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Planet formation occurs around a wide range of stellar masses and stellar system architectures. An improved understanding of the formation process can be achieved by studying it across the full parameter space, particularly toward the extremes. Earlier studies of planets in close-in orbits around high-mass stars have revealed an increase in giant planet frequency with increasing stellar mass until a turnover point at 1.9 solar masses, above which the frequency rapidly decreases. This could potentially imply that planet formation is impeded around more massive stars, and that giant planets around stars exceeding 3 solar masses may be rare or non-existent. However, the methods used to detect planets in small orbits are insensitive to planets in wide orbits. Here we demonstrate the existence of a planet at 560 times the Sun-Earth distance from the 6-10 solar mass binary b Centauri through direct imaging. The planet-to-star mass ratio of 0.10-0.17% is similar to the Jupiter-Sun ratio, but the separation of the detected planet is ~100 times wider than that of Jupiter. Our results show that planets can reside in much more massive stellar systems than what would be expected from extrapolation of previous results. The planet is unlikely to have formed in-situ through the conventional core accretion mechanism, but might have formed elsewhere and arrived to its present location through dynamical interactions, or might have formed via gravitational instability., Comment: Manuscript version. Published in Nature 9 December 2021

We investigate the origin of the measured over-abundance 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., 10 pages, 5 figures, 1 table, accepted for publication in MNRAS

We investigate mantle stripping giant impacts (GI) between super-Earths with masses between 1 M$_{\oplus}$ and 20 M$_{\oplus}$. We infer new scaling laws for the mass of the largest fragment and its iron mass fraction, as well as updated fitting coefficients for the critical specific impact energy for catastrophic disruption, $Q_{RD}^{*}$. With these scaling laws, we derive equations that relate the impact conditions, i.e., target mass, impact velocity and impactor-to-target mass ratio, to the mass and iron mass fraction of the largest fragment. This allows one to predict collision outcomes without performing a large suite of simulations. Using these equations we present the maximum and minimum planetary iron mass fraction as a result of collisional stripping of its mantle for a given range of impact conditions. We also infer the radius for a given mass and composition using interior structure models and compare our results to observations of metal-rich exoplanets. We find good agreement between the data and the simulated planets suggesting that GI could have played a key role in their formation. Furthermore, using our scaling laws we can further constrain the impact conditions that favour their masses and compositions. Finally, we present a flexible and easy-to-use tool that allows one to predict mass and composition of a planet after a GI for an arbitrary range of impact conditions which in turn allows to assess the role of GI in observed planetary systems., Comment: 12 pages, 9 figures, 1 table, accepted for publication in MNRAS

We assess the dependence of Earth’s disk-integrated mid-infrared thermal emission spectrum on observation geometries and investigate which and how spectral features are impacted by seasonality on Earth. We compiled an exclusive data set containing 2690 disk-integrated thermal emission spectra for four different full-disk observing geometries (North and South Pole-centered and Africa and Pacific-centered equatorial views) over four consecutive years. The spectra were derived from 2378 spectral channels in the wavelength range from 3.75-15.4 μm (nominal resolution ≈1200) and were recorded by the Atmospheric Infrared Sounder on board the Aqua satellite. We learned that there is significant seasonal variability in Earth’s thermal emission spectrum, and the strength of spectral features of bioindicators, such as N2O, CH4, O3, and CO2 depends strongly on both season and viewing geometry. In addition, we found a strong spectral degeneracy with respect to the latter two indicating that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Even for Earth and especially for equatorial views, the variations in flux and strength of absorption features in the disk-integrated data are small and typically ≤ 10%. Disentangling these variations from the noise in future exoplanet observations will be a challenge. However, irrespectively of when the planet will be measured (i.e., day or night or season) the results from mid-infrared observations will remain the same to the zeroth order, which is an advantage over reflected light observations., The Astrophysical Journal, 946 (2), ISSN:0004-637X, ISSN:2041-8213

