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Thiswebsitewouldliketoremindyou:Yourbrowser(Safari7)isoutofdate.Updateyourbrowserfor moresecurity,comfortandthebestexperienceonthissite. EncyclopedicEntry meteorite Forthecompleteencyclopedicentrywithmediaresources,visit: http://nationalgeographic.org/encyclopedia/meteorite/ MeteoritesarespacerocksthatfalltoEarth’ssurface. Meteoritesarethelaststageintheexistenceofthesetypeofspacerocks.Before theyweremeteorites,therocksweremeteors.Beforetheyweremeteors,they weremeteoroids.Meteoroidsarelumpsofrockormetalthatorbitthesun. MeteoroidsbecomemeteorswhentheycrashintoEarth’satmosphereandthe gasessurroundingthembrieflylightupas“shootingstars.”Whilemostmeteors burnupanddisintegrateintheatmosphere,manyofthesespacerocksreach Earth’ssurfaceintheformofmeteorites. Dust-sizedparticlescalledmicrometeoritesmakeup99percentofthe approximately50tonsofspacedebristhatfallsontheEarth’ssurfaceeveryday. Somemeteorites,however,areaslargeasboulders. ThelargestmeteoritefoundonEarthistheHobameteoritediscoveredinNamibia in1920.TheHobameteoriteweighsroughly54,000kilograms(119,000pounds). TheHobameteoriteissobig,andsoheavy,ithasneverbeenmovedfromwhere itwasfound! MostmeteoriteslookverymuchlikerocksfoundonEarth,exceptmeteorites usuallyhaveadark,burnedexterior.Thisexteriorisformedasfrictionfromthe atmospheremeltsthemeteoriteasitcrashestowardEarth.Knownasthermal ablation,thisprocesscanalsogivemeteoritesaroughened,smooth,or thumbprintsurface.Thermalablationcreatesthesedifferenttexturesdueto differentchemicalspresentinthemeteorite. Meteoritescrashthroughtheatmospheresofallplanetsandmoonsinoursolar system.Someplanetsandmoonsdon'thaveenoughatmospheretobreakapart 1of9 × meteors,resultinginlargemeteorites.Theselargermeteoritescreatedeep,round impactcratersthatcanbefoundalloverourMoon,Mercury,andMars.In2005, thefirstmeteoritefoundonanotherplanetwasdiscoveredbyOpportunity,oneof NASA’sMarsroverspacecraft.In2014,Opportunity’ssisterspacecraft,Curiosity, discoveredameteoritethatwas2meters(7feet)wide,makingitthelargestyet discoveredonMars. TypesofMeteorites Morethan60,000meteoriteshavebeenfoundonEarth.Scientistshavedivided thesemeteoritesintothreemaintypes:stony,iron,andstony-iron.Eachofthese typeshasmanysub-groups. StonyMeteorites Stonymeteoritesaremadeupofmineralsthatcontainsilicates—materialmadeof siliconandoxygen.Theyalsocontainsomemetal—nickelandiron.Therearetwo majortypesofstonymeteorites:chondritesandachondrites. Chondritesthemselvesareclassifiedintotwomajorgroups:ordinaryand carbonaceous.Ordinarychondritesarethemostcommontypeofstony meteorite,accountingfor86percentofallmeteoritesthathavefallentoEarth. Theyarenamedforthehardeneddropletsoflava,calledchondrules,embeddedin them.Chondritesformedfromthedustandsmallparticlesthatcametogetherto formasteroidsintheearlysolarsystem,morethan4.5billionyearsago.Because theywereformedatthesametimeasthesolarsystem,chondritesareintegralto thestudyofthesolarsystem’sorigin,age,andcomposition. Ordinarychondritescanbeclassifiedintothreemaingroups.Thegroupsindicate themeteorite’squantityofiron.TheHchondritegrouphasahighamountofiron. TheLchondritegrouphasalowamountofiron.TheLLgrouphasalowamount ofironandalowamountofmetalingeneral. Carbonaceouschondritesaremuchmorerarethanordinarychondrites. Astronomersthinkcarbonaceouschondritesformedfarawayfromthesunasthe