric retrievals using an isothermal prescription for the pressure–temperature profile consistently results in wrongly retrieved atmospheric parameters when compared to the known input parameters. For an underlying p–T profile with a fully positive lapse rate, we find that a two-point profile is sufficient to retrieve the known atmospheric parameters, while under the presence of an atmospheric temperature inversion, we find that a more complex profile is necessary. Conclusions. Our investigation shows that, for a data quality scenario mirroring state-of-the-art observations of a hot Jupiter with JWST, an isothermal p–T prescription is insufficient to correctly retrieve the known atmospheric parameters. We find a model complexity preference dependent on the underlying pressure–temperature structure, but we argue that a p–T prescription on the complexity level of a four-point profile should be preferred. This represents the overlap between the lowest number of free parameters and the highest model preference in the cases investigated in this work. [ABSTRACT FROM AUTHOR]

Jupiter's icy moon Ganymede has a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only atomic hydrogen and oxygen have been directly detected in this exosphere. Here, we present observations of Ganymede's CO2 exosphere obtained with the James Webb Space Telescope. CO2 gas is observed over different terrain types, mainly over those exposed to intense Jovian plasma irradiation, as well as over some bright or dark terrains. Despite warm surface temperatures, the CO2 abundance over equatorial subsolar regions is low. CO2 vapor has the highest abundance over the north polar cap of the leading hemisphere, reaching a surface pressure of 1 pbar. From modeling we show that the local enhancement observed near 12 h local time in this region can be explained by the presence of cold traps enabling CO2 adsorption. However, whether the release mechanism in this high-latitude region is sputtering or sublimation remains unclear. The north polar cap of the leading hemisphere also has unique surface-ice properties, probably linked to the presence of the large atmospheric CO2 excess over this region. These CO2 molecules might have been initially released in the atmosphere after the radiolysis of CO2 precursors, or from the sputtering of CO2 embedded in the H2O ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO2 precursors. CO2 molecules would then be redistributed via cold trapping on ice-rich terrains of the polar cap and be diurnally released and redeposited on these terrains. Ganymede's CO2 exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons. [ABSTRACT FROM AUTHOR]

Aims. Following several reports announcing the detection or non-detection of minor species above the clouds of Venus, we have searched for other possible signatures of PH3, HCN, and NH3 in the infrared range. Methods. Since 2012, we have performed ground-based observations of Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified spectral intervals where transitions of PH3 (around 955 cm−1), HCN (around 747 cm−1), and NH3 (around 951cm−1) are present. Results. From the absence of any feature at these frequencies, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 3 ppbv for the PH3 mixing ratio, 0.5 ppbv for HCN, and 0.3 ppbv for NH3, assuming that these species have a constant mixing ratio throughout the atmosphere. Maps of the Venus disk recorded at the center position of the lines show that there is no evidence for local detection anywhere over the Venus disk. Conclusions. Our results bring new constraints on the maximum abundance of these species at the cloud top and in the lower mesosphere of Venus. [ABSTRACT FROM AUTHOR]

Motivated by the observed ~30% variations in flux from the L7 dwarf VHS 1256 b, we subjected its time-resolved Hubble Space Telescope (HST) WFC3 spectra (measured in two epochs: 2018 and 2020), as well as medium-resolution Very Large Telescope (VLT) X-shooter and Early Release Science James Webb Space Telescope (JWST) spectra to a suite of both standard Bayesian (nested sampling) and machine-learning (random forest) retrievals. We find that both HST and VLT data require vertically varying abundance profiles of water in order to model the spectra accurately. Despite the large flux variations observed in the HST data, the temporal variability cannot be attributed to a single varying atmospheric property. The retrieved atmospheric quantities are consistent with being invariant across time. However, we find that model grids offer relatively poor fits to the measured HST spectra and are unsuitable for quantifying the temporal variability of atmospheric properties. Additionally, our analysis of JWST spectra using model grids indicates consistency in terms of the retrieved properties across different wavelength channels. Despite the temporal variability in flux, the retrieved properties between HST and VLT, as well those as between HST and JWST, are consistent within the respective posterior uncertainties. Such an outcome bodes well for future retrieval analyses of exoplanetary atmospheres, which are expected to exhibit weaker flux variations. [ABSTRACT FROM AUTHOR]

Context. The known population of short-period giant exoplanets around M-dwarf stars is slowly growing. These planets present an extraordinary opportunity for atmospheric characterisation and defy our current understanding of planetary formation. Furthermore, clouds and hazes are ubiquitous in warm exoplanets, but their behaviour is still poorly understood. Aims. We studied the case of a standard warm Jupiter around an M-dwarf star to show the opportunity of this exoplanet population for atmospheric characterisation. We aimed to derive the cloud, haze, and chemical budget of such planets using JWST. Methods. We leveraged a 3D global climate model, the generic PCM, to simulate the cloudy and cloud-free atmosphere of warm Jupiters around an M dwarf. We then post-processed our simulations to produce spectral phase curves and transit spectra as would be seen with JWST. Results. We show that, using the amplitude and offset of the spectral phase curves, we can directly infer the presence of clouds and hazes in the atmosphere of such giant planets. Chemical characterisation of multiple species is possible with an unprecedented signal- to-noise ratio, using the transit spectrum in one single visit. In such atmospheres, NH3 could be detected for the first time in a giant exoplanet. We make the case that these planets are key to understanding the cloud and haze budget in warm giants. Finally, such planets are targets of great interest for Ariel. [ABSTRACT FROM AUTHOR]

We present improved empirical density profiles of Uranus and interpret them in terms of their temperature and composition using a new random algorithm. The algorithm to determine the temperature and composition is agnostic with respect to the temperature gradient in non-isentropic regions and chooses amongst all possible gradients randomly that are stable against convection and correspond to an Equation of State (EoS) compatible composition. Our empirical models are based on an efficient implementation of the Theory of Figures (ToF) up to tenth order including a proper treatment of the atmosphere. The accuracy of tenth order ToF enables us to present accurate calculations of the gravitational moments of Uranus up to J14: J6 = (5.3078 ± 0.3312) 10−7, J8 = (−1.1114 ± 0.1391) 10−8, J10 = (2.8616 ± 0.5466) 10−10, J12 = (−8.4684 ± 2.0889) 10−12, and J14 = (2.7508 ± 0.7944) 10−13. We consider two interior models of Uranus that differ with respect to the maximal number of materials allowed per layer of Uranus (three versus four composition components). The case with three materials does not allow Hydrogen and Helium (H-He) in deeper parts of Uranus and results in a higher water (H2O) abundance which leads to lower central temperatures. On the other hand, the models with four materials allow H-He to be mixed into the deeper interior and lead to rock-dominated solutions. We find that these four composition components' models are less reliable due to the underlying empirical models' incompatibility with realistic Brunt frequencies. Most of our models are found to be either purely convective with the exception of boundary layers, or only convective in the outermost region above ~80% of the planets' radius rU. Almost all of our models possess a region ranging between ~(0.75–0.9) rU that is convective and consists of ionic H2O which could explain the generation of Uranus' magnetic field. [ABSTRACT FROM AUTHOR]