The low luminosity of Uranus is still a puzzling phenomenon and has key implications for the thermal and compositional gradients within the planet. Recent studies have shown that planetary volatiles become ionically conducting under conditions that are present in the ice giants. Rapidly growing electrical conductivity with increasing depth would couple zonal flows to the background magnetic field in the planets, inducing poloidal and toroidal field perturbations $\mathbf{B}^{\omega} = \mathbf{B}^{\omega}_P + \mathbf{B}^{\omega}_T$ via the $\omega$-effect. Toroidal perturbations $\mathbf{B}^{\omega}_T$ are expected to diffuse downwards and produce poloidal fields $\mathbf{B}^{\alpha}_P$ through turbulent convection via the $\alpha$-effect, comparable in strength to those of the $\omega$-effect; $\mathbf{B}^{\omega}_P$. To estimate the strength of poloidal field perturbations for various Uranus models in the literature, we generate wind decay profiles based on Ohmic dissipation constraints assuming an ionically conducting H$_2$-He-H$_2$O interior. Due to the higher metallicities in outer regions of hot Uranus models, zonal winds need to decay to $\sim$0.1% of their surface values in the outer 1% of Uranus to admit decay solutions in the Ohmic framework. Our estimates suggest that colder Uranus models could potentially have poloidal field perturbations that reach up to $\mathcal{O}(0.1)$ of the background magnetic field in the most extreme case. The possible existence of poloidal field perturbations spatially correlated with Uranus' zonal flows could be used to constrain Uranus' interior structure, and presents a further case for the $\textit{in situ}$ exploration of Uranus., Comment: Accepted for publication in MNRAS. 6 pages, 2 figures. Typos corrected (v2). Typos corrected (v3)

Of all the myriad environments in our Solar System, the least explored are the distant Ice Giants Uranus and Neptune, and their diverse satellite and ring systems. These ‘intermediate-sized’ worlds are the last remaining class of Solar System planet to be characterised by a dedicated robotic mission, and may shape the paradigm for the most common outcome of planetary formation throughout our galaxy. In response to the 2019 European Space Agency call for scientific themes in the 2030s and 2040s (known as Voyage 2050), we advocated that an international partnership mission to explore an Ice Giant should be a cornerstone of ESA’s science planning in the coming decade, targeting launch opportunities in the early 2030s. This article summarises the inter-disciplinary science opportunities presented in that White Paper [1], and briefly describes developments since 2019.

Introduction The detailed observations by the NASA Juno spacecraft has advanced Jupiter’s interior structure models which can be used to improve our understanding of Jupiter’s origin. In this study, we investigate the potential origin of Jupiter's enriched atmosphere. We revisit the planetesimal accretion during Jupiter’s formation: in previous studies, the planetesimal accretion rate is calculated using N-body simulations that model the swam of planetesimals around proto-Jupiter. It was concluded that the heavy-element enrichment in Jupiter's envelope can be explained by the planetesimal accretion if Jupiter formed in a planetesimal disk that is at least five times more massive than the minimum mass solar nebulae (MMSN). However, this conclusion was inferred under the assumption that the total mass of captured planetesimals linearly increases with the surface density of planetesimals. In reality, in such a massive disk the gravitational interactions between planetesimals and embryos becomes so strong that the initial eccentricity and inclination are excited to 〜0.1 at most. In this study, we investigate this scenario in detail accounting for the change of the eccentricity and inclination of the planetesimals and show its affect off Jupiter’s growth rate and final composition. Model Figure 1: The surface density of planetesimals used in this study. This surface density profile is obtained by Kobayashi & Tanaka (2021). We adopt a planetesimal disk obtained by Kobayashi & Tanaka (2021) where the collisional evolution of dust grains in the protoplanetary disk results in a dense-compact planetesimal disk because of pebble drift from the outer disk. Figure 1 shows the surface density profile of planetesimals we use in this study. We start the N-body simulations with a swam of planetesimals around proto-Jupiter which enters the runaway gas accretion phase and increases its mass from 10 M⊕ to 318 M⊕. During its formation, we assume that proto-Jupiter slightly migrates inward due to type II migration. If a planetesimal collides on the surface of proto-Jupiter or loses its escape energy from Jupiter's Hill sphere, we assume that the planetesimal is captured by proto-Jupiter. We set the initial eccentricities and inclinations of planetesimals as input parameters. Since the choice of the planetesimal’s size can significantly affect the accretion rate we consider various planetesimal sizes. Results Figure 2: The cumulative mass of captured planetesimals as a function of time. Black, red, green and blue lines show correspond to different assumed initial eccentricities of ‹e0›1/2=10-3,10-2,10-1, and 0.4, respectively. The initial inclination is set as ‹i0›1/2=0.5‹e0›1/2. In a massive planetesimal disk, proto-Jupiter accretes tens Earth-masses of heavy elements by the end of runaway gas accretion. Figure 2 shows the cumulative mass of captured planetesimals vs. time. We find that the increase of the initial eccentricity and inclination: weakens resonant trapping and leads to an enhancement of planetesimal accretion, reduces the capture probability of planetesimals. Due to the combination of these effects, the captured mass of planetesimals decreases with the increase of the initial eccentricity and inclination. Discussion Figure 3: Total mass of captured planetesimals as a function of planetesimal size and the initial eccentricity. The initial inclination is set as ‹i0›1/2=0.5‹e0›1/2. The solid and dashed black line shows the equilibrium eccentricity of planetesimals with and without embryos, respectively. The initial eccentricity and inclination of planetesimals are determined by the scattering from other planetesimals/embryos. In a massive planetesimal disk as assumed here, embryos other than proto-Jupiter would form and be in the “oligarchic regime”. Considering the eccentricity and inclination excitation from the embryos, we conclude that the total mass of captured planetesimals is about 5-10 M⊕, and is larger for larger planetesimals. The bulk metallicity of Jupiter is still a matter of debate (e.g., Stevenson 2020). Planetesimal accretion could explain structure models with ~10 M⊕ of heavy elements in Jupiter’s outer envelope. However, if Jupiter’s enrichment is found to be higher, as suggested by some structure models (e.g., Miguel et al. 2022), an additional enrichment mechanism would be required. Such an enrichment could be a result of giant impacts of embryos. Such impacts have been suggested by Liu et al. (2019) for the formation of Jupiter’s fuzzy core. We also compare our results with those presented by Shibata & Helled (2022), where planetesimal accretion was considered for the case of a migrating Jupiter from 20 au to 5 au. We find that the timing of planetesimal accretion must occur earlier for the in-situ formation case, which enriches Jupiter's interior rather than the outer envelope or atmosphere. We suggest that a determination of the heavy-element distribution in Jupiter’s envelope could constrain Jupiter’s formation location and formation history. References Kobayashi, H., & Tanaka, H. 2021, ApJ, 922, 16, doi: 10.3847/1538-4357/ac289c Liu, S.-F., Hori, Y., M ̈uller, S., et al. 2019, Nature, 572, 355, doi: 10.1038/s41586-019-1470-2 Miguel, Y., Bazot, M., Guillot, T., et al. 2022, arXiv e-prints, arXiv:2203.01866. https://arxiv.org/abs/2203.01866 Shibata, S., & Ikoma, M. 2019, MNRAS, 487, 4510, doi: 10.1093/mnras/stz1629 Shibata, S., & Helled, R. 2022, ApJL, 926, L37, doi: 10.3847/2041-8213/ac54b1 Stevenson, D. J. 2020, Annu. Rev. Earth Planet. Sci., 48, 465

