Forming Binary Near-Earth Asteroids From Tidal Disruptions

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Figure 4.3: Comparison of this work, using HNBODY to calculate binary disruption probability(solid line), with results presented in (Bottke & Melosh 1996a, squares).counter distance is determined for each binary semi-major axis as the distance at which50% of randomly oriented binaries disrupt due to the tidal forces of the close encounter.The statistical encounter probabilities for each critical distance then determine lifetimebetween binary-disrupting encounters (Table 4.1). The lifetime for very close binariesof 4 or 6 R pri is only 2 or 1.6 Myr, suggesting that many of the observed NEA binariesare potentially quite young. The NEA binary Hermes has a semi-major axis of 5 R pri ,91
which means it should have a critical encounter every 1.75 Myr, despite requiring similartimescales to tidally revolve to its doubly synchronous state. This result for Hermes highlightsthe nature of this calculation, that it is a statistical average, and does not considerresonant encounters, or dynamically stable orbits within the NEA population.A second implementation of the code included inline 3-body integrations to model abinary encounter with a planet within the simulation itself. In this implementation theexact semi-major axis and mass ratio of the binary is used to setup and run a 3-body integrationin pkdgrav of that binary with <strong>Earth</strong> with randomly selected encounter parametersof close approach distance and speed. Again, no eccentricity is given to this initial binary.After the encounter the new semi-major axis and eccentricity of the binary replace thepre-encounter values. If the binary was disrupted the resultant body is treated as a singleasteroid again. This implementation offers a level of sophistication greater than the previouslydescribed runs via the lookup table by providing binary orbital changes induced bythe encounter, rather than just indicating whether or not the binary was disrupted. However,the overall results in this work are not very sensitive to which method of 3-bodyencounters was used, and generally we would only expect inclusion of this to decreasethe binary fraction due to the increases in eccentricity that are tracked.4.1.4 Migrating binary MBAsA large unknown in the study of binary NEAs is the extent of any migration of binaryasteroids from the Main Belt population. If binary asteroids can migrate successfullyfrom MBA orbits into NEA orbits then the numbers and properties of these binaries maybe extremely important in shaping the binary NEA population.In this work binary MBAs were included in the steady-state simulation as a variablepercentage of the incoming asteroids. The binary properties were drawn from a previousstudy of a family-forming collisions modeled with SPH code and pkdgrav (Durda92
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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
Page 53 and 54: various complications of measuring
Page 55 and 56: etween ω pri and L bin ), with clo
Page 57 and 58: prolate-like), the oblate-like bodi
Page 59 and 60: Figure 2.9: Plots comparing T-PROS
Page 61 and 62: Figure 2.10: Comparison of S-class
Page 63 and 64: 2.3.5 Triples and hierarchical syst
Page 65 and 66: a/R pri based on a simple conversio
Page 67 and 68: Figure 2.13: The eccentricity dampi
Page 69 and 70: Main Belt. Work by Chauvineau & Far
Page 71 and 72: (1992), with a target range of slig
Page 73 and 74: The observations were made from the
Page 75 and 76: peaked period, with a lower signifi
Page 77 and 78: and suggests that it is possibly a
Page 79 and 80: fit for the period of the lightcurv
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
Page 91 and 92: Typically observations of eclipse o
Page 93 and 94: Chapter 4Steady-State Model of the
Page 95 and 96: values between 0.2-0.6. There is on
Page 97 and 98: asteroids in the Main Belt is suffi
Page 99 and 100: Figure 4.2: Percent of surviving NE
Page 101 and 102: 4.1.3 Binary evolutionBasic stabili
Page 103: Table 4.1.Lifetimes for binary NEAs
Page 107 and 108: Figure 4.4: The total number of bin
Page 109 and 110: the original eccentricity distribut
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
Page 117 and 118: quickly altered, or involved in bin
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
Page 125 and 126: cently this large pool of observers
Page 127 and 128: differences in results when a lower
Page 129 and 130: Table A.1.Number of binaries produc
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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