When a planetary tidal disk—like Saturn's rings—spreads beyond the Roche radius (inside which planetary tides prevent aggregation), satellites form and migrate away. Here, we show that most regular ...satellites in the solar system probably formed in this way. According to our analytical model, when the spreading is slow, a retinue of satellites appear with masses increasing with distance to the Roche radius, in excellent agreement with Saturn's, Uranus', and Neptune's satellite systems. This suggests that Uranus and Neptune used to have massive rings that disappeared to give birth to most of their regular satellites. When the spreading is fast, only one large satellite forms, as was the case for Pluto and Earth. This conceptually bridges the gap between terrestrial and giant planet systems.
Context. Planet traps and snow lines are structures that may promote planetary formation in protoplanetary disks. They are very sensitive to the disk density and temperature structure. It is ...therefore necessary to follow the time evolution of the disk thermal structure throughout its viscous spreading. Since the snowlines are thought to generate density and temperature bumps, it is important to take into account the disk opacity variations when the various dust elements are sublimated. Aims. We track the time evolution of planet traps and snowlines in a viscously evolving protoplanetary disk using an opacity table that accounts for the composition of the dust material. Methods. We coupled a dynamical and thermodynamical disk model with a temperature-dependent opacity table (that accounts for the sublimation of the main dust components) to investigate the formation and evolution of snowlines and planet traps during the first million years of disk evolution. Results. Starting from a minimum mass solar nebula, we find that the disk mid-plane temperature profile shows several plateaux (0.1−1 AU wide) at the different sublimation temperatures of the species that make up the dust. For water ice, the corresponding plateau can be larger than 1 AU, which means that this is a snow “region” rather than a snow “line”. As a consequence, the surface density of solids in the snow region may increase gradually, not abruptly. Several planet traps and desert regions appear naturally as a result of abrupt local changes in the temperature and density profiles over the disk lifetime. These structures are mostly located at the edges of the temperature plateaux (surrounding the dust sublimation lines) and at the heat-transition barrier where the disk stellar heating and viscous heating are of the same magnitude (around 10 AU after 1 Myr). Conclusions. Several traps are identified: although a few appear to be transient, most of them slowly migrate along with the heat-transition barrier or the dust sublimation lines. These planet traps may temporarily favor the growth of planetary cores.
Context.
Pressure maxima are regions in protoplanetary disks in which pebbles can be trapped because the regions have no local pressure gradient. These regions could be ideal places in which ...planetesimals might be formed or to isotopic reservoirs might be isolated. Observations of protoplanetary disks show that dusty ring structures are common, and pressure maxima are sometimes invoked as a possible explanation. In our Solar System, pressure bumps have been suggested as a possible mechanism for separating reservoirs with different nucleosynthetic compositions that are identified among chondrites and iron meteorites. In this paper, we detail a mechanism by which pressure maxima form just inward of the snow line in stratified disks (with a dead zone and an active layer). This mechanism does not require the presence of a planet.
Aims.
We investigate the conditions for the formation of pressure maxima using a vertically averaged
α
viscosity model and release of water vapor at the snow line.
Methods.
We considered a 1D
α
disk model. Using a combination of analytical and numerical investigations, we explored the range of conditions for a pressure maximum to form inside the dead zone and just inward of the snow line.
Results.
When the vertically averaged
α
is a decreasing function of the surface density, then the release of water vapor at the snow line decreases the sound velocity, and a pressure bump appears in turn. This requires a constant inflow of icy pebbles with a ratio of the pebble influx to gas influx >0.6 for a power-law disk with a 1% ice-to-gas ratio, and >1.8 for a disk with an ice-to-gas ratio ~0.3%. If these conditions are met, then a pressure maximum appears just inward of the snow line due to a process that couples the dead and active layers at the evaporation front. The pressure bump survives as long as the icy pebble flux is high enough. The formation of the pressure bump is triggered by the decrease in sound velocity inward of the snow line through the release of water vapor.
