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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...
Tidal disruption of rubble-pile bodies (stony or icy aggregates held together by self-gravity) during close Earth encounters may produce significant numbers of Tunguska-sized (50 m) fragments. Using an N-body simulation to model encounters between strengthless, elongated, rotating, particulate bodies and the Earth, two disruption categories were found which produce small bodies: (a) ''Shoemaker-Levy-9...
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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