Planetary rings provide natural laboratories for studying the fundamental processes that govern the evolution of planetary systems. However, several key features, such as the sharp inner edges of Saturn's rings, remain unresolved. In this Letter, we introduce and quantify the eclipse-Yarkovsky (EY) effect, a thermal torque arising from asymmetric thermal emission of particles during planetary eclipses, which is effective for particles larger than millimeters in size. We formulate this effect within a continuum framework appropriate for collisionally coupled planetary rings and derive the continuum evolution equation that includes the EY torque and viscous diffusion (Equation (26)), constraining its magnitude using ring particle spin distributions obtained from N-body simulations. We find that the EY effect systematically produces a positive angular momentum flux that could overcome the viscous torque, driving ring material outward and leading to long-term decretion. The total EY torque principally depends on the optical depth, in which we identify three dynamical regimes: dense, transitional, and tenuous, each exhibiting distinct evolutionary pathways. In the dense and transitional regimes, the EY torque can produce a sharp inner edge such as that of Saturn's A ring. In the tenuous regime, it can drive an entire ring outward while preserving shape. This outward transport may also facilitate satellite formation beyond the Roche limit. We also quantitatively show that planetary thermal radiation exerts an opposing torque, namely the planetary-Yarkovsky effect, whose importance depends on planetary emissivity and ring-particle albedo, and may lead to inward transport in Saturn's close-in rings.

At the end of the Cassini mission, Saturn's rings have been claimed to be spectacularly young compared to the age of the Solar System: their unusual ice-rich composition corresponds to initially pure ice rings polluted by interplanetary dust particles for 100 to 400 Myr. Since then, this exposure age has been commonly accepted as the real age of the rings. In this paper, we review the processes that are involved in determining the exposure age. We aim to see how the exposure age depends on various parameters and how relevant it is to define the real rings age. First, a new expression for the gravitational focusing onto planar rings, important parameter but crudely defined in the literature, is derived. Then, an analytical formula describing how the dust fraction varies with time in static or viscously evolving rings is provided, including possible vaporisation at impact. Finally, we introduce a cleaning process from space weathering to possibly alter dust and reduce its amount to make rings look younger than they are. We first found that the gravitational focusing is 5 times less important than previously thought, which automatically increases the exposure age from 0.5 to 2 Gyr. Moreover, depending on the impact properties (vaporisation rate, space weathering efficiency), several billion years can easily be reached. Finally, we find that the dust fraction in the rings converges towards a finite value which, in particular with an efficient space weathering mechanism, can be close to the observed one in the current rings. In this case, neither the age nor the initial composition of the rings can be derived, and the measure of the dust fraction and bombardment rate only constrains the physical parameters of the impacts and the efficiency of the space weathering. As long as the latter parameters are not known, the exposure age argument in favour of young rings is completely undercut.

The recent discovery of strong tidal dissipation in Saturn’s interior has radically changed our view of the Saturnian system. While some questions are naturally answered by the new paradigm, others are emerging and require further measurement. This article presents the next key questions to be addressed by future space missions and analysis. Suggestions for space measurements to discriminate between different scenarios concerning the formation, evolution and internal state of the Saturnian system are given.

The origin of Saturn’s rings is a long standing mystery in planetary science, for which the age of this system is a critical constraint. After having clarified what the age of the rings may mean, this article reviews several aspects of this question. We discuss the exposure age, which was recently found to be on the order a few 100 Myrs based on the rings’ composition and their bombardment rate by micrometeoroids. The derivation of this age is explained, and the possible caveats are discussed, including the idea of a putative phenomenon of cleaning of the rings. We address the age of structures such as the Cassini division, plateaux, ramps, and how they are constrained by interactions with satellites and the effects of bombardment. We then address the dynamical evolution of the rings, due to viscosity, micrometeoroid bombardment, and satellite torques. Initially massive rings are found to viscously spread and lose mass quickly and then converge to the present mass in billions of years. However, the dynamical effects of micrometeoroid bombardment can take the reins over viscosity and may wipe the rings out efficiently. Naturally, consideration of ring origin also motivates us to review the ring formation models existing in the literature, and discuss their implications on the composition and age of the rings, in particular in the frame of large tidal dissipation inside Saturn. Finally, putting together and synthesizing these results, we conclude that a fully consistent picture for the origin and age of Saturn’s rings has yet to be established and more work remains to be done to resolve this important question.