Conclusions.
This mechanism is promising for isolating early reservoirs carrying different isotopic signatures in the Solar System and for promoting dry planetesimal formation inward of the snow line, provided the vertically averaged description of a dead zone is valid.
Context. In most current debris disc models, the dynamical and the collisional evolutions are studied separately with N-body and statistical codes, respectively, because of stringent computational ...constraints. In particular, incorporating collisional effects (especially destructive collisions) into an N-body scheme has proven a very arduous task because of the exponential increase of particles it would imply. Aims. We present here LIDT-DD, the first code able to mix both approaches in a fully self-consistent way. Our aim is for it to be generic enough to be applied to any astrophysical case where we expect dynamics and collisions to be deeply interlocked with one another: planets in discs, violent massive breakups, destabilized planetesimal belts, bright exozodiacal discs, etc. Methods. The code takes its basic architecture from the LIDT3D algorithm for protoplanetary discs, but has been strongly modified and updated to handle the very constraining specificities of debris disc physics: high-velocity fragmenting collisions, radiation-pressure affected orbits, absence of gas that never relaxes initial conditions, etc. It has a 3D Lagrangian-Eulerian structure, where grains of a given size at a given location in a disc are grouped into super-particles or tracers whose orbits are evolved with an N-body code and whose mutual collisions are individually tracked and treated using a particle-in-a-box prescription designed to handle fragmenting impacts. To cope with the wide range of possible dynamics for same-sized particles at any given location in the disc, and in order not to lose important dynamical information, tracers are sorted and regrouped into dynamical families depending on their orbits. A complex reassignment routine that searches for redundant tracers in each family and reassignes them where they are needed, prevents the number of tracers from diverging. Results. The LIDT-DD code has been successfully tested on simplified cases for which robust results have been obtained in past studies: we retrieve the classical features of particle size distributions in unperturbed discs and the outer radial density profiles in ~r-1.5 outside narrow collisionally active rings as well as the depletion of small grains in dynamically cold discs. The potential of the new code is illustrated with the test case of the violent breakup of a massive planetesimal within a debris disc. Preliminary results show that we are able for the first time to quantify the timescale over which the signature of such massive break-ups can be detected. In addition to studying such violent transient events, the main potential future applications of the code are planet and disc interactions, and more generally, any configurations where dynamics and collisions are expected to be intricately connected.
Survival of Exomoons Around Exoplanets Dobos, V.; Charnoz, S.; Pál, A. ...
Publications of the Astronomical Society of the Pacific,
09/2021, Letnik:
133, Številka:
1027
Journal Article
Recenzirano
Odprti dostop
Abstract
Despite numerous attempts, no exomoon has firmly been confirmed to date. New missions like CHEOPS aim to characterize previously detected exoplanets and potentially discover exomoons. In ...order to optimize search strategies, we need to determine those planets which are the most likely to host moons. We investigate the tidal evolution of hypothetical moon orbits in systems consisting of a star, one planet, and one test moon. We study a few specific cases with ten billion years integration time where the evolution of moon orbits follows one of these three scenarios: (1) “locking,” in which the moon has a stable orbit on a long timescale (≳10
9
yr); (2) “escape scenario” where the moon leaves the planet’s gravitational domain; and (3) “disruption scenario,” in which the moon migrates inwards until it reaches the Roche lobe and becomes disrupted by strong tidal forces. Applying the model to real cases from an exoplanet catalog, we study the long-term stability of moon orbits around known exoplanets. We calculate the survival rate which is the fraction of the investigated cases when the moon survived around the planet for the full integration time (which is the age of the star, or if not known, then the age of the Sun). The most important factor determining the long-term survival of an exomoon is the orbital period of the planet. For the majority of the close-in planets (<10 days orbital periods) there is no stable orbit for moons. Between 10 and 300 days we find a transition in survival rate from about zero to 70%. Our results give a possible explanation for the lack of successful exomoon discoveries for close-in planets. Tidal instability causes moons to escape or being tidally disrupted around close-in planets which are mostly favored by current detection techniques.