Recent studies show that planetary “ices” such as water and ammonia become ionically conducting under conditions present in Uranus and Neptune. Moreover, within the ionic liquid regime of water present in the outer layers of the planets, dissociation of hydrogen in H2-H2O mixtures has a significant ionic contribution to electrical conductivity. At the same time, the interiors of Uranus and Neptune are poorly constrained, and can be fitted with varying amount of ice-to-rock ratios, challenging the view of Uranus and Neptune being “ice giants”. Understanding the behaviour of electrical conductivity within Uranus and Neptune has a direct implication on understanding their observed multipolar and non-axisymmetric magnetic fields, the extents of their dynamo generation region, their composition, and the complex secondary fields due to the background magnetic field—zonal flow coupling. We present a method for calculating electrical conductivity profiles of ionically conducting H2-He-H2O mixtures using results from ab initio simulations. We then apply this prescription on several published interior structure models of Uranus and Neptune. We find that the conductivity increases rapidly with depth in the outer 20% for both planets. With rapidly increasing electrical conductivity, fast zonal winds on Uranus and Neptune inevitably couple to the background magnetic field, inducing electrical currents and magnetic field perturbations spatially correlated with zonal flows. Induced currents generate Ohmic dissipation, which can be used to constrain the depth of the zonal winds when considering the energy/entropy flux budget throughout the planetary interior. Constraining the zonal wind decay is not only important for understanding the atmosphere dynamics on Uranus and Neptune, but can also be used to estimate the strength of magnetic field perturbations. We find that the poloidal component of these perturbations can reach

Disk instability remains the leading formation pathway for some of observed giant planets. In particular, this model can more naturally explain giant planets at large separation, giant planets around M stars, and very young giant planets. However, there are still many open questions regarding this formation mechanism, and the expected population of planets.We are working on a new disc instability population synthesis (DIPSY) that aims to address these questions and make predictions about the expected population of planets that can be tested observationally.We find that fragmentation (the formation of bound clumps in the disc, a necessary condition for planet formation in the disc instability model) depends sensitively on the precise physics during the disc formation (infall). We show that infall models that form discs compatible in size with observed young discs are likely to fragment, though this may happen only in a minority of systems. Furthermore, we demonstrate how the intrinsics of orbital migration, mass accretion and clump interaction influence the fate of the formed clumps.The figure shows the fraction of systems that fragment as a function of the final stellar mass for different parameters studied [1].The results of the population synthesis, combined with current and future observations, will deepen our understanding of planet formation irrespective of the formation model. Fig. 1: Fraction of fragmenting discs as a function of the final stellar mass for different parameters. When an infall model motivated by non-ideal MHD simulations is applied, no fragmentation occurrs. In contrast, infall informed by radiation hydrodynamic simulations leads to a substantial fraction of discs fragmenting, especially at higher masses. References: [1] Schib, O., Mordasini, C., Wenger, N., Marleau, G. D., & Helled, R. 2021, Astronomy and Astrophysics, 645, A43