Context. Complete, accurate, and precise catalogues of exoplanet host star (EHS) properties are essential to deriving high-quality exoplanet parameters. These datasets can then be used to study individual planets, planet populations, and planet formation within their Galactic context. Aims. This paper is aimed at homogeneously parameterising EHS and their exoplanets, selected from the Encyclopedia of Exo-planetary Systems and the NASA Exoplanets Archive, using Gaia astrometric, photometric, and GSP-Spec spectroscopic data, complemented by some ground-based spectroscopic survey information. Methods. From the atmospheric parameters of 2573 EHS, we computed their luminosity, radius, and mass, with no prior assumption from stellar evolution models. Their Galactic positions, kinematic and orbital properties were also derived. We then re-scaled the mass and radius of 3556 exoplanets, fully consistently with the stellar data (when available). Results. The Gaia spectroscopic stellar effective temperatures, luminosities, and radii are in rather good agreement with literature values but are more precise. In particular, stellar radii are derived with typically less than 3% uncertainty (instead of similar to 8% in the literature); this reduces the uncertainty on the planetary radii significantly and allows for a finer analysis of the decrease in the number of planets around 1.8 R-circle plus (evaporation valley). Larger differences, however, were found for the masses that are more difficult to estimate by any methods. We note that the EHS population is rather diverse in terms of the chemical and Galactic properties, although they are all found in the Solar vicinity, close to the Local spiral arm. Most EHS belong to the thin disc, but some older thick disc and halo members have also been identified. For the less massive planets (log(M-p/M-Jup) less than or similar to -0.6), the average planet radius increases with the metallicity of the host star. For giant planets, a dichotomy between dense and inflated planets is found. Denser planets (R-p less than or similar to 1.1 R-Jup) tend to be more massive as the metallicity of the host star increases, while inflated planets are more massive for less metallic hosts. If confirmed, this bimodality implies that the diversity of giant exoplanets depends on their Galactic birth locus, with dense giant planets being more numerous than inflated ones when [M/H] is higher than similar to 1.5 times Solar, as in the central Milky Way regions. Conclusions. The Gaia spectroscopic catalogue of exoplanets and their host stars is large, homogeneous, and precise. Thus, it would be a useful added-value for planetary studies. Since it is based on literature data, it can also easily be updated thanks to future Gaia data releases and other space- and ground-based surveys.

Gravitational systems in astrophysics often comprise a body – the primary – that far outweights the others, and which is taken as the centre of the reference frame. A fictitious acceleration, also known as the indirect term, must therefore be added to all other bodies in the system to compensate for the absence of motion of the primary. In this paper, we first stress that there is not one indirect term but as many indirect terms as there are bodies in the system that exert a gravitational pull on the primary. For instance, in the case of a protoplanetary disc with two planets, there are three indirect terms: one arising from the whole disc, and one per planet. We also highlight that the direct and indirect gravitational accelerations should be treated in a balanced way: the indirect term from one body should be applied to the other bodies in the system that feel its direct gravitational acceleration, and only to them. We point to situations where one of those terms is usually neglected however, which may lead to spurious results. These ideas are developed here for star-disc-planets interactions, for which we propose a recipe for the force to be applied onto a migrating planet, but they can easily be generalized to other astrophysical systems.

We report the finding of a linear, non-axisymmetric, global instability in gas discs around stars, which may be relevant to other astrophysical discs. It takes the form of an m=1 mode that grows in the disc density distribution while the star-barycentre distance rises exponentially with a characteristic timescale that is orders of magnitude longer than the orbital period. We present results of hydrodynamical simulations with various codes and numerical methods, using either barycentric or stellocentric reference frames, with or without the disc's self gravity: all simulations consistently show an unstable mode growing exponentially. The instability disappears if, and only if, the reflex motion of the star due to the disc's asymmetry is not taken into account in the simulations. For this reason we refer to this instability as the reflex instability. We identify a feedback loop as a possible origin, whereby the acceleration of the star excites the eccentricity of the disc, yielding an m=1 mode in the density distribution which, in turn, pulls the star. The growth timescale of the instability decreases with increasing disc mass and is a few hundred orbits for disc-to-star mass ratios of a few percent. If truly physical, and not due to a numerical artifact that would be common to all the codes we have employed, the reflex instability could have a dramatic impact on protoplanetary discs evolution and planetary formation.