Context. More than 15 years after its landing on the surface of Titan, the data returned by the Huygens probe remain the only available in situ information on Titan's lower atmosphere and its methane content. Aims. In this work, we present a reanalysis of the Huygens probe data obtained by the Gas Chromatograph Mass Spectrometer (GCMS) instrument on board Huygens. GCMS measured the atmospheric composition almost continuously during the Huygens probe descent by acquiring mass spectra between 145 km of altitude and Titan's surface. We first focus on the recollection, reconstruction, and recalibration of the GCMS dataset to facilitate similar future work. Methods. We then reevaluate the methane vertical profile in Titan's lower atmosphere by applying novel mass spectra data-treatment methods to this dataset. Results. In addition to finding a slightly lower methane mixing ratio than those previously reported using GCMS measurements above the Huygens probe landing site, our work has revealed several kilometric to subkilometric-scale oscillations in the methane vertical profile below 30 km of altitude. Conclusions. We discuss several hypotheses that could explain these features, such as multiple layers of optically thin clouds or local convection cells, and strongly encourage the reanalysis of other Huygens datasets to further investigate these variations in the methane mixing ratio. [ABSTRACT FROM AUTHOR]

Aims. Following several reports announcing the detection or non-detection of minor species above the clouds of Venus, we have searched for other possible signatures of PH3, HCN, and NH3 in the infrared range. Methods. Since 2012, we have performed ground-based observations of Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified spectral intervals where transitions of PH3 (around 955 cm−1), HCN (around 747 cm−1), and NH3 (around 951cm−1) are present. Results. From the absence of any feature at these frequencies, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 3 ppbv for the PH3 mixing ratio, 0.5 ppbv for HCN, and 0.3 ppbv for NH3, assuming that these species have a constant mixing ratio throughout the atmosphere. Maps of the Venus disk recorded at the center position of the lines show that there is no evidence for local detection anywhere over the Venus disk. Conclusions. Our results bring new constraints on the maximum abundance of these species at the cloud top and in the lower mesosphere of Venus. [ABSTRACT FROM AUTHOR]

We report the spectroscopic confirmation and fundamental properties of TOI |$-$| 757 b, a mini |$-$| Neptune on a 17.5 |$-$| d orbit transiting a bright star (⁠|$V\, =\, 9.7$| mag) discovered by the TESS mission. We acquired high |$-$| precision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired space |$-$| borne transit photometry with the CHEOPS space telescope to place stronger constraints on the planet radius, supported with ground |$-$| based LCOGT photometry. WASP and KELT photometry were used to help constrain the stellar rotation period. We also determined the fundamental parameters of the host star. We find that TOI |$-$| 757 b has a radius of |$R_{\mathrm{p}} = 2.5 \pm 0.1 R_{\oplus }$| and a mass of |$M_{\mathrm{p}} = 10.5^{+2.2}_{-2.1} M_{\oplus }$|⁠ , implying a bulk density of |$\rho _{\text{p}} = 3.6 \pm 0.8$| g cm |$^{-3}$|⁠. Our internal composition modelling was unable to constrain the composition of TOI |$-$| 757 b, highlighting the importance of atmospheric observations for the system. We also find the planet to be highly eccentric with e = 0.39 |$^{+0.08}_{-0.07}$|⁠ , making it one of the very few highly eccentric planets among precisely characterized mini |$-$| Neptunes. Based on comparisons to other similar eccentric systems, we find a likely scenario for TOI |$-$| 757 b's formation to be high eccentricity migration due to a distant outer companion. We additionally propose the possibility of a more intrinsic explanation for the high eccentricity due to star |$-$| star interactions during the earlier epoch of the Galactic disc formation, given the low metallicity and older age of TOI |$-$| 757. [ABSTRACT FROM AUTHOR]

This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted on to seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Rogers et al. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulphur volatile contents, including one white dwarf that shows the most enhanced sulphur abundance seen to date. Three white dwarfs show tentative evidence (2–3 |$\sigma$|⁠) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material. One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important. Less than 1 per cent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies. From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase. [ABSTRACT FROM AUTHOR]

White dwarf atmospheres are frequently polluted by material from their own planetary systems. Absorption features from Ca, Mg, Fe, and other elements can provide unique insights into the provenance of this exoplanetary material, with their relative abundances being used to infer accretion of material with core- or mantle-like composition. Across the population of white dwarfs, the distribution of compositions reveals the prevalence of geological and collisional processing across exoplanetary systems. By predicting the distribution of compositions in three evolutionary scenarios, this work assesses whether they can explain current observations. We consider evolution in an asteroid belt analogue, in which collisions between planetary bodies that formed an iron core lead to core- or mantle-rich fragments. We also consider layer-by-layer accretion of individual bodies, such that the apparent composition of atmospheric pollution changes during the accretion of a single body. Finally, we consider that compositional spread is due to random noise. We find that the distribution of Ca, Fe, and Mg in a sample of 202 cool DZs is consistent with the random noise scenario, although 7 individual systems show strong evidence of core-mantle differentiation from additional elements and/or low noise levels. Future surveys that detect multiple elements in each of a few hundred white dwarfs, with well-understood biases, have the potential to confidently distinguish between the three models. [ABSTRACT FROM AUTHOR]

A systematic, population-level discrepancy exists between the densities of exoplanets whose masses have been measured with transit timing variations (TTVs) versus those measured with radial velocities (RVs). Since the TTV planets are predominantly nearly resonant, it is still unclear whether the discrepancy is attributed to detection biases or to astrophysical differences between the nearly resonant and non resonant planet populations. We defined a controlled, unbiased sample of 36 sub-Neptunes characterised by Kepler, TESS, HARPS, and ESPRESSO. We found that their density depends mostly on the resonant state of the system, with a low probability (of 0.002−0.001+0.010) that the mass of (nearly) resonant planets is drawn from the same underlying population as the bulk of sub-Neptunes. Increasing the sample to 133 sub-Neptunes reveals finer details: the densities of resonant planets are similar and lower than non-resonant planets, and both the mean and spread in density increase for planets that are away from resonance. This trend is also present in RV-characterised planets alone. In addition, TTVs and RVs have consistent density distributions for a given distance to resonance. We also show that systems closer to resonances tend to be more co-planar than their spread-out counterparts. These observational trends are also found in synthetic populations, where planets that survived in their original resonant configuration retain a lower density; whereas less compact systems have undergone post-disc giant collisions that increased the planet's density, while expanding their orbits. Our findings reinforce the claim that resonant systems are archetypes of planetary systems at their birth. [ABSTRACT FROM AUTHOR]

With four companions at separations from 16 to 71 au, HR 8799 is a unique target for direct imaging, presenting an opportunity for a comparative study of exoplanets with a shared formation history. Combining new VLTI/GRAVITY observations obtained within the ExoGRAVITY program with archival data, we performed a systematic atmospheric characterisation across all four planets. We explored different levels of model flexibility to understand the temperature structure, chemistry, and clouds of each planet using both petitRADTRANS atmospheric retrievals and fits to self-consistent radiative–convective equilibrium models. Using Bayesian model averaging to combine multiple retrievals (a total of 89 across all four planets), we find that the HR 8799 planets are highly enriched in metals, with [M/H] ≳1, and have stellar to superstellar atmospheric C/O ratios. The C/O ratio increases with increasing separation from 0.55−0.10+0.12 for d to 0.78−0.04+0.03 for b, with the exception of the innermost planet, which has a C/O ratio of 0.87 ± 0.03. Such high metallicities are unexpected for these massive planets, and challenge planet-formation models. By retrieving a quench pressure and using a disequilibrium chemistry model, we derive vertical mixing strengths compatible with predictions for high-metallicity, self-luminous atmospheres. Bayesian evidence comparisons strongly favour the presence of HCN in HR 8799 c and e, as well as CH4 in HR 8799 c, with detections at > 5σ confidence. All of the planets are cloudy, with no evidence of patchiness. The clouds of c, d, and e are best fit by silicate clouds lying above a deep iron cloud layer, while the clouds of the cooler HR 8799 b are more likely composed of Na2S. With well-defined atmospheric properties, future exploration of this system is well positioned to unveil further details of these planets, extending our understanding of the composition, structure, and formation history of these siblings. [ABSTRACT FROM AUTHOR]