The origin of Uranus and Neptune remains a challenge for planet formation models. A potential explanation is that the planets formed from a population of a few planetary embryos with masses of a few Earth masses which formed beyond Saturn's orbit and migrated inwards. These embryos can collide and merge to form Uranus and Neptune. In this work we revisit this formation scenario and study the outcomes of such collisions using 3D hydrodynamical simulations. We investigate under what conditions the perfect-merging assumption is appropriate, and infer the planets' final masses, obliquities and rotation periods, as well as the presence of proto-satellite disks. We find that the total bound mass and obliquities of the planets formed in our simulations generally agree with N-body simulations therefore validating the perfect-merging assumption. The inferred obliquities, however, are typically different from those of Uranus and Neptune, and can be roughly matched only in a few cases. In addition, we find that in most cases the planets formed in this scenario rotate faster than Uranus and Neptune, close to break-up speed, and have massive disks. We therefore conclude that forming Uranus and Neptune in this scenario is challenging, and further research is required. We suggest that future planet formation models should aim to explain the various physical properties of the planets such as their masses, compositions, obliquities, rotation rates and satellite systems., 15 pages, 10 figures, submitted to MNRAS, comments welcome

Understanding the distribution of angular momentum during the formation of planetary systems is a key topic in astrophysics. Data from the $\textit{Kepler}$ and $\textit{Gaia}$ missions allow to investigate whether stellar rotation is correlated with the presence of planets around Sun-like stars. Here, we perform a statistical analysis of the rotation period of 493 planet-hosting stars. These are matched to a control sample, without detected planets, with similar effective temperatures, masses, radii, metallicities, and ages. We find that planet-hosting stars rotate on average $1.63 \pm 0.40$ days slower. The difference in rotation is statistically significant both in samples including and not including planets confirmed by radial velocity follow-up observations. We also analyse the dependence of rotation distribution on various stellar and planetary properties. Our results could potentially be explained by planet detection biases depending on the rotation period of their host stars in both RV and transit methods. Alternatively, they could point to a physical link between the existence of planets and stellar rotation, emphasising the need to understand the role of angular momentum in the formation and evolution planetary systems., 10 pages, 8 figures, 3 Appendix sections (10 pages, 13 figures). Accepted in MNRAS on April 4 2022

The origin of Uranus and Neptune is still unknown. In particular, it has been challenging for planet formation models to form the planets in their current radial distances within the expected lifetime of the solar nebula. In this paper, we simulate the in situ formation of Uranus and Neptune via pebble accretion and show that both planets can form within ∼3 Myr at their current locations, and have final compositions that are consistent with the heavy element to H–He ratios predicted by structure models. We find that Uranus and Neptune could have been formed at their current locations. In several cases a few earth masses (M ⊕ ) of heavy elements are missing, suggesting that Uranus and/or Neptune may have accreted ∼1–3 M⊕ of heavy elements after their formation via planetesimal accretion and/or giant impacts.

Observations and models of giant planets indicate that such objects are enriched in heavy elements compared to solar abundances. The prevailing view is that giant planets accreted multiple Earth masses of heavy elements after the end of core formation. Such late solid enrichment is commonly explained by the accretion of planetesimals. Planetesimals are expected to form at the edges of planetary gaps, and here we address the question of whether these planetesimals can be accreted in large enough amounts to explain the inferred high heavy element contents of giant planets. We perform a series of N-body simulations of the dynamics of planetesimals and planets during the planetary growth phase, taking into account gas drag as well as the enhanced collision cross-section caused by the extended envelopes. We consider the growth of Jupiter and Saturn via gas accretion after reaching the pebble isolation mass and we include their migration in an evolving disk. We find that the accretion efficiency of planetesimals formed at planetary gap edges is very low: less than 10% of the formed planetesimals are accreted even in the most favorable cases, which in our model corresponds to a few Earth-masses. When planetesimals are assumed to form beyond the feeding zone of the planets, extending to a few Hill radii from a planet, accretion becomes negligible. Furthermore, we find that the accretion efficiency increases when the planetary migration distance is increased and that the efficiency does not increase when the planetesimal radii are decreased. Based on these results we conclude that it is difficult to explain the large heavy element content of giant planets with planetesimal accretion during the gas accretion phase. Alternative processes most likely are required, e.g. accretion of vapor deposited by drifting pebbles., Accepted for publication in A&A

