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Radiative-transfer (RT) is a fundamental part of modelling exoplanet atmospheres with general circulation models (GCMs). An accurate RT scheme is required for estimates of the atmospheric energy transport and for gaining physical insight from model spectra. We implement three RT schemes for Exo-FMS: semi-grey, non-grey `picket fence', and real gas with correlated-k. We benchmark the Exo-FMS GCM using these RT schemes to hot Jupiter simulation results from the literature. We perform a HD 209458b-like simulation with the three schemes and compare their results. These simulations are then post-processed to compare their observable differences. The semi-grey scheme results show qualitative agreement with previous studies in line with variations seen between GCM models. The real gas model reproduces well the temperature and dynamical structures from other studies. After post-processing our non-grey picket fence scheme compares very favourably with the real gas model, producing similar transmission spectra, emission spectra and phase curve behaviours. Exo-FMS is able to reliably reproduce the essential features of contemporary GCM models in the hot gas giant regime. Our results suggest the picket fence approach offers a simple way to improve upon RT realism beyond semi-grey schemes., MNRAS accepted 22 June 2021 - V2, typos fixed

The work described in this paper harnesses an open-source astrodynamics engine and visualization to quantify the performance of on-board optical navigation. It introduces the Hough Circles transfor...

The existence of a population of gas giants on very short-period orbits (\(\lesssim 10\)days) known as hot Jupiters has conventionally been attributed to formation at large heliocentric distances followed by a phase of dramatic inward migration. An outstanding issue with this picture is that hot Jupiters are observed to have a much lower occurrence rate of close-in planetary companions than their more distant analogs, known as warm Jupiters. In this work, we demonstrate through numerical simulations and analytic considerations that this is a natural dynamical consequence assuming an in situformation scenario, where super-Earth cores attain gas giant status. Unless positioned in a dynamical "sweet spot", hot Jupiters will clear out neighboring companions, leaving their inner regions empty but commonly retaining distant outer companions. To contrast, in situ-formed warm Jupiters can more readily maintain nearby companions, especially if they have formed outward of the giant. Furthermore, we show that the surviving outer companions of hot Jupiters often sit below modern detection sensitivity limits, suggesting that these close-in giants are not as isolated as previous observations suggest.

We investigate the impact of pre-main sequence stellar luminosity evolution on the thermal and chemical properties of disc mid-planes. We create template disc models exemplifying initial conditions for giant planet formation for a variety of stellar masses and ages. These models include the 2D physical structure of gas as well as 1D chemical structure in the disc mid-plane. The disc temperature profiles are calculated using fully physically consistent radiative transfer models for stars between 0.5 and 3 M⊙ and ages up to 10 Myr. The resulting temperature profiles are used to determine how the chemical conditions in the mid-plane change over time. We therefore obtain gas and ice-phase abundances of the main carbon and oxygen carrier species. While the temperature profiles produced are not markedly different for the stars of different masses at early stages (≤1 Myr), they start to diverge significantly beyond 2 Myr. Discs around stars with mass ≥1.5 M⊙ become warmer over time as the stellar luminosity increases, whereas low-mass stars decrease in luminosity leading to cooler discs. This has an observable effect on the location of the CO snowline, which is located >200 au in most models for a 3 M⊙ star, but is always within 80 au for 0.5 M⊙ star. The chemical compositions calculated show that a well-defined stellar mass and age range exists in which high C/O gas giants can form. In the case of the exoplanet HR8799b, our models show that it must have formed before the star was 1 Myr old.

NASA’s Mars Design Reference Architecture 5.0 presents architecture options for a crewed Mars mission. This paper compares the cryogenic chemical-propulsion option in that study with an alternative...

The Cassini and Juno probes have revealed large coherent cyclonic vortices in the polar regions of Saturn and Jupiter, a dramatic contrast from the east-west banded jet structure seen at lower latitudes. Debate has centered on whether the jets are shallow, or extend to greater depths in the planetary envelope. Recent experiments and observations have demonstrated the relevance of deep convection models to a successful explanation of jet structure and cyclonic coherent vortices away from the polar regions have been simulated recently including an additional stratified shallow layer. Here we present new convective models able to produce long-lived polar vortices. Using simulation parameters relevant for giant planet atmospheres we find flow regimes that are in agreement with geostrophic turbulence (GT) theory in rotating convection for the formation of large scale coherent structures via an upscale energy transfer fully three-dimensional. Our simulations generate polar characteristics qualitatively similar to those seen by Juno and Cassini: they match the structure of cyclonic vortices seen on Jupiter; or can account for the existence of a strong polar vortex extending downwards to lower latitudes with a marked spiral morphology and the hexagonal pattern seen on Saturn. Our findings indicate that these vortices can be generated deep in the planetary interior. A transition differentiating these two polar flows regimes is described, interpreted in terms of different force balances and compared with previous shallow atmospheric models which characterised polar vortex dynamics in giant planets. In addition, the heat transport properties are investigated confirming recent scaling laws obtained in the context of reduced models of GT., Comment: 18 pages, 13 figures and 3 tables

Materials at high pressures and temperatures are of great interest for planetary science and astrophysics, warm dense-matter physics and inertial confinement fusion research. Planetary structure models rely on an understanding of the behaviour of elements and their mixtures under conditions that do not exist on Earth; at the same time, planets serve as natural laboratories for studying materials at extreme conditions. The topic of dense hydrogen is timely given the recent accurate measurements of the gravitational fields of Jupiter and Saturn, the current and upcoming progress in shock experiments, and the advances in numerical simulations of materials at high pressure. In this Review we discuss the connection between modelling planetary interiors and the high-pressure physics of hydrogen and helium. We summarize key experiments and theoretical approaches for determining the equation of state and phase diagram of hydrogen and helium. We relate this to current knowledge of the internal structures of Jupiter and Saturn, and discuss the importance of high-pressure physics to their characterization. Understanding the behaviour of materials at high pressures and temperatures is of great importance to planetary science and the physics of warm dense matter. This Review addresses the close connection between modelling the interiors of gaseous planets and the high-pressure physics of hydrogen and helium.