earlysolarsystemdeveloped.Astheirnameimplies,carbonaceouschondrites containtheelementcarbon,usuallyintheformoforganiccompoundssuchas 2of9 aminoacids.Carbonaceouschondritesalsooftencontainwaterormaterialthat wasshapedbythepresenceofwater. Likeordinarychondrites,carbonaceouschondritescanbemoreminutelyclassified basedontheirmineralcomposition.Allgroupsofcarbonaceouschondritesare markedwithatwo-orthree-lettercodestartingwithC.Carbonaceouschondrites areoftennamedafterthefirstspecimenofthattyperecovered.TheCIgroup,for instance,isnamedaftertheIvunameteorite,whichcrashedintoTanzaniain1938. CImeteoriteshaveahighamountofcarbon,aswellasclays.Carbonaceous chondritescanalsobenamedaftertheplacewherethefirstspecimenofthetype wasfound.TheCVgroupisnamedafterameteoritethatcrashednearthecityof Vigarano,Italy,in1910.ThemostfamousCVmeteoriteisprobablytheAllende meteorite,whichfelltoEarthnearPueblodeAllende,Chihuahua,Mexico,in1969. TheAllendemeteoritehasthousandsoftinychondrulesmadeofthemineral olivine.TheAllendemeteoritealsohasgrainsofaspecialkindofcarbon— diamonds.Thesediamondsareactuallyolderthanthesolarsystem,and astronomersthinktheywereproducedasblastmaterialfromanearby,ancient supernova. Achondritesdonotcontainthelavadroplets(chondrules)presentinchondrites. Theyareveryrare,makingupabout3percentofallknownmeteorites. Achondritesformfromthebrittleouterlayerofanasteroid,whichissimilarto Earth’scrust. Therearemanyclassificationsofachondrites.The“primitiveachondrite”group, forinstance,hasaverysimilarmineralcompositiontochondrites.Lunar meteoritesareachondritesthatcrashedtoEarthfromtheMoon,whileMartian achondritescrashedtoEarthfromourneighborplanet,Mars. Veryfewmeteorites,onlyabout0.2percent,comefromMarsandtheMoon. TheseachondritesaretheresultsofMarsandtheMoon’sownmeteoriteimpacts. LargemeteoriteshitthesurfaceofMarsandtheMoon,blastingoffbitsofrock. Theserockbitsrarelymaketheirwaytoouratmosphereasmeteorsandeven morerarelyhittheEarth’ssurface. IronMeteorites Ironmeteoritesaremostlymadeofironandnickel.Theycomefromthecoresof 3of9 asteroidsandaccountforabout5percentofmeteoritesonEarth. Ironmeteoritesarethemostmassivemeteoriteseverdiscovered.Theirheavy mineralcomposition(ironandnickel)oftenallowsthemtosurvivetheharsh plummetthroughEarth’satmospherewithoutbreakingintosmallerpieces.The largestmeteoriteeverfound,Namibia’sHobameteorite,isanironmeteorite. Stony-IronMeteorites Stony-ironmeteoriteshavenearlyequalamountsofsilicateminerals(chemicals thatcontaintheelementssiliconandoxygen)andmetals(ironandnickel). Onegroupofstony-ironmeteorites,thepallasites,containsyellow-greenolivine crystalsencasedinshinymetal.Astronomersthinkmanypallasitesarerelicsofan asteroid’score-mantleboundary.Theirchemicalcompositionissimilartomany ironmeteorites,leadingastronomerstothinkmaybetheycamefromdifferent partsofthesameasteroidthatbrokeupwhenitcrashedintoEarth’s atmosphere. MeteoriteImpactCraters MeteoritescrashthroughtheEarth’satmospherewithtremendousforce.The largestmeteoritesleaveenormousholesinthegroundcalledimpactcraters. Thebest-preservedimpactcraterintheworldistheBarringerMeteoriteCrater, nearWinslow,Arizona.There,morethan50,000yearsago,ameteoriteweighing about270,000metrictons(300,000tons)slammedintotheEarthwiththeforce of2.5milliontonsofTNT.Theimpactblastedahole1kilometer(.6miles)wideand