The recently adopted Ariel ESA mission will measure the atmospheric composition of a large number of exoplanets. This information will then be used to better constrain planetary bulk compositions. While the connection between the composition of a planetary atmosphere and the bulk interior is still being investigated, the combination of the atmospheric composition with the measured mass and radius of exoplanets will push the field of exoplanet characterisation to the next level, and provide new insights of the nature of planets in our galaxy. In this white paper, we outline the ongoing activities of the interior working group of the Ariel mission, and list the desirable theoretical developments as well as the challenges in linking planetary atmospheres, bulk composition and interior structure., Experimental Astronomy, 53, ISSN:0922-6435, ISSN:1572-9508

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made., The goal of the Ariel space mission is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. The planetary bulk and atmospheric compositions bear the marks of the way the planets formed: Ariel’s observations will therefore provide an unprecedented wealth of data to advance our understanding of planet formation in our Galaxy. A number of environmental and evolutionary factors, however, can affect the final atmospheric composition. Here we provide a concise overview of which factors and effects of the star and planet formation processes can shape the atmospheric compositions that will be observed by Ariel, and highlight how Ariel’s characteristics make this mission optimally suited to address this very complex problem. © The Author(s) 2021., D.T., S.F., S.M., E.S., and A.N. acknowledge the support of the Italian Space Agency (ASI) through the ASI-INAF contract 2018-22-HH.0. D.T., C.C., D.F., and L.P. acknowledge the support of the PRIN-INAF 2016 “The Cradle of Life - GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA”. D.T., S.F., S.M. D.F, J.M., F.O., P.W. acknowledge the support of the Italian National Institute of Astrophysics (INAF) through the INAF Main Stream project “Ariel and the astrochemical link between circumstellar discs and planets” (CUP: C54I19000700005). S.M. acknowledges support from the European Research Council via the Horizon 2020 Framework Programme ERC Synergy “ECOGAL” Project GA-855130. M.K. acknowledges funding by the University of Tartu ASTRA project 2014-2020.4.01.16-0029 KOMEET “Benefits for Estonian Society from Space Research and Application”, financed by the EU European Regional Development Fund. J.M.D.K. gratefully acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through an Emmy Noether Research Group (grant number KR4801/1-1) and the DFG Sachbeihilfe (grant number KR4801/2-1), as well as from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). The research of O.P. is funded by the Royal Society, through Royal Society Dorothy Hodgkin Fellowship DH140243. M.P. thanks the support to NuGrid from STFC (through the University of Hull’s Consolidated Grant ST/R000840/1), and access to VIPER, the University of Hull High Performance Computing Facility. M.P. acknowledges the support from the ”Lendulet-2014” Program of the Hungarian Academy of Sciences (Hungary), from the ERC Consolidator Grant (Hungary) funding scheme (Project RADIOSTAR, G.A. n. 724560), by the National Science Foundation (NSF, USA) under grant No. PHY-1430152 (JINA Center for the Evolution of the Elements). M.P. also thanks the UK network BRIDGCE and the ChETEC COST Action (CA16117), supported by COST (European Cooperation in Science and Technology). M.I. thanks the support by JSPS KAKENHI 18H05439. C.D. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), and the Group project Ref. PID2019-110689RB-I00/AEI/10.13039/501100011033.