The discovery of living organisms under extreme environmental conditions of pressure, temperature, and chemical composition on Earth has opened up the possibility of existence and persistence of life in extreme environment pockets across the solar system. These environments range from the many intriguing moons, to the deep atmospheres of Venus and even the giant gas planets, to the small icy worlds of comets and Kuiper Belt Objects (KBOs). Exploring these environments can ascertain the range of conditions that can support life and can also identify planetary processes that are responsible for generating and sustaining habitable worlds. These environments are also time capsules into early formation of the solar system and will provide vital clues of how our early solar system gave way to the current planets and moons. Over the last few decades, numerous missions started with flyby spacecraft, followed by orbiting satellites and missions with orbiter/lander capabilities. Since then, there have been numerous missions that have utilized rovers of ever-increasing size and complexity, equipped with state-of-the-art laboratories on wheels. Although current generations of rovers achieve mobility through wheels, there are fundamental limitations that prevent these rovers from accessing rugged environments, cliffs, canyons, and caves. These rugged environments are often the first places geologist look to observe stratification from geohistorical processes. There is an important need for new robot mobility solutions, like hopping, rolling, crawling, and walking that can access these rugged environments like cliffs, canyons, and caves. These new generations of rovers have some extraordinary capabilities including being able to grip onto rocks like NASA/JPL LEMUR 2, operate in swarms such as MIT’s microbots, or have high-specific energy fuel cell power supply that is approximately 40-fold higher than conventional lithium ion batteries to Stanford/NASA JPL’s Hedgehog which is able to hop and somersault in low-gravity environments such asteroids. All of these mobility options and supporting technologies have been proposed and developed to explore these hard-to-reach unconventional environments. This article provides a review of the robotic systems developed over the past few decades, in addition to new state-of-the-art concepts that are leading contenders for future missions to explore extreme environments on Earth and off-world.

We analyse the transmission spectra of KELT-20b/MASCARA-2b to search for possible thermal inversion agents. The data consist of three transits obtained using HARPSN and one using CARMENES. We removed stellar and telluric lines before cross-correlating the residuals with spectroscopic templates produced using a 1D plane-parallel model, assuming an isothermal atmosphere and chemical equilibrium at solar metallicity. Using a likelihood-mapping method, we detect Fe i at > 13σ, Ca ii H$\&$K at > 6σ and confirm the previous detections of Fe ii, Ca ii IR Triplet, and Na i D. The detected signal of Fe i is shifted by −3.4 ± 0.4 km s−1 from the planetary rest frame, which indicates a strong day–night wind. Our likelihood-mapping technique also reveals that the absorption features of the detected species extend to different altitudes in the planet’s atmosphere. Assuming that the line lists are accurate, we do not detect other potential thermal inversion agents (NaH, MgH, AlO, SH, CaO, VO, FeH, and TiO) suggesting that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed Ti- and V-bearing species from the upper atmosphere. Our results, therefore, show that KELT-20b/MASCARA-2b cannot possess an inversion layer caused by a TiO/VO-related mechanism. The presence of an inversion layer would therefore likely be caused by metal atoms such as Fe i and Fe ii. Finally, we report a double-peak structure in the Fe i signal in all of our data sets that could be a signature of atmospheric dynamics. However, further investigation is needed to robustly determine the origin of the signal.

The ice giant planets, Uranus and Neptune, are fundamentally different from the gas giant and terrestrial planets. Though ice giants represent the most common size of exoplanet and possess characteristics that challenge our understanding of the way our solar system formed and evolved, they remain the only class of planetary object without a dedicated spacecraft mission. The inclusion of a Uranus orbiter as the third highest priority Flagship mission in the NASA Planetary Science Decadal Survey “Vision and Voyages for Planetary Science in the Decade 2013–2022” indicates a high level of support for exploration of the ice giants by the planetary science community. However, given the substantial costs associated with a flagship mission, it is critical to explore lower cost options if we intend to visit Uranus within an ideal launch window of 2029–2034 when a Jupiter gravity assist becomes available. In this paper, we describe the Quest to Uranus to Explore Solar System Theories (QUEST), a New Frontiers class Uranus orbiter mission concept study performed at the 30th Annual NASA/JPL Planetary Science Summer Seminar. The proposed QUEST platform is a spin-stabilized spacecraft designed to undergo highly elliptical, polar orbits around Uranus during a notional one-year primary science mission. The proposed major science goals of the mission are (1) to use Uranus as a natural laboratory to better understand the dynamos that drive magnetospheres in the solar system and beyond and (2) to identify the energy transport mechanisms in Uranus' magnetic, atmospheric, and interior environments in contrast with the other giant planets. With substantial mass, power, and cost margins, this mission concept demonstrates a compelling, feasible option for a New Frontiers Uranus orbiter mission.