This article explores the different formation scenarios of the Kronian moons system in the context of a highly dissipative Saturn, with the objective of identifying the most likely of these scenarios. First, we review the diversity of objects – moons and rings – orbiting solar system giant planets, and the diversity of their architectures, which formation scenarios must reproduce. We then identify in this broader context the specific features of the Saturn system, such as the particularly large spectrum of its moon masses, the uniqueness of Titan and the presence of both dense and tenuous rings, before discussing the applicability of the different giant planet moon formation scenarios to the Saturn case. We discuss each of the most relevant scenarios and their respective merits. Finally, we tentatively propose a “favorite” scenario and we identify the key observations to be made by future space missions and/or Earth-based telescopic observations to validate this scenario or possibly alternative ones.

The European Space Agency has selected PLATO (PLAnetary Transits and Oscillations of stars) for its M3 launch which is scheduled for 2026. With its extremely large field of view, PLATO is designed to obtain photometric measurements over an extended period for bright stars in order to detect and characterise (primarily) rocky planets in the habitable zones of solar type stars. The PLATO measurements will have sufficient sensitivity to determine the mass, radius and age of the host stars with unprecedented accuracy. The PLATO planet database will provide the first large-scale catalogue of accurately and homogeneously characterised small planets at intermediate orbital periods, which will can be used to severely constraint planet formation theories. This would facilitate large scale comparative exo-planetology. In addition the bright PLATO host stars will be ideal targets for atmospheric study with next generation facilities such as the ELT. The PLATO sensitivity will be sufficient to detect pulsations from stars across the HR diagram allowing a deep understanding of stellar structure and evolution to be developed using parameters determined from asteroseismology.

Saturn's rings are well known for many good reasons, one of them being their brightness. Made of almost 99% water ice, they are by far the most ice-rich object of the solar system, and their composition is still a puzzle. Most formation models rely on the stripping of the icy mantle of a large body, be it by colision with a comet or tidal disruption of a passing centaur or a migrating satellite, providing the rings with an initial pure water composition. However, the rings are constantly bombarded by micrometeorites, which are made of at least half non icy material (hereafter "dust"). Based on the percentage of dust in the rings (Zhang et al. 2017a,b), the mass of the rings (Iess et al. 2019), and estimates of the bombardment rate, an exposure age of 10 to 100 million years has been derived. This age is simply the time it would take to bring all the dust observed in the rings through a constant bombardment at the present rate, assuming the rings are initially devoid of dust and keep all the pollution they recieve. It had been initially interpreted as the physical age of the rings (as illustrated by Figure 1). Crida et al. (2019) have shown that the exposure age and the formation age are actually two different concepts and could differ. This claim is supported by the results by Hsu et al. (2018) and Waite et al. (2018) who have found that the rings lose non icy material into Saturn ; this suggests the existence of some unknown but non-negligible cleaning mechanism.Here, we explore the possibility of a cleaning mechanism in the rings, and perform numerical simulations and analytical calculations of the evolution of the pollution rate in the rings for various scenarios. When the cleaning is modeled by a characteristic time τc such that the time derivative of the dust density d is -d/τc , an equilibrium dust profile exists, and the dust fraction doesn't grow linearly with time. In fact, if the initial composition of the rings is more dust-rich than the equilibrium profile, the dust fraction then decreases with time to converge towards this equilibrium. Such a (yet unknown) cleaning mechanism would open the possibility for initially non-pure ice rings, if the cleaning time is shorter than the age of the solar system.More interestingly, the equilibrium profile is similar to the one obtained without cleaning but for a ring age of τc . In other words, there is no way of deciding whether the exposure age represents the real age of the rings or their cleaning time, as illustrated by how similar the figures 1 and 2 are. We find parameters that allow to reproduce the present rings density and pollution after 4.5 Gyr of evolution (figure 2). This shows that old rings are still a valid possiblity, and that the theory of their cleaning desserves further investigation. Figure 1 : Ring density profile (blue) and dust density profile (orange) after 100 Myrs of viscous evolution with a meteoritic bombardement following the parameters used by Zhang et al. (2017a), starting with a density profile equal to the one shown in figure 2, but with zero dust. No cleaning is used in this simulation. The result is similar to the actual A and B rings, showing that they correspond to 100 Myrs exposure age. Figure 2 : Ring density profile (blue) and dust density profile (orange) after 4.5 Gyrs of viscous evolution reproducing Salmon et al. (2010), with a meteoritic bombardement following the parameters used by Zhang et al. (2017a) and a cleaning time τc = 100 Myrs. The result is almost identical to the one of Figure 1, and doesn't depend on the initial dust content of the rings, showing that an efficient cleaning mechanism can reconcile old rings with their apparent youth. References:Crida A., Charnoz S., Hsu H.-W., Dones L. (2019) Are Saturn's rings actually young ? Nature Astronomy 876, 437Hsu H.-W. et al. (2018) In situ collection of dust grains falling from Saturn’s rings into its atmosphere. Science 362, eaat3185Iess L. et al. (2019) Measurement and implications of Saturn’s gravity field and ring mass. Science 364, eaat2965Salmon J., Charnoz S., Crida A., Brahic A. (2010) Long-term and large-scale viscous evolution of dense planetary rings Icarus 209,771-785Waite J. R. et al. (2018) Chemical interactions between Saturn’s atmosphere and its rings. Science 362, eaat2382Zhang, Z. et al. (2017) Exposure age of Saturn’s A and B rings, and the Cassini Division as suggested by their non-icy material content. Icarus 294, 14–42Zhang, Z. et al. (2017) Cassini microwave observations provide clues to the origin of Saturn’s C ring. Icarus 281, 297–321.

