On the dynamical evolution and end states of binary centaurs

In this paper,we perform a numerical integration of 666 fictitious binary Centaurs coming from the trans Neptunian space. Our population is restricted to tight binaries whose components have sizes between 30 and 100 km. We included the dynamical perturbations from the giant planets, Kozai Cycles induced by the Sun and tidal friction on the orbits of the binaries. We found that most binaries are disrupted during one of the close planetary encounters, making the mean lifetime of binary Centaurs much shorter than the one of single Centaurs. Nearly 10 per cent of the binaries reach a very tight circular orbit, arguing in favour of the existence of a non-negligible population of contact Centaurs. Another 10 per cent survive as a binary during their lifetime as Centaur. Our simulations favour the existence of a small population of very tight binary Centaurs.Facultad de Ciencias Astronómicas y Geofísica

Dynamical and collisional evolution of Kuiper belt binaries

We present numerical simulations of the evolution of synthetic Trans Neptunian Binaries (TNBs) under the influence of solar perturbations, tidal friction, and collisions with the population of Classical Kuiper Belt Object (KBOs). We show that these effects, acting together, have strongly sculpted the primordial population of TNBs. If the population of Classical KBOs have a power law size distribution as the ones that are inferred from the most recent deep ecliptic surveys (Adams et al. 2014, Fraser at al. 2014), the fraction of surviving binaries at present would be of only ∼ 70 % of the primordial population. The orbits of the surviving systems match reasonably well the observed sample. Because of the impulse imparted during the collisional process, only ∼ 10 % of the objects reach total orbital circularization (e ≤ 10−4 ), and very few contact binaries should exist in the Trans Neptunian region. Ultra wide binaries are naturally obtained in number and orbital distribution similar to the ones of the observed population, as a natural result of the combined action of KCTF and collisional evolution on an initial population of tight binaries.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y GeofísicasGrupo de Ciencias Planetaria

Dynamical and collisional evolution of Kuiper belt binaries

We present numerical simulations of the evolution of synthetic Trans Neptunian Binaries (TNBs) under the influence of solar perturbations, tidal friction, and collisions with the population of Classical Kuiper Belt Object (KBOs). We show that these effects, acting together, have strongly sculpted the primordial population of TNBs. If the population of Classical KBOs have a power law size distribution as the ones that are inferred from the most recent deep ecliptic surveys (Adams et al. 2014, Fraser at al. 2014), the fraction of surviving binaries at present would be of only ∼ 70 % of the primordial population. The orbits of the surviving systems match reasonably well the observed sample. Because of the impulse imparted during the collisional process, only ∼ 10 % of the objects reach total orbital circularization (e ≤ 10−4 ), and very few contact binaries should exist in the Trans Neptunian region. Ultra wide binaries are naturally obtained in number and orbital distribution similar to the ones of the observed population, as a natural result of the combined action of KCTF and collisional evolution on an initial population of tight binaries.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y GeofísicasGrupo de Ciencias Planetaria

A tree code for planetesimal dynamics: Comparison with a hybrid direct code

We present a tree code for simulations of collisional systems dominated by a central mass. We describe the implementation of the code and the results of some test runs with which the performance of the code was tested. A comparison between the behaviour of the tree code and a direct hybrid integrator is also presented. The main result is that tree codes can be useful in numerical simulations of planetary accretion, especially during intermediate stages, where possible runaway accretion and dynamical friction lead to a population with a few large bodies in low-eccentricity and low-inclination orbits embedded in a large swarm of small planetesimals in rather excited orbits. Some strategies to improve the performance of the code are also discussed.Facultad de Ciencias Astronómicas y Geofísica

On the dynamical evolution and end states of binary centaurs

In this paper,we perform a numerical integration of 666 fictitious binary Centaurs coming from the trans Neptunian space. Our population is restricted to tight binaries whose components have sizes between 30 and 100 km. We included the dynamical perturbations from the giant planets, Kozai Cycles induced by the Sun and tidal friction on the orbits of the binaries. We found that most binaries are disrupted during one of the close planetary encounters, making the mean lifetime of binary Centaurs much shorter than the one of single Centaurs. Nearly 10 per cent of the binaries reach a very tight circular orbit, arguing in favour of the existence of a non-negligible population of contact Centaurs. Another 10 per cent survive as a binary during their lifetime as Centaur. Our simulations favour the existence of a small population of very tight binary Centaurs.Facultad de Ciencias Astronómicas y Geofísica

Orbital migrations in planetesimal discs: N-body simulations and the resonant dynamical friction

