19 93MNRAS.264. . .93A 91 123 2 3 17 16 x 4 5 Mon. Not.R.Astron.Soc.264,93-105(1993) The Tauridmeteoroidcomplexcontainsobjectsatallsize Asteroids intheTauridComplex the calendaryearandindaytimemid-year;seee.g. visual meteorsinwell-knownbroadshowers(atnightlate fireballs (<10g)andtheTunguskafireball~of example aswarmofmeteoroidswithindividualmassesupto detections verylikelyassociatedwiththeTaurids,for ranges -submicrondust(e.g.Roosen,Berg&Farlow1973; Accepted 1993February18.Received16;inoriginalform1992November13 D. J.Asher,S.V.M.ChibeandI.Steel Stohl &Porubcan1990).Athighermassestherehavebeen Singer &Stanley1980),andparticlesthatproduceradar Anglo-Australian Observatory,PrivateBag,Coonabarabran,NSW2357,Australia DepartmentofPhysicsandMathematicalPhysics,UniversityAdelaide,SA5001,Australia tion history,theputativeoriginalgiantcomethasalsogiven most ofthepresent-dayzodiacalcomplex(Whipple1967; has) longbeenregardedastheparentbodyandsourceof is CometP/Encke(~10g),whichhas(orwhoseprogenitor rise tokm-sized(~10g,say)asteroids(Clube&Napier the intermediateevolutionarystagebetweenmore ingly demonstratedbythehugesporadicmeteoroidstream Kresák 1980).ThesizeoftheTCisperhapsmostconvinc- 1 INTRODUCTION DepartmentofPhysics,UniversityOxford,KebleRoad,Oxford0X13RH 1978; Oberst&Nakamura1987,1991),manyordinary surrounding theTauridstream(Stohl1986)andrepresenting 1908 June30(Kresák1978;Chyba,Thomas&Zahnle meteor observationsandused meteoroidorbitalelement demonstrated thestructureofTCasdelineatedby structured Tauridstreamandthezodiacalbackground. 1993). Itisnotsurprisingthat,duringitsviolentfragmenta- past ~10yr,atime-scaleconceivably supportedbyinde- distributions tomodeltheevolution ofthecomplexover 1984). ThelargestknownobjectintheTauridComplex(TC) pendent (non-dynamical)evidence bymeansoftheproposed preferred modelwasonewhere largefragmentssplitfrom association oftheFarmington meteoritewiththeTC.Our the coreobject nearperihelion,thesethenbecoming second- ~ 10gincidentontheMoonin1975June(Dormanetal. In apreviouspaper(Steel,Asher&Clube1991)we © Royal Astronomical Society • Provided by the NASA Astrophysics Data System ABSTRACT We showthatastatisticallysignificantnumberofEarth-crossingasteroidsarepart the TauridComplexofinterplanetaryobjects.Wealsoidentifyanothergroupwhich these twocomplexes,whichmayhaveacommonorigin. Key words:comets:individual:P/Encke-TauridComplex evolution thatsuchasteroidsundergoandconsidertheimplicationsforhistoryof appears alignedwith(2212)Hephaistos.Inaddition,wedescribethekindoforbital progenitor -meteoroidsminorplanets. been demonstratedforradarmeteorsbyOlsson-Steel intention hereistoextendthisworkbyinvestigatingEarth- phic disruptiononcolhsionsintheasteroidbelt.The the pictureofbreakuplargeparentbodiesininner crossing asteroids,whicharelikelytohavearoleassecond- asteroids witheachotherandmeteoroidstreams, Stohl &Yana(1992).Otherassociationsofnear-Earth (1988), andforprecisephotographicmeteorsbyPorubcan, asteroids (asopposedtosimplywiththeTCasawhole)has ary parentobjects(Stohl&Porubcan1992). ary parentbodieswhichundergofurthersplittingorcatastro- also withoneortwoJupiter-familycomets,furthersupport The linkagebetweenfourobservedmeteorshowersand Solar system(Obrubov1991). Apollo asteroidsdiscoveredisincreasingrapidlythrough type asteroidswerelikewiseassociated.VariousnewTC COMPLEX (Olsson-Steel 1987a;Steel1992).However,thenumberof associations havebeensuggestedinthepastfewyears since Clube&Napier(1984)proposedthatsomeApollo- Comet P/Enckeiswellknown,anditnowalmostadecade 2 MEMBERSHIPOFTHETAURID demonstrating theexistence of thekm-sizedasteroidcom- repeatedly toimprovethestatisticalsignificanceofresults asteroids inanever-expandingdataset,andthechance search programmes,givingusthechancetolookforTC ponent oftheTC.Apreliminary versionofteststheform (1993). discussed herehasbeengiven byAsher,Clube&Steel ences between thedefinitions.Steeletal.(1991) usedthe defined a‘D-criterion’oforbital similarity,withslightdiffer- The associationofmeteoroidswithsomeindividualTC Authors, followingSouthworth &Hawkins(1963),have 19 93MNRAS.264. . .93A 3 2 +e 2=0102 within 50°of140°;theinclinationgivenisobserved Marsden 1991). value ofa<2aubeingconceivable(Marsden,private the valueofitssemimajoraxisishighlyuncertain,even a value, notadjustedforlong-termperturbations).Appended ‘aligned withTaurids’ifthelongitudeofperihelionor is determined towithin2per cent(Scotti,Rabinowitz& Despite 1991BAbeingone of thesmallestasteroidsever et al.1984andMcFadden, Gaffrey&McCord1984]. activity inthecaseof(2201)Oljato waspresentedbyRussell known intheTC[thoughtentative evidenceforcometary communication), andCometP/Encke,theonlyactivecomet asteroids withthesmallestvaluesofD(listedincolumn asteroids completeto1992March.Table1showsthe25 formalism (qinsteadof0)isthatformeteoroidstheperi- Steel 1987a)butwhichisomittedfromthisanalysisbecause are 5025P-L,whichislikelytobeaTCmember(Olsson- full weighttheuncertaintyinmeteoroidvelocity;follow- observed, at5-10m,itsorbit isaccuratelyknown,witha helion distanceqisgenerallymoreaccuratelydetermined following definitionforTauridmeteoroids: with a=2.1auande,iasabove.TheD-criterionis than atodemonstratetheexistenceofTCasteroids.On ing this,Asher(1991)usedaD-criterioninvolvingqrather than thesemimajoraxisa,lattertendingtoreflectwith with q=0.375an,e0.82andi*!4°.Thereasonforthis ing changeinDislessthan0.01nearlyallcases. much lesssignificantwithregardtotheD-criterionthan meteor tobeproduced(seeSteeletal.1991).Thereare that theparticleorbitmustintersectEarth’sfora TC meteoroids,becauseiisconstrainedtobelowbythefact Jovian perturbations,andthereforeaconventionallongitude between twoorbits,andtheresultsarebroadlysame essentially anempiricalmethodofdefiningthedifference other hand,sinceaisknownaccuratelyforasteroids,inthis due tovaryinge;hereweincludeit,andfindthattheresult- corresponding variationsineccentricitye,buttheseare perturbation theory(computationaldetailsinAsher1991)to time-scales oforder10yr,weuseBrouwer’s(1947)secular term intheD-criterionwouldhavetoolargeacontribution whilst appropriateformany(narrow)streams,theTaurids D-(
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