about230meters(750feet)deep.Thefragmentsleftofthespacerockshowthat itwasanironmeteorite. MorethanahundredimpactcratershavebeenidentifiedonEarth.Perhapsthe mostfamousistheChicxulubCrater,inYucatan,Mexico.TheChicxulubCrater canbeidentifiedonland,beneathdozensofmetersofsediment,althoughabout halfofthefeatureissubmergedintheGulfofMexico.Itisoneofthelarges impactcraterseverdiscoveredonEarth. Despiteitssize,theChicxulubCraberisfamousforanotherreason.Many 4of9 scientiststhinkthelargemeteoritethatcreatedtheChicxulubCrater—measuring roughly10kilometers(6miles)wide—triggeredtheextinctionofthedinosaursand otheranimalandplantlife65millionyearsago. Vocabulary Term Partof Definition Speech removalofmaterialfromthesurfaceofanobject, ablation noun account noun achondrite noun typeofstonymeteoritecontainingnohardeneddroplets (chondrules). aminoacid noun nutrientcontainingcarbon,hydrogen,oxygen,and nitrogenthatiscriticalforalllife. includingmelting,evaporation,orerosion. oralorwrittendescriptionofevents. ancient adjective veryold. approximately adjective generallyornearanexactfigure. irregularlyshapedplanetarybody,rangingfrom6 asteroid noun astronomer noun personwhostudiesspaceandtheuniversebeyond Earth'satmosphere. atmosphere noun layersofgasessurroundingaplanetorothercelestial body. boulder boundary noun noun largerock. lineseparatinggeographicalareas. brittle adjective fragileoreasilybroken. typeofstonymeteorite(chondrite)thatcontainsthe carbonaceous noun chondrite chondrite noun chondrule noun clay noun meters(20feet)to933kilometers(580miles)in diameter,orbitingthesunbetweenMarsandJupiter. elementcarbon,usuallyintheformoforganic compoundssuchasaminoacids. typeofstonymeteoritecontaininghardeneddroplets, calledchondrules,ofsilicateminerals. smalldropletofsilicatemineralfoundinstony meteorites. typeofsedimentaryrockthatisabletobeshapedwhen wet. 5of9 Term Partof Speech Definition composition noun arrangementofthepartsofaworkorstructurein relationtoeachotherandtothewhole. core noun theextremelyhotcenterofEarth,anotherplanet,ora star. crust noun rockyoutermostlayerofEarthorotherplanet. noun typeofmineralthatisclearand,whenviewedundera microscope,hasarepeatingpatternofatomsand crystal molecules. remainsofsomethingbrokenordestroyed;waste,or debris noun diamond noun dinosaur noun discover verb disintegrate verb dust noun element noun embed enormous verb toattachfirmlytoasurroundingsubstance. adjective verylarge. exterior adjective, ontheoutsideoroutdoors. noun extinction noun processofcompletedisappearanceofaspeciesfrom Earth. fragment friction noun pieceorpart. noun forceproducedbyrubbingonethingagainstanother. garbage. typeofcrystalthatispurecarbonandthehardest knownnaturalsubstance. verylarge,extinctreptilechieflyfromtheMesozoicEra, 251millionto65millionyearsago. tolearnorunderstandsomethingforthefirsttime. tofallapartanddisappear. microscopicparticlesofrocksormineralsdriftingin space.Alsocalledcosmicdustorspacedust. chemicalthatcannotbeseparatedintosimpler substances. harsh stateofmatterwithnofixedshapethatwillfillany noun containeruniformly.Gasmoleculesareinconstant, randommotion. adjective extreme. impact noun gas collisionorcrash. 