Super-Earths are by far the most dominant type of exoplanet, yet their formation is still not well understood. In particular, planet formation models predict that many of them should have accreted enough gas to become gas giants. Here we examine the role of the protoplanetary disk in the cooling and contraction of the protoplanetary envelope. In particular, we investigate the effects of 1) the thermal state of the disk as set by the relative size of heating by accretion or irradiation, and whether its energy is transported by radiation or convection, and 2) advection of entropy into the outer envelope by disk flows that penetrate the Hill sphere, as found in 3D global simulations. We find that, at 5 and 1 AU, this flow at the level reported in the non-isothermal simulations where it penetrates only to ~ 0.3 times the Hill radius has little effect on the cooling rate since most of the envelope mass is concentrated close to the core, and far from the flow. On the other hand, at 0.1 AU, the envelope quickly becomes fully-radiative, nearly isothermal, and thus cannot cool down, stalling gas accretion. This effect is significantly more pronounced in convective disks, leading to envelope mass orders of magnitude lower. Entropy advection at 0.1 AU in either radiative or convective disks could therefore explain why super-Earths failed to undergo runaway accretion. These results highlight the importance of the conditions and energy transport in the protoplanetary disk for the accretion of planetary envelopes., Comment: 10 pages, 6 figures, accepted for publication in MNRAS

Recent ALMA observations indicate that while a range of disk sizes exist, typical disk radii are small, and that radial dust drift affects the distribution of solids in disks. Here we explore the consequences of these features in planet population synthesis models. A key feature of our model is planet traps - barriers to otherwise rapid type-I migration of forming planets - for which we include the ice line, heat transition, and outer edge of the dead zone. We find that the ice line plays a fundamental role in the formation of warm Jupiters. In particular, the ratio of super Earths to warm Jupiters formed at the ice line depend sensitively on the initial disk radius. Initial gas disk radii of $\sim$50 AU results in the largest super Earth populations, while both larger and smaller disk sizes result in the ice line producing more gas giants near 1 AU. This transition between typical planet class formed at the ice line at various disk radii confirms that planet formation is fundamentally linked to disk properties (in this case, disk size), and is a result that is only seen when dust evolution effects are included in our models. Additionally, we find that including radial dust drift results in the formation of more super Earths between 0.1 - 1 AU, having shorter orbital radii than those produced in models where dust evolution effects are not included., Comment: 24 pages, 13 figures. Submitted to MNRAS; revised in response to referee

The ice giants Uranus and Neptune have hydrogen-based atmospheres with several constituents that condense in their cold upper atmospheres. A small number of bright cloud systems observed in both planets are good candidates for moist convective storms, but their observed properties (size, temporal scales and cycles of activity) differ from moist convective storms in the gas giants. These clouds and storms are possibly due to methane condensation and observations also suggest deeper clouds of hydrogen sulfide (H 2 S) at depths of a few bars. Even deeper, thermochemical models predict clouds of ammonia hydrosulfide (NH 4 SH) and water at pressures of tens to hundreds of bars, forming extended deep weather layers. Because of hydrogen’s low molecular weight and the high abundance of volatiles, their condensation imposes a strongly stabilizing vertical gradient of molecular weight larger than the equivalent one in Jupiter and Saturn. The resulting inhibition of vertical motions should lead to a moist convective regime that differs significantly from the one occurring on nitrogen-based atmospheres like those of Earth or Titan. As a consequence, the thermal structure of the deep atmospheres of Uranus and Neptune is not well understood. Similar processes might occur at the deep water cloud of Jupiter in Saturn, but the ice giants offer the possibility to study these physical aspects in the upper methane cloud layer. A combination of orbital and in situ data will be required to understand convection and its role in atmospheric dynamics in the ice giants, and by extension, in hydrogen atmospheres including Jupiter, Saturn and giant exoplanets. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

We investigate the origins of cold sub-Saturns (CSS), an exoplanetary population inferred from microlensing surveys. If confirmed, these planets would rebut a theorised gap in planets' mass distribution between those of Neptune and Jupiter caused by the rapid runaway accretion of super-critical cores. In an attempt to resolve this theoretical-observational disparity, we examine the outcomes of giant collisions between sub-critical protoplanets. Due to the secular interaction among protoplanets, these events may occur in rapidly depleting discs. We show that impactors ~ 5% the mass of near-runaway envelopes around massive cores can efficiently remove these envelopes entirely via a thermally-driven super-Eddington wind emanating from the core itself, in contrast with the stellar Parker winds usually considered. After a brief cooling phase, the merged cores resume accretion. But, the evolution timescale of transitional discs is too brief for the cores to acquire sufficiently massive envelopes to undergo runaway accretion despite their large combined masses. Consequently, these events lead to the emergence of CSS without their transformation into gas giants. We show that these results are robust for a wide range of disc densities, grain opacities and silicate abundance in the envelope. Our fiducial case reproduces CSS with heavy (>= 30 M_Earth) cores and less massive (a few M_Earth) sub-critical envelopes. We also investigate the other limiting cases, where continuous mergers of comparable-mass cores yield CSS with wider ranges of core-to-envelope mass ratios and envelope opacities. Our results indicate that it is possible for CSS and Uranus and Neptune to emerge within the framework of well studied processes and they may be more common than previously postulated., Accepted for publication in MNRAS, 17 pages, 9 figures

High eccentricity migration is a possible formation channel for hot Jupiters. However, in order for it to be consistent with the observed population of planets, tides must circularize the orbits in less than $\approx$ a Myr. A potential mechanism for such rapid circularization is the diffusive growth of the tidally driven planetary f-mode. Such growth occurs if the f-mode's phase at pericenter varies chaotically from one pericenter passage to the next. Previous studies focused on the variation of the orbital period due to tidal back-reaction on the orbit as the source of chaos. Here we show that nonlinear mode interactions can also be an important source. Specifically, we show that nonlinear interactions between a parent f-mode and daughter f-/p-modes induce an energy-dependent shift in the oscillation frequency of the parent. This frequency shift varies randomly from orbit to orbit because the parent's energy varies. As a result, the parent's phase at pericenter varies randomly, which we find can trigger it to grow diffusively. We show that the phase shift induced by nonlinear mode interactions in fact dominates the shift induced by tidal back-reaction and significantly lowers the one-kick energy threshold for diffusive growth by about a factor of 5 compared to the linear theory's prediction. Nonlinear interactions could thus enhance the formation rate of hot Jupiters through the high-eccentricity migration channel and potentially mitigate the discrepancy between the observed and predicted occurrence rates for close-in gas giants as compared to those further from the star., 19 pages, 5 figures; submitted to ApJ

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.

