Table Of Content

ACCRETIONOFINTERPLANETARYDUSTPARTICLESBYTHEEARTH By STEPHENJOHNKORTENKAMP ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITY OFFLORIDA 1996 ToMomandDad. ACKNOWLEDGMENTS IthankmyadvisorStanDermottforhishelpoverthelastfewyearsandforinstilling inmeasenseofaweforanythingpublishedinNature. IalsothankHumbertoCampins forhissupportinthefirstyearofmystayattheUniversityofFlorida.Thanksalsogoto theothermembersofmycommittee.BoGustafson,HenryKandrupandPaulMueller. Finally,Ithankmyparentsforraisingmethewaytheydid. TABLEOFCONTENTS £age ACKNOWLEDGMENTS iii LISTOFTABLES vi LISTOFFIGURES vii ABSTRACT xix CHAPTERS 1 INTRODUCTION 1 2 DUSTINTHEZODIACALCLOUD 4 3 THEMECHANICSOFACCRETION 15 AverageSpatialDensity 15 RelativeEncounterVelocity 24 GravitationalCross-Section 25 CaptureRate 28 4 THEORIGINOFIDPS 30 InitialParentBodyPopulation 31 GenerationandEvolutionofDustParticleOrbits 32 CaptureRates 36 ContributiontotheIDPs 37 5 VARIATIONSINTHERATEOFACCRETION 62 InitialConditions 63 GenerationandEvolutionofDustParticleOrbits 64 VariableCaptureRates 68 ComparisonWithOtherRecords 73 6 SUMMARY 95 ConclusionsandDiscussion 95 FutureWork-TheRoleofResonance 97 IV BIBLIOGRAPHY 104 BIOGRAPHICALSKETCH 108 V LIST OFTABLES Table page 4- 52--1: Theareaofdustcontributedfromeachfamilyisthesameinboththe 2.°5andthe3.°5models. However,inthe3.5°modelmaterialis distributedbetweentheasteroidbeltandtheSunwhereasinthe2.°5 modelthematerialisconfinedtotheasteroidbelt 14 1: Normalizedaveragecapturerates 39 1: Properelementsanddispersionsfor1microndiameterparticlesat lAU 67 5-2: Properelementsanddispersionsfor10microndiameterparticlesat lAU 68 VI LIST OFFIGURES Figure page 2-1: IRASobservationofthezodiacalcloudinthe25/iminfraredwaveband (soliduppercurve). Thisobservationwasmadeat90°solarelongation angle(theanglebetweenthetelescopepointingdirectionandthe Earth-Sunline)inthedirectionleadingtheEarthinitsorbitwhenthe planetwasataneclipticlongitudeof293°. Thedustbandscanbeseen asprojecting“shoulders”near±10°and0°latitude. Thestructure around60°latitudeisduetodustintheplaneoftheGalaxy. By applyingaFourierfiltertotheIRASobservationasmoothbackground profile(underlyingdashedcurve)isseparatedfromahighfrequency dustbandprofile(solidlowercurve). Thisfilteredhighfrequencydust bandprofileismerelyaresidualrepresentingthe“tipoftheiceberg”in termsofthedustbandmaterialinthezodiacalcloud 10 2-2: FilteredIRASdustbandprofiles(solidlines)foreightdifferent longitudesoftheEarth(A©). Allprofilesweremadeat90°solar elongationangleinthedirectionleadingtheEarthinitsorbit. Model dustbandswereconstructedusingparticlesfromtheThemisand Koronisfamiliesforthecentralband-pairandtheEosfamilyforthe10° band-pair. Adispersionof2.°5wasimposedontheproperinclination oftheEosmaterialinthismodel. Allofthematerialinthismodelwas confinedtotheasteroidbelt. Eightsimulatedprofiles(dashedlines) whichmimictheIRAS25//minfraredwavebandweremadethrough thesemodeldustbandsatthesamelongitudesandelongationangleas theIRASprofiles. Thesesimulatedprofileswerefilteredinafashion identicaltothatusedtogeneratetheIRASprofiles. Dashedvertical linesareplacedat±10°forreference. Allprofileshaveanamplitudeof around2MJy/Srbutarestaggeredinthefigureforconvenience 11 2-3: SameasinFigure2-2exceptthesefilteredmodeldustbandprofiles (dashedlines)areforthe3.°5modelinwhichtheEosmaterialis distributedfromtheasteroidbelttotheSun 12 VII 2- 4: UnfilteredIRASobservationshowninFigure2-1. Thelowerand middlecurvesaresimulatedunfilteredprofilesmimickingtheIRAS 25/fminfraredwavebandtakenthroughtwodifferentdustbandmodels. Eachofthesedustbandmodelswasconstructedusingparticlesfrom onlythethreeasteroidfamiliesEos,ThemisandKoronis.Themodel profilelabeled2.°5usesEosparticleshavinga2.°5dispersioninproper inclinationandconfinesallparticlestotheasteroidbelt. Themodel profilelabeled3.°5isconstructedusingEosparticleswitha3.°5 3- dispersioninproperinclinationandbyallowingtheEosmaterialto stretchfromtheasteroidbelttotheinnerSolarSystem. Thedifference inthepeakintensitybetweenagivenmodelprofileandtheIRAS profileindicatesthedustbandcontributiontotheentirezodiacalcloud, listedinTable2-1 13 1; Demonstrationoftheconceptofforcedandproperorbitalelements. ... 16 3-2: Osculatingorbitalelementsfor357membersoftheThemisasteroid family 17 33--3: Radialdependenceofthespatialdensity 19 4— 3-4: Latitudedependenceofthespatialdensityandvolumeoflatitude elementofsphericalshell 22 3-5: Latitude(left)andradial(right)averagespatialdensitydistributions. Anorbitwitha=1,e=0.05andI=l.