THE UPPER ATMOSPHERE OF VENUS OBSERVED BY VENUS EXPRESS MIGUEL A - PDF document

Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress 1IntroductionAnewairfullofnewdatais\rowingovertheresearchontheatmospheresoftheterrestrialplanets,MarsandVenus.Thesecond,inparticular,hasbeenseverelyaectedbythelackofdetailedobservationsfromspaceformorethantwodecades.Thisisspeciallysevereinthecaseoftheupperatmosphere,thelayersabovethetropopauseorequivalentlayer(seeFigure1).TherecentVenusExpressmissionistryingtochangethetrend,anditsrecentresultspromisetopartiallyllthisgap. 100 200 300 400 500 600 700 Temperatura (K) 102 100 10-2 10-4 10-6 10-8 10-10 10-12 Presion (atm) VENUS MARS TITAN EARTH VENUS Figure1:Left:VisibleandradarviewsofVenus,fromMariner10andMagellan,mappingthecloudlayerandthesurface.Center:artisticvisionofPioneerVenusinorbit;credit:NASA.Right:TypicalprolesofatmospherictemperatureinEarth,Mars,VenusandTitanAbouteightyearsago,inareviewonComparativeAeronomyintheSolarSystem[11],anumberofdevelopmentsinatmosphericmodelingoftheupperatmospheresoftheterrestrialplanetswerereported,butmostlybasedonthedatafrommissiontoMarsandVenusinthe70sand80s.Asanexample,inthecaseoftheseplan-ets'ionospheres,NagyandCravensmentionedinthatreviewthatthefewweknowaboutthemcomesfromtheVenuscase,andfromonesinglemission,PioneerVenus(PVO,hereonafter),andmuchofwhatwasfoundatthattimewasextrapolatedtoMarsgiventheexpectedsimilarity[12].Onlyafewyearslater,however,apeculiarthirdionosphericlayerwasfoundbytheradioscienceexperimentonMarsExpress([13]),andalsothatincontrasttoVenus,asuddenionopauseseemstobeabsent,aresultrecentlyconrmedbyVenusExpress[14].AlsoBougherandcolleaguescon-cludedthen[23]thatinspiteofthefruitfulmodelingofthebasicparametersoftheupperatmospheresoftheterrestrialplanets,likethegoverningpatternsoftheirgen-eralcirculationortheirexospherictemperatures,thecurrentmodelssuerfroma\geocentricperspective"whichshouldberevisedonceglobalmeasurementsofcom-14LNEAIII,2008.A.Ulla&M.Manteiga(editors). Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress position,temperatureandwindmeasurementsaretaken.Thesesucetostresstheneedofdata,ideallyonasystematicbasis,asabasicrequirementforasoundedadvanceinourunderstandingoftheselayers.However,soundingoftheupperatmosphereisadicultgoalforseveralreasons.In-situmeasurements,eitherfromballoonsorduringtheperiapsisofsatelliteorbits,cannormallystudyeitherthelowerortheupperboundariesoftheupperatmo-sphere.Mostpartofwhatwecalltheupperatmosphere,requiresremotesoundingtechniquesforitsobservation.Moreoverthelowdensitiesatthesealtitudesdemandalimbsounding.Thelackoforbiterswithtechnologicalcapabilitiesforlimbsoundinghasbeenforalongtimeaseriouslimitation.ThistechniquewasrstappliedtotheinvestigationoftheEarth'supperatmosphereinthelate70swiththeNASANimbusseriesofsatellites.InstrumentsonNimbus7scrutinizedourstratospherefortemper-atureandcompositionwithapointingandapreciseinversionwhichwerenoveltiesatthattime.Theserstlimbradiometerswerefollowedbyasubsequentseriesofim-provedinstrumentationontheUpperAtmosphereResearchSatellite,inthe80s,withtechnologicalimprovementsbutstillmostlyradiometers[16].AnotherstepinlimbsoundingoftheEarth'satmospherewasperformedinthe80