Atmospheric temperature is an important parameter controlled by the outward transport of internal energy and the absorption of solar radiation and auroral heating. It is used widely in models of cloud formation, photochemistry, retrieval of elemental abundances from observations, vertical extrapolation of cloud level winds, and as a boundary condition for interior models. The Galileo probe made very precise in situ measurements of Jupiter’s temperature from the upper atmosphere down to a pressure level of ~22 bars. However, those data correspond to a single location of the probe entry site, which also turned out to be a 5-micron hotspot. Other data covering a wider range of latitude and longitude locations are available from the Voyager radio occultation measurements (Lindal et al. JGR 86, A10, 8721, 1981). The use of S and X bands (2.3 GHz and 8.4 GHz) on Voyager allowed measurements of atmospheric refractivity from approximately 1 millibar to the 1 bar level. However, the temperatures derived from these observations were based on the then-available information on refractivities and composition, which have since been refined. Tabulated data are largely not available and so we have first digitized the data from the published figures of all available Voyager radio occultations and verified their fidelity. We then applied correction factors to the pressures and temperatures based on current laboratory data on radio refractivities of gases relevant to the radio occultation regime (H2, He, CH4, PH3, Ne and Ar) and used the gas abundances measured by the Galileo probe, also accounting for their implied revision of the assumed molecular weight. Depending on the set of radio occultation observations, the corrected temperature is greater by as much as 3 K at the 1-bar level and 6 K at the 1-millibar level compared to the originally published profile (Lindal et al. 1981). Considering all available radio occultation data sets the corrected temperature at the 1-bar level is 168.69±6.13 K, including some allowance for small latitudinal, longitudinal, and temporal variations. That allows for the possibility of a wider temperature range of 163-175 K at the 1-bar level than the commonly assumed value of 166 K from the Galileo probe. The profile itself provides an alternative a priori profile for retrieval of temperatures from remote sensing of thermal emission. Temperature at the 1-bar level is a particularly important reference since it serves as an “anchor” in models for retrieving the atmospheric composition and thus has a potential effect on the derived water abundance. It also broadens the range of acceptable upper boundary temperatures for interior models. The corrected data will also serve as a baseline for the radio occultation of Jupiter observations planned in Juno’s extended mission.

Uranus and Neptune exhibit strong zonal winds reaching up to 200 m/s and 400 m/s relative to their assumed bulk rotation, respectively. Furthermore, recent studies show that planetary ices such as water and ammonia become ionically conducting under conditions present in the ice giants. With rapidly increasing electrical conductivity, zonal flows inevitably couple to the background magnetic field, inducing electrical currents and magnetic field perturbations spatially correlated with zonal flows. Induced currents generate Ohmic dissipation, which can be used to constrain the depth of the zonal winds via the energy/entropy flux throughout the planetary interior. Constraining the zonal wind decay can be used to estimate the strength of magnetic field perturbations. Flows coupled to the background magnetic field induce poloidal and toroidal field perturbations through the ω-effect. Toroidal perturbations are expected to diffuse downwards and produce poloidal fields through turbulent convection, which are comparable to those induced by the ω-effect.We present a method for calculating electrical conductivity profiles of ionically conducting H-He-H2O mixtures using results from ab-initio simulations. We then apply this prescription on several published interior structure models of Uranus and Neptune, assuming the heavy elements are represented by water. Structure models with higher water abundances (hot models) also have larger electrical conductivity values and their zonal winds need to decay faster compared to colder models. Using our solutions for the zonal wind decay, we estimate the strength of magnetic field perturbations induced by the zonal flows. We find that colder models could potentially have poloidal field perturbations that reach up to O(0.1) of the background magnetic field in the most extreme case. The possible existence of poloidal field perturbations spatially correlated with zonal flows could be used to constrain the interior structure of Uranus and Neptune.

Gas giants transiting bright nearby stars are key objects for our understanding of planetary system formation and evolution mechanisms. This paper presents a new transiting exoplanet discovered by the WASP-South transit survey, WASP-193b. WASP-193b orbits its Vmag = 12.0 F9 main-sequence host star every 6.25d. Our analyses found that WASP-193b has a mass of Mp = 0.146 ± 0.033 M_Jup, a radius of R_p = 1.58 ± 0.14R_Jup, translating into an extremely low density of rho_p = 0.049 ± 0.015g/cm3. The planet was confirmed photometrically by the 0.6-m TRAPPIST-South and 1.0-m SPECULOOS-South telescopes and spectroscopically by the ESO-3.6-m/HARPS and Euler-1.2-m/CORALIE spectrographs. The combination of its large transit depth (dF≈1.4%), its super-low density, its high-equilibrium temperature (T_eq = 1275 ± 40K), and the infrared brightness of its host star (magnitude Kmag=10.7) makes WASP-193b an exquisite target for a detailed atmospheric characterization by transmission spectroscopy.