The characterization of super-Earth- to Neptune-sized exoplanets relies heavily on our understanding of their formation and evolution. In this study, we link a model of planet formation by pebble accretion to the planets' long-term observational properties by calculating the interior evolution, starting from the dissipation of the protoplanetary disk. We investigate the evolution of the interior structure in 5–20 M⊕ planets, accounting for silicate redistribution caused by convective mixing, rainout (condensation and settling), and mass loss. Specifically, we have followed the fate of the hot silicate vapor that remained in the planet's envelope after planet formation as the planet cools. We find that disk dissipation is followed by a rapid contraction of the envelope from the Hill or Bondi radius to about one-tenth of that size within 10 Myr. Subsequent cooling leads to substantial growth of the planetary core through silicate rainout accompanied by inflated radii, in comparison to the standard models of planets that formed with core-envelope structure. We examined the dependence of rainout on the planet's envelope mass, on the distance from its host star, on its silicate mass, and on the atmospheric opacity. We find that the population of planets that formed with polluted envelopes can be roughly divided into three groups based on the mass of their gas envelopes: bare rocky cores that have shed their envelopes, super-Earth planets with a core-envelope structure, and Neptune-like planets with diluted cores that undergo gradual rainout. For polluted planets that formed with envelope masses below 0.4 M⊕, we anticipate that the inflation of the planet's radius caused by rainout will enhance the mass loss by a factor of 2–8 compared to planets with unpolluted envelopes. Our model bridges the gap between the predicted composition gradients in massive planets and the core-envelope structure in smaller planets. [ABSTRACT FROM AUTHOR]

Aims. Impacts between differentiated planetesimals are ubiquitous in protoplanetary discs and may mix materials from the core, mantle, and crust of planetesimals, thus forming stony-iron meteorites. The surface composition of the asteroid (16) Psyche represents a mixture of metal and non-metal components. However, the velocities, angles, and outcome regimes of impacts that mixed metal and silicate from different layers of planetesimals are debated. Our aim is to investigate the impacts between planetesimals that can mix large amounts of metal and silicate, and the mechanism of stony-iron meteorite formation. Methods. We used smooth particle hydrodynamics to simulate the impacts between differentiated planetesimals with various initial conditions that span different outcome regimes. In our simulations, the material strength was included and the effects of the states of planetesimal cores were studied. Using a statistical approach, we quantitatively analysed the distributions of metal and silicate after impacts. Results. Our simulations modelled the mass, depth, and sources of the metal–silicate mixture in different impact conditions. Our results suggest that the molten cores in planetesimals could facilitate mixing of metal and silicate. Large amounts of the metal–silicate mixture could be produced by low-energy accretional impacts and high-energy erosive impacts in the largest impact remnant, and by hit-and-run and erosive impacts in the second-largest impact remnant. After impact, most of the metal-silicate mixture was buried at depth, consistent with the low cooling rates of stony-iron meteorites. Our results indicate that mesosiderites potentially formed in an erosive impact, while pallasites potentially formed in an accretional or hit-and-run impact. The mixing of metal and non-metal components on Psyche may also be the result of impacts. [ABSTRACT FROM AUTHOR]

The radius valley, i.e. a dearth of planets with radii between 1.5 and 2 Earth radii, provides insights into planetary formation and evolution. Using homogenously revised planetary parameters from Kepler 1-min short cadence light curves, we remodel transits of 72 small planets mostly orbiting low-mass stars, improving the precision and accuracy of planet parameters. By combining this sample with a similar sample of planets around higher mass stars, we determine the depth of the radius valley as a function of stellar mass. We find that the radius valley is shallower for low-mass stars compared to their higher mass counterparts. Upon comparison, we find that theoretical models of photoevaporation underpredict the number of planets observed inside the radius valley for low-mass stars: with decreasing stellar mass, the predicted fraction of planets inside the valley remains approximately constant whereas the observed fraction increases. We argue that this provides evidence for the presence of icy planets around low-mass stars. Alternatively, planets orbiting low-mass stars undergo more frequent collisions and scatter in the stars' high-energy output may also cause planets to fill the valley. We predict that more precise mass measurements for planets orbiting low-mass stars would be able to distinguish between these scenarios. [ABSTRACT FROM AUTHOR]

Ultrahot Jupiters (UHJs) undergo intense irradiation by their host stars and are expected to experience non-local thermodynamic equilibrium (NLTE) effects in their atmospheres. Such effects are computationally intensive to model but, at the low pressures probed by high-resolution cross-correlation spectroscopy (HRCCS), can significantly impact the formation of spectral lines. The UHJ WASP-121 b exhibits a highly inflated atmosphere, making it ideal for investigating the impact of NLTE effects on its transmission spectrum. Here, we formally introduce cloudy for exoplanets , a cloudy -based modelling code, and use it to generate 1D LTE and NLTE atmospheric models and spectra to analyse archival HARPS WASP-121 b transmission spectra. We assessed the models using two HRCCS methods: (i) Pearson cross-correlation, and (ii) a method that aims to match the average observed line depth for given atmospheric species. All models result in strong detections of Fe  i (7.5 < S / N < 10.5). However, the highest S/N model (LTE) does not agree with the best-matching model of the average line depth (NLTE). We also find degeneracy, such that increasing the isothermal temperature and metallicity of the LTE models can produce average line depths similar to cooler, less metal rich NLTE models. Thus, we are unable to conclusively remark on the presence of NLTE effects in the atmosphere of WASP-121 b. We instead highlight the need for standardized metrics in HRCCS that enable robust statistical assessment of complex physical models, e.g. NLTE or 3D effects, that are currently too computationally intensive to include in HRCCS atmospheric retrievals. [ABSTRACT FROM AUTHOR]

Anharmonic quantum chemical computations reveal a strong, narrow (width = 0.075 |$\mu$| m) band in the 4.3–4.5 |$\mu$| m region of the absorption spectra of the cyano-substituted polycyclic aromatic hydrocarbons (CN-PAHs) cyanonaphthalene, cyanoanthracene, cyanophenanthrene, and cyanopyrene. This narrow window with intense IR lines implies that CN-PAHs of various shapes and sizes offer little variation in both wavelength and intensity in this region. Subsequently, this band can be used as a tracer for CN-PAHs. The distinct features making up the band are assigned to mixed vibrational states consisting of the CN stretch fundamental and various combination bands, including in-plane CH bends, CC skeletal bends, and CC skeletal breathing motions. The extraordinarily large intrinsic intensity of the fundamental CN stretch is redistributed to nearby states via anharmonic coupling, which is readily captured when using second order vibrational perturbation theory with resonance polyad matrices. This redistribution of intensity leads to a complex spectrum. The intense bands in this wavelength region may contribute to the baseline continuum and undulating macroscopic structure seen in recent JWST NIRSpec observations. [ABSTRACT FROM AUTHOR]

ABSTRACT: The composition of forming planets is strongly affected by the protoplanetary disc’s thermal structure. This thermal structure is predominantly set by dust radiative transfer and viscous (accretional) heating and can be impacted by gaps – regions of low dust and gas density that can occur when planets form. The effect of variations in dust surface density on disc temperature has been poorly understood to date. In this work, we use the radiative transfer code MCMax to model the 2D dust thermal structure with individual gaps corresponding to planets with masses of 0.1 MJ –5 MJ and orbital radii of 3, 5, and 10 au. Low dust opacity in the gap allows radiation to penetrate deeper and warm the mid-plane by up to 16 K, but only for gaps located in the region of the disc where stellar irradiation is the dominant source of heating. In viscously heated regions, the mid-plane of the gap is relatively cooler by up to 100 K. Outside of the gap, broad radial oscillations in heating and cooling are present due to disc flaring. These thermal features affect local dust–gas segregation of volatile elements (H2O, CH4, CO2, and CO). We find that icelines experience dramatic shifts relative to gapless models: up to 6.5 au (or 71 per cent) closer to the star and 4.3 au (or 100 per cent) closer to the mid-plane. While quantitative predictions of iceline deviations will require more sophisticated models, which include transport, sublimation/condensation kinetics, and gas–dust thermal decoupling in the disc atmosphere, our results suggest that planet-induced iceline variations represent a potential feedback from the planet on to the composition of material it is accreting.

