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5.A200-kilometre-wideviewofthesouth-eastedgeofMareImbriuTheruggedterraiishighlandcrustupliftedinpartofthebasinriThedarker，smootherareaiismarebasaltsthathavefloodedthelround.A1-kilometre-widetrenamedHadleyRillewindsfromsouthtonorthacrossthetreoftheview，andthisisbelievedtobeapathwayalongwhichlavaflowedfrelyobscuredbyshadoollo15laoHadleyRille，hemiddleoftheimage
Mercury
MercuryismuchlesswellknownthantheMoon.UnderhalfofitwasimagedbyNASA’sMariner10in1974–5，aheeduntilNASA’sMESSENGERprobebeganaseriesoffly-bysin2008.Thisrevealeddetailssuffiostpeople’sscepticismovertheextentofvolerple，ihesmoothterrainiandfillingthe120-kilometre-diameterbasinjustabhtoftreisedasvolic.PreviousdhtehatMercurylacksthetrastinalbedo（reflectedbrightweenpalerhighlandsahatmakesthemariasoobviousohisseemstobebecausethemineralsmakingupMercury’slavasuchlessironthanistypiar（arial）basalts.PlainsformedbylavaprobablystitutethemajorityofMercury’ssurfaareoldenoughtodatebacktotheeraofthelateheavybombardmentandaredeered，eraerssuperimposedonthe
MESSENGERimagedafewvoltsandalsoetre-sizedblotebright，somedark–thatmaybesitesofparticularlyyoungexplosiveeruptions.HowloayedvolicallyactiveislikelytoremainuilaspacecraftachievesorbitaboutMerdreagessystematidiail.ThefirstcewillbewhenMESSEheorbitalphaseofitsmissionin2011，andiftheissueremaishouldbesettledbytheEuropeanSpacy’sBepiissionthatisduetoarriveatMer2020.Atpresent，itissafetosaythatextensiveareasoflavawereemplagaperiatleast4to3billio，andpossiblyextendingtowithibillionyears.Sugdurationofvolicaerotanticipated，afromthesamemysteriousheatsourcethatkeepspartofitsolten.
Venus
VenusismuchbiggerthassizeandmasswouldsuggestalmostasmuchradiogeproduastheEarth，andhenceasimilarlevelofvolicactivity.However，beuslacksplateteioperatesratherdifferently.
Venushasadelyosphere，whichkeptthesurfaysteryuntilitbecamepossibletostudyitbymeansure6sheofpartofVenusobtainedbyNASA’sMagellanprobe，edalmosttheebetween1990and1994.Radarimagesareassembledbyplexanalysisoftheecedbarespooaualstringofradarpulsesbeamedatthesurfaostpurposes，youtreatradarimagesliketheblad-whiteopticalimagesthattheyresemble，thoughiureisainlybyhhthelocalsurfaceis，ratherthanitsalbedoi.
Figure6typifiesmuus.Itshowsnumerousindividuallavaflows–sher（brighter）aher（darker）–thatflowedfromwesttoeastaage.ThelobatepatternoftheindividualflowscloselyresemblesthatoflavaflowsohandMars，butwhichishardtodisoonandMercurywheretheflinshavebeedegradedbyimpacts.
Aswellaslavaflabouthalfitssurfaushasmanyclearlyidentifiablevoloes.Figure7shole.Inthebadisa5-kilhvolowithgentlyslopingflanksofthekindkhasa‘shieldvolo’thatresultsfromrepeatederuptionofbasaltthroughasi.Someindividuallavaflowsbemadeoutontheflanks.Nooneissurehowlongagothisvoldotherslikeitlasterupted.Therehavebeenintriguinghintsbutnoproofofretorpresent-dayavoloessuchasthis，ahertoosmallforreliablecrater-gstatistics.Thisparticularvoloisbuiltupoerrainunitthatissmoother，exerousfracturesupothefroundisprobablyuhtlavaflowsimmediatelytoitsleft.
