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We present a new code (companion) that identifies bound systems of particles in O(NlogN) time. Simple binaries consisting of pairs of mutually bound particles and complex hierarchies consisting of collections of mutually bound particles are identifiable with this code. In comparison, brute force binary search methods scale as O(N2) while full hierarchy searches can be as expensive as O(N3), making...
We present numerical experiments investigating the shape and spin limits of self-gravitating “perfect” rubble piles that consist of identical, smooth, rigid, spherical particles with configurable normal coefficient of restitution and no sliding friction. Such constructs are currently employed in a variety of investigations, ranging from the formation of asteroid satellites to the dynamical properties...
We present results of 161 numerical simulations of impacts into 100-km diameter asteroids, examining debris trajectories to search for the formation of bound satellite systems. Our simulations utilize a 3-dimensional smooth-particle hydrodynamics (SPH) code to model the impact between the colliding asteroids. The outcomes of the SPH models are handed off as the initial conditions for N-body simulations,...
In this paper, we analyze the effect of the internal structure of a parent body on its fragment properties following its disruption in different impact energy regimes. To simulate an asteroid breakup, we use the same numerical procedure as in our previous studies, i.e., a 3D SPH hydrocode to compute the fragmentation phase and the parallel N-body code pkdgrav to compute the subsequent gravitational...
We present results of 161 numerical simulations of impacts into 100-km diameter asteroids, examining debris trajectories to search for the formation of bound satellite systems. Our simulations utilize a 3-dimensional smooth-particle hydrodynamics (SPH) code to model the impact between the colliding asteroids. The outcomes of the SPH models are handed off as the initial conditions for N-body simulations,...
This paper builds on preliminary work in which numerical simulations of the collisional disruption of large asteroids (represented by the Eunomia and Koronis family parent bodies) were performed and which accounted not only for the fragmentation of the solid body through crack propagation, but also for the mutual gravitational interaction of the resulting fragments. It was found that the parent body...
We present results from direct N-body simulations of collisions between gravitational aggregates of varying size as part of a study to parameterize planetesimal growth in the Solar System. We find that as the ratio of projectile to target mass departs from unity, the impact angle has less effect on the outcome. At the same time, the probability of planetesimal growth increases. Conversely, for a fixed...
There is increasing evidence that many kilometer-sized bodies in the Solar System are piles of rubble bound together by gravity. We present results from a project to map the parameter space of collisions between kilometer-sized spherical rubble piles. The results will assist in parameterization of collision outcomes for Solar System formation models and give insight into disruption scaling laws. We...
We describe a new direct numerical method for simulating planetesimal dynamics in which N~10 6 or more bodies can be evolved simultaneously in three spatial dimensions over hundreds of dynamical times. This represents several orders of magnitude improvement in resolution over previous studies. The advance is made possible through modification of a stable and tested cosmological code optimized...
We present results of numerical simulations that show that Earth's tidal forces can both distort and disrupt Earth-crossing asteroids that have weak “rubble-pile” structures. Building on previous studies, we consider more realistic asteroid shapes and trajectories, test a variety of spin rates and axis orientations, and employ a dissipation algorithm to treat more accurately collisions between the...
Crater chains, presumably formed by weak asteroids or comets stretched apart by planetary tides, have been tentatively identified on both the Earth and Moon. By modeling tidal disruption by the Earth and Moon of ''rubble-pile'' bodies, we find that the Earth disrupts enough objects over the last 3.8 billion years to account for one or two lunar crater chains, but that the reciprocal production rate...
We have carefully monitored the radial velocities of 21 bright, solar-type stars for 12 years, None has shown any reflex motion due to a substellar companion to an upper limit of between 1 and 3 Jupiter masses (X sin i) for orbital periods less than 15 years, We can also rule out companions of more than 3 to 10 Jupiter masses (X sin i) at much longer periods based on long-term trends in the radial...
A self-consistent numerical treatment for modeling fractal aggregate dynamics is presented. Fractal aggregates play an important role in a number of complex astrophysical regimes, including the early solar nebula and the interstellar medium. Aggregates can be of various forms and sizes, ranging from tiny dust particles to ice chunks in planetary rings and possibly even comets. Many observable properties,...
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