JWST observations are leading to important new insights into exoplanetary atmospheres through transmission spectroscopy. In order to harness the full potential of the broad spectral range and high sensitivity of JWST , atmospheric retrievals of exoplanets require a high level of robustness and accuracy in the underlying models. We present the VIRA retrieval framework which implements a range of modelling and inference capabilities motivated by early JWST observations of exoplanet transmission spectra. This includes three complementary approaches to modelling atmospheric composition, three atmospheric aerosol models, including a physically motivated Mie scattering approach, and consideration of correlated noise. VIRA enables a cascading retrieval architecture involving a sequence of retrievals with increasing sophistication. We demonstrate VIRA using a JWST transmission spectrum of the hot Saturn WASP-39b in the ∼1–5  |$\mu$| m range. In addition to confirming prior chemical inferences, we retrieve molecular abundances for H2O, CO, CO2, SO2, and H2S, resulting in supersolar elemental abundances of log(O/H) = −2.0 ± 0.2, log(C/H) = −2.1 ± 0.2, and log(S/H) = −3.6 ± 0.2, along with C/O and S/O ratios of |$0.83^{+0.05}_{-0.07}$| and |$0.029^{+0.012}_{-0.009}$|⁠ , respectively, in the free chemistry case. The abundances correspond to |$20.1^{+10.5}_{-8.1}\times$|⁠ , |$28.2^{+16.3}_{-12.1}\times$|⁠ , and |$20.8^{+10.3}_{-7.5}\times$| solar values for O/H, C/H, and S/H, respectively, compared to C/H = 8.67 ± 0.35 × solar for Saturn. Our results demonstrate how JWST transmission spectroscopy combined with retrieval frameworks like VIRA can measure multi-elemental abundances for giant exoplanets and enable comparative characterization with solar system planets. [ABSTRACT FROM AUTHOR]

Numerous chemical constraints have been possible for exoplanetary atmospheres thanks to high-resolution spectroscopy (HRS) from ground-based facilities as well as low-resolution spectroscopy (LRS) from space. These two techniques have complementary strengths, and hence combined HRS and LRS analyses have the potential for more accurate abundance constraints and increased sensitivity to trace species. In this work, we retrieve the atmosphere of the ultra-hot Jupiter WASP-76 b, using high-resolution CARMENES/CAHA (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs) and low-resolution Hubble Space Telescope 's (HST) Wide Field Camera 3 (WFC3) and Spitzer observations of the primary eclipse. As such, hot planets are expected to have a substantial fraction of H2O dissociated, we conduct retrievals including both H2O and OH. We explore two retrieval models, one with self-consistent treatment of H2O dissociation and another where H2O and OH are vertically homogeneous. Both models constrain H2O and OH, with H2O primarily detected by LRS and OH through HRS, highlighting the strengths of each technique and demonstrating the need for combined retrievals to fully constrain chemical compositions. We see only a slight preference for the H2O-dissociation model given that the photospheric constraints for both are very similar, indicating |$\log (\mathrm{OH/H_2O}) = 0.7^{+0.3}_{-0.3}$| at 1.5 mbar, showing that the majority of the H2O in the photosphere is dissociated. However, the bulk O/H and C/O ratios inferred from the models differs significantly, and highlights the challenge of constraining bulk compositions from photospheric abundances with strong vertical chemical gradients. Further observations with JWST and ground-based facilities may help shed more light on these processes. [ABSTRACT FROM AUTHOR]

We report the confirmation and mass determination of a mini-Neptune transiting the M3.5 V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA's TESS space mission in the sectors 40, 52, and 53. In order to validate the planet TOI-4438 b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438 b has a radius of Rb = 2.52 ± 0.13 R⊕ (5% precision), which together with a mass of Mb = 5.4 ± 1.1 M⊕ (20% precision), results in a bulk density of ρb = 1.85−0.44+0.51 g cm−3 (~28% precision), aligning the discovery with a volatile-rich planet. Our interior structure retrieval with a pure water envelope yields aminimum water mass fraction of 46% (1σ). TOI-4438 b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO2, and CH4. The primary star has a J-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136 ± 13. Taking into account the relatively warm equilibrium temperature of Teq = 435 ± 15 K, and the low activity level of its host star, TOI-4438 b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies. [ABSTRACT FROM AUTHOR]

Context. Out of the more than 5000 detected exoplanets, a considerable number belong to a category called "mini-Neptunes". Interior models of these planets suggest that they have primordial H–He-dominated atmospheres. As this type of planet is not found in the Solar System, understanding their formation is a key challenge in planet formation theory. Unfortunately, quantifying how much H–He planets have, based on their observed mass and radius, is impossible due to the degeneracy of interior models. Aims. Another approach to estimating the range of possible primordial envelope masses is to use formation theory. As different assumptions in planet formation can heavily influence the nebular gas accretion rate of small planets, it is unclear how large the envelope of a protoplanet should be. We explore the effects that different assumptions regarding planet formation have on the nebular gas accretion rate, particularly by exploring the way in which solid material interacts with the envelope. This allows us to estimate the range of possible post-formation primordial envelopes. Thereby, we demonstrate the impact of envelope enrichment on the initial primordial envelope, which can be used in evolution models. Methods. We applied formation models that include different solid accretion rate prescriptions. Our assumption is that mini-Neptunes form beyond the ice line and migrate inward after formation; thus, we formed planets in situ at 3 and 5 au. We considered that the envelope can be enriched by the accreted solids in the form of water. We studied how different assumptions and parameters influence the ratio between the planet's total mass and the fraction of primordial gas. Results. The primordial envelope fractions for low- and intermediate-mass planets (total mass below 15 M⊕) can range from 0.1% to 50%. Envelope enrichment can lead to higher primordial mass fractions. We find that the solid accretion rate timescale has the largest influence on the primordial envelope size. Conclusions. Rates of primordial gas accretion onto small planets can span many orders of magnitude. Planet formation models need to use a self-consistent gas accretion prescription. [ABSTRACT FROM AUTHOR]

The number of super-Earth and mini-Neptune planet discoveries has increased significantly in the last two decades thanks to transit and radial velocity (RV) surveys. When it is possible to apply both techniques, we can characterise the internal composition of exoplanets, which in turn provides unique insights on their architecture, formation and evolution. We performed a combined photometric and RV analysis of TOI-238 (TYC 6398-132-1), which has one short-orbit super-Earth planet candidate announced by NASA's TESS team. We aim to confirm its planetary nature using radial velocities taken with the ESPRESSO and HARPS spectrographs, to measure its mass, and to detect the presence of other possible planetary companions. We carried out a joint analysis by including Gaussian processes and Keplerian orbits to account for the stellar activity and planetary signals simultaneously. We detected the signal induced by TOI-238 b in the RV time series, and the presence of a second transiting planet, TOI-238 c, whose signal appears in RV and TESS data. TOI-238 b is a planet with a radius of 1.402−0.086+0.084R⊕ and a mass of 3.40−0.45+0.46M⊕. It orbits at a separation of 0.02118 ± 0.00038 au of its host star, with an orbital period of 1.2730988 ± 0.0000029 days, and has an equilibrium temperature of 1311 ± 28 K. TOI-238 c has a radius of 2.18 ± 0.18 R⊕ and a mass of 6.7 ± 1.1 M⊕. It orbits at a separation of 0.0749 ± 0.0013 au of its host star, with an orbital period of 8.465652 ± 0.000031 days, and has an equilibrium temperature of 696 ± 15 K. The mass and radius of planet b are fully consistent with an Earth-like composition, making it a likely rocky super-Earth. Planet c could be a water-rich planet or a rocky planet with a small H-He atmosphere. [ABSTRACT FROM AUTHOR]