Context. Planet traps are necessary to prevent forming planets from falling onto their host star by type I inward migration. Surface mass density and temperature gradient irregularities favor the ...apparition of traps (planet accumulation region) and deserts (planet depletion zone). These features are found at the dust sublimation lines and heat transition barriers. Aims. We study how planets may remain trapped or escape these traps as they grow and as the disk evolves viscously with time. Methods. We numerically model the temporal viscous evolution of a protoplanetary disk by coupling its dynamics, thermodynamics, geometry, and composition. The resulting midplane density and temperature profiles allow the modeling of the interactions of this type of evolving disk with potential planets, even before the steady state is reached. Results. We follow the viscous evolution of a minimum mass solar nebula and compute the Lindblad and corotation torques that this type of disk would exert on potential planets of various masses that are located within the planetary formation region. We determine the position of planet traps and deserts in relationship with the sublimation lines, shadowed regions, and heat transition barriers. We notice that the planet mass affects the trapping potential of the mentioned structures through the saturation of the corotation torque. Planets that are a few tens of Earth masses can be trapped at the sublimation lines until they reach a certain mass while planets that are more massive than 100 M⊕ can only be trapped permanently at the heat transition barriers. They may also open gaps beyond 5 au and enter type II migration. Conclusions. Coupling a bimodal planetary migration model with a self-consistent evolved disk, we were able to distinguish several potential planet populations after five million years of evolution: two populations of giant planets that could stay trapped around 5.5 and 9 au and possibly open gaps, some super-Earths trapped around 5 and 7.5 au, and a population of close-in super-Earths, which are trapped inside 1 au. The traps that correspond to the last group could help to validate the in situ formation scenarios of the observed close-in super-Earths.
This study is a companion paper to Baillié et al., in which we showed that a past episode of inward migration of Mimas could have created the Cassini Division. We here investigate the possible causes ...of this inward migration. We suggest two scenarios: one based on a past intense heating of Mimas, and another one on a past intense heating of Enceladus, which would have itself driven an inward migration of Mimas due to a mean-motion resonance. These two scenarios are challenged with numerical modelling of the orbital motion of the satellites, and energy budget, which are confronted to our present knowledge of the interior of Mimas and Enceladus. We show that a past hot Mimas requires an eccentricity of 0.22, while a past hot Enceladus would have needed an eccentricity of 0.25. While the scenario of a past hot Mimas preserves the stability of the mid-sized satellites of Saturn, it threatens Janus and Epimetheus and is inconsistent with the observations of impact basins at the surface of Mimas. However, a past hot Enceladus which would have almost fully melted could be consistent with its differentiated interior, but would probably not have preserved the stability of Tethys, given the high eccentricity required. Both of these scenarios would have challenged the stability of Aegaeon, Methone, Pallene, and Anthe, and implied that the Cassini Division would be younger than 10 Myr.
Violent stochastic collisional events have been invoked as a possible explanation for some debris discs displaying pronounced azimuthal asymmetries or having a luminosity excess exceeding that ...expected for systems at collisional steady-state. We perform the first fully self-consistent modeling of the aftermath of massive breakups in debris discs. We follow the collisional and dynamical evolution of dust released after the breakup of a Ceres-sized body at 6 AU from its central star. We investigate the duration, magnitude, and spatial structure of the signature left by such a violent event, as well as its observational detectability. We use the recently developed LIDT-DD code, which handles the coupled collisional and dynamical evolution of debris discs. The main focus is placed on the complex interplay between destructive collisions, Keplerian dynamics, and radiation pressure forces. The breakup of a Ceres-sized body at 6 AU creates an asymmetric dust disc that is homogenized by the coupled action of collisions and dynamics on a timescale of a few 10sup 5 years.
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