Jupiter's atmosphere is enriched with heavy elements by a factor of about 3 compared to proto-solar. The origin of this enrichment and whether it represent the bulk composition of the planetary envelope remain unknown. Internal structure models of Jupiter suggest that its envelope is separated from the deep interior and that the planet is not fully mixed. This implies that Jupiter's atmosphere was enriched with heavy elements just before the end of its formation. Such enrichment can be a result of late planetesimal accretion. However, in-situ Jupiter formation models suggest the decreasing accretion rate with increasing planetary mass, which cannot explain Jupiter's atmospheric enrichment. In this study, we model Jupiter's formation and show that an migration of proto-Jupiter from $\sim$ 20 AU to its current location can lead to a late planetesimal accretion and atmospheric enrichment. Late planetesimal accretion does not occur if proto-Jupiter migrates only a few AU. We suggest that if Jupiter's outermost layer is fully-mixed and is relatively thin (up to $\sim$ 20\% of its mass), such late accretion can explain its measured atmospheric composition. It is therefore possible that Jupiter underwent significant orbital migration followed by late planetesimal accretion., 18 pages, 8 figures, Accepted for ApJL

Uranus and Neptune are still poorly understood. Their gravitational fields, rotation periods, atmosphere dynamics, and internal structures are not well determined. In this paper we present empirical structure models of Uranus and Neptune where the density profiles are represented by polytropes. By using these models, that are set to fit the planetary gravity field, we predict the higher order gravitational coefficients $J_6$ and $J_8$ for various assumed rotation periods, wind depths, and uncertainty of the low-order harmonics. We show that faster rotation and/or deep winds favour centrally concentrated density distributions. We demonstrate that an accurate determination of $J_6$ or $J_8$ with a relative uncertainty no larger than $10\%$ could constrain wind depths of Uranus and Neptune. We also confirm that the Voyager rotation periods are inconsistent with the measured shapes of Uranus and Neptune. We next demonstrate that more accurate determination of the gravity field can significantly reduce the possible range of internal structures. Finally, we suggest that an accurate measurement of the moment of inertia of Uranus and Neptune with a relative uncertainty of $\sim1\%$ and $\sim0.1\%$, could constrain their rotation periods and depths of the winds, respectively., Comment: 14 pages, 12 figures, 2 tables, accepted for publication in MNRAS

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution., Comment: Ariel Definition Study Report, 147 pages. Reviewed by ESA Science Advisory Structure in November 2020. Original document available at: https://www.cosmos.esa.int/documents/1783156/3267291/Ariel_RedBook_Nov2020.pdf/

We present the bright (V$_{mag} = 9.12$), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be $30.5 \pm 0.7$ days using archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 $\pm$ 0.04 R$_{\oplus}$, a mass of $3.07 \pm 0.35$ M$_{\oplus}$, and a density of $8.0 \pm 1.0$ g cm$^{-3}$; TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of $3.29 \pm 0.09$ R$_{\oplus}$, a mass of $9.90^{+1.53}_{-1.49}$ M$_{\oplus}$, and a density of $1.36 \pm 0.25$ g cm$^{-3}$. We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an $M \sin i$ of $2.83^{+0.41}_{-0.34}$ M$_{\oplus}$, and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves., Comment: 21 pages, 11 figures, 3 appendices, accepted for publication in MNRAS

Uranus and Neptune exhibit fast surface zonal winds that can reach up to few hundred meters per second. Previous studies on zonal gravitational harmonics and Ohmic dissipation constraints suggest that the wind speeds diminish rapidly in relatively shallow depths within the planets. Through a case-by-case comparison between the missing dynamical gravitational harmonic $J^\prime_4$ from structure models, and with that expected from fluid perturbations, we put constraints on zonal wind decay in Uranus and Neptune. To this end, we generate polytropic empirical structure models of Uranus and Neptune using $4^{\rm th}$-order Theory of Figures (ToF) that leave hydrostatic $J_4$ as an open parameter. Allotting the missing dynamical contribution to density perturbations caused by zonal winds (and their dynamic self-gravity), we find that the maximum scale height of zonal winds are $\sim 2-3\%$ of the planetary radii for both planets. Allowing the models to have $J_2$ solutions in the $\pm 5 \times 10^{-6}$ range around the observed value has similar implications. The effect of self-gravity on $J^\prime_4$ is roughly a factor of ten lower than that of zonal winds, as expected. The decay scale heights are virtually insensitive to the proposed modifications to the bulk rotation periods of Uranus and Neptune in the literature. Additionally, we find that the dynamical density perturbations due to zonal winds have a measurable impact on the shape of the planet, and could potentially be used to infer wind decay and bulk rotation period via future observations., Comment: Accepted for publication in ApJ