Context. The bulk abundances of CHNOS-bearing species of a planet have a profound effect on its interior structure and evolution. Therefore, it is key to investigate the behavior of the local abundances of these elements in the solid phase in the earliest stages of planet formation, where micrometer-sized dust grows into larger and larger aggregates. However, the physical and chemical processes occurring in planet-forming disks that shape these abundances are highly coupled and nonlocal. Aims. We aim to quantify the effects of the interplay between dynamical processes (turbulent diffusion, dust settling and radial drift), collision processes (coagulation and fragmentation), and the adsorption and desorption of ices on the abundances of CHNOS in local disk solids as a function of position throughout the planet-forming region. Methods. We used SHAMPOO (Stochastic Monomer Processor), which tracks the ice budgets of CHNOS-bearing molecules of a dust monomer as it undergoes nonlocal disk processing in a Class I disk. We used a large set of individual monomer evolutionary trajectories to make inferences about the properties of the local dust populations via a stochastic analysis of 64 000 monomers on a preexisting spatial grid. Results. We find that spatially, monomers can travel larger distances farther out in the disk, leading to a larger spread in positions of origin for a dust population at, for example, r = 50 AU compared to r = 2 AU. However, chemically, the inner disk (r ≲ 10 AU) is more nonlocal due to the closer spacing of ice lines in this disk region. Although to zeroth order the bulk ice mantle composition of icy dust grains remains similar compared to a fully local dust population, the ice mass associated with individual chemical species can change significantly. The largest differences with local dust populations were found near ice lines where the collisional timescale is comparable to the adsorption and desorption timescales. Here, aggregates may become significantly depleted in ice as a consequence of microscopic collisional mixing, a previously unknown effect where monomers are stored away in aggregate interiors through rapid cycles of coagulation and fragmentation. Conclusions. Nonlocal ice processing in a diffusion-dominated, massive, smooth disk has the most significant impact on the inner disk (r ≲ 10 AU). Furthermore, microscopic collisional mixing can have a significant effect on the amounts of ice of individual species immediately behind their respective ice lines. This suggests that ice processing is highly coupled to collisional processing in this disk region, which implies that the interiors of dust aggregates must be considered and not just their surfaces. [ABSTRACT FROM AUTHOR]

We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200−200+400 Myr. TOI-8l5b has a 11.2-day period and a radius of 2.94 ± 0.05 R⊕ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-8l5c, has a radius of 2.62 ± 0.10 R⊕, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M⊕ (ρP = 1.64−0.31+0.33 g cm−3) and 23.5 ± 2.4 M⊕ (ρP = 7.2−1.0+1.1 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system's orbital architecture, and probably hints at an eventful dynamical history. [ABSTRACT FROM AUTHOR]

Context. The CO2-dominated thick atmosphere of Venus coexists with an ionosphere that is mainly formed, on the dayside, via the ionization of atmospheric neutrals by solar extreme ultraviolet and soft X-ray photons. Despite extensive modeling efforts that have reproduced the electron distribution reasonably well, we note two main shortcomings with respect to prior studies. The effects of pro-tonation and Coulomb interaction are crucial to unveiling the structure and composition of the Venusian ionosphere. Aims. We evaluate the role of protonated species on the structure of the dayside Venusian ionosphere for the first time. We also evaluate the role of ion-ion Coulomb collisions, which are neglected in many existing models. Methods. Focusing on the solar minimum condition for which the effect of protonation is expected to be more prominent, we constructed a detailed one-dimensional photochemical model for the dayside Venusian ionosphere, incorporating more than 50 ion and neutral species (of which 17 are protonated species), along with the most thorough chemical network to date. We included both ion-neutral and ion-ion Coulomb collisions. Photoelectron impact processes were implemented with a two-stream kinetic model. Results. Our model reproduces the observed electron distribution reasonably well. The model indicates that protonation tends to diverge the ionization flow into more channels via a series of proton transfer reactions along the direction of low to high proton affinities for parent neutrals. In addition, the distribution of O2+ is enhanced by protonation by a factor of nearly 2 at high altitudes, where it is efficiently produced via the reaction between O and OH+. We find that Coulomb collisions influence the topside Venusian ionosphere not only directly by suppressing ion diffusion, but also indirectly by modifying ion chemistry. Two ion groups can be distinguished in terms of the effects of Coulomb collisions: one group preferentially produced at high altitudes and accumulated in the topside ionosphere, which is to be compared with another group that is preferentially produced at low altitudes and, instead, depleted in the topside ionosphere. Conclusions. Both protonation and Coulomb collisions have appreciable impacts on the topside Venusian ionosphere, which account for many of the significant differences in the model ion distribution between this study and early calculations. [ABSTRACT FROM AUTHOR]

During protoplanetary disk formation, dust grains located in the outer disk retain their pristine icy composition, while solids in the inner stellar-heated disk undergo volatile loss. This process may have left a fossil record in Solar System material, showing different nucleosynthetic imprints that have been attributed to different degrees of thermal processing. However, it remains unclear how a large mass fraction of thermally processed inner-disk pebbles is produced and how these grains are subsequently transported throughout the disk. In this work, we numerically investigate the evolution in time of a two-component pebble disk consisting of both pristine pebbles and those that underwent ice sublimation. We find that stellar outbursts exceeding 1000 times the solar luminosity are efficient in thermally altering, through ice sublimation, a large mass fraction of pebbles (around 80%). After the establishment of this initial radial dust composition gradient throughout the disk, the subsequent mixing and inward drift of pristine outer-disk pebbles alter the inner disk bulk composition from processed to more unprocessed in time. Therefore, if processed pebbles without ice mantles have an isotopic composition similar to ureilite meteorites from the inner Solar System, inner-disk minor bodies forming from the early pebble flux (<1 Myr) will be isotopically ureilite-like, while later-formed bodies will be increasingly admixed with the signature of the lateincoming, CI chondrite-like unprocessed pebbles. This appears to be largely consistent with the trend seen between the accretion age of different meteoric classes and their different stable isotope composition anomalies (in μ54Cr, μ48Ca, μ30Si, and μ58Ni), but further work may be needed to explain the role of isotopically anomalous refractory inclusions and anomaly trends in other elements. Our findings further support an early thermal processing of ice mantles via stellar outbursts that are common around young Sun-like stars. [ABSTRACT FROM AUTHOR]