s,withtheuseofhighspectralresolutioninterferometers,likeATMOS,ontheSpaceLab[17].Andinthe90s,withlighterversionswhichsoundedevenhigher,liketheMIPASinterferometeronboardtheEuropeanENVISATsatellite[1,18].Thewealthofdataacquiredbythesemissionsincludedetailedphotochemistryoftheozonehole[19],studiesoftheglobaldynamicsofthestratosphereandthepolarvortex[20],thedetectionoftheatmosphericresponsetosolarstormsandenergeticparticles[21],thedevelopmentoflocalclimatologies,orthetrackingoftrendsandclimaticchangesaectingthehigheratmosphere[22,18].AlsoonMars,thewaveofmissionstotheredplanetduringthelastdecadehasimprovedthestudyoftheupperatmospheresignicantly.Thisstartedin1997withthedescentofPathnderthroughtheMartianatmosphere,andcontinuedwithMarsGlobalSurveyorandMarsOdysseyorbiters,withexcitingresultsathighaltitudes.Detailscanbefoundinacompanionpaperinthisissue[23].TherearealsointerestingresultsabouttheupperatmosphereofMarsobtainedbyMarsExpress[5],amissionwhichwillcontinueinoperationuntil2009,atleast.ThismissionincludedsomeoftheobservationalimprovementswhichweresosuccessfulontheEarth'supperatmosphere,likelimbsoundingandarelativelyhighspectralresolution.ThisisthecaseofthePlanetaryFourierSpectrometer,PFS[24],withlimbcapabilitiesintheinfraredataresolutionof1.5cm-1,orthecaseofSPICAM[25],anstellaroccultationexperiment,whichissoundingdensitieswellabove140km,orthecaseoftheOMEGAinstrument[26],withafantasticverticalresolutionatthelimb(about400m[27]).TheteamsoftheseinstrumentsarereportingthedetectionofauroralemissionsonMars[28],highaltitudeCO2iceclouds[29],ordaytime\ruorescencebyCO2andCO[30];thelastonesoccuratmesosphericandthermosphericlayersandconrmatlastLNEAIII,2008.A.Ulla&M.Manteiga(editors).15 Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress oldpredictionsbynon-localthermodynamicequilibrium(non-LTE)models[31,32].ResearchontheVenusatmospherewascertainlybehindthedevelopmentsintheirneighborplanets.Demandsofnewdatabythescienticcommunityinthe90s[7,33],togetherwithinterestingandnewgroundbasedobservations[34,36],andwiththeavailabilityofoptimalinstrumentationfromothermissions(RosettaandMarsExpress),pavedthewayforESAtotaketheinitiativeofpromotingamissiontostudyVenusinthe2001[37].VEXwasnallylaunchedinNovember2005,andrepresents,inthecaseofthestudyoftheVenusatmosphere,therstmissiondesignedforsuchpurposeinmorethan25years.ThispaperfocusesonareviewoftheVEXmissionanditsabilitytostudytheupperatmosphereofVenus.Thetermupperatmosphereisusedfreelybydierentscienticcommunities.Inourwork,thisregionisdenedasthatfractionoftheVenusatmospherelayingabovethecloudtops,aboveabout70km.VEXisinnormalscienticoperationsaroundourneighborplanetsinceJune2006.FirstndingshavebeenrecentlypublishedinaspecialissueinNature[9].Thisisanexcitingtimewherenewresultsarestartingtoemergeandtobepublished.WeaimhereatdescribinginaglobalsensehowVEXinstrumentsandobservationalstrategyarepreparedtocontributetoourunderstandingofthisspecialregioninVenus,itsupperatmosphere,addingtowhatisknownsofaraboutit.Westartinsection2withasmallreviewofthecurrentdescriptionoftheVenusatmosphere,withbasicresultsfrompreviousobservationsandspacemissions.Insection3wefocusonitsupperregions,scienticinterestandparticularproblemswhichremainopen.Thenwedescribebrie\rytheVEXinstrumentation,insection4.Wepresentresultsfromoneoftheseexperiments,VIRTIS,insection5,andinSection6discussthesynergywithotherinstrumentsonVEX.WewillsummarizeourperspectivesforthecomingyearsofVEXinsection7.2PeculiaritiesoftheatmosphereofVenusThebasiccharacteristicsoftheatmosphereofVenuscanbereviewedfromanhistor-icalperspective,followingaselectionofhighlightsofitsobservations.VenusissometimesconsideredasthetwinplanetofEarth,sharingsimilarsize,density,formationageanddistancefromtheSun[10,8].However,strongdierencesexistbetweenthetwoplanetsinatmosphericbasicproperties,theseincludingveryhightemperaturesandpressuresatthesurface,about730Kand90bar,analmostpureCO2composition,andaskyfullyandcontinuouslycoveredbythickcloudswithacomplexlayeredstructurecontainingsulfuricaciddroplets.Alsotheplanet'srotationisretrograde(177degreeinclination,hencenoseasonalchanges)andveryslow(243Earth'sdays),whichnowadaysisrecognizedasonekeyingredientoftheverydierentandpeculiaratmosphericdynamicsonVenus[39,40].TheseharshconditionsatthesurfaceexplainthefactthatVenusresearchwasneglectedfora16LNEAIII,2008.A.Ulla&M.Manteiga(editors). Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress Figure2:LaunchofVEXfromBaikonur,November25,2005(leftpanel),compositionofpicturestodepictitsseparationfromtheFregatvehicle(centralpanel),anddiagramofthelimbsoundingoftheatmospherebystellaroccultation(rightpanel).longtime,giventheimpossibilitytoharboreventualhumanexploration[33].2.1MicrowaveobservationsItthe50s,duringtheearlydaysofradioastronomy,strongmicrowaveemissionsindi-catedveryhighsurfacetemperatures[38].TherotationperiodwasalsodetectedbyradioobservationsfromEarthintheearly60s.ThisgaveVenusthehonorablerstplaceintheobjectivesofspaceexplorationofthattime:theMariner2missionwassenttoVenusin1962[41].Stillnowadaysradioground-basedobservationsofVenusareperformedfrequently,whichareusefultosoundtheVenusmesosphere.TheseobservationsaresupplyingwindsanddistributionofminorcompoundslikeCOatthosealtitudes[42].DuringtheVenusExpressmissionmicrowaveobservationsareparticularlyusefulfortheiradditionofcomplementaryobservations,andwerepartofarecentVEXvalidationcampaignbyground-basedobservations[45].Aftertherstmicrowavemeasurementsconrmedtherotationofthesolidbody,thesuperrotationoftheVenusatmospherewasestablished.Stilltheoriginandmechanismsofthiseectisanopenissue,withdebatableandalternativestheories.Thegeneralviewisthatitisinducedorrelatedtotheslowrotationoftheplanet,combinedwithsomeeectivetransferofmomentumfromtheloweratmospheretotheclouds'altitude.2.2SpacecraftsandlandersMorethan30missionshavemadethetriptoVenus[9],includingtheMarinerseriesof\ry-byfrom1962to1975,theVeneraseries(descentprobeswithlanders)from1967to1985,thePioneerVenusmission(oneorbiterandfourprobes)from1978to1982,thetwoVegamissions(including2balloonstationsand2landers)on1985,theLNEAIII,2008.A.Ulla&M.Manteiga(editors).17 Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress AmericanorbiterMagellanfrom1990to1994,andthe\ry-bybyGalileoandCassiniin1991and2001,respectively.Reviewsofallofthemcanbefoundelsewhere[8].Theatmosphericcomposition,densityandthermalstructureareessentialprop-ertiesofanatmosphere,andwereamongtherstobjectivesoftherstmissions.TherstprobesplungedintotheVenusatmospherefoundalmostidenticalthermalproles,withfewhorizontalvariations[44].Thiswasnotsurprising,giventhelargedensityoftheatmosphere;themassoftheVenusatmosphereshouldstoreanddis-tributeheateciently.InthoseearlyyearsofVenusexplorationtherewereseriousproblemstounderstandthegreenhouseeectobserved,thehightemperaturesatthesurface.Aftertherstdeterminationsoftheprecisecompositionoftheatmosphere,itwasclearthatsuchaCO2-dominatedatmosphereshouldhavenumerousgapsintheinfraredwhereradiationcouldescapetospace,andconsequently,cooltheatmo-sphere.Thesmallamountsofwatervaporpresentbelowthecloudsdidnotclosethoseinfraredwindows[7].Aquantitativeunderstandingonlystartedmuchlater,afterthecompositionofthetopcloudswasdeterminedbytheseriesofprobes(H2SO4dropletsareecientabsorbersinthenear-IRandhighlytransparentinthevisible),afteradvancesinspectroscopichightemperaturedatabases,andafteranimprovedtreatmentoflineshapeeectsintoradiativetransfermodels[47].AlotofwhatweknowabouttheVenusatmospherecomesfromthePioneerVenusmission,orbiterandprobes,whichreachedVenusin1978.Oneofthemanyinnovativeinvestigationsfromtheorbiterwastousecamerasatdierentwavelengthsforthestudyofthecloudsandthesurfaceemissivity.Theseconrmedthesuperrotationoftheloweratmosphereandfoundthatthemaximumoccurredatthealtitudeoftheclouds.Theirmeasurementofradiative\ruxesattheclouddeckdemonstratedthathalfthesolarradiationabsorbedintheVenusatmosphereisactuallydepositedthere,bysomeecientandunknownabsorberintheUV[7].Manyquestionsstillremainregardingtheclouds,liketheiractualroleindrivingthecirculationatthosealtitudes.Theymaymerelyrespondtomicrophysicalprocessesandphotochemicalreactions,whichmightbehighlyindependentontheatmosphere'smovements.AnumberofkeymeasurementsoftheatmosphereofVenusabovethecloudswereobtainedbyPVO,includingthethermalstructure,thedynamicsofthemesosphere,andtheionosphere.Wediscusstheminthenextsection.3TheupperatmosphereofVenus.Theupperlayersofanatmosphereareexcitingfromvariousviewpointsordisciplinesinplanetaryscience.Diverseescapeprocessesoccurthereandconstituteonekeyfactorinthelongtermevolutionoftheatmosphereandoftheplanet.Theinteractionwiththesolarwindisstrongestatthesealtitudes;thesolarradiationislteredandpartiallytransmittedtolowerregions,andtherefore,theconditionsbelowandatthe18LNEAIII,2008.A.Ulla&M.Manteiga(editors). Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress planet'ssurfacedependonthedensitiesandcompositionshigherup.Inaddition,thesepeculiarconditionsoeranexcellentbenchmarktostudyspecicchemicalandphysicalprocesseswhichtestourunderstandingineldslikespectroscopy,radiativetransfer,convectionandhydrodynamics,tomentionafew.Theselayerscansupplyalsousefulinformationtoinfergeophysicalpropertiesoftheplanet,likeitsinternalstructure,andtosupplycorrectboundaryconditionsforthegeneraldynamicsandchemistryofthewholeatmosphere.Anadvantageoftheoutermostlayersistheiraccessibility,sometimesbetterthanlowerlayers;theycanbereachedbyloworbitingsatellites,andbytheremotesoundingofthedierentairglowemissionsproducedatthesealtitudes.Describingindetailthoseemissionsandusingtheselayer'sdensitiestomodifythesatellitesorbitsarealsoamongtheobjectivesoftheresearchontheupperatmosphere.AlltheseconditionsconcurinthecaseoftheVenusthermosphere,andhavebeeninvestigatedwiththedataavailablesofar.Inthissectionwereviewbrie\ryaselectionoftheresultsandproblemswhichrequirefurthermeasurements.3.1ThermalstructureThethermalstructureobtainedbyradiooccultationandbythePVOinfraredra-diometerandprobes,respondedtoconvectiveandradiativeprocessesuptoabout90km,asexpected[44,46,47],butshowedpeculiarlatitudinalvariations,withapositivegradienttowardsthepolesataltitudebetween70and90km[48].Athighlatitudestheatmosphereatthatlayeriswellstratied,withacolderregionbelow,termedthecoldcollar,andwhichseemstosurroundthepole[52].Itisnotknownifthiscoldcollarisfrequentornot(Magellanradiooccultationdidnotrevealit[60]).Atransitiontotheupperatmosphere,withanisothermalorinversionlayerequiv-alenttotheEarth'stropopause,abovewhichtheenergybalanceiscontrolledbyradiation,isnotaswellmarkedinVenusasitisonEarth.NormallytheVenusmesosphereissimplytakenasthatregionfromthecloudtop,tothebaseofthethermosphere,typicallyat0.1b,aroundorabove120km.One-dimensionalglobalmodelspredictedamesopeak,producedbysolarabsorptioninCO2near-IRbandsandlocatedaround1b,orabout100kmaltitude.Thislayerseemstobeconrmedbyground-basedmicrowaveobservations,andhasbeenusedasadierentdenitionofthemesopause,[43],sincelargevariabilityisobservedaboveit.Butithasnotbeendescribedinasystematicmannerfrominstrumentationinorbit.AninterestingresultreportedatthosealtitudesfromSPICAMonVEX,andnotobservedpreviously,isastronginversionlayerreportedthere[51],whichopensanadditionaldebateaboutitssourceanditsrelationwiththemesopeak.ThecoldcollarmentionedaboveandtidalwavesobservedonVenusupperatmo-sphere,aredeviationsfromtheradiativeequilibriumsituation[44],andwhichmightbepartlyrelatedtothesuperrotation;theypresentchallengestofutureglobalmod-ellingoftheVenusatmosphere.Also,itisnotknownwhylargelatitudinalvariationsLNEAIII,2008.A.Ulla&M.Manteiga(editors).19 Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress sions,orfromEarthobservations.Thelargeellipticityoftheorbit,whichimposestringentlimitationsforclosemappingandlimbsounding,isanadvantagehoweverforanumberofstudies.Theseincludeimagetrackingandglobalviewing,whichmaypermitobservationsofplanetarywaves,polarvortexstudies,andtimeevolutionofdynamicalfeatures,likewindsandturbulence;aswellaslowperiapsispasses,forin-situexplorationoftheupperthermosphere. Figure4:ListofVEXinstruments,descriptionandobjectives5ExploringtheupperatmospherewithVIRTISHerewepresentnewdataontheupperatmosphereofVenusbytheinstrumentVIR-TIS.Wefocusonlimbobservations,whicharespeciallyadequateforsuchpurpose,andalsoon\ruorescentemissionsbyCO2at4.3m,andtheircomparisonwiththe-oreticalmodelpredictions.VIRTISisoperatedtoobserveVenusinnadir/discviewingwhenVEXisfarfromVenus,butalsoinalimbsoundinggeometryduringperiapsis.AlthoughthelargeellipticityofVEXtakesVIRTISasfaras60000kmaway,theimagesfromapoapsiscanstillbeusedtoobservetheatmosphericlimboftheplanet.Figure5showsaportionoftheVenusdisc,acquiredduringorbit#25,neartheapoapsisoftheVEXorbit.TheLNEAIII,2008.A.Ulla&M.Manteiga(editors).25 Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Radiance (mW m-2 sr-1 mm-1) 