The Dawn mission recently visited the asteroid 4 Vesta and the observations performed by the spacecraft revealed more pieces of the intriguing mosaic of its history. Among the first results obtained ...by the Dawn mission was the confirmation of the link between the howardite–eucrite–diogenite (HED) group of meteorites and Vesta. This link implies that Vesta was one of the first objects to form in the Solar System and that the differentiation of the asteroid likely completed before the formation of Jupiter. As a consequence, the bombardment triggered by the formation and migration of the giant planet, the Jovian Early Bombardment (JEB), contributed to the collisional evolution of the asteroid at a time where most of its interior was still molten. This work explores the implications of the JEB for the evolution of the primordial Vesta, in particular in terms of crater saturation, crustal excavation and surface erosion. Both scenarios assuming the planetesimals having formed in a quiescent or a turbulent nebula were explored and both primordial and collisionally evolved size–frequency distributions were considered. The results obtained indicate that, if the basaltic surface of Vesta was already formed, the JEB would saturate it with craters and could erode it to depths that vary from hundreds of meters to tens of kilometres. In the latter cases, the surface erosion caused by the JEB would be comparable with the thickness of the eucritic and diogenitic layers of Vesta. In the cases where the global surface erosion is limited, however, large impactors, if too abundant, can excavate the whole crust and extract significant quantities of material from the vestan mantle, incompatible with the present understanding of HED meteorites. This appears to be the case if the impacting planetesimals formed in a turbulent nebula and Jupiter migrated by 0.5AU or more. Globally, the results obtained suggest that the scenarios where the planetesimal formed in a quiescent nebula and Jupiter underwent a modest migration (i.e. up to 0.5AU) are the most consistent with our understanding of Vesta, even if the cases of planetesimals formed in a turbulent nebula with Jupiter undergoing limited (i.e. about 0.25AU) or no migration cannot be ruled out. Recent results on the differentiation of the asteroid, however, raised the possibility that Vesta originally possessed a now-lost undifferentiated crust. In this case, the favoured scenarios would be those where the planetesimals formed in a quiescent nebula and Jupiter underwent a more significant migration (i.e. between 0.5AU and 1AU).
•The vestan surface evolution across the Jovian Early Bombardment (JEB) is investigated.•Different SFDs of planetesimals and Jovian displacements are considered.•The JEB causes crater saturation and significant mass loss from the vestan surface.•High abundance of large planetesimals or large displacements of Jupiter are ruled out.•Most likely formation environment for planetesimals appears to be quiescent nebula.
Context. Previous works focused on exoplanets discovered with the radial velocity (RV) method reported an anti-correlation between the orbital eccentricities of the exoplanets and the multiplicity M ...(i.e., the number of planets) of the systems they inhabit. Aims. We further investigate this reported anti-correlation here using a dataset comprising exoplanets discovered with both the RV and transit methods, searching for hints of its causes by exploring the connection between the number of planets and the dynamical state of the exosystems. Methods. In order to examine the correlation between multiplicity and orbital eccentricity, for every multiplicity case considered (2 ≤ M ≤ 6), we computed the weighted average eccentricities instead of the median eccentricities used previously. The average eccentricities were calculated using the inverse of the uncertainty on the eccentricity values as weights. The analysis of the dynamic state of the exosystems was performed by computing their angular momentum deficit (AMD), which is a diagnostic parameter successfully used in the study of the solar system and recently applied to exosystems as well. Results. Our results confirm the reported multiplicity-eccentricity anti-correlation and show that the use of the uncertainties on the orbital eccentricities in the analysis allows for a better agreement between the data and the fits. Specifically, our best fit reproduces well the behaviour of the average eccentricities for all systems with M> 1, including the additional cases of TRAPPIST-1 (M = 7) and of the solar system (M = 8). The AMD analysis, while not conclusive due to the limited number of exosystems that could be analysed, also suggests the existence of an anti-correlation between the multiplicity and the AMD of exosystems. This second anti-correlation, if confirmed by future studies, raises the possibility that the population of low-multiplicity exosystems is contaminated by former high-multiplicity systems that became dynamically unstable and lost some of their planets.