Context. A number of bodies in the Solar System are characterized by dark surfaces, from carbonaceous asteroids to the enigmatic surface of Phobos and Deimos. Our understanding of the spectroscopic behavior of low-albedo surfaces remains incomplete. To improve the interpretation of remote sensing data, laboratory studies continue to serve as a pivotal tool for unveiling the physical state and composition of such surfaces. Aims. Several processes can be simulated in the laboratory, however, the preparation and analysis of a complex mixing of analog material is one of the most fundamental among them, while also being one of the most complex when multiple components are used. In this work, we aim to study how dark material mixed with basaltic material at different grain sizes can affect the spectroscopic features from the near- to mid- infrared (1.25–25 µm). Methods. Our sample set includes four series of basaltic mix (feldspar and pyroxene) at different grain sizes from <50 µm to 1000 µm, mixed with amorphous carbon at increasing weight percentages ranging from 1% to 50%. We analyzed several features on the spectrum of each mineral mixture. In particular, we investigated the behavior of the: (i) near-infrared slope; (ii) 2.7 µm OH-stretching band; (iii) Christiansen features; and (iv) Reststrahlen band and Transparency feature. Results. The measurements presented in this work, which take into account a large wavelength range for the first time, point toward a critical effect of dark material, but with a different outcomes for each grain size. Some of the most interesting results involve the slope trend of modification with dark material and the variant behavior of the Reststrahlen band and Transparency feature. Conclusions. This dataset will offer a key support in the interpretation of data collected on dark surfaces by past and future space missions. This knowledge will be also important in the context of linking analyses of returned samples with remote sensing data collected on planetary surfaces. [ABSTRACT FROM AUTHOR]

Context. Understanding the formation history of planets is one of the goals of studying exoplanet atmospheres. The atmospheric composition of planets can provide insights into the formation pathways of planets. Even though the mapping of the atmospheric composition onto a formation pathway is not unambiguous, with the increasing sensitivity of modern instruments, we can derive promising constraints. Aims. In this work, we aim to understand the formation pathway of WASP-39b. We discuss whether the detection of SO2 in its atmosphere would impact our understanding of the formation of the planet and whether it enables us to determine the formation pathway of the planet with greater accuracy. Methods. We used the JWST transit observation of the planet together with the available HST and Spitzer observations. We used a formation model coupled with a radiative transfer retrieval model to derive the planet's atmospheric characteristics and formation history. Furthermore, we used a photochemical model to derive the impact of photochemistry on the atmosphere of the planet. Results. In this work, we show that the planet is most likely to have initiated beyond the CO2 ice line of its natal disk. Furthermore, the planet is likely to have have accreted some planetesimals during its formation. We show that the sulfur abundance in the atmosphere of the planet is probably lower than 2.27 × 10−4. This abundance indicates that the planet is likely to exhibit a lower metallicity than suggested by the retrievals. Furthermore, such an abundance for sulfur is more likely if WASP-39b had been formed beyond the CO ice line of its natal disk. [ABSTRACT FROM AUTHOR]

The number of discovered exoplanets now exceeds 5500 allowing statistical analyses of planetary systems. Multi-planet systems are mini-laboratories of planet formation and evolution, and analysing their system architectures can help us to constrain the physics of these processes. Recent works have found evidence of significant intrasystem uniformity in planet properties such as radius, mass, and orbital spacing, collectively termed 'peas in a pod' trends. In particular, correlations in radius and mass have been interpreted as implying uniformity in planet bulk density and composition within a system. However, the samples used to assess trends in mass tend to be small and biased. In this paper, we re-evaluate correlations in planet properties in a large sample of systems with at least two planets for which mass and radius have been directly measured, and therefore bulk density can be calculated. Our sample was assembled using the most up-to-date exoplanet catalogue data, and we compute the relevant statistics while using a procedure to 'weight' the data points according to measurement precision. We find a moderate correlation in radius and a weak correlation in the densities of adjacent planets. However, masses of neighbouring planets show no overall correlation in our main sample and a weak correlation among pairs of planets similar in size or pairs restricted to Mp<100 M⊕, Rp<10 R⊕. Similarly, we show that the intrasystem dispersion in radius is typically less than that in mass and density. We identify ranges in stellar host properties that correlate with stronger uniformity in pairs of adjacent planets: low Teff for planet masses, and low metallicity and old age for planet densities. Furthermore, we explore whether peas in a pod trends extend into planet compositions or interior structures. For small neighbouring planets with similar radii, we show that their masses and interior structures are often disparate, indicating that even within the same system, similarity in radii is not necessarily a good proxy for similarity in composition or the physical nature of the planets. [ABSTRACT FROM AUTHOR]

Molecular mapping is a supervised method exploiting the spectral diversity of integral field spectrographs to detect and characterise resolved exoplanets blurred into the stellar halo. We present an update to the method, aimed at removing the stellar halo and the nuisance of telluric features in the datacubes and accessing a continuum-subtracted spectra of the planets at R ~ 4000. We derived the planet atmosphere properties from a direct analysis of the planet telluric-corrected absorption spectrum. We applied our methods to the SINFONI observation of the planet β Pictoris b. We recovered the CO and H2O detections in the atmosphere of β Pic b by using molecular mapping. We further determined some basic properties of its atmosphere, with Teq=1748−4+3 K, sub-solar [Fe/H]=− 0.235−0.013+0.015 dex, and solar C/O=0.551 ±0.002. These results are in contrast to values measured for the same exoplanet with other infrared instruments. We confirmed a low projected equatorial velocity of 25−6+5 km s−1. We were also able to measure, for the first time and with a medium-resolution spectrograph, the radial velocity of β Pic b relative to the central star at MJD=56910.38 with a km s−1 precision of −11.3±1.1 km s−1. This result is compatible with the ephemerides, based on the current knowledge of the β Pic system. [ABSTRACT FROM AUTHOR]

Context. Using emission lines from metals, we investigate the three-dimensional distribution of temperature and chemistry in ultra-hot Jupiters. Aims. Existing observations of WASP-121 b have suggested an underabundance of titanium and titanium oxide in its terminator region. In this study, we aim to determine whether this depletion is global by investigating the dayside emission spectrum. Methods. We analyzed eight epochs of high-resolution spectra obtained with the ESPRESSO spectrograph, targeting orbital phases when the dayside is in view. We used a cross-correlation method to search for various atoms, TiO, and VO, and compare the results to models. We constrained the velocities and phase function of the emission signal using a Bayesian framework. Results. We report significant detections of Ca I, V I, Cr I, Mn I, Fe I, Co I, and Ni I, but not Ti or TiO. Models containing titanium are unable to reproduce the data. The detected signals are consistent with the known orbital and systemic velocities and with peak emission originating from the substellar point. Conclusions. We find that titanium is depleted from regions of the atmosphere where transmission and emission spectroscopy are sensitive. Supported by recent HST observations of the nightside, we interpret this as evidence for the nightside condensation of titanium, which prevents it from being mixed back into the upper layers of the atmosphere elsewhere on the planet. Species with lower condensation temperatures are unaffected, implying that sharp chemical transitions exist between ultra-hot Jupiters that have slight differences in temperature or dynamical properties. As TiO can act as a strong source of stratospheric heating, cold-trapping creates a coupling between the thermal structures on the dayside and nightside, and thus condensation chemistry needs to be included in global circulation models. Observed elemental abundances in hot Jupiters will not reliably be representative of bulk abundances unless nightside condensation is robustly accounted for or the planet is hot enough to avoid nightside cold traps entirely. Secondary eclipse observations by JWST/NIRISS have the potential to confirm an absence of TiO bands at red-optical wavelengths. We also find that the abundance ratios of metal oxides to their atomic metals (e.g., TiO/Ti) depend strongly on the atmospheric C/O ratio, and that planetary rotation may significantly lower the apparent orbital velocity of the emission signal. [ABSTRACT FROM AUTHOR]