60 80 100 120 140 160 Altitude (km) VIRTIS-M NLTE MODEL Figure5:Leftpanel:MapofCO2radiancesfromVIRTIS-M,fromOrbit#25,fromapoap-sis.Rightpanel:Zoomtodetailthelimbsoundingcapabilities.Seetext.Lowerpanel:Radianceproleandmodelsimulationradiancemapcorrespondsto4.32m,andclearlyshowsalimbbrightening,coloredhereinred.Azoomoftheframeillustratesmoreclearlythelimbemission.Thepixelsizeisdepictedbytheoscillationinthetworeferencelinesadded,tomarkthesurfaceandthe60kmtangentaltitude.Thisshowsaclearpeakemissionaround120km,andatarelativelycoarseverticalresolution,butstill,similartotheonlyotherdetectionofthisemissioninVenus,fromNIMS/Galileo.Thehorizontalresolutionismuchbetter,andrepresentsauniqueviewofthisemission.Thepeakintensityandaltitudelocation,theverticalprole,andthesolarilluminationvariationsareanumberoffeatureswhichposechallengestotheoreticalsimulations.WebuiltaverticalproleatthelimbfromthisV-Mimage,atoneparticularlocationandatoneofthecentralwavelengthsoftheCO2emissionband,at4.28m.ItisshowninFigure5.Themodelsimulation,forasimilarsolarzenithangleandforatypicalatmospherictemperature/densityprole,isalsoshowninthegure.Anywavelengthcanbeused,and[59]presentasimilarcomparisonat4.33m.Thedataseemtofollowthemodelprediction,boththeshapeoftheproleandthepeak's26LNEAIII,2008.A.Ulla&M.Manteiga(editors). Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress atmosphere,butagoodtofthemeasurementsrequiretorevisethenon-LTEmodelbyaddingthoseminortransitions.Alternatively,someextraexcitationsource,stillunidentied,maybepresent.Thisworkisinprogress.Oneofouraimsistoperformadetailedanalysisoftheemissionandtheirdierentcontributingbands.Suchstudymayresultinmodelimprovements,likemodicationsinthewaythemodeldescribeshowthesolarenergyistransferedbetweenthedierentCO2vibrationalstates,whichincludescollisionalprocessesnotwelldeterminedyet.TherearehopesalsothatthesehighresolutiondatafromVIRTISmayteachusaboutsomemicroscopicenergytransfermechanisms.OtherinterestinglimbatmosphericresultsfromVIRTISregardthenighttimeemissionsofO2at1.27m,whichindicatetimeandspatialvariationsathighreso-lutionforthersttime.Thisisthetopicofacompanionworkinthisissue[35].6SynergybetweenVenusExpressinstrumentsVIRTISisnottheonlyinstrumentonboardVEXtostudytheupperatmosphere(seeFigure4).SomeofthemwillsupplyusefulinformationfordirectandindirectcorrelationwithVIRTISdata,andvice-versa.AkeyprogressbyVEXisexpectedinthedescriptionoftheglobaltemperatureanddensitystructureoftheupperatmosphere,includingtrackingofminorneutralspeciesandions.ThesewillbetackleddirectlybySPICAVusingstellarandsolaroccultation,byVERAusingradiooccultation,byASPERAwithin-situdata,andindirectlybyVIRTIS,viathestrongnon-LTEemissionsthere;theseareaectedbytheactualdensityandthedistributionoftheemittingspecies.TheVERAteamplanstoassumecyclostrophicbalancetousethemeridionaldistributionofatmospherictemperaturetoobtainthezonalwinddistribution.Therstresultsfromthisinstrumentshowneattemperatureproles,withverysmallmeasurementnoise,frombelowtheclouddeck,around45km,uptoabout90km.TheupperboundaryofVERAisaboutthelowerrangeoftemperaturesoundingforSPICAV,thisextendinguptoatleast140kmaltitude,asreportedrecently[51].Althoughtheresultsseemtomatch,thereisaintriguingresultfromSPICAV,asystematicwarmlayerjustaboveitsboundarylayer,around100km.PreviousdatafromPVOandmicrowaveobservationsalsohaveupperboundariesabout100km,withnotgoodqualitydeterminations.Thisaltituderangeisthereforesubjecttospeciallydicultmeasurements.Thoseotherpreviousdeterminationssuggestsomesmallheating,butnothinglikethemorethan40KobtainedbySPICAVinsomeproles.IfSPICAVdataareconrmed,somestrongheatingmechanismmaybeneededthere.Sincethedatapresentedcorrespondtonightside,theSPICAVteamsuggesttheheatingmaybeproducedbyadiabaticcompressioninthedownwellingbranchoftheglobalthermosphericcirculation,somethingsimulatedpreviouslyby28LNEAIII,2008.A.Ulla&M.Manteiga(editors). Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress models,butwithnotsuchintensity[23].Anargumentinfavorofthisinterpretationistheincreasingmagnitudeoftheinversionasthesolarzenithalangle(SZA)increases(closertotheanti-solarpoint).Theyalsoextendtheirresultstoestimateadownwardvelocityforthetotalatmosphere;theirestimationdoesnotinclude,however,non-LTEeectsandisthereforeoverestimated.However,thedatacontainstheinformationforamoredetailcalculation.RegardingthecorrelationwithVIRTIS,presentvalidationactivitiesanddataanalysisarefocusedonthecharacterizationoftheemissions.Theforeseeablederiva-tionofdensitiesfromtheCO2non-LTEemissionswillstilltakesometime.StrongemissionsfromVIRTISareobservedfromthecloudtopsupward,evenuptoabove160kminsomeindividualspectra.However,eventualretrievalswillhavetocopewithopacitypropertiesandwillsurelybeusefulonlyaroundthepeakemissionandupward.AstheVERAandSPICAVdensitiesarealreadyavailable,weplantousetheseasinputtoourmodelsimulationsforVIRTIS,whichisanindirectcomparisonstrategybetweenthem.Ideally,adirectcorrelationbetweenallthreeinstrumentsshouldbeperformedonindividualproles.However,thisisdicultgiventhedierentobservationalrequire-mentsbyindividualinstruments.VIRTIS,forexample,isdetectingsolarpumpingemissions,whilemostofSPICAVdatacorrespondtonighttimestellaroccultations.SOIRdataaremoreinteresting,butalsooccurathighSZA,nominallyat90degree,wheretheCO2excitationislow.Therefore,eachinstrumentwillbuilditsownglobalmapsofdensities,andtheseshouldbecompared.7SummaryandperspectivesAnewmissiontoVenus,theEuropeanVEX,isatlastinorbitaroundVenus,obtain-ingexcitingnewdataandresultsforaboutoneyearandhalftodate.Firstanalysisofthedataarestartingtobepublished,althoughthevalidationactivityandsystematicanalysisofthedataisstillon-going.Atthisearlystage,overviewsliketheonepresentedhere,focusedontheatmo-sphericlayersabovethecloudtops,may(andhopefully,will)beobsoletesoon,asnewresultsareemergingquickly.Regardlessofwhicheverspecicresultsaretobefoundinthenearfuture,wearelistinganddiscussingbrie\ryanumberofscienticproblemsoftheupperatmosphereofVenuswhichrequirenewdata,andweareframingsomeofourhopesonthenewtechniquesandobservationalabilitiesoftheVEXmission.Regardingtheupperatmosphere,threeinstruments,SPICAV,VERA,andVIR-TISarespeciallypronetocorrelativemeasurementsofthedensityandtemperaturestructureofthisregion.TheemissionsofVIRTIS,understudy,aregivingforthersttime,adetailedpicturewithspatialandtimevariations,whichconrmmodelpredic-tionsandoerchancestolearnaboutdensityvariations,turbulenