1,389 research outputs found
Shifting of the resonance location for planets embedded in circumstellar disks
No full textContext. In the early evolution of a planetary system, a pair of planets may be captured in a mean motion resonance while still embedded in their nesting circumstellar disk.
Aims. The goal is to estimate the direction and amount of shift in the semimajor axis of the resonance location due to the disk gravity as a function of the gas density and mass of the planets. The stability of the resonance lock when the disk dissipates is also tested.
Methods. The orbital evolution of a large number of systems is numerically integrated within a three-body problem in which the disk potential is computed as a series of expansion. This is a good approximation, at least over a limited amount of time.
Results. Two different resonances are studied: the 2:1 and the 3:2. In both cases the shift is inwards, even if by a different amount, when the planets are massive and carve a gap in the disk. For super-Earths, the shift is instead outwards. Different disk densities, Σ, are considered and the resonance shift depends almost linearly on Σ. The gas dissipation leads to destabilization of a significant number of resonant systems, in particular if it is fast.
Conclusions. The presence of a massive circumstellar disk may significantly affect the resonant behavior of a pair of planets by shifting the resonant location and by decreasing the size of the stability region. The disk dissipation may explain some systems found close to a resonance but not locked in it
Ring dynamics around an oblate body with an inclined satellite: the case of Haumea
No full textContext. The recent discovery of rings and massive satellites around minor bodies and dwarf planets suggests that they may often coexist, as for example around Haumea.
Aims. A ring perturbed by an oblate central body and by an inclined satellite may disperse on a short timescale. The conditions under which a ring may survive are explored both analytically and numerically.
Methods. The trajectories of ring particles are integrated under the influence of the gravitational field of a triaxial ellipsoid and (a) massive satellite(s), including the effects of collisions.
Results. A ring initially formed in the equatorial plane of the central body will be disrupted if the satellite has an inclination in the Kozai–Lidov regime (39.2° < i < 144.8). For lower inclinations, the ring may relax to the satellite orbital plane thanks to an intense collisional damping. On the other hand, a significant J2 term easily suppresses the perturbations of an inclined satellite within a critical semi-major axis, even in the case of Kozai–Lidov cycles. However, if the ring is initially inclined with respect to the equatorial plane, the same J2 perturbations are not a protective factor but instead disrupt the ring on a short timescale. The ring found around Haumea is stable despite the rise in the impact velocities that is due to the asymmetric shape of the body and the presence of a 3:1 resonance with the rotation of the central body.
Conclusions. A ring close to an oblate central body should be searched for in the proximity of the equatorial plane, where the J2 perturbations protect it against the perturbations of an external inclined satellites. In an inclined configuration, the J2 term is itself disruptive
Planet–planet scattering in systems of multiple planets of unequal mass
No full textA large sample of planet-planet scattering events for three planet systems with different orbital separations and masses is analysed with a multiple regression model. The dependence of the time for the onset of instability on the masses of the planets and on their initial orbital separations is modelled with a quadratic function. The same analysis is applied to the timespan of the chaotic evolution dominated by mutual close encounters. The configurations with the less massive planet on an outside orbit are stable over longer time-scales. The same configuration leads to shorter chaotic evolution times before the ejection of one planet. In about 70 per cent of the cases, the lighter planet is the one escaping from the system. If a different separation is assumed between the inner and outer planet pairs, then the dominant effect on the instability time is due to the pair with the smaller separation, as a first approximation
Influence of general-relativity effects, dynamical tides, and collisions on planet–planet scattering close to the star
No full textContext. Planet–planet (P–P) scattering is an efficient and robust dynamical mechanism for producing eccentric exoplanets. Coupled to tidal interactions with the central star, this phenomenon can also explain close-in giant planets on circularized and potentially misaligned orbits.
Aims. We explore scattering events occurring close to the star and test if they can reproduce the main features of the observed orbital distribution of giant exoplanets on tight orbits.
Methods. In our modeling we exploited a numerical integration code based on the Hermite algorithm and including the effects of general relativity, dynamical tides, and two-body collisions.
Results. We find that P–P scattering events occurring in systems with three giant planets initially moving on circular orbits close to their star produce a population of planets similar to that presently observed, including eccentric and misaligned close-in planets. The contribution of tides and general relativity is relevant in determining the final outcome of the chaotic phase.
Conclusions. Even if two-body collisions dominate the chaotic evolution of three planets in crossing orbits close to their star, the final distribution shows a significant number of planets on eccentric orbits. The highly misaligned close-in giant planets are instead produced by systems where the initial semimajor axis of the inner planet was around 0.2 au or beyond
Secular evolution of close-in planets: the effects of general relativity
No full textPairs of planets in a system may end up close to their host star on eccentric orbits as a consequence of planet–planet scattering, Kozai, or secular migration. In this scenario, general relativity and secular perturbations have comparable time-scales and may interfere with each other with relevant effects on the eccentricity and pericenter evolution of the two planets. We explore, both analytically and via numerical integration, how the secular evolution is changed by general relativity for a wide range of different initial conditions. We find that when the faster secular frequency approaches the general relativity precession rate, which typically occurs when the outer planet moves away from the inner one, it relaxes to it and a significant damping of the proper eccentricity of the inner planet occurs. The proper eccentricity of the outer planet is reduced as well due to the changes in the secular interaction of the bodies. The lowering of the peak eccentricities of the two planets during their secular evolution has important implications on their stability. A significant number of two-planet systems, otherwise chaotic because of the mutual secular perturbations, are found stable when general relativity is included
The formation and collisional/dynamical evolution of the Ida/Dactyl system as a part of the Koronis family
No full textThe Ida/Dactyl system is the first confirmed asteroid/satellite pair as well as the first family asteroid to be studied in detail by a spacecraft. We explore consequences for Ida of formation by disruption of the Koronis parent body. A significant flux of projectiles onto Ida in a few years following the formation of the family is found, based on models of the disruption of the Koronis parent body by Marzari et al. (Marzari, F., D. Davis, and V. Vanzani 1995. Icarus 113, 168-187). This flux generated craters at a rate much higher than the current crater production rate; however, the flux decreases rapidly as fragment orbits become randomized. Also, we compare the figure of Ida with figures of equilibrium fluid bodies and find that the interior of Ida is nearly stress-free and that Ida could be a rubble pile. Finally, collisional models predict that Dactyl would have been shattered several times in the past 2 billion years, the lower bound on Ida's age derived from its cratered surface. However, some of the ejecta from such disruptions would be trapped in orbit about Ida, subsequently re-accumulating into a satellite. This process could explain the rather regular shape of Dactyl as well as explaining how Dactyl now exists, given its short (compared with Ida's age) collisional disruption lifetime
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