Forming Binary Near-Earth Asteroids From Tidal Disruptions

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population of binaries migrating to the near-Earth population from the Main Belt.In Section 4.1 we describe the details of the Monte Carlo steady-state model. Wepresent the results of the simulations in detail in Section 4.2 and discuss the implicationsof these results in Section 4.3.4.0.1 Previous workSubstantial modeling work has been done on the tidal disruption of rubble pile asteroidsin regards to the formation of binary NEAs. Richardson et al. (1998) investigated tidaldisruption outcomes in terms of the body’s close approach distance and speed, shape andspin, spin-axis and body-axis orientation. This work suggested that tidal disruption couldaccount for 1–2 observed crater chains on the Moon, as well as the population of binaryNEAs. Using similar but improved methods Chapter 2 presented an exhaustive set ofsimulations of tidal disruption to characterize the properties of binaries formed during adisruption.Chapter 2 found that binary asteroids formed during a tidal disruption event sharemany characteristics with the observed population of binary NEAs, namely1. The semi-major axis distribution of the binaries is strongly peaked below 10 R pri ,though the simulations also show a long tail out beyond the 1 AU Hill sphere at 130R pri . Large separations are neither expected nor observed in the NEA populationbecause close planetary encounters will easily separate very wide binaries and allbut one of the observed binary NEAs have semi-major axes smaller than 10 R pri ,with all but 4 smaller than 5 R pri .2. The size ratios in the simulations are peaked between R sec /R pri = 0.1 – 0.2, witha significant tail towards higher values, i.e. equal size components. The observedpopulation, though biased against size ratios below R sec /R pri ∼ 0.2, almost all have81
values between 0.2–0.6. There is only one observed binary with equal-sized components,also a rarity in simulations.3. The rotation rate of the primary body is narrowly bracketed between 4–6 h in thesimulations. Nearly all binary NEAs have rapidly rotating primaries though theytypically have somewhat faster rotation rates between 2.2–3.5 h.Some questions either unanswered or subsequently raised in Chapter 2, are;1. What is the overall steady-state binary fraction for NEAs caused by tidal disruption?2. Why do simulations not match the rapid rotation rates of the primary bodies?3. Will the binaries created by tidal disruption, which generally start with high eccentricity,survive long enough to have their eccentricity tidally damped to the observedlow values (almost all observed below 0.1 for the few well-measured systems)?4. Do binary NEAs with large semi-major axes exist unobserved as Chapter 2 suggests,or are they disrupted during subsequent close approaches with Earth?The main focus of the current work is to apply the results of Chapter 2 to determinehow many present-day NEA binaries may be tidal disruption outcomes, and what thepopulation of this subset of binaries will look like in steady-state. We use these results ina Monte Carlo routine to simulate the transport of bodies from the Main Belt to the near-Earth population, their encounters with Earth, and the formation and subsequent evolutionof binaries. We also determine the effect of pre-existing binary MBAs migrating into thenear-Earth population.82
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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
Page 43 and 44: shedding mass and distorting prior
Page 45 and 46: Figure 2.3: Snapshots of a tidal di
Page 47 and 48: Figure 2.4: Normalized probability
Page 49 and 50: Figure 2.5: Normalized probability
Page 51 and 52: 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: Chapter 4Steady-State Model of the
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 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
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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