°5wasused,theSunisatthe originoffthefiguretotheleft 23 3-6: Velocityvectorrelationshipfordeterminingencountervelocity 24 7: HyperbolicdeflectionofaparticleencounteringtheEarth 26 1; Distributionofosculatinginclinationversessemi-majoraxisfor118 shortperiodJupiterfamilycomets 41 4-2: Distributionofosculatingeccentricityversessemi-majoraxisfor118 shortperiodJupiterfamilycomets. Thedashedlinemarkstheextreme limitoftheJupiter-crossingregime,usingasemi-majoraxisand eccentricityofa=5.203,e=0.062forJovianorbit. Thesegivea perihelionofq=4.88AU,whichwefurtherreducebysubtractingthe sphereofactionoftheplanet.Da~0.365AU, 42 viii 4-3; Histogramsshowingtheinclinationandeccentricitydistributionsofthe cometsplottedinFigures4—1 and4-2 43 4-4: DwiistthriabbustoilounteofmaprgonpietrudienclHina<ti1o1nv(e1r0s5e3sassetmeir-oimdasj)o.rTahxiisspfloortalilsasshtoerwonids onthesamescaleasFigure4-1 (withashiftoflAUinsemi-major axis)andshowsthattheJupiterfamilyofcometsspanthesamerange ofinclinationastheasteroidsinthemainbelt.TheasteroidfamilyEos istheclusteratapproximately3AUand10°inclination. TheKoronis andThemisfamiliesarethelowinclinationclusterstotheleftandright of3AU,respectively.NoticethattheEosandThemisfamilieshavea higherdispersioninproperinclinationthantheKoronisfamily 44 4-5: ThetopplotisahistogramofthealltheasteroidsshowninFigure4-4. ThemiddleplotshowsonlythoseasteroidsofFigure4-4thatare associatedwithfamilies.Thebottomplotisalltheremainingbackground asteroidsthatarenotassociatedwithfamilies. ThefamiliesThemisand Koronisappeartogetheratthefeatureinsideof3°properinclination, Eosisat 10°andthenextlargestfamilyMariaisat15°. Severalsmall familiesarealsovisible.Fromthisplotweseethatalargemajorityofthe lowinclinationasteroidsbelongtotheThemisandKoronisfamiliesand thatmorethanhalfoftheasteroidsat10°belongtotheEosfamily. . . 45 4-6: DasitsetrroiibdustiwointohfapbrsoolpuetreemccaegnntirticuidteyHver<ses11se(m1i0-5m3ajasotreraoxiidss)f.orThalilsplot, whichisshownonthesamescaleasFigure4-2(withashiftoflAUin semi-majoraxis),revealstheprimarydifferencebetweentheJupiter familycometarypopulationandtheasteroidalpopulation. Thecomets havemuchhighereccentricities. TheasteroidfamiliesEosandKoronis areapparentat3AU,andjustinsideof3AUrespectively. TheThemis familyisslightlymoredifficulttodiscernherethaninFigure4-4,lying between3.1and3.2AUatabout0.15inpropereccentricity 46 4-7: ThetopplotisahistogramofthealltheasteroidsshowninFigure4-6. ThemiddleplotshowsonlythoseasteroidsofFigure4-6thatare associatedwithfamilies. Thebottomplotisalltheremaining backgroundasteroidsthatarenotassociatedwithfamilies 47 4-8: Distributionofosculatinginclinationversessemi-majoraxisfor Earth-crossingorbitsofcometarydustparticles.Theobvioustrackingis duetothecontinuingevolutionofparticlesfromasinglecomet 48 IX 4-9: Distributionofosculatingeccentricityversessemi-majoraxisfor Earth-crossingorbitsofcometarydustparticles.Theobvioustrackingis duetothecontinuingevolutionofparticlesfromasinglecomet 49 4-10: Smootheddistributionofosculatinginclinationversessemi-majoraxis forEarth-crossingorbitsofcometarydustparticles. Weusethemean anddispersionoftheorbitalelementsshowninFigure4-8togenerate arandomgaussiandistributionofEarth-crossingcometaryorbits 50 4-11: Smootheddistributionofosculatingeccentricityversessemi-majoraxis forEarth-crossingorbitsofcometarydustparticles. Weusethemean anddispersionoftheorbitalelementsshowninFigure4—9togenerate arandomgaussiandistributionofEarth-crossingcometaryorbits 51 4-12: Distributionofproperinclinationversessemi-majoraxisfor Earth-crossingorbitsofnon-familyasteroidalparticles. Thisplotis shownonthesamescaleasFigure4-10andshowsthatthe Earth-crossingcometarypopulationspansthesamerangeofinclination astheEarth-crossingasteroidalpopulation 52 4-13: Distributionofpropereccentricityversessemi-majoraxisforEarth- crossingorbitsofnon-familyasteroidalparticles. Thisplot,whichis shownonthesamescaleasFigure4-11revealstheprimarydifference betweentheEarth-crossingcometarypopulationandtheEarth-crossing asteroidalpopulation. Thecometaryorbitshavemuchhigher eccentricities.Aswewillsee,thisleadstosubstantiallyhighergeocentric encountervelocitiesforcometaryparticlesthanforasteroidalparticles.. . 53 4-14: Theorbitalevolutionofawaveof10microndiameterdustparticles fromtheEosfamilyastheirorbitsdecayfromtheasteroidfamilyat 3AUintotheinnerSolarSystem. Themiddleplottrackstheevolution oftheproperinclinationanddispersioninproperinclinationofthe particlesastheirsemi-majoraxesdecayduetoP-Rdrag. The displacementfromtheoriginofthedistributionsintheuppertwoplots isduetotheforcedinclination,whichisshowninthelowerplot 54 X