Forming Binary Near-Earth Asteroids From Tidal Disruptions

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A.2 Resolution of ProgenitorThe resolution, or number of particles per progenitor, was about 1000 in our standardruns, designed to represent a ∼ 3 km aggregate consisting of ∼ 150 m sized particles. Theevidence for 150 m building blocks comes from numerical simulations and the observedspin frequency cutoff for asteroids (Benz & Asphaug 1999; Pravec et al. 2002). However,this logic would demand that progenitors with smaller diameters have a lower resolutionin simulations, and similarly require higher resolution for larger-diameter objects. Ourignorance about the true makeup of a gravitational aggregate justifies experiments withhigher- and lower-resolution bodies. Thus a test of resolution over an order of magnitudewas run, using progenitors with 200, 500, and 2000 particles over a subset of parameters.The parameters used for these simulations are the same as those in Section A.1, exceptthe 6 h spin rate. The resulting size ratios for the simulations all peak at a higher value(larger secondaries) for lower resolution and at lower values (smaller secondaries) forhigher resolution (see Fig. A.1).The number of binaries produced at each resolution differed by over a factor of three(see Table A.1). The disparity in binaries formed is likely due to the numerical techniqueused to find companions (Leinhardt & Richardson 2005). Only clumps with 3 or moreparticles were entered into the search, and each companion around a primary counts as abinary. Thus for higher-resolution runs it is significantly easier to have debris in the formof a 3+ particle clump orbiting a large primary thereby driving up the number of totalbinaries.Also listed in Table A.1 is the count of the number of simulations in which a binaryis produced. This statistic should reduce the advantage that higher-resolution simulationshave in creating multiple binaries, and just count situations that produce at least one binary.This number still increases with resolution, but not as dramatically, as the 2000115
Table A.1.Number of binaries produced at varying resolutions.Number of particles Total binaries Sims with binariesper progenitor200 686 543500 962 6481000 1549 9212000 2262 939Note. — The number of binaries produced for each subsetof runs testing progenitor resolution.particle runs produce less than twice as many as the 500 particle simulations.The properties of the binaries show minor changes in primary spin rate and semimajoraxis with resolution. Lower resolution pushes secondaries towards faster spin, andsmaller semi-major axis. The shape of the primary is also affected, with lower resolutionproducing slightly more spherical primaries.A.3 Packing Efficiency of ProgenitorIn tidal disruption simulations, binaries are formed from reaccumulation of disrupted debris.Previously the progenitors were constructed using hexagonal closest packing ofspheres for simplicity, meaning the particles were organized very precisely and the resultingassemblage had a lower porosity than a random assemblage of identical spheres 1 .1 The densest arrangement of similar-sized spheres is a problem that dates back to Kepler, when hehypothesized in 1611 that the maximum density for packing comes from cubic or hexagonal close packingwith a packing density π/(3 √ 2) ≈ 74.408%. Many attempts to prove this culuminated in a published proofby Hales (2005), making extensive use of computer calculation and 12 reviewers attempting to verify itsvalidity (Conway & Sloane 1993).116
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AbstractTitle of Dissertation:Formi
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Forming Binary Near-Earth Asteroids
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PrefaceMuch of the work in this dis
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AcknowledgementsI would not have ma
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2.3 Results and Discussion . . . .
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List of Tables1.1 Binary NEA proper
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4.8 Percentage of migrated binaries
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of the system mass M by way of Kepl
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the largest lightcurve amplitudes o
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1.1.3 Binary Main-Belt asteroidsRec
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Lightcurve discoveriesA lightcurve
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Figure 1.1: (Top) The primary rotat
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1.2.1 CaptureIn this scenario two a
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ever, understanding the mechanism i
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off the equator or off one end of a
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3 Denotes a secure result with no a
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nostic.Recent results have demonstr
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another intermediate source of NEAs
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1.5.2 Rubble pilesThe evidence for
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Chapter 2Formation of Binary Astero
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∼ 60%, making a bulk density of
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shedding mass and distorting prior
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Figure 2.3: Snapshots of a tidal di
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Figure 2.4: Normalized probability
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Figure 2.5: Normalized probability
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Figure 2.6: (a) Satellite eccentric
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various complications of measuring
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etween ω pri and L bin ), with clo
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prolate-like), the oblate-like bodi
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Figure 2.9: Plots comparing T-PROS
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Figure 2.10: Comparison of S-class
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2.3.5 Triples and hierarchical syst
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a/R pri based on a simple conversio
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Figure 2.13: The eccentricity dampi
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Main Belt. Work by Chauvineau & Far
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(1992), with a target range of slig
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The observations were made from the
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peaked period, with a lower signifi
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Page 81 and 82: Table 3.2.Orbital, physical and lig
Page 83 and 84: Figure 3.2: Asteroid lightcurves.70
Page 85 and 86: Figure 3.4: Asteroid lightcurves.72
Page 87 and 88: 3.4.4 Spin and shape properties amo
Page 89 and 90: Figure 3.7: The lightcurve amplitud
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Page 93 and 94: Chapter 4Steady-State Model of the
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Page 99 and 100: Figure 4.2: Percent of surviving NE
Page 101 and 102: 4.1.3 Binary evolutionBasic stabili
Page 103 and 104: Table 4.1.Lifetimes for binary NEAs
Page 105 and 106: which means it should have a critic
Page 107 and 108: Figure 4.4: The total number of bin
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Page 111 and 112: Figure 4.6: Properties of the binar
Page 113 and 114: Figure 4.8: Binary percentage for m
Page 115 and 116: Figure 4.9: Effects of tidal evolut
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Page 119 and 120: tidal disruption. However, the impl
Page 121 and 122: Chapter 5ConclusionsA general concl
Page 123 and 124: small additions to the angular mome
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Page 127: differences in results when a lower
Page 131 and 132: Thus the reaccumulated bodies in th
Page 133 and 134: of 2.2 h observed is significantly
Page 135 and 136: Benner, L. A. M., Nolan, M. C., Ost
Page 137 and 138: V7.0:LCREF TAB, 35, 4Harris, A. W.,
Page 139 and 140: Storrs, A. D., Close, L. M., & Mena
Page 141 and 142: 122Pravec, P., Kušnirá, P., Hicks
Page 143 and 144: Shepard, M. K., Schlieder, J., Nola
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Forming Binary Near-Earth Asteroids From Tidal Disruptions

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