We present a TESS discovered planetary system with a short-period sub-Neptune,HD 307842 (orTOI 784), to confirm and characterize its distant gas giant companion using radial velocity (RV) observations.Observational and statistical studies indicate that long-period gas giants are more common around stars hosting super-Earths or sub-Neptunes. In addition, simulations show that the growth of a Jupiter-mass planet in a protoplanetary disk may drive the instability of the disk and in turn influence inner small planet formation. Observations and simulations both hint in correlations between inner planet properties and the presence or absence of an outer companion. Our program investigates such links between the long-period giants and inner small planets by systematically search and characterize giant planets in systems with known transiting planets. HD 307842 is a V = 9.4 solar-type mid-G star observed by TESS. Transiting data shows that around HD 307842, there is one planet candidate TOI 784.01 with period P = 2.8 days and R = 1.86 R_{Earth}. The radial velocity measurements by the Magellan/PFS suggest that there is likely an additional long-period planet in the system. In this work, we aim to confirm the outer long-period planet or at least give constraints on its properties. The preliminary RV fitting results suggest an orbital period ~110days anda minimum massof ~90 M_{Earth}.Next, we will collect more RV data fromMagellan/PFSand LCOGT/NRES to map out the entire orbit of the giant planet candidate.

We investigate how radiatively driven heating and cooling in the upper atmosphere (at pressures below 1 bar) influences the interior temperature profile (at pressures between 1 to 700 bar) by means of dynamical heat transport. To achieve this goal, we perform fully coupled 3D-radiation-hydrodymamical models with the new full RT 3D climate model MITgcm/ExoRadPRT for WASP-43 b and HD209458 b. We show in our simulations under which conditions the interior temperature profile converges to a hot deep adiabat. Furthermore, we show if differences occur between the non inflated WASP-43 b and the inflated HD209458 b due to different flow structures at depth for similar irradiation.

‘Sol’ is the Roman god that personified the Sun. It is the brightest object in the sky and the hottest body in the Solar System. More than 99.8% of all the matter in the Solar System resides in the Sun; it is 1,000 times more massive than the largest planet, Jupiter. The Sun is 73% hydrogen and 25% helium, with traces of the other elements making up the remaining. In 1868, English astronomer Norman Lockyer identified an element in the Sun that was unknown on Earth at the time; he called it helium after Helios. Like the Gas Giants, the Sun rotates differentially, with a period of 25 days at the equator, decreasing to 35 days at the poles. In the Sun, the proton-proton cycle converts 620 billion kilograms of hydrogen into helium every second, releasing an enormous amount of energy in the form of gamma rays.

In China, Gan De's observations of Jupiter also date to the 4th century BCE. Within 200 years, Chinese astronomers were familiar with the retrograde motion of five planets, including Saturn. The inhabitants of the outer Planetary System are the Jovian Planets after their archetype, Jupiter. More specifically, the Gas Giants are closest to the Sun; Jupiter is inarguably giant. Jupiter is the most voluminous planet; 1,300 Earths could fit inside it. Obviously, Jupiter must be made of very low-density elements, of which the list quickly narrows down to two: hydrogen and helium. Jupiter's magnetic field traps electrically charged particles from the Sun and some sputtered off Jupiter's satellites in tori surrounding Jupiter just like the Van Allen Belts encircle the Earth. Less violently, Jupiter's magnetic field also produces the most powerful and brightest aurorae on any planet, seen in Jupiter's polar regions. Jupiter's magnetosphere is truly huge, 20,000 times greater in volume than that of the Earth's.

Constraining the melting behavior of magnesium oxide, a major constituent of gaseous and rocky planets, is key to benchmarking their evolutionary models. Using a double-shock technique, we extended the MgO melt curve measurements to 2 TPa; this is twice the pressure achieved by previous melting experiments on any material. A temperature plateau is observed between 1218 and 1950 GPa in the second-shock states, which is attributed to latent heat of melting. At 1950 GPa, the measured melting temperature is 17 600 K, which is 17% lower than recent theoretical predictions. The melting curve is steeper than that of ${\mathrm{MgSiO}}_{3}$, indicating that MgO is likely solid in the interior of Saturn-sized gas giants and extra-solar super-Earth planets.

We present a high-precision radial velocity (RV) survey of 719 FGKM stars, which host 164 known exoplanets and 14 newly discovered or revised exoplanets and substellar companions. This catalog updated the orbital parameters of known exoplanets and long-period candidates, some of which have decades-longer observational baselines than they did upon initial detection. The newly discovered exoplanets range from warm sub-Neptunes and super-Earths to cold gas giants. We present the catalog sample selection criteria, as well as over 100,000 radial velocity measurements, which come from the Keck-HIRES, APF-Levy, and Lick-Hamilton spectrographs. We introduce the new RV search pipeline RVSearch that we used to generate our planet catalog, and we make it available to the public as an open-source Python package. This paper is the first study in a planned series that will measure exoplanet occurrence rates and compare exoplanet populations, including studies of giant planet occurrence beyond the water ice line, and eccentricity distributions to explore giant planet formation pathways. We have made public all radial velocities and associated data that we use in this catalog., Accepted to ApJS