Context. In the context of low-viscosity protoplanetary discs (PPDs), the formation scenarios of the Solar System should be revisited. In particular, the Jupiter-Saturn pair has been shown to lock in the 2:1 mean motion resonance while migrating generally inwards, making the Grand Tack scenario impossible. Aims. We explore what resonant chains of multiple giant planets can form in a low-viscosity disc, and whether these configurations can evolve into forming the Solar System in the post gas disc phase. Methods. We used hydrodynamical simulations with the code FARGOCA to study the migration of the giant planets in a disc with viscosity parameter of α = 10 −4 . After a transition phase to a gas-less configuration, we studied the stability of the obtained resonant chains through their interactions with a disc of leftover planetesimals by performing N-body simulations using rebound. Results. The gaps opened by giant planets are wider and deeper for lower viscosity, reducing the damping effect of the disc. Thus, when planets enter a resonance, the resonant angle remains closer to circulation, making the chain weaker. Exploring numerous configurations, we found five stable resonant chains of four or five planets. In a thin (cold) PPD, the four giant planets revert their migration and migrate outwards. After disc dispersal, under the influence of a belt of planetesimals, some resonant chains undergo an instability phase while others migrate smoothly over a billion years. For three of our resonant chains, about ~1% of the final configurations pass the four criteria to fit the Solar System. The most successful runs are obtained for systems formed in a cold PPD with a massive planetesimal disc. Conclusions. This work provides a fully consistent study of the dynamical history of the Solar System’s giant planets, from the protoplanetary disc phase up to the giant planet instability. Although building resonant configurations is difficult in low-viscosity discs, we find it possible to reproduce the Solar System from a cold, low-viscosity protoplanetary disc.

Planets form in proto-planetary disks. In this review, we describe the structure and properties of such disks, and the various phenomenons that lead to the final product: a planetary system. First, micrometre dust settles and coagulates. Then, a complex interplay between the gas and centimetre aggregates leads to efficient phenomenons such as the streaming instability and the pebble accretion. Finally, gas accretion Once the gas disk is dissipated, giant planets may form satellites from massive rings, the terrestrial planets assemble from smaller embryos, and global dynamical instabilities give the planetary systems their final

Free-floating planets (FFPs) can result from dynamical scattering processes happening in the first few million years of a planetary system's life. Several models predict the possibility, for these isolated planetary-mass objects, to retain exomoons after their ejection. The tidal heating mechanism and the presence of an atmosphere with a relatively high optical thickness may support the formation and maintenance of oceans of liquid water on the surface of these satellites. In order to study the timescales over which liquid water can be maintained, we perform dynamical simulations of the ejection process and infer the resulting statistics of the population of surviving exomoons around free-floating planets. The subsequent tidal evolution of the moons' orbital parameters is a pivotal step to determine when the orbits will circularize, with a consequential decay of the tidal heating. We find that close-in ($a \lesssim 25 $R$_{\rm J}$) Earth-mass moons with CO$_2$-dominated atmospheres could retain liquid water on their surfaces for long timescales, depending on the mass of the atmospheric envelope and the surface pressure assumed. Massive atmospheres are needed to trap the heat produced by tidal friction that makes these moons habitable. For Earth-like pressure conditions ($p_0$ = 1 bar), satellites could sustain liquid water on their surfaces up to 52 Myr. For higher surface pressures (10 and 100 bar), moons could be habitable up to 276 Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable conditions for long timescales, and during the ejection of the FFP remain bound with the escaping planet, being less affected by the close encounter.