Determining the composition of giant exoplanets is crucial for understanding their origin and evolution. However, the planetary bulk composition is not measured directly but must be deduced from a combination of mass-radius measurements, knowledge of the planetary age and evolution simulations. Accurate determinations of stellar ages, mass-radius, and atmospheric compositions from upcoming missions can significantly improve the determination of the heavy-element mass in giant planets. In this paper, we first demonstrate the importance of an accurate age measurement, as expected from Plato, in constraining the planetary properties. Well-determined stellar ages can reduce the bulk-metallicity uncertainty up to about a factor of two. We next infer the bulk metallicity of warm giants from the Ariel mission reference sample and identify the Ariel high-priority targets for which a measured atmospheric metallicity can clearly break the degeneracy in the inferred composition. We show that knowledge of the atmospheric metallicity can broadly reduce the bulk-metallicity uncertainty by a factor of four to eight. We conclude that the accurate age determination from Plato and atmospheric measurements by Ariel and the James Webb Space Telescope will play a key role in revealing the composition of giant exoplanets., Comment: 11 pages, 12 figures, 2 tables, accepted for publication in Astronomy & Astrophysics; grammar and typos corrected; additional typo corrected

Giant planet evolution models play a crucial role in interpreting observations and constraining formation pathways. However, the simulations can be slow or prohibitively difficult. To address this issue, we calculate a large suite of giant planet evolution models using a state-of-the-art planetary evolution code. Using these data, we create the python program planetsynth that generates synthetic cooling tracks by interpolation. Given the planetary mass, bulk & atmospheric metallicity, and incident stellar irradiation, the program calculates how the planetary radius, luminosity, effective temperature, and surface gravity evolve with time. We demonstrate the capabilities of our models by inferring time-dependent mass-radius diagrams, estimating the metallicities from mass-radius measurements, and by showing how atmospheric measurements can further constrain the planetary bulk composition. We also estimate the mass and metallicity of the young giant planet 51 Eri b from its observed luminosity. Synthetic evolution tracks have many applications, and we suggest that they are valuable for both theoretical and observational investigations into the nature of giant planets., 9 pages, 8 figures, 1 table, accepted for publication in MNRAS

Determining the heavy-element accretion rate of growing giant planets is crucial for understanding their formation and bulk composition. The solid (heavy-element) accretion rate should be carefully modelled during the various stages of giant planet formation and therefore the planetary capture radius must be determined. In some simulations that model the heavy-element accretion rate, such as in N-body simulations, the presence of the gaseous envelope is either neglected or treated in an oversimplified manner. In this paper, we present an approximation for the capture radius that does not require the numerical solution of the stellar structure equations. Our approximation for the capture radius works extremely well for various planetesimal sizes and compositions. We show that the commonly assumed constant density assumption for inferring the capture radius leads to a large error in the calculated capture radius and we therefore suggest that our approximation should be implemented in future simulations.

Previous studies using Kepler data suggest that planets orbiting the same star tend to have similar sizes. However, due to the faintness of the stars, only a few of the planets were also detected with radial velocity follow-ups, and therefore the planetary masses were mostly unknown. It therefore yet to be determined whether planetary systems indeed behave as "peas in a pod". Follow-up programs of TESS targets significantly increased the number of confirmed planets with mass measurements, allowing for a more detailed statistical analysis of multi-planet systems. In this work we explore the similarity in radii, masses, densities, and period ratios of planets within planetary systems. We show that planets in the same system that are similar in radii could be rather different in mass and vice versa. Nevertheless, planets are somewhat similar in mass up to masses of ~100Me and radii of ~10Re. We find that in general, the planetary radii of a given planetary system are more similar than the masses. We conclude that other quantities like the density may be crucial to fully understand the nature of planetary systems and that, due to the diversity of planets within a planetary system, increasing the number of detected systems is crucial for understanding the exoplanetary demographics.&nbsp

Despite many similarities, there are significant observed differences between Uranus and Neptune: while Uranus is tilted and has a regular set of satellites, suggesting their accretion from a disk, Neptune's moons are irregular and are captured objects. In addition, Neptune seems to have an internal heat source, while Uranus is in equilibrium with solar insulation. Finally, structure models based on gravity data suggest that Uranus is more centrally condensed than Neptune. We perform a large suite of high resolution SPH simulations to investigate whether these differences can be explained by giant impacts. For Uranus, we find that an oblique impact can tilt its spin axis and eject enough material to create a disk where the regular satellites are formed. Some of the disks are massive and extended enough, and consist of enough rocky material to explain the formation of Uranus' regular satellites. For Neptune, we investigate whether a head-on collision could mix the interior, and lead to an adiabatic temperature profile, which may explain its larger flux and higher moment of inertia value. We find that massive and dense projectiles can penetrate towards the centre and deposit mass and energy in the deep interior, leading to a less centrally concentrated interior for Neptune. We conclude that the dichotomy between the ice giants can be explained by violent impacts after their formation., 18 pages, 15 figures, 1 table, accepted to MNRAS