Jovian planet formation has been shown to be strongly correlated with host star metallicity, which is thought to be a proxy for disk solids. Observationally, previous works have indicated that jovian planets preferentially form around stars with solar and super solar metallicities. Given these findings, it is challenging to form planets within metal-poor environments, particularly for hot Jupiters that are thought to form via metallicity-dependent core accretion. Although previous studies have conducted planet searches for hot Jupiters around metal-poor stars, they have been limited due to small sample sizes, which are a result of a lack of high-quality data making hot Jupiter occurrence within the metal-poor regime difficult to constrain until now. We use a large sample of halo stars observed by TESS to constrain the upper limit of hot Jupiter occurrence within the metal-poor regime (-2.0 $\leq$ [Fe/H] $\leq$ -0.6). Placing the most stringent upper limit on hot Jupiter occurrence, we find the mean 1-$\sigma$ upper limit to be 0.18 $\%$ for radii 0.8 -2 R$_{\rm{Jupiter}}$ and periods $0.5- 10$ days. This result is consistent with previous predictions indicating that there exists a certain metallicity below which no planets can form., Comment: Accepted, ApJ. This entry will be updated with journal reference and DOI when available. Corrected typos on Figure 2

At least 30\% of main sequence stars host planets with sizes of between 1 and 4 Earth radii and orbital periods of less than 100 days. We use N-body simulations including a model for gas-assisted pebble accretion and disk--planet tidal interaction to study the formation of super-Earth systems. We show that the integrated pebble mass reservoir creates a bifurcation between hot super-Earths or hot-Neptunes ($\lesssim15M_{\oplus}$) and super-massive planetary cores potentially able to become gas giant planets ($\gtrsim15M_{\oplus}$). Simulations with moderate pebble fluxes grow multiple super-Earth-mass planets that migrate inwards and pile up at the inner edge of the disk forming long resonant chains. We follow the long-term dynamical evolution of these systems and use the period ratio distribution of observed planet-pairs to constrain our model. Up to $\sim$95\% of resonant chains become dynamically unstable after the gas disk dispersal, leading to a phase of late collisions that breaks the original resonant configurations. Our simulations naturally match observations when they produce a dominant fraction ($\gtrsim95\%$) of unstable systems with a sprinkling ($\lesssim5\%$) of stable resonant chains (the Trappist-1 system represents one such example). Our results demonstrate that super-Earth systems are inherently multiple (${\rm N\geq2}$) and that the observed excess of single-planet transits is a consequence of the mutual inclinations excited by the planet--planet instability. In simulations in which planetary seeds are initially distributed in the inner and outer disk, close-in super-Earths (abridged)., Accepted in A&A, version including language editing

Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH2, CH3 and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini–Huygens fly-by of Jupiter., The vacuum ultraviolet photodissociation dynamics of ethane provide clues for modelling the atmospheric chemistry of the gas giants.

Giant planets are thought to form by runaway gas accretion onto solid cores. Growth must eventually stop running away, ostensibly because planets open gaps (annular cavities) in their surrounding discs. Typical models stop runaway by artificially capping the accretion rate and lowering it to zero over an arbitrarily short time-scale. In reality, post-runaway accretion persists as long as the disc remains. During this final and possibly longest phase of formation, when the planet is still emerging from the disc, its mass can more than double, and its radius contracts by orders of magnitude. By drawing from the theory of how gaps clear, we find that post-runaway accretion luminosities diverge depending on disc viscosity: luminosities fall in low-viscosity discs but continue to rise past runaway in high-viscosity discs. This divergence amounts to a factor of $10^2$ by the time the disc disperses. Irrespective of the specifics of how planets interact with discs, the observed luminosity and age of an accreting planet can be used to calculate its instantaneous mass, radius, and accretion rate. We perform this exercise for the planet candidates embedded within the discs orbiting PDS 70, HD 163296, and MWC 758, inferring masses of $1-10\, M_{\rm J}$, accretion rates of $0.1-10\, M_{\rm J}$/Myr, and radii of $1-10\, R_{\rm J}$. Our radii are computed self-consistently from the planet's concurrent contraction and accretion and do not necessarily equal the value of $2R_{\rm J}$ commonly assumed; in particular, the radius depends on the envelope opacity as $R \propto \kappa^{0.5}$., Comment: Accepted to MNRAS

Helium, ammonia and ice are among the major components of giant gas planets, and predictions of their chemical structures are therefore crucial in predicting planetary dynamics. Here we demonstrate a strong driving force originating from the alternation of the electrostatic interactions for helium to react with crystals of polar molecules such as ammonia and ice. We show that ammonia and helium can form thermodynamically stable compounds above 45 GPa, while ice and helium can form thermodynamically stable compounds above 300 GPa. The changes in the electrostatic interactions provide the driving force for helium insertion under high pressure, but the mechanism is very different to those that occur in ammonia and ice. This work extends the reactivity of helium into new types of compounds and demonstrates the richness of the chemistry of this most stable element in the periodic table. The reactivity of small molecule gases at high pressure has implications for astrochemistry. Here helium is shown in silico to form stable compounds with water and ammonia at gigapascal pressures.

Short-period gas giants (hot Jupiters) on circular orbits are expected to be tidally locked into synchronous rotation, with permanent daysides that face their host stars, and permanent nightsides that face the darkness of space. Thermal flux from the nightside of several hot Jupiters has been measured, meaning energy is transported from day to night in some fashion. However, it is not clear exactly what the physical information from these detections reveals about the atmospheric dynamics of hot Jupiters. Here we show that the nightside effective temperatures of a sample of 12 hot Jupiters are clustered around 1100 K, with a slight upward trend as a function of stellar irradiation. The clustering is not predicted by cloud-free atmospheric circulation models. This result can be explained if most hot Jupiters have nightside clouds that are optically thick to outgoing longwave radiation and hence radiate at the cloud-top temperature, and progressively disperse for planets receiving greater incident flux. Phase curve observations at a greater range of wavelengths are crucial to determining the extent of cloud coverage, as well as the cloud composition on hot Jupiter nightsides., Comment: 18 pages, 3 figures. Submitted August 13th, 2018, accepted for publication July 5th 2019. Added a second, parallel analysis. Interpretation of results unchanged from previous version. Updated main text to reflect the published version, and removed a sentence in the Methods that misquoted Beatty+ 2019

