Forming Binary Near-Earth Asteroids From Tidal Disruptions

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evolution in some situations.2.4 ConclusionThis study used N-body simulations to model the tidal disruption of strengthless asteroids,or rubble piles, during close encounters with <strong>Earth</strong>. We presented distributions for theresultant physical and orbital properties of the binaries formed, citing similarities anddifferences with the observed population of NEA binaries. The spin of the primary bodyis bracketed in a similar fashion to the observed population, though the simulation’s rangeof primary spin periods is centered on a somewhat slower spin period. Similarly, sizeratios are smaller and less distributed than the observed binaries. Eccentricity poses oneof the largest differences, with the simulations producing eccentricities greater than 0.1 fornearly all cases, whereas all observed binaries have eccentricity less than 0.1. Roughlyhalf the simulated binaries had separations below 10 R pri , which is the upper limit fornearly all observed NEA binaries.Due to the nature of the simulations, and the expensive computations involved, thismany N-body runs cannot all be simulated forward to map the evolution of the overallpopulation. Instead this task will have to be handled on a case-by-case basis, partly usinganalytical techniques developed by Scheeres (2002) to model evolution of binary systemswith non-spherical primaries and secondaries. Other numerical techniques in development,such as freezing the rubble piles into rigid aggregates, thereby eliminating collisioncalculations, would reduce computation time making some stability and evolution simulationsmore practical.As young binaries evolve and new binaries form, a steady-state distribution of propertiesmay develop. Modeling this would help determine which binaries are created in theinner solar system via tidal disruption and which, if any, may have entered intact from the55
Main Belt. Work by Chauvineau & Farinella (1995) and Bottke & Melosh (1996a) suggestfurther encounters of binaries with planets may increase the separation of binaries.Synthesis of these studies with this presented work could provide estimates of evolutionarytracks and help establish the steady-state distribution of properties.An improvement in our knowledge of physical traits of small MBAs would help determinewhat effect tidal disruption has on the NEA population as a whole. Better determinationof very small MBA shape and spin distributions will help set the initial conditionsfor future studies.Overall this work points towards a population of NEA binaries yet to be discovered,those with small size ratio, and with separations greater than 10 R pri . This populationcould very well be formed in equal numbers as the current known small-separation binaries.These binaries may have elongated primaries, more eccentric orbits, and small sizeratios. The long-term survival of such binaries is questionable as distant encounters witha planet will likely keep lifetimes very short.AcknowledgmentsThe simulations were run on the borg and vampire computing clusters at the Departmentof Astronomy, University of Maryland. Thanks to Bill Bottke for providing encounterdistributions and for manuscript comments. Thanks also to Doug Hamilton for manuscriptcomments. We thank the referees for helpful comments that improved the manuscript.This material is based upon work supported by the National Science Foundation underGrant No. AST0307549.56
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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
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 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: Figure 2.13: The eccentricity dampi
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 and 116: Figure 4.9: Effects of tidal evolut
Page 117 and 118: 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
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Shepard, M. K., Schlieder, J., Nola
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Forming Binary Near-Earth Asteroids From Tidal Disruptions

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