Accretion of interplanetary dust particles by the earth

130 Pages·1996·4.6 MB·English

by  Kortenkamp, Stephen John, 1968-

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