6.A500-kilometre-wideMagellaofVenus.Theareaismostlylava，fedfromasouretreswestoftheimage，butih-easterissedterraiheVenus.Runningfromnorthtosouthiheimageisamouedandfracturedterrainthatisbreachedbythelavaflows
Circularorellipticalpatternsoftricfracturestermed‘ae’，ofwhichmorethan300havebeeifiedonVehoughttoshareaii-ribasinsoftheMooheyythingfrom200metrestoover2，000kilometresadareusuallyassociatedwithsomeformofvolisProbablyeaarksasitewelliheastheleimpihebaseofthelithosphere.aewheretheplumeisstillpreseedasverybroaddomes，whereasolderones，edbyamantleplume，havesagged.Thesagging，inparticular，explairicfractures.
7.puter-gehree-dimeiveviewshowingthevolohiswasmadebydrapingaradarimageoveramodelofthetopographyobtainedbyradaraltimetry.Verticalscaleisexaggeratedtenfold.Bothsetsofdatawerecollectedbythe Magellaheimpacttherightfroundis23kilometresacross
ImpactVenusaremoreonthasiderablylessabundantthanontheMoonandMercury（youwillnotfindanyiherearetwofactorsatplayhere.Craterslessthanabout3kilometresacrossareefromVesdemosphereshieldsthesurfaallimpactors.Hercratersareformedbyobjectsgtoomuergytobeaffectedbytheatmosphere.Theirladaobeexplaiheyouhesurface，whichworksoutetobebetweenabout500millionand700millioherearesofterraiobeverymuugerthanthegle.
&aionforthisinthe1990srettymuchthewholeplawasresurfayofvolismthatbegan500–700millio，andlastedhaensofmilliohiswouldbetwithVenus’slackofplateteigtomostheatfromthedeepermarappedbelowthelithospheritilmuchoftheuppermostastheed.Eventually，theselithospherewouldfouhebuoyantmagmafrombelowwoulderupt.Somethingsimilarcouldhaveoccurredhalfadozentimessinuswasformed，acouldhappenagainwithi100millionyears.
Thismodelgflobalvolismhasretlybeenged，onthegroundsthatthegstatistiotruleradualprressivelysmallerareascouldhavebeenresurfacedbylavasatrahroughoutthepasthalfbillionyears.
&h
&h，voldplatetebiheiandthuspreventmajorastheemperatureexsofthekindpostulatedforVenus.Onlyaboutohirdoftheheatgehelithosphereleaksoutbyostoftheheatisveyedtothetopofthelithospherebyeruptionatmid-es（whereerialisaddedtplates）and，toasmallerexteionsatvoloesabovesubduesandatvarious‘hotspots’abovemaheasthenosphereiscooledbythereincorporationintoitoftheold，coldpartsoflithosphericplatesatsubdues.
&wegettoaVenus-likevoliccatastropheiswheensofmilliiohousaresacrossisburiedbytheeruptionofuptotenetresofbasaltlava.Thisisknownasa‘floodbasalt’.The‘DeTraps’ofIndia（66millioheBrito-Arcticfloodbasalts（Greenlah-westernBritishIsles，57millionyears），andthebiaRiverfloodbasalts（ernUSA，16millionyears）areamoer-knoles.Thesemajorbutrareeventscouldbecapableofiingsomuiotablysulfurdioxide，plusfisofvoliownas‘ash’，imlobalclimatecouldbeseverelyaffected.Figure8sholeoflavaflowsoh，forparisonwiththeimagesfromotherplas.
Thewayinwhiohprobablydiffersmostfromtheotherplahatexpansionofgaswithinrisingmagmatendstomakeasubstantialproportioionsexplosiveihisisfortworeasoisthatrecycledwater，dioxide，andsulfurdioxideesgupwardsabovesubduesaddsgreatlytotheleakagefromthedeeperinteriorases，sotheEarthhasmasavailabletodriveeruptionsexplosively.Thesedisthattheexisteialcrustfacilitatesgeionofmagmawithahighersilitthanbasalt.Thesesilicarichmagmasaremorevisbasalt，smentmoreeasily.Classic‘picture-book’steeplyioessutFujiinJapaoh，becausetheyaresymptomaticofrelativelysilidpartlyexplosiveeruptions.