Direct imaging (DI) surveys suggest that gas giants beyond 20 AU are rare around FGK stars. However, it is not clear what this means for the formation frequency of Gravitational Instability (GI) protoplanets due to uncertainties in gap opening and migration efficiency. Here we combine state-of-the-art calculations of homogeneous planet contraction with a population synthesis code. We find DI constraints to be satisfied if protoplanet formation by GI occurs in tens of percent of systems if protoplanets `super migrate' to small separations. In contrast, GI may occur in only a few percent of systems if protoplanets remain stranded at wide orbits because their migration is `quenched' by efficient gap opening. We then use the frequency of massive giants in radial velocity surveys inside 5 AU to break this degeneracy - observations recently showed that this population does not correlate with the host star metallicity and is therefore suspected to have formed via GI followed by inward migration. We find that only the super-migration scenario can sufficiently explain this population whilst simultaneously satisfying the DI constraints and producing the right mass spectrum of planets inside 5 AU. If massive gas-giants inside 5 AU formed via GI, then our models imply that migration must be efficient and that the formation of GI protoplanets occurs in at least a tens of percent of systems., Accepted to MNRAS

Massive planetary cores embedded in protoplanetary discs are believed to accrete extended atmospheres, providing a pathway to forming gas giants and gas-rich super-Earths. The properties of these atmospheres strongly depend on the nature of the coupling between the atmosphere and the surrounding disc. We examine the formation of gaseous envelopes around massive planetary cores via three-dimensional inviscid and isothermal hydrodynamic simulations. We focus the changes in the envelope properties as the core mass varies from low (sub-thermal) to high (super-thermal) values, a regime relevant to close-in super-Earths. We show that global envelope properties such as the amount of rotational support or turbulent mixing are mostly sensitive to the ratio of the Bondi radius of the core to its physical size. High-mass cores are fed by supersonic inflows arriving along the polar axis and shocking on the densest parts of the envelope, driving turbulence and mass accretion. Gas flows out of the core's Hill sphere in the equatorial plane, describing a global mass circulation through the envelope. The shell of shocked gas atop the core surface delimits regions of slow (inside) and fast (outside) material recycling by gas from the surrounding disc. While recycling hinders the runaway growth towards gas giants, the inner regions of protoplanetary atmospheres, more immune to mixing, may remain bound to the planet., Comment: 16 pages, 15 figures, accepted for publication in MNRAS

The Solar System gas giants are each surrounded by many moons, with at least 50 prograde satellites thought to have formed from circumplanetary material. Just like the Sun is not the only star surrounded by planets, extrasolar gas giants are likely surrounded by satellite systems. Here, we report on ALMA observations of four, 6 pages, 3 figures, accepted for publication in MNRAS

With no analogues in the Solar System, the discovery of thousands of exoplanets with masses and radii intermediate between Earth and Neptune was one of the big surprises of exoplanet science. These super-Earths and sub-Neptunes likely represent the most common outcome of planet formation. Mass and radius measurements indicate a diversity in bulk composition much wider than for gas giants; however, direct spectroscopic detections of molecular absorption and constraints on the gas mixing ratios have largely remained limited to planets more massive than Neptune. Here, we analyze a combined Hubble/Spitzer Space Telescope dataset of 12 transits and 20 eclipses of the sub-Neptune GJ 3470 b, whose mass of 12.6 $M_\oplus$ places it near the half-way point between previously studied exo-Neptunes (22-23 $M_\oplus$) and exoplanets known to have rocky densities (7 $M_\oplus$). Obtained over many years, our data set provides a robust detection of water absorption (>5$\sigma$) and a thermal emission detection from the lowest irradiated planet to date. We reveal a low-metallicity, hydrogen-dominated atmosphere similar to a gas giant, but strongly depleted in methane gas. The low, near-solar metallicity (O/H=0.2-18) sets important constraints on the potential planet formation processes at low masses as well as the subsequent accretion of solids. The low methane abundance indicates that methane is destroyed much more efficiently than previously predicted, suggesting that the CH$_4$/CO transition curve has to be revisited for close-in planets. Finally, we also find a sharp drop in the cloud opacity at 2-3 $\mu$m characteristic of Mie scattering, which enables narrow constraints on the cloud particle size and makes GJ 3470b a keystone target for mid-IR characterization with JWST., Comment: Published in Nature Astronomy (July 1, 2019)

Cassini's last look at Saturn's ringsDuring the final stages of the Cassini mission, the spacecraft flew between the planet and its rings, providing a new view on this spectacular system (see the Perspective by Ida). Setting the scene, Spilker reviews the numerous discoveries made using Cassini during the 13 years it spent orbiting Saturn. Iesset al.measured the gravitational pull on Cassini, separating the contributions from the planet and the rings. This allowed them to determine the interior structure of Saturn and the mass of its rings. Burattiet al.present observations of five small moons located in and around the rings. The moons each have distinctive shapes and compositions, owing to accretion of ring material. Tiscarenoet al.observed the rings directly at close range, finding complex features sculpted by the gravitational interactions between moons and ring particles. Together, these results show that Saturn's rings are substantially younger than the planet itself and constrain models of their origin.Science, this issue p.1046, p.eaat2965, p.eaat2349, p.eaau1017; see also p.1028