To keep current global warming below 1.5{\deg}C compared with the pre-industrial era, measures must be taken as quickly as possible in all spheres of society. Astronomy must also make its contribution. In this proceeding, and during the workshop to which it refers, different levers of actions are discussed through various examples: individual efforts, laboratory-level actions, impact evaluation and mitigation in major projects, institutional level, and involvement through collectives.

Context. When considering the migration of Jupiter and Saturn, a classical result is to find the planets migrating outwards and locked in the 3:2 mean motion resonance (MMR). These results were obtained in the framework of viscously accreting discs, in which the observed stellar accretion rates constrained the viscosity values. However, it has recently been shown observationally and theoretically that discs are probably less viscous than previously thought. Aims. Therefore, in this paper, we explore the dynamics of pairs of giant planets in low-viscosity discs. Methods. We performed two-dimensional hydrodynamical simulations using the grid-based code FARGOCA. Results. In contrast to classical viscous discs, we find that the outer planet never crosses the 2:1 resonance and the pair does not migrate outwards. After a wide parameter exploration, including the mass of the outer planet, we find that the planets are primarily locked in the 2:1 MMR and in some cases in the 5:2 MMR. We explain semi-analytically why it is not possible for the outer planet to cross the 2:1 MMR in a low-viscosity disc. Conclusions. We find that pairs of giant planets migrate inwards in low-viscosity discs. Although, in some cases, having a pair of giant planets can slow down the migration speed with respect to a single planet. Such pairs of slowly migrating planets may be located, at the end of the disc phase, in the population of exoplanets of 'warm Jupiters'. However, the planets never migrate outwards. These results could have strong implications on the Solar System's formation scenarios if the Sun's protoplanetary disc had a low viscosity.

AbstractUsing 2D hydrodynamical simulations, we show that in a low viscosity protoplanetary disc, Jupiter and Saturn get locked in the 2:1 mean motion resonance and migrate slowly inwards, unlike cases at higher viscosities. We conclude that in such discs the scenario of the Grand-Tack is not possible. Additionally, we investigate how the migration of the four (potentially five) giant planets in low viscous discs may affect the initial conditions of another important model for the formation history of our Solar System: the Nice Model. Adding ice giants in our hydrodynamical simulations, we find different possible resonant chains induced by migration. We then let the disc evolve until the gas phase dissipates and study the dynamical stability of the system. We find it possible to recreate the Solar System from such resonant chains, however the likelihood of this outcome remains low.

Planets form in protoplanetary discs and their interactions with the gas give rise to migration. For a long time, discs were believed to have a non-negligible viscosity to justify the high accretion rates of gas onto the central star. However, it has recently been shown observationally and theoretically that protoplanetary discs are probably much less viscous than previously thought. In our study, we use a new paradigm for the theoretical modelling of discs where the accretion onto the central star is done through the superficial layers while the mid-plane has a close to zero viscosity (Lega et al. 2022). In such discs, the migration of a single giant planet differs from the classical Type-II migration regime and depends on the thickness of the accretion layer. It is therefore interesting to consider the migration of a pair of giant planets in this new model. We have started this project, in the simplified framework of 2D hydrodynamical simulations (using the code FARGOCA) with an α viscosity parameter of 10−5 (in the standard Shakura & Sunyaev 1973 viscosity parametrization). We first consider a pair of Jupiter and Saturn mass planets, then extend our study to a wider range of planetary masses. In classical viscous discs (corresponding to an α=10−3), Jupiter and Saturn systems are most often locked in the 3:2 mean motion resonance and may migrate outwards. Instead in our case (α=10−5), we find that the pair of planets gets locked in the 2:1 resonance and has a stalled or slightly inward migration. We confirmed this result for a range of disc masses and thicknesses as well as different starting positions of Saturn. This result is also independent of the mass of the outer planet. In order to explain our result, we have a used a criterion for resonance crossing based on Batygin, 2015 . Unlike in classical discs, a planet growing and migrating in a low viscosity disc does not reach the migration speed required to cross the 2:1 MMR. The only case in which outward migration is observed, is the "ad-hoc" scenario where Saturn would form inside the 2:1 resonance and get locked in the 3:2. However, owing to the large width of Jupiter's gap, this scenario seems unlikely. If the Solar System formed from such a low-viscosity disc, this result has strong implications for the Grand Tack and Nice models, which both assume Jupiter and Saturn to be inside the 2:1 resonance. The stalled migration could, however, explain the so called warm-Jupiters population among the detected exoplanets, providing that these are in multi-planet systems. Additionally, we remark that the only system with two giant planets observed in a disc of gas, namely PDS70, occurs to be close to the 2:1 resonance. Figure 1: Surface density of a 2D simulation after nearly 300 000 years of evolution, displaying Jupiter (filled circle) and Saturn (empty circle) in their common gap. The planets are stably locked in the 2:1 mean motion resonance and are following a very slow inward migration at a speed of one a.u. per million years. References: E. Lega et al., “Migration of Jupiter Mass Planets in Discs with Laminar Accretion Flows,” Astronomy & Astrophysics 658 (2022) Konstantin Batygin, “Capture of Planets into Mean-Motion Resonances and the Origins of Extrasolar Orbital Architectures,” Monthly Notices of the Royal Astronomical Society 451, no. 3 (August 11, 2015)

