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EncyclopedicEntry
meteorite
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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
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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
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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
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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
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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.
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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.
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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.
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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.
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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
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NASASolarSystemExploration:Meteors&Meteorites
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