Forming Binary Near-Earth Asteroids From Tidal Disruptions

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∼100 km are rubble piles.1.6 This DissertationThis dissertation was designed to investigate the role of tidal disruption in the formationof binary NEAs. At the heart of this work is the attempt to answer the following threequestions,1. What are the properties of tidal-disruption-formed binaries and how do they compareto the observed NEA binaries?2. What is the spin and shape distribution for small MBAs, how does it compare toNEAs and large MBAs?3. What is the overall steady-state binary fraction for NEAs caused by tidal disruption?We present theoretical and observational studies to address all three questions in thefollowing chapters. First, in Chapter 2, we describe our models of the tidal disruptionof strengthless “rubble pile” asteroids, using N-body simulations. Results from manysimulations covering a large parameter space are presented, with characterization of thebinaries formed.In Chapter 3 an observing campaign designed to study the shape and spin of smallMBAs is presented. Observations of 28 asteroids are combined with previously publishedlightcurves to determine the shape and spin distribution for small MBAs.The results from the observations in Chapter 3 are used along with the simulation resultsin Chapter 2, to create a steady-state model of the binary NEA population presentedin Chapter 4. This model tracks binary NEAs as they are formed, evolve and eventuallyreplaced when they reach the end of their lifetime.In Chapter 5 we summarize the main results and present conclusions.25
Chapter 2Formation of Binary Asteroids via TidalDisruption of Rubble PilesWalsh & Richardson, 2006, Formation of Binary Asteroids via Tidal Disruption of Rubble Piles,Icarus 180, 201–2162.1 OverviewIn this chapter we adopt numerical techniques similar to those of previous N-body rubblepile simulations, and cover parameters previously shown to produce catastrophic tidalencounters, but in much greater detail. This study is unique in the large number of simulationsperformed and detailed investigation into the physical and orbital attributes of theresulting binaries. In Section 2.2 the details of the simulations and analysis are explained,and the results are discussed in Section 2.3. Conclusions and future work are presentedin Section 2.4.26
Page 1 and 2: AbstractTitle of Dissertation:Formi
Page 3 and 4: Forming Binary Near-Earth Asteroids
Page 5 and 6: PrefaceMuch of the work in this dis
Page 7 and 8: AcknowledgementsI would not have ma
Page 9 and 10: 2.3 Results and Discussion . . . .
Page 11 and 12: List of Tables1.1 Binary NEA proper
Page 13 and 14: 4.8 Percentage of migrated binaries
Page 15 and 16: of the system mass M by way of Kepl
Page 17 and 18: the largest lightcurve amplitudes o
Page 19 and 20: 1.1.3 Binary Main-Belt asteroidsRec
Page 21 and 22: Lightcurve discoveriesA lightcurve
Page 23 and 24: Figure 1.1: (Top) The primary rotat
Page 25 and 26: 1.2.1 CaptureIn this scenario two a
Page 27 and 28: ever, understanding the mechanism i
Page 29 and 30: off the equator or off one end of a
Page 31 and 32: 3 Denotes a secure result with no a
Page 33 and 34: nostic.Recent results have demonstr
Page 35 and 36: another intermediate source of NEAs
Page 37: 1.5.2 Rubble pilesThe evidence for
Page 41 and 42: ∼ 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
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Figure 3.7: The lightcurve amplitud
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Typically observations of eclipse o
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Chapter 4Steady-State Model of the
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values between 0.2-0.6. There is on
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asteroids in the Main Belt is suffi
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Figure 4.2: Percent of surviving NE
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4.1.3 Binary evolutionBasic stabili
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Table 4.1.Lifetimes for binary NEAs
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which means it should have a critic
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Figure 4.4: The total number of bin
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the original eccentricity distribut
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Figure 4.6: Properties of the binar
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Figure 4.8: Binary percentage for m
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Figure 4.9: Effects of tidal evolut
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quickly altered, or involved in bin
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tidal disruption. However, the impl
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Chapter 5ConclusionsA general concl
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small additions to the angular mome
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cently this large pool of observers
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differences in results when a lower
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Table A.1.Number of binaries produc
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Thus the reaccumulated bodies in th
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of 2.2 h observed is significantly
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Benner, L. A. M., Nolan, M. C., Ost
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V7.0:LCREF TAB, 35, 4Harris, A. W.,
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Storrs, A. D., Close, L. M., & Mena
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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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