Context. The 98{\deg}-obliquity of Uranus is commonly attributed to giant impacts that occurred at the end of the planetary formation. This picture, however, is not devoid of weaknesses. Aims. On a billion-year timescale, the tidal migration of the satellites of Jupiter and Saturn has been shown to strongly affect their spin-axis dynamics. We aim to revisit the scenario of tilting Uranus in light of this mechanism. Methods. We analyse the precession spectrum of Uranus and identify the candidate secular spin-orbit resonances that could be responsible for the tilting. We determine the properties of the hypothetical ancient satellite required for a capture and explore the dynamics numerically. Results. If it migrates over 10 Uranus' radii, a single satellite with minimum mass 4e-4 Uranus' mass is able to tilt Uranus from a small obliquity and make it converge towards 90{\deg}. In order to achieve the tilting in less than the age of the Solar System, the mean drift rate of the satellite must be comparable to the Moon's current orbital expansion. Under these conditions, simulations show that Uranus is readily tilted over 80{\deg}. Beyond this point, the satellite is strongly destabilised and triggers a phase of chaotic motion for the planet's spin axis. The chaotic phase ends when the satellite collides into the planet, ultimately freezing the planet's obliquity in either a prograde, or plainly retrograde state (as Uranus today). Spin states resembling that of Uranus can be obtained with probabilities as large as 80%, but a bigger satellite is favoured, with mass 1.7e-3 Uranus' mass or more. Yet, a smaller ancient satellite is not categorically ruled out, and there is room for improving this basic scenario in future studies. Interactions among several pre-existing satellites is a promising possibility.

The Saturn System has been studied in detail by the Cassini-Huygens Mission. A major thrust of those investigations has been to understand how Saturn formed and evolved and to place Saturn in the context of other gas giants and planetary systems in general. Two models have been proposed for the formation of the giant planets,the core accretion model and the disk instability model. The heavy element enrichment, core size, and internal structure of Saturn, compared to Jupiter strongly favor the core accretion model as for Jupiter. Two features of the core accretion model that are distinct from the disk instability model are the growth of a core with a mass several times that of the Earth, followed by runaway collapse of gas onto the core once a mass threshold is reached. The heavy element core grows slowly over millions of years through accretion of cm-m sized pebbles, even larger bodies, and moon sized embryos in the gaseous disk. The abundance pattern of heavy elements is thus a key constraint on formation models. C, N, S, and P at Saturn are presently known to varying degree of uncertainty. The He to H ratio in the atmosphere is crucial for understanding heat balance, interior processes, and planetary evolution, but present values at Saturn range from low to high, allowing for a wide range of possibilities. While the very low values are favored to explain excess luminosity, high values might indicate presence of layered convection in the interior, resulting in slow cooling. Additional insight into Saturn's formation comes from the unique data on the rings from Cassini's Grand Finale orbits. While the solar system is the only analog for the extra solar systems, detection of the alkali metals and water in giant exoplanets is useful for understanding the formation and evolution of Saturn, where such data are presently lacking.