6of9 Term Partof Speech Definition circularsurfacedepressionmadebytheimpactofa meteorite. verb todisplayorshow. adjective veryimportant. impactcrater noun indicate integral ironmeteorite noun rock,madeofironandnickel,thathascrashedtoEarth fromoutsidetheatmosphere. moltenrock,ormagma,thateruptsfromvolcanoesor fissuresintheEarth'ssurface. lava noun lunar adjective mantle noun Mars massive noun fourthplanetfromthesun,betweenEarthandJupiter. adjective verylargeorheavy. categoryofelementsthatareusuallysolidandshinyat noun roomtemperature. metal meteor noun meteorite noun meteoroid noun micrometeoritenoun mineral noun havingtodowithEarth'smoonorthemoonsofother planets. middlelayeroftheEarth,madeofmostlysolidrock. rockydebrisfromspacethatentersEarth'satmosphere. Alsocalledashootingstarorfallingstar. typeofrockthathascrashedintoEarthfromoutside theatmosphere. small,rockybodytravelingaroundthesun. dust-sizeparticleofspacedebristhatburnsupasit entersEarth'satmosphere. inorganicmaterialthathasacharacteristicchemical minute moon compositionandspecificcrystalstructure. adjective verysmallamount. noun naturalsatelliteofaplanet. Moon noun Earth'sonlynaturalsatellite. nickel noun chemicalelementwiththesymbolNi. olivine noun orbit verb typeofsilicatemineral. tomoveinacircularpatternaroundamoremassive object. organic compound noun chemicalsubstancethatcontainstheelementcarbon. 7of9 Term Partof Speech Definition typeofstony-ironmeteoritecontainingolivineorperidot crystalsembeddedinaniron-nickelwebbing. pallasite noun particle noun planet noun plummet verb primitive quantity relic adjective simpleorcrude. noun amount. noun mementoorsurvivingobjectofthepast. rock noun rover noun sediment noun silicate noun solarsystem noun spacecraft noun specimen noun stony-iron meteorite noun stony meteorite noun rock,madeofsilicateminerals,thathascrashedtoEarth fromoutsidetheatmosphere. submerge verb toputunderwater. sun supernova noun staratthecenterofoursolarsystem. noun sudden,violentexplosionofamassivestar. adjective, physicalortactilecharacteristicsofasubstance. noun adjective havingtodowithheatortemperature. texture thermal smallpieceofmaterial. large,sphericalcelestialbodythatregularlyrotates aroundastar. tofallsharply. naturalsubstancecomposedofsolidmineralmatter. vehiclethatremotelyexploresaregion,suchasthe surfaceofamoon,planet,orothercelestialbody. solidmaterialtransportedanddepositedbywater,ice, andwind. mostcommongroupofminerals,allofwhichincludethe elementssilicon(Si)andoxygen(O). thesunandtheplanets,asteroids,comets,andother bodiesthatorbitaroundit. vehicledesignedfortraveloutsideEarth'satmosphere. individualorganismthatisatypicalexampleofits classification. rock,madeofnearlyequalpartsmetalandsilicate minerals,thathascrashedtoEarthfromoutsidethe atmosphere. 8of9 Term TNT Partof Speech noun Definition (trinitrotoluene)chemicalcompoundoftenusedasa predictable,reliableexplosivematerialwithrelativelysafe handlingproperties. tremendous adjective verylargeorimportant. trigger verb tocauseorbeginachainofevents. Articles&Profiles NationalGeographicNews:MeteoriteImpactReformulatedEarth’sCrust Interactives TheMeteoriticalSociety:SearchtheMeteoriticalBulletinDatabase Websites MeteorCraterEnterprises:MeteorCrater NationalGeographicProjects:PatagoniaMeteoriteImpactFieldProject NASASolarSystemExploration:Meteors&Meteorites AmericanMeteorSociety ©1996–2016NationalGeographicSociety.Allrightsreserved. 9of9