8.A70-kilometre-wideviewfromspagthe‘oon’lavafieldinIdaho，USA.Thesourceoftheflowswasaseriesoffissuresheruggedhighlah-west.parethelobateformofthelavaflowswiththeflowsonVenusinFigure6
Mars
paredtotheEarthandVenus，Marshasrelativelyfewvoloes.However，theirsmallnumbersarepensatedbylargesize.MajsebasalticshieldvoloesotheTharsisregion（muchofwhiFigure9）andtheElysiumregion.OlympusMoTharsisvoleasuringabout600kilometresacrossitsbaseand24kilometresfromtoptobottom，whichmakesitthelargestvoltheentireSolarSysteTherearetworeasonswhyMarshassuchbigvoloes.ThefirstisthatMarsisa‘o’.Itslithosphereisanintactshell（asiivelystationarywithrespecttotheunderlyihenosphere.Uh，whereplatesdriftarouomaplume-fedvoloesarecarriedawayandtheirmagmasupplyafteronlyafewmillionyears，amantleplumeonMarssuppliesmagmatothesamespotihospherefastheplumeremainsaonsmayhavebeguructedmorethanabillio.Wehavenowaytotell，becausewelydate（bycraterg）osedatthesurfacetoday，and’tseetheolder，buried，iheedifice.Thereareseveralcalderasatitssummit，whosefloorsaredatedataround100to200milliotheyoulavaflowsontheflaobeonlyabout2millionyearsold，anditislikelythatOlympusMoagaihervoltheTharsisregioelyolder，andareprobably.
9.A3，000-kilometre-widemosaiagesshowingseveralenormousshieldvolars.OisOlympusMons，theSolarSystem’slargestvoltheright-haharsisTholus，andrunnifromthetreofthese，alihree:PavonisMons，Ass，aholus
Thesearshassuchbigvoloesis‘becauseit’.Ithasaclithosphere，abouttwiceasthickastheEarth’s.IfyoutransplantedOlympusMohorVeivelythinlithosphereswouldsagbeheload，andthevolowouldloseheight.
High-resolutionimagesrevealdetailsoflavaflowsontheplaihelargevoldiherregionsofMars.However，therearealsardedbysomeasvolicthathavearousedsiderabletrure10shole.mentsofimpactejearshavebeehasmeteorites.Theyarealleitherbasaltiorecoarselyeis，spanniallizatioendingfrom4.5billiooasyoungas160millionyears.WeferthatigneousrockmakesupthebulkoftheMartiancrustatdepth，eventhetractsofsurfacehaveaveofvariouskinds.
10.A50-kilometre-wideimageofatroversialareaofMarsobtainedbyESA’sMarsExpressorbiter.Somesaytheplatysurfaceisalavaflowwithafracturedgcrust.Othersseethisasbrokenpaowdust-covered）onthesurfaceofafrozewoimpactcratersareolderthaysurfadtheirrimswerehighenoughtopreveeriorsfromfloodiersareactuallyciroutliareforeshortehisobliqueview
Surfaceprocesses
&hahering
Volismisdrivenfromi，butplaarylandsbesculptedjustasmuchbyprocessesthatotiallyatthesurfaabodythatisairlessandthereforeuedfromspace，byfarthedomiihesurfaeesaes.Fragmeerial（‘ejecta’）thrownoutfromcratersblahesurfacetoadepthofseveralmetres，andsiteswheresolidbedrockisvisibleatthesurfacearerare（Figure11）.Thelunarsoil，knolith’，inwhichtheApolloastroheirfootprintsisposedofgrainsmostlyafraillimetreinsize，prisisofcrystal，tinybitsofrodglassyspherulesthatarefrozesofmeltgeheheatoftheimpact.Regolithisuallyrearrangedoyofscalesbyexofddispersalofejecta，apropaing’.OnMercury，eedsarefaster，regolithgrain-sizeisexpectedtobeaboutohatolith.Ifthereisnoatmosphere，solarultravioletlightreachthesurface，whereitmay，overtime，breakchemiipad（ifthereisicfield）chargedpartithesolarwindalsoaffectsurfacechemistry，soairlessbodiesexperieeofprocesses，collectivelydescribedas‘spaceweathering’，thatslowlyalterthepositionofthesurfaple，thebondslinkingiroomsbebroken，allowioesdleavingsubmicroscopietal，anophaseiron’.