Studies of internal structure of gas giant planets suggest that their envelopes are enriched with heavier elements than hydrogen and helium relative to their central stars. Such enrichment likely occurred by solid accretion during late formation stages of gas giant planets in which gas accretion dominates protoplanetary growth. Some previous studies performed orbital integration of planetesimals around a growing protoplanet with the assumption of an uniform circumstellar disc to investigate how efficiently the protoplanet captures planetesimals. However, not only planetesimals but also disc gas are gravitationally perturbed by the protoplanet in its late formation stages, resulting in gap opening in the circumstellar disc. In this study, we investigate the effects of such gap formation on the capture of planetesimals by performing dynamical simulations of planetesimals around a growing proto-gas giant planet. Gap formation reduces the surface density of disc gas, makes a steep pressure gradient and limits the growth rate of the protoplanet. We find that the first effect enhances the capture of planetesimals, while the others reduce it. Consequently the amount of planetesimals captured during the gas accretion is estimated to be at most ~3 Mearth. We conclude that the in-situ capture of planetesimals needs the initial solid surface density more than five times higher than that of the minimum mass solar nebula for explaining the inferred large amount of heavy element in Jupiter. For highly dense warm Jupiters, we would need additional processes enhancing the capture and/or supply of planetesimals., Comment: 15 pages, 13 figures, this is a pre-copyedited, author-produced version of an article accepted for publication in MNRAS following peer review

Earth grew through collisions with Moon-sized to Mars-sized planetary embryos from the inner Solar System, but it also accreted material from greater heliocentric distances1,2, including carbonaceous chondrite-like bodies, the likely source of Earth’s water and highly volatile species3,4. Understanding when and how this material was added to Earth is critical for constraining the dynamics of terrestrial planet formation and the fundamental processes by which Earth became habitable. However, earlier studies inferred very different timescales for the delivery of carbonaceous chondrite-like bodies, depending on assumptions about the nature of Earth’s building materials5–11. Here we show that the Mo isotopic composition of Earth’s primitive mantle falls between those of the non-carbonaceous and carbonaceous reservoirs12–15, and that this observation allows us to quantify the accretion of carbonaceous chondrite-like material to Earth independently of assumptions about its building blocks. As most of the Mo in the primitive mantle was delivered by late-stage impactors10, our data demonstrate that Earth accreted carbonaceous bodies late in its growth history, probably through the Moon-forming impact. This late delivery of carbonaceous material probably resulted from an orbital instability of the gas giant planets, and it demonstrates that Earth’s habitability is strongly tied to the very late stages of its growth. Measurements of Mo in meteorites constrain the time when the Earth accreted carbonaceous material from the outer Solar System (a likely source of Earth’s water and volatiles) to late in the Earth’s growth history—probably in the same event that formed the Moon.

Flight into the gas giant planets involves atmospheric entry velocities between 20 and 50 km/s, which are mostly beyond the capabilities of current ground testing facilities that make use of test ...

We present a numerical model that reveals a mechanism governing the polar atmospheric dynamics of Jupiter, Saturn, Uranus and Neptune. Exploration of the polar regions of the gas giants has produced surprisingly diverse results, with Cassini finding a single, intense, compact polar cyclone precisely centered on each pole of Saturn, and Voyager data and ground-based observations suggesting Uranus and Neptune have dominant, single polar cyclones as well. The Juno spacecraft at Jupiter finds several tightly packed cyclones surrounding a central cyclone offset from the poles. These discoveries raise questions about the mechanism that differentiates these polar atmospheric dynamics regimes. To help determine what physical mechanisms control these differences, we use the Explicit Planetary Isentropic Coordinate (EPIC) model to carry out forced-turbulence shallow-water simulations in a gamma-plane configuration, i.e. a Cartesian grid with a pole placed at the center. The model is forced by small-scale stochastic mass pulses that parametrically represent cumulus storms. The effects of three parameters, the planetary Burger number, Bu = (Ld / a)2 (Ld is the Rossby deformation radius, a is the planetary radius), input storm strength, s, and proportion of cyclonic and anticyclonic storms injected into the domain, α, are systematically investigated. Bu emerges to be the most important, able to distinguish between four distinct dynamical regimes, matching those of the giant planets, which from large to small Bu, are: i) a large cyclonic polar vortex (i.e., Uranus/Neptune-like), ii) a compact intense cyclonic polar vortex (Saturn-like), iii) two large vortices or one vortex offset from the pole (transitional), and iv) meandering jets with no centrally dominant vortex, or with multiple circumpolar cyclones (Jupiter-like). The boundaries of these regimes are found to be only slightly modulated by the values of s and α. By applying this correlation with respect to Bu in reverse, an observation of a particular polar regime could in principle be used to constrain Ld.

Gas clumps formed within massive gravitationally unstable circumstellar discs are potential seeds of gas giant planets, brown dwarfs and companion stars. Simulations show that competition between three processes -- migration, gas accretion and tidal disruption -- establishes what grows from a given seed. Here we investigate the robustness of numerical modelling of clump migration and accretion with the codes PHANTOM, GADGET, SPHINX, SEREN, GIZMO-MFM, SPHNG and FARGO. The test problem comprises a clump embedded in a massive disc at an initial separation of 120 AU. There is a general qualitative agreement between the codes, but the quantitative agreement in the planet migration rate ranges from $\sim 10$% to $\sim 50$%, depending on the numerical setup. We find that the artificial viscosity treatment and the sink particle prescription may account for much of the differences between the codes. In order to understand the wider implications of our work, we also attempt to reproduce the planet evolution tracks from our hydrodynamical simulations with prescriptions from three previous population synthesis studies. We find that the disagreement amongst the population synthesis models is far greater than that between our hydrodynamical simulations. The results of our code comparison project are therefore encouraging in that uncertainties in the given problem are probably dominated by the physics not yet included in the codes rather than by how hydrodynamics is modelled in them., submitted to MNRAS. This is version 2 of the paper after considering referees comments and changes

Infrared absorption spectra of isobutane (C4H10) were recorded in the CH stretching spectral region (2500–3280 cm−1) by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR). These spectra were taken at temperatures and pressures appropriate for the gas giant planets Jupiter and Saturn, as well as for Saturn's moon Titan. Absorption cross sections were obtained for pure samples and with broadening gases relevant in those atmospheres, hydrogen and nitrogen, to further simulate the astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.

Ultra-hot Jupiters are tidally locked gas giants with dayside temperatures high enough to dissociate hydrogen and other molecules. Their atmospheres are vastly non-uniform in terms of chemistry, temperature and dynamics, and this makes their high-resolution transmission spectra and cross-correlation signal difficult to interpret. In this work, we use the SPARC/MITgcm global circulation model to simulate the atmosphere of the ultra-hot Jupiter WASP-76b under different conditions, such as atmospheric drag and the absence of TiO and VO. We then employ a 3D Monte-Carlo radiative transfer code, HIRES-MCRT, to self-consistently model high-resolution transmission spectra with iron (Fe I) lines at different phases during the transit. To untangle the structure of the resulting cross-correlation map, we decompose the limb of the planet into four sectors, and we analyse each of their contributions separately. Our experiments demonstrate that the cross-correlation signal of an ultra-hot Jupiter is primarily driven by its temperature structure, rotation and dynamics, while being less sensitive to the precise distribution of iron across the atmosphere. We also show that the previously published iron signal of WASP-76b can be reproduced by a model featuring iron condensation on the leading limb. Alternatively, the signal may be explained by a substantial temperature asymmetry between the trailing and leading limb, where iron condensation is not strictly required to match the data. Finally, we compute the $K_{p}-V_{sys}$ maps of the simulated WASP-76b atmospheres, and we show that rotation and dynamics can lead to multiple peaks that are displaced from zero in the planetary rest frame., Accepted for publication in MNRAS, 25 pages, 24 figures

(Abridged) Short-period gas giant exoplanets are susceptible to intense atmospheric escape due to their large scale heights and strong high-energy irradiation. This process is thought to occur ubiquitously, but to date we have only detected direct evidence of atmospheric escape in hot Jupiters and warm Neptunes. The paucity of cases for intermediate, Saturn-sized exoplanets at varying levels of irradiation precludes a detailed understanding of the underlying physics in atmospheric escape of hot gas giants. Our objectives here are to assess the high-energy environment of the warm ($T_\mathrm{eq} = 970$ K) Saturn WASP-29 b and search for signatures of atmospheric escape. We used far-ultraviolet (FUV) observations from the Hubble Space Telescope to analyze the flux time series of H I, C II, Si III, Si IV, and N V during the transit of WASP-29 b. At 3$\sigma$ confidence, we rule out any in-transit absorption of H Ilarger than 92% in the Lyman-$\alpha$ blue wing and 19% in the red wing. We found an in-transit flux decrease of $39\%^{+12\%}_{-11\%}$ in the ground-state C II emission line at 133.45 nm. But due to this signal being significantly present in only one visit, it is difficult to attribute a planetary or stellar origin for the ground-state C II signal. We place 3$\sigma$ absorption upper limits of 40%, 49% and 24% for Si III, Si IV, and for excited-state C II at 133.57 nm, respectively. Low activity levels and the faint X-ray luminosity suggest that WASP-29 is an old, inactive star. An energy-limited approximation combined with the reconstructed EUV spectrum of the host suggests that the planet is losing its atmosphere at a rate of $4 \times 10^9$ g s$^{-1}$. The non-detection at Lyman-$\alpha$ could be partly explained by a low fraction of escaping neutral hydrogen, or by the state of fast radiative blow-out we infer from the reconstructed stellar Lyman-$\alpha$ line., Comment: 10 pages, 8 figures, accepted for publication in Astronomy & Astrophysics. v2 with a few text changes for consistency

The weather layers of the gas giant planets, Jupiter and Saturn, comprise the shallow atmospheric layers that are influenced energetically by a combination of incoming solar radiation and localised latent heating of condensates, as well as by upwelling heat from their planetary interiors. They are also the most accessible regions of those planets to direct observations. Recent analyses in Oxford of cloud-tracked winds on Jupiter have demonstrated that kinetic energy is injected into the weather layer at scales comparable to the Rossby radius of deformation and cascades both upscale, mostly into the extra-tropical zonal jets, and downscale to the smallest resolvable scales in Cassini images. The large-scale flow on both Jupiter and Saturn appears to equilibrate towards a state which is close to marginal instability according to Arnol'd's 2nd stability theorem. This scenario is largely reproduced in a hierarchy of numerical models of giant planet weather layers, including relatively realistic models which seek to predict thermal and dynamical structures using a full set of parameterisations of radiative transfer, interior heat sources and even moist convection. Such models include the Jason GCM, developed in Oxford, which also represents the formation of (energetically passive) clouds of NH3, NH4SH and H2O condensates and the transport of condensable tracers. Recent results show some promise in comparison with observations from the Cassini and Juno missions, but some observed features (such as Jupiter's Great Red Spot and other compact ovals) are not yet captured spontaneously by any weather layer model. We review recent work in this vein and discuss a number of open questions for future study., 27 pages, including 7 figures. Submitted to Geoscience Letters as invited review from 2019 assembly of the Asia-Oceania Geosciences Society

Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring campaign of an M dwarf system, composed of twenty-one $\approx$8 hour epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3$\sigma$ detection rate of 90$^{+5}_{-8}$% when a noise floor of $\approx$0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984$\pm$0.003 days. We observe no periodicity in the radio data, but the sampling of our radio observations produces a window function that would hide the near two-day signal., Comment: Accepted for publication in A&A, 16 pages, 7 figures, 2 tables