The amount of dust present in circumstellar disks is expected to steadily decrease with age due to the growth from m-sized particles to planetesimals and planets. Mature circumstellar disks, however, ...can be observed to contain significant amounts of dust and possess high dust-to-gas ratios. Using HD 163296 as our case study, we explore how the formation of giant planets in disks can create the conditions for collisionally rejuvenating the dust population, halting or reversing the expected trend. We combine N-body simulations with statistical methods and impact scaling laws to estimate the dynamical and collisional excitation of the planetesimals due to the formation of HD 163296's giant planets. We show that this process creates a violent collisional environment across the disk that can inject collisionally produced second-generation dust into it, significantly contributing to the observed dust-to-gas ratio. The spatial distribution of the dust production can explain the observed local enrichments in HD 163296's inner regions. The results obtained for HD 163296 can be extended to any disk with embedded forming giant planets and may indicate a common evolutionary stage in the life of such circumstellar disks. Furthermore, the dynamical excitation of the planetesimals could result in the release of transient, nonequilibrium gas species like H2O, CO2, NH3, and CO in the disk due to ice sublimation during impacts and, due to the excited planetesimals being supersonic with respect to the gas, could produce bow shocks in the latter that could heat it and cause a broadening of its emission lines.
Pebble accretion is an efficient mechanism that is able to build up the core of the giant planets within the lifetime of the protoplanetary disc gas-phase. The core grows via this process until the ...protoplanet reaches its pebble isolation mass and starts to accrete gas. During the growth, the protoplanet undergoes a rapid, large-scale, inward migration due to the interactions with the gaseous protoplanetary disc. In this work, we have investigated how this early migration would have affected the minor body populations in our solar system. In particular, we focus on the Jupiter Trojan asteroids (bodies in the coorbital resonance 1:1 with Jupiter, librating around the L4 and L5 Lagrangian points called, respectively, the leading and the trailing swarm) and the Hilda asteroids. We characterised their orbital parameter distributions after the disc dispersal and their formation location and compare them to the same populations produced in a classical in situ growth model. We find that a massive and eccentric Hilda group is captured during the migration from a region between 5 and 8 au and subsequently depleted during the late instability of the giant planets. Our simulations also show that inward migration of the giant planets always produces a Jupiter Trojans’ leading swarm more populated than the trailing one, with a ratio comparable to the current observed Trojan asymmetry ratio. The in situ formation of Jupiter, on the other hand, produces symmetric swarms. The reason for the asymmetry is the relative drift between the migrating planet and the particles in the coorbital resonance. The capture happens during the growth of Jupiter’s core and Trojan asteroids are afterwards carried along during the giant planet’s migration to their final orbits. The asymmetry and eccentricity of the captured Trojans correspond well to observations, but their inclinations are near zero and their total mass is three to four orders of magnitude higher than the current population. Future modelling will be needed to understand whether the dynamical evolution of the Trojans over billions of years will raise the inclinations and deplete the masses to observed values.
Abstract
The composition of giant planets is imprinted by their migration history and the compositional structure of their hosting disks. Studies in recent literature have investigated how the ...abundances of C and O can constrain the formation pathways of giant planets forming within few tens of au from a star. New ALMA observations, however, suggest planet-forming regions possibly extending to hundreds of au. We explore the implications of these wider formation environments through
n
-body simulations of growing and migrating giant planets embedded in planetesimal disks, coupled with a compositional model of the protoplanetary disk where volatiles are inherited from the molecular cloud and refractories are calibrated against extrasolar and Solar System data. We find that the C/O ratio provides limited insight on the formation pathways of giant planets that undergo large-scale migration. This limitation can be overcome, however, thanks to nitrogen and sulfur. Jointly using the C/N, N/O, and C/O ratios breaks any degeneracy in the formation and migration tracks of giant planets. The use of elemental ratios normalized to the respective stellar ratios supplies additional information on the nature of giant planets, thanks to the relative volatility of O, C, and N in disks. When the planetary metallicity is dominated by the accretion of solids C/N* > C/O* > N/O* (* denoting this normalized scale), otherwise N/O* > C/O* > C/N*. The S/N ratio provides an additional independent probe into the metallicity of giant planets and their accretion of solids.