We have performed N-body numerical simulations of the exchange of angular momentum between a massive planet and a 3D Keplerian disc of planetesimals. Our interest is directed at the study of the classical analytical expressions of the lineal theory of density waves, as representative of the dynamical friction in discs 'dominated by the planet' and the orbital migration of the planets with regard to this effect. By means of a numerical integration of the equations of motion, we have carried out a set of numerical experiments with a large number of particles (N ≥ 10 000), and planets with the mass of Jupiter, Saturn and one core mass of the giant planets in the Solar system (Mc = 10M⊕). The torque, measured in a phase in which a 'steady forcing' is clearly measurable, yields inward migration in a minimum-mass solar disc (∑ ∼ 10 g cm-2 ), with a characteristic drift time of ∼ a few 106 yr. The planets predate the disc, but the orbital decay rate is not sufficient to allow accretion in a time-scale relevant to the formation of giant planets. We found reductions of the measured torque on the planet, with respect to the linear theory, by a factor of 0.38 for Mc, 0.04 for Saturn and 0.01 for Jupiter, due to the increase in the perturbation on the disc. The behaviour of planets whose mass is larger than Mc is similar to the one of type II migrators in gaseous discs. Our results suggest that, in a minimum mass, solar planetesimals disc, type I migrations occur for masses smaller than Mc, whereas for this mass value it could be a transition zone between the two types of migration.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

A possible long-lived asteroid population at the equilateral Lagrangian points of Saturn

The Lagrangian equilateral points of a planetary orbit are points of equilibrium that trail at 60°, ahead (L4) or behind (L5), the trajectory of a planet. Jupiter is the only major planet in our Solar system harbouring a known population of asteroids at those locations. Here we report the existence of orbits close to the Lagrangian points of Saturn, stable at time-scales comparable to the age of the Solar system. By scaling with respect to the Trojan population we have estimated the number of objects that would populate the regions, which gives a significant figure. Moreover, mutual physical collisions over the age of the Solar system would be very rare, so the evaporation rate of this swarm arising from mutual interactions would be very low. A population of asteroids not self-collisionally evolved after their formation stage would be the first to be observed in our planetary system. Our present estimations are based on the assumption that the capture efficiency at Saturn's equilateral points is comparable with the one corresponding to Jupiter, thus our figures may be taken as upper limits. In any case, observational constraints on their number would provide fundamental clues to our understanding of the history of the outer Solar system. If they existed, the surface properties and size distribution of those objects would represent unusually valuable fossil records of our early planetary system.Facultad de Ciencias Astronómicas y Geofísica

Orbital migrations in planetesimal discs: N-body simulations and the resonant dynamical friction

We have performed N-body numerical simulations of the exchange of angular momentum between a massive planet and a 3D Keplerian disc of planetesimals. Our interest is directed at the study of the classical analytical expressions of the lineal theory of density waves, as representative of the dynamical friction in discs 'dominated by the planet' and the orbital migration of the planets with regard to this effect. By means of a numerical integration of the equations of motion, we have carried out a set of numerical experiments with a large number of particles (N ≥ 10 000), and planets with the mass of Jupiter, Saturn and one core mass of the giant planets in the Solar system (Mc = 10M⊕). The torque, measured in a phase in which a 'steady forcing' is clearly measurable, yields inward migration in a minimum-mass solar disc (∑ ∼ 10 g cm-2 ), with a characteristic drift time of ∼ a few 106 yr. The planets predate the disc, but the orbital decay rate is not sufficient to allow accretion in a time-scale relevant to the formation of giant planets. We found reductions of the measured torque on the planet, with respect to the linear theory, by a factor of 0.38 for Mc, 0.04 for Saturn and 0.01 for Jupiter, due to the increase in the perturbation on the disc. The behaviour of planets whose mass is larger than Mc is similar to the one of type II migrators in gaseous discs. Our results suggest that, in a minimum mass, solar planetesimals disc, type I migrations occur for masses smaller than Mc, whereas for this mass value it could be a transition zone between the two types of migration.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Dynamics of the Edgeworth-Kuiper Belt beyond 50 AU : Spread of a primordial thin disk

In this paper we report numerical simulations of the dynamical evolution of the region a > 50 AU. We found that some dynamical effects such as high-order secular resonances with the rate of precession of Neptune's node of the form kΩ· − Ω·Nep with k = 4,5, ... or combined mean motion resonances with Uranus and Neptune of the form knN + jnU + mn ∼ 0 may increase the area of a very thin primordial disk in this region by a factor of up to 2 after 4.5 Gy of evolution.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

On the accretion of Uranus and Neptune

In this paper, we discuss some problems concerning the formation of Uranus and Neptune. We find that the adoption of reduced Hill spheres as the region of close interaction between planetesimals introduces an enhancement of the gravitational cross-sections in previous numerical simulations. We also discuss a way to make possible the formation of Uranus and Neptune on time-scales shorter than the age of the Solar system.Facultad de Ciencias Astronómicas y Geofísica