Forming Binary Near-Earth Asteroids From Tidal Disruptions

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Table 4.2.Binary fractions for all simulations.Progenitor Tidal MBA Tidal disruption Migrated Totaldistribution evolution binaries binaries binaries binariesSMBA (10%) ON 100 Myr 1.2% 0.2% 1.4%NEA (10%) ON 100 Myr 1.4% 0.3% 1.7%SMBA (10%) OFF 100 Myr 1.7% 0.1% 1.8%SMBA (10%) ON 0 Myr 1.2% 0.2% 1.4%SMBA (20%) ON 100 Myr 1.2% 0.3% 1.5%SMBA (50%) ON 100 Myr 1.2% 0.7% 1.8%SMBA (80%) ON 100 Myr 1.1% 1.0% 2.1%Note. — Binary fraction of both NEA and MBA binaries are listed with respectto the primary model parameter setting. The column “Progenitor distribution”refers to the shape and spin distribution of the asteroids being injected into thesystem, with the percentage of binary progenitors in parentheses. Tidal Evolutionrefers to whether or not binary systems would actively be altered tidally throughoutthe simulation. One simulation was run where the binary MBA population did nothave any tidal evolution (compared to the nominal case of 100 Myr); it is listed as0 Myr under the “MBA binaries” column. The final three columns list the percentageof asteroids in the simulation that were formed from tidal disruption, migratedfrom the Main Belt, and the total combined percentage of binaries.4.2.5 Estimates on the properties of binary NEAs formed by tidaldisruptionThe properties of the steady-state binaries are largely dominated by the preference ofplanetary encounters to eliminate widely separated systems. This effect is so strong thatit may eliminate any significant fingerprint of the formation mechanism that exists in thepopulation (possibly other than primary spin and shape). The eccentricities are dampedsubstantially, with values between 0 and 0.1 dominating the distribution.The binaries in the steady-state system otherwise retain the fast spinning primary.This potentially diagnostic property may be the only significant observable property not103
quickly altered, or involved in binary lifetimes. However, with all observed NEA binarieshaving fast rotation rates it certainly appears that a rotational spin-up origin for mostsystems is likely. Similarly the observed primaries generally appear quite spherical, whichcould be a diagnostic feature in future work.Differentiating between tidally disrupted binaries and those formed from another mechanismwill be quite difficult. Any binaries observed are likely to have survived due toselected binary properties, namely a small semi-major axis. Primary spin and shape mayalso be diagnostic, but currently all the observed binaries look the same with fast-spinningand spherical primaries, both of which are seen in tidal disruption simulations (Walsh &Richardson 2006).4.2.6 Estimates of migrated binaries’ numbers and propertiesThe properties assumed for migrating MBA binaries is such that their lifetime againstdisruption from a planetary encounter is very short. Thus the steady-state number of binarieshaving migrated from the MBA population is very small, nearly zero at any giventime. However, as mentioned above, this value is highly dependent on the MBA binaryproperties used in the model. If a formation mechanism is found to create MBA binarieswith consistently small separations, their lifetime against disruption would increasedramatically, allowing for a significant presence in the steady-state population.One factor working in the favor of migrating binaries could be the ability to avoidresonant encounters with planets. Binaries created by tidal disruption by definition haveplanet-crossing orbits, and therefore an increased chance for future encounters. It maybe possible that binaries migrating from the Main Belt could survive longer than is calculatedin this study by avoiding close planetary encounters, therefore increasing theircontribution to the steady-state population.104
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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
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 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: Figure 4.9: Effects of tidal evolut
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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