&oviewlookingacrossHadleyRille，takenbyApolloastrohe2-metre-thitallayerrunningatheleftisarareexampleofbedrock（probablyalavaflow），hereexposedonasteepslope.Everywhereelseiscinsizefrombouldersdowntodust
lahasanatmosphere，o，a，impareachthesurfaceathighspeed.Forexample，imosphere，stonyasteroidslessthanabout150metresiobeshearedapart.Theresultisaresmallenoughtobesloweddownbyfri，sobythetimetheyreachthegroundtheyhavelostalmostalltheiriy，anddonotformcraters.Meteoriticdust，whiieteoritesbutalsmentsfriallyablatedfrermeteorites，settlestothegroundatanaverageacrateof0.1–1mmpermilliohisdustmakessuytributioalrateofsedimentationthatitistotallysedbyothersedimeondeepofloorfarfromland.
Erosionandtransport
Impaingaside，processesthatwearafragmentsarewind，flowingwater，andmovingice（glaciers）.Wateralsodissolverchemicalweatherissolutionbyearelsewhere，beiedihisappliesespeciallytosaltdeposits，andalsotomanyformsofaterocks.However，olimestone（calciumate）isfmentsoftheshellsainganimportantbiologicalstepinturningdissolvedate（ordissolveddioxidegas）intosolidmaterialthaterock.
&ormsonMarsarefamous，havieles1809.Atperihelion，whenMarsreythanataphelion，windsinexetresperseliftsomuchdusthighimostofthesurfaceisobscuredforseveralweeks.SometimeslittlebeseenphotherthaofOlympusMons.Becauseofthecloudsthatoftehere，thisoftenlookswhite，hesformernameofNyxOlympiowsofOlympus），whichwasrevisedwhenimagesfromspacecraftshoasreallygoingon.ManysigionofwindonMarsbeseenfromround（Figure12）intheformofsanddunesandalsosmallerwihesurfacedust.Someofthedunesactivelysculptedbythewind，butothershaveprobablyheirformformillionsofyears.Wind-bloentoferosiononMars.Theloherisitymeansthataableoftranspsandgrainshastobeblowingmuchfasterthah，andsomeexposedlayersofrockhavebeecuriouslysculptedbyabrasion.
12.Somesanddunes，needingonlytreeforsfact，thispicturewastakenbyNASA’sOpportuhesurfaars，lookingobliquelydownfromtherimofatoafieldofduerfloor.Thevisibleareaisabout100metresacross
&hlings，flowingwaterisusuallythemostfamiliaragentfortranspsediment–inariver，oraswavesoheSolarSystem，hahtlyhassurfaditionsallowingliquidwatertobestable.Venusisfartoohot，andalthoughtheureonMarscreepwellabove0°C，itsatmosphereissotenuousthaticeatthesurfasdirectlytovapourratherthaihereisabuhatwateroncefliousvolumesacrossthesurfaars（Figure13）.MarshassufferedextremesofclimateatleasttheequalofEarth’s，andbillionsoitsatmospherewassuffitlydeopermitrainfallandcatastrophig.ThelargestintheSolarSystem，VallesMariheValleysoftheMarierbeingdisagesreturheprobeMariner9in1971），isa4，00riftsysteminitiatedbyfragofthecrust，butwidenedbyerosioerflhit.
13.Aseriesofeast–westfracturesatteststothetears’sVallesMarinerisplex，ofwhilyafraiscoveredbythis800-kilometre-wideview.helyinoitfromthesouth，whichshowtheroleplayedbyfloideningthemain
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