Forming Binary Near-Earth Asteroids From Tidal Disruptions

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of size ratios, including contact-binary formations.In the course of modeling asteroid family formation via reaccumulation of debris followinga catastrophic impact, Michel et al. (2001, 2004) found many companions of thelargest remnant. The works were focused on, and matched, many dynamical and physicalproperties of some asteroid families, but no comprehensive analysis of any binaries wascompleted.Durda et al. (2004) simulated large-scale (100 km diameter target body) catastrophiccollisions of asteroids to determine the efficiency of forming binaries via collision. Similarto Michel et al. (2001, 2004) these simulations used a smoothed particle hydrodynamics(SPH) code to model the collision and an N-body code to simulate the post-collisionevolution and re-accumulation of the fragments. The collisions were efficient at creatingbound systems out of the re-accumulated debris and many of the binaries producedare qualitatively similar to those observed in the Main Belt. Two main types of outcomesfrom these simulations were observed and classified as SMATS (SMAshed TargetSatellites) and EEBs (Escaping Ejecta Binaries). The SMATS consist of re-accumulatedfragments orbiting the largest remnant from the collision, whereas the EEBs are small andusually similar-sized fragments that have escaped from the largest remnant and becomebound to each other.Of the observed MBA binaries discovered via high-resolution imaging most are similarto SMATS, with primaries significantly larger than the secondaries. Some binarieswith small, nearly equal-sized components and large separations are suspected EEBs (see(4674) Pauling, (1509) Esclangona, (22899) 199 TO 14 , and (17246) GL 74 in Table 1.2).In the NEA population the collisional lifetimes are significantly longer than the veryshort dynamical lifetimes (∼10 Myr as determined through numerical simulations), makingcollisions an unlikely local source of binaries. The binaries observed in collisionsimulations typically have larger separations than is observed with NEA binaries. How-13
ever, understanding the mechanism is important as collisionally formed binaries in theMain Belt may migrate to the NEA population.1.2.3 Rotational disruptionRotational disruption has been credited with a large role in binary formation among NEAsdue to some of the prominent similar properties shared by these binaries (Merline et al.2002c; Margot et al. 2002). Rapidly-rotating primaries, very near the theoretical breakuplimit for strengthless bodies, have been a signature of binary NEAs and have recentlybeen seen among small MBAs. The fastest-rotating NEAs have periods no shorter than ∼2 h, and the primaries of the observed binaries nearly all have periods below 3 h. Thus aformation related to rotational disruption when an asteroid is made to spin faster than thecritical limit has been favored for this population.Tidal disruptionTidal disruption of a rubble pile has been invoked to explain the disruption of CometD/Shoemaker–Levy 9 (SL9) and has also been applied to asteroid studies. SL9 disruptedwhen the comet passed within ∼ 1.36 R J of Jupiter on 1992 July 7. The comet was tornapart and ∼ 21 fragments or reaccumulated clumps were later observed. N-body studieshave since matched many of the comet’s basic post-disruption features (train length, positionangle and morphology) using a strengthless rubble pile model (Solem 1994; Asphaug& Benz 1996; Walsh et al. 2003).Solem & Hills (1996) used similar N-body techniques to simulate the change in elongation(ratio of long axis to short axis length) of an asteroid due to a planetary closeapproach. Citing 1620 Geographos as an extreme case with an elongation of 2.7, encounterswith Earth between close approach distance q = 1.02 and 2.03 Earth radii (R ⊕ ) weresampled with a range of v ∞ (the speed at infinity of a hyperbolic encounter) between ∼14
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: 1.2.1 CaptureIn this scenario two a
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 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
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fit for the period of the lightcurv
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Table 3.2.Orbital, physical and lig
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Figure 3.2: Asteroid lightcurves.70
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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
Page 135 and 136:
Benner, L. A. M., Nolan, M. C., Ost
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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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