Forming Binary Near-Earth Asteroids From Tidal Disruptions

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to create or change binaries within both populations.1.3 Shape and Spin Distributions for NEAs and MBAsThe shape and spin distributions for NEAs and MBAs tells a significant story about eachpopulation. The first theories that asteroids may be strengthless, or even rubble piles,came from analysis of the spin periods derived from lightcurves (Burns 1975; Harris1996). As well, it was concerted campaigns to collect lightcurves of NEAs which starteddiscovering binaries (Pravec & Hahn 1997). The spin and shape of asteroids has alsoproven to be important parameters in determining the outcome of tidal disruption simulations(Richardson et al. 1998), which is why they are of interest in this work. <strong>From</strong> themeasured lightcurve, an asteroid’s rotational period can be estimated assuming that anynormal elongation will produce a double-peaked periodic curve. The amplitude of thiscurve is related to the axis ratio of the asteroid via equation 1.3.1.3.1 Existing lightcurve dataThe repository for published asteroid lightcurves contains the best parameters for all observedsmall bodies (Harris et al. 2005a). A rating system is employed to differentiatebetween data of different quality,0 Result later proven incorrect. This appears only on records of individual observations.1 Result based on fragmentary lightcurve(s), may be completely wrong.2 Result based on less than full coverage, so that the period may be wrong by 30 percentor so. Also, a quality of 2 is used to note results where an ambiguity exists as to thenumber of extrema per cycle or the number of elapsed cycles between lightcurves.Hence the result may be wrong by an integer ratio.17
3 Denotes a secure result with no ambiguity and full lightcurve coverage.4 In addition to full coverage, denotes that a pole position is reported.Significant temporal coverage of an asteroid’s rotation period is required to estimate theperiod with any certainty, and, as the rating system implies, even extensive observationscan still leave certain parameters in doubt. When compiling statistics about differentpopulation’s shape and spin from lightcurve data, the rating system is an important toolin understanding previously published data.Currently in the lightcurve repository there are 60 Main Belt objects with a diameter< 5 km for which a minimum quality (Q) of 2 is listed. There are 225 such observationsfor bodies with diameter D < 10 km and 480 with D < 20 km. <strong>From</strong> this list none ofthe small (D < 5 km) MBAs are binary asteroids, and there are 289 NEAs listed in therepository, among which 15 are binaries.1.3.2 Recent studiesBinzel et al. (1992) presented the results of a dedicated survey of MBAs smaller thanD < 5 km. The survey covered 32 objects and presented 30 periods and 32 amplitudesfrom lightcurves. Overall the results suggested that the sample had a rotational frequencyfaster than the population of larger MBAs. This was the first survey of this kind, and nosimilar dedicated survey of small MBAs (SMBAs) lightcurves has followed.Pravec et al. (2002) summarizes asteroid rotations highlighting how spin rate varieswith size. Using a running box statistical method they report that the geometric mean spinperiod for D > 40 km is ∼13 h, and decreases to ∼ 6 h for D ∼ 10 km. The distributionfor asteroids with D > 40 km, is fit well with a maxwellian distribution, whereas for 0.15< D < 10 km is not. This group of smaller asteroids, which includes NEAs, has strongpopulations of slow (∼30 h) and fast (∼3.5 h) rotators, with an apparent maximum spin18
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: off the equator or off one end of 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
Page 79 and 80: 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
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
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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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