Context.
Population studies of the orbital characteristics of exoplanets in multi-planet systems have highlighted the existence of an anticorrelation between the average orbital eccentricity of ...planets and the number of planets of their host system, that is, its multiplicity. This effect was proposed to reflect the varying levels of violence in the dynamical evolution of planetary systems.
Aims.
Previous work suggested that the relative violence of the dynamical evolution of planetary systems with similar orbital architectures can be compared through the computation of their angular momentum deficit (AMD). We investigated the possibility of using a more general metric to perform analogous comparisons between planetary systems with different orbital architectures.
Methods.
We considered a modified version of the AMD, the normalized angular momentum deficit (NAMD), and used it to study a sample of 99 multi-planet systems containing both the currently best-characterized extrasolar systems and the solar system, that is, planetary systems with both compact and wide orbital architectures.
Results.
We verified that the NAMD allows us to compare the violence of the dynamical histories of multi-planet systems with different orbital architectures. We identified an anticorrelation between the NAMD and the multiplicity of the planetary systems, of which the previously observed eccentricity–multiplicity anticorrelation is a reflection.
Conclusions.
Our results seem to indicate that phases of dynamical instabilities and chaotic evolution are not uncommon among planetary systems. They also suggest that the efficiency of the planetary formation process in producing high-multiplicity systems is likely to be higher than that suggested by their currently known population.
Jupiter's aurorae are produced in its upper atmosphere when incoming high-energy electrons precipitate along the planet's magnetic field lines. A northern and a southern main auroral oval are ...visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street. Well downstream of the main auroral spots the extended tail is split in two. Both of Ganymede's footprints also appear as a pair of emission features, which may provide a remote measure of Ganymede's magnetosphere. These features suggest that magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.
The mineralogy of Vesta, based on data obtained by the Dawn spacecraft's visible and infrared spectrometer, is consistent with howardite-eucrite-diogenite meteorites. There are considerable regional ...and local variations across the asteroid: Spectrally distinct regions include the south-polar Rheasilvia basin, which displays a higher diogenitic component, and equatorial regions, which show a higher eucritic component. The lithologic distribution indicates a deeper diogenitic crust, exposed after excavation by the impact that formed Rheasilvia, and an upper eucritic crust. Evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta. This is broadly consistent with magma-ocean models, but spectral variability highlights local variations, which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates. Overall, Vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle.
ABSTRACT
The atmospheric C/O ratio of exoplanets is widely used to constrain their formation. To guarantee that the C/O ratio provides robust information, we need to accurately quantify the amount of ...C and O in exoplanetary atmospheres. In the case of O, water and carbon monoxide are generally studied as the two key carriers. However, oxygen is a very reactive element and does not bind only with carbon; depending on the temperature, it also binds to refractory elements. Estimating the amount of oxygen bound to refractory elements is therefore critical for unbiased estimates of the C/O ratio. In this work, we investigate the oxygen deficit due to refractory elements and its effects on the atmospheric C/O ratio of giant exoplanets as a function of their metallicity and equilibrium temperature. We model the composition of planetary atmospheres assuming chemical equilibrium and using as input physically justified elemental mixtures arising from detailed planet formation simulations. Our results show how the interplay between the atmospheric temperature and non-solar abundances of oxygen and refractory elements can sequester large fractions of oxygen, introducing significant biases in evaluating the C/O ratio when this effect is not accounted for. We apply our results to the case of Jupiter in the Solar system and show how the currently estimated water abundance points to a true oxygen abundance that is four times the solar one.
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