Forming Binary Near-Earth Asteroids From Tidal Disruptions

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single bodies at the end of their lifetime. The steady-state population that evolves can thenbe compared with the observed population, revealing the importance of tidal disruptionin forming binary NEAs.1.4.1 Near-Earth asteroid population dynamicsThe NEA population consists of those asteroids with perihelion distances q ≤ 1.3 AUand aphelion distances Q ≥ 0.983 AU (Rabinowitz 1994; Bottke et al. 2002). Earth andMoon cratering records suggest an impact flux that has remained roughly constant overthe past 3 Gyr, implying that the NEA population has not varied drastically in numbersover that time (Grieve & Shoemaker 1994). Therefore bodies being removed from theNEA population (via collision with a planet or the Sun, or by ejection from the innersolar system) must be replaced to keep the population constant.Prior to the first studies indicating that resonances can cause significant increases inan asteroid’s eccentricities, it was thought that many NEAs were extinct cometary nuclei.However, eccentricity-boosting resonances provide a means for MBAs to migrateonto planet-crossing orbits and eventually into near-Earth space (Wetherill 1979; Wisdom1983). It was thought that frequent catastrophic collisions or large impacts withejected debris would cause material to be injected into two powerful resonances in theinner Main Belt: the ν 6 secular resonance with Saturn and the 3:1 mean motion resonance(MMR) with Jupiter. Once material is injected into these resonances, it will haveits eccentricity pumped and enter an Earth-crossing orbit on a short timescale. MonteCarlo simulations of the asteroid transport into these two resonances and subsequentlyinto near-Earth space traced the evolution of asteroids into NEAs, but did not account forthe inherently chaotic environment later revealed with the first numerical investigations(Wetherill 1988; Rabinowitz 1997a,b; Gladman et al. 2000).A series of works has suggested that Mars-crossing asteroids can be considered as21
another intermediate source of NEAs in addition to the two previously cited resonances.Migliorini et al. (1998) asserted that the Mars-crossers that are not NEAs (q > 1.3 AU)have histories inconsistent with an origin from the 3:1 MMR or the ν 6 secular resonance.It was also shown that a series of weak mean-motion resonances with Jupiter or Mars,along with three-body mean-motion resonances with Jupiter and Saturn, can increase anasteroid’s eccentricities until it is on a Mars-crossing orbit (Morbidelli & Nesvorny 1999).From a Mars-crossing orbit an asteroid can evolve into an NEA on timescales of only tensof millions of years (Migliorini et al. 1998; Michel et al. 2000).Bottke et al. (2002) modeled the transport of asteroids from 5 different source populationsin the Main Belt, matching their resultant NEA orbits to a debiased NEO populationfit to Spacewatch data. This work found that the majority (∼61%) of the NEA populationmigrates from the inner Main Belt (a < 2.5 AU), with the central Main Belt (2.5 < a < 2.8AU) contributing ∼24%. This established the NEA population as a steady-state populationconsisting mostly of inner Main Belt asteroids that migrated via one of three mainsources; the two inner Main Belt resonances or from intermediate Mars-crossers.1.5 Background1.5.1 Tidal disruptionThe model for a tidal disruption of a small, non-rotating, liquid satellite in orbit arounda massive body was initially provided by Roche (1847) (see Chandrasekhar 1969). Thiswork solved for the orbital radius inside of which the small body on a circular orbit cannotmaintain an equilibrium figure under the strain of tidal forces. This limit is( ) 1/3 ( ) 1/3 Mpρpr Roche = 1.52 = 2.46R p (1.4)ρ s ρ swhere M p , R p and ρ p are the mass, radius and density of the planet, and ρ s is the density22
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: nostic.Recent results have demonstr
Page 37 and 38: 1.5.2 Rubble pilesThe evidence for
Page 39 and 40: Chapter 2Formation of Binary Astero
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
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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
Page 95 and 96:
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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