Optical phase curves of hot Jupiters can reveal global scattering properties. We implemented a Bayesian inference framework for optical phase curves with flux contributions from: reflected light from a potentially inhomogeneous atmosphere, thermal emission, ellipsoidal variations, Doppler beaming, and stellar rotation via a Gaussian process in the time domain. We probed for atmospheric homogeneity and time variability using the reflected light inferences for highly precise Kepler light curves of five hot Jupiters. We also investigated the scattering properties that constrain the most likely condensates in the inhomogeneous atmospheres. Cross validation prefers inhomogeneous albedo distributions for Kepler-7 b and Kepler-41 b, and a weak preference for inhomogeneity for KOI-13 b. None of the five planets exhibit significant variations in geometric albedo on 1-yr timescales, in agreement with theoretical expectations. We show that analytic reflected light phase curves with isotropic multiple scattering are in excellent agreement with full Rayleigh multiple scattering calculations, allowing for accelerated and analytic inference. In a case study of Kepler-41 b, we identified perovskite, forsterite, and enstatite as possible scattering species consistent with the reflected light phase curves, with condensate particle radii in the range 0.01–0.1 µm. [ABSTRACT FROM AUTHOR]

We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 (M *  = 1.17 M⊙, R *  = 1.31 R⊙) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS , we measure the radius and mass from the transit and radial velocity observations, and find that the planet, HD 77946 b, orbits with period P b  =  |$6.527282_{-0.000020}^{+0.000015}$| d, has a mass of M b = 8.38 ± 1.32 M⊕, and a radius of |$R_{\rm b} = 2.705_{-0.081}^{+0.086}$| R⊕. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a ∼1  per cent H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with |$T_{\rm eq}~= 1248^{+40}_{-38}~$| K, water may be in a supercritical state. The characterization of HD 77946 b, adding to the small sample of well-characterized sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets. [ABSTRACT FROM AUTHOR]

During the final stage of planetary formation, different formation pathways of planetary embryos could significantly influence the observed variations in planetary densities. Of the approximately 5000 exoplanets identified to date, a notable subset exhibits core fractions reminiscent of Mercury, potentially a consequence of high-velocity giant impacts. In order to better understand the influence of such collisions on planetary formation and compositional evolution, we conducted an extensive set of smoothed particle hydrodynamics giant impact simulations between two-layered rocky bodies. These simulations spanned a broad range of impact velocities from 1 to 11 times the mutual escape velocity. We derived novel scaling laws that estimate the mass and core mass fraction of the largest post-collision remnants. Our findings indicate that the extent of core vaporization markedly influences mantle stripping efficiency at low impact angles. We delineate the distinct roles played by two mechanisms – kinetic momentum transfer and vaporization-induced ejection – in mantle stripping. Our research suggests that collisional outcomes for multilayered planets are more complex than those for undifferentiated planetesimal impacts. Thus, a single universal law may not encompass all collision processes. We found a significant decrease in the mantle stripping efficiency as the impact angle increases. To form a 5 M⊕ super-Mercury at 45°, an impact velocity over 200 km s−1 is required. This poses a challenge to the formation of super-Mercuries through a single giant impact, implying that their formation would favour either relatively low-angle single impacts or multiple collisions. [ABSTRACT FROM AUTHOR]

Transport-induced quenching in hot Jupiter atmospheres is a process that determines the boundary between the part of the atmosphere at chemical equilibrium and the part of the atmosphere at thermochemical (but not photothermochemical) disequilibrium. The location of this boundary, the quench level, depends on the interplay between the dynamical and chemical time-scales in the atmosphere, with quenching occurring when these time-scales are equal. We explore the sensitivity of the quench level position to an increase in the planet's atmospheric metallicity using aerosol-free 3D general circulation model simulations of a hot Jupiter WASP-96b. We find that the temperature increase at pressures of ∼104–107 Pa that occurs when metallicity is increased could shift the position of the quench level to pressures dominated by the jet, and cause an equatorial depletion of CH4, NH3, and HCN. We discuss how such a depletion affects the planet's transmission spectrum, and how the analysis of the evening–morning limb asymmetries, especially within ∼3–5  μ m, could help distinguish atmospheres of different metallicities that are at chemical equilibrium from those with the upper layers at thermochemical disequilibrium. [ABSTRACT FROM AUTHOR]

Recent studies have suggested the possibility of Hycean worlds, characterized by deep liquid water oceans beneath H2-rich atmospheres. These planets significantly widen the range of planetary properties over which habitable conditions could exist. We conduct internal structure modelling of Hycean worlds to investigate the range of interior compositions, ocean depths and atmospheric mass fractions possible. Our investigation explicitly considers habitable oceans, where the surface conditions are limited to those that can support potential life. The ocean depths depend on the surface gravity and temperature, confirming previous studies, and span 10s to ∼1000 km for Hycean conditions, reaching ocean base pressures up to ∼6 × 104 bar before transitioning to high-pressure ice. We explore in detail test cases of five Hycean candidates, placing constraints on their possible ocean depths and interior compositions based on their bulk properties. We report limits on their atmospheric mass fractions admissible for Hycean conditions, as well as those allowed for other possible interior compositions. For the Hycean conditions considered, across these candidates we find the admissible mass fractions of the H/He envelopes to be ≲10−3. At the other extreme, the maximum H/He mass fractions allowed for these planets can be up to ∼4–8 per cent, representing purely rocky interiors with no H2O layer. These results highlight the diverse conditions possible among these planets and demonstrate their potential to host habitable conditions under vastly different circumstances to the Earth. Upcoming JWST observations of candidate Hycean worlds will allow for improved constraints on the nature of their atmospheres and interiors. [ABSTRACT FROM AUTHOR]

The radii of planets serve as significant constraints for their internal structure. Despite the complexity of planetary internal structure compared to stars, substantial advancements have been made in this field. The most critical uncertainties stem from the chemical composition and equation of state of planetary material. Using the MESA code, we construct rotating and non-rotating interior models for Jupiter and Saturn and sought to align these models to the observed radii. Rotation exerts a significant influence on their structures, distorting planetary, and stellar structures in distinct ways. Regarding gas planets' structure, two pivotal uncertain parameters depend on a possible separation between hydrogen and helium in the protosolar disc gas due to unequal evaporation between these two gases. In an extreme scenario where only hydrogen is lost and no heavy elements or helium are lost, Jupiter and Saturn would have a core mass of zero. However, this approach fails to yield a solution for Uranus and Neptune. Instead, our models indicate that hydrogen and helium were likely lost together during the protosolar disc phase, resulting in core masses of approximately 40, 25, 14, and 12 M⊕ for Jupiter, Saturn, Neptune, and Uranus, respectively. These findings are highly compatible with the observed mass–radius relationship of exoplanets, as well as the seismic and Juno data for Jupiter's near-surface temperature. [ABSTRACT FROM AUTHOR]

Whilst the formation of Solar system planets is constrained by meteoritic evidence, the geophysical history of low-mass exoplanets is much less clear. The bulk composition and climate states of rocky exoplanets may vary significantly based on the composition and properties of the planetesimals they form. An important factor influenced by planetesimal composition is water content, where the desiccation of accreting planetesimals impacts the final water content of the resultant planets. While the inner planets of the Solar system are comparatively water-poor, recent observational evidence from exoplanet bulk densities and planetary formation models suggests that rocky exoplanets engulfed by substantial layers of high-pressure ices or massive steam atmospheres could be widespread. Here, we quantify variations in planetesimal desiccation due to potential fractionation of the two short-lived radioisotopes 26Al and 60Fe relevant for internal heating on planetary formation time-scales. We focus on how order of magnitude variations in 60Fe can affect the water content of planetesimals, and how this may alter the formation of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause of planetesimal heating in any Solar system analogue scenario, thus validating previous works focussing only on this radioisotope. However, 60Fe can become the primary heating source in the case of high levels of supernova enrichment in massive star-forming regions. These diverging scenarios can affect the formation pathways, bulk volatile budget, and climate diversity of low-mass exoplanets. [ABSTRACT FROM AUTHOR]

Electron density profiles obtained from radio occultation experiments reveal significant ionization occurring at altitudes below 120 km in the Venusian ionosphere. The presence of such ionization remains unexplained when considering only major neutrals and the resulting ion chemistry. In this study, we investigate the role of minor neutrals, including NO, O2, C, Ar, H2, and H, in the lower altitudes of the Venusian ionosphere using a one-dimensional photochemical model and Akatsuki radio science measurements. We derive the density of minor neutrals from the profiles of major neutrals. Our analysis demonstrates that NO+ and O |$_2^+$| ions exhibit a notable presence below 140 km. When we incorporate the minor neutrals, electron density increases below 115 km but remains unchanged above this altitude. Specifically, the density of NO+ increases below 125 km, with corresponding reductions in O |$_2^+$|⁠. The increase in NO+ above 115 km can be attributed to the charge-exchange reaction between O |$_2^+$| and NO. However, below 115 km, the photoionization of NO results in a net increase in NO+ and electron density. These findings highlight the significant role played by minor neutrals, particularly below 115 km, in shaping the Venusian ionosphere at low altitudes. [ABSTRACT FROM AUTHOR]

In this work, we develop a rocky planet interior model and use it to investigate the evolution of catastrophically evaporating rocky exoplanets. These planets, detected through the dust tails produced by evaporative outflows from their molten surfaces, can be entirely destroyed in a fraction of their host star's lifetime. To allow for the major decrease in mass, our interior model can simultaneously calculate the evolution of the pressure and density structure of a planet alongside its thermal evolution, which includes the effects of conduction, convection and partial melting. We first use this model to show that the underlying planets are likely to be almost entirely solid. This means that the dusty tails are made up of material sampled only from a thin dayside lava pool. If one wishes to infer the bulk compositions of rocky exoplanets from their dust tails, it is important to take the localized origin of this material into account. Secondly, by considering how frequently one should be able to detect mass loss from these systems, we investigate the occurrence of sub-Earth mass exoplanets, which is difficult with conventional planet detection surveys. We predict that, depending on model assumptions, the number of progenitors of the catastrophically evaporating planets is either in line with, or higher than, the observed population of close-in (substellar temperatures around 2200 K) terrestrial exoplanets. [ABSTRACT FROM AUTHOR]

Catastrophically evaporating rocky planets provide a unique opportunity to study the composition of small planets. The surface composition of these planets can be constrained via modelling their comet-like tails of dust. In this work, we present a new self-consistent model of the dusty tails: we physically model the trajectory of the dust grains after they have left the gaseous outflow, including an on-the-fly calculation of the dust cloud's optical depth. We model two catastrophically evaporating planets: KIC 1255 b and K2-22 b. For both planets, we find the dust is likely composed of magnesium–iron silicates (olivine and pyroxene), consistent with an Earth-like composition. We constrain the initial dust grain sizes to be ∼ 1.25–1.75 μm and the average (dusty) planetary mass-loss rate to be ∼ 3 |$\, M_{\oplus } \mathrm{Gyr^{-1}}$|⁠. Our model shows that the origin of the leading tail of dust of K2-22 b is likely a combination of the geometry of the outflow and a low radiation pressure force to stellar gravitational force ratio. We find the optical depth of the dust cloud to be a factor of a few in the vicinity of the planet. Our composition constraint supports the recently suggested idea that the dusty outflows of these planets go through a greenhouse effect–nuclear winter cycle, which gives origin to the observed transit depth time variability. Magnesium–iron silicates have the necessary visible-to-infrared opacity ratio to give origin to this cycle in the high mass-loss state. [ABSTRACT FROM AUTHOR]

As the characterization of exoplanet atmospheres proceeds, providing insights into atmospheric chemistry and composition, a key question is how much deeper into the planet we might be able to see from its atmospheric properties alone. For small planets with modest atmospheres and equilibrium temperatures, the first layer below the atmosphere will be their rocky surface. For such warm rocky planets, broadly Venus-like planets, the high temperatures and moderate pressures at the base of their atmospheres may enable thermochemical equilibrium between rock and gas. This links the composition of the surface to that of the observable atmosphere. Using an equilibrium chemistry code, we find a boundary in surface pressure–temperature space which simultaneously separates distinct mineralogical regimes and atmospheric regimes, potentially enabling inference of surface mineralogy from spectroscopic observations of the atmosphere. Weak constraints on the surface pressure and temperature also emerge. This regime boundary corresponds to conditions under which SO2 is oxidized and absorbed by calcium-bearing minerals in the crust, thus the two regimes reflect the sulphidation of the crust. The existence of these atmospheric regimes for Venus-like planets is robust to plausible changes in the elemental composition. Our results pave the way to the prospect of characterizing exoplanetary surfaces as new data for short period rocky planet atmospheres emerge. [ABSTRACT FROM AUTHOR]

We report on the precise radial velocity follow-up of TOI-544 (HD 290498), a bright K star (V  = 10.8), which hosts a small transiting planet recently discovered by the Transiting Exoplanet Survey Satellite (TESS). We collected 122 high-resolution High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N spectra to spectroscopically confirm the transiting planet and measure its mass. The nearly 3-yr baseline of our follow-up allowed us to unveil the presence of an additional, non-transiting, longer-period companion planet. We derived a radius and mass for the inner planet, TOI-544 b, of 2.018 ± 0.076 R⊕ and 2.89 ± 0.48 M⊕, respectively, which gives a bulk density of |$1.93^{+0.30}_{-0.25}$|  g cm−3. TOI-544 c has a minimum mass of 21.5 ± 2.0 M⊕ and orbital period of 50.1 ± 0.2 d. The low density of planet-b implies that it has either an Earth-like rocky core with a hydrogen atmosphere, or a composition which harbours a significant fraction of water. The composition interpretation is degenerate depending on the specific choice of planet interior models used. Additionally, TOI-544 b has an orbital period of 1.55 d and equilibrium temperature of 999 ± 14 K, placing it within the predicted location of the radius valley, where few planets are expected. TOI-544 b is a top target for future atmospheric observations, for example with JWST , which would enable better constraints of the planet composition. [ABSTRACT FROM AUTHOR]

Investigating the response of icy dust aggregates to water ice sublimation is essential for understanding the formation and properties of planetesimals in protoplanetary discs. However, their fate remains unclear, as previous studies suggest that aggregates could either survive or completely fall apart to (sub)μm-sized grains. Protoplanetary discs around stars undergoing accretion outbursts represent a unique laboratory to study the ice sublimation process, as the water snowline is pushed outward to regions accessible to current observatories. In this work, we aim to understand the aggregates' response to ice sublimation by focusing on V883 Ori, a system currently undergoing a powerful accretion outburst. We present new analysis of archival high-resolution ALMA observations of the protoplanetary disc of V883 Ori at 0.88, 1.3, 2.0, and 3.1 mm, and derive new radial spectral index profiles, which we compare with predictions from one-dimensional dust evolution simulations. In the region of V883 Ori where water ice has sublimated, we find lower spectral indices than previously obtained, indicating the presence of cm-sized particles. Coupled with our dust evolution models, we find that the only way to explain their presence is to assume that they formed before the outburst and survived the sublimation process. The resilience of dust aggregates to such intense events leads us to speculate that it may extend to other environments with more gentle heating, such as pebbles drifting through the water snowline in quiescent protoplanetary discs. In that case, it may alter the formation pathway of dry planetesimals interior to the snowline. [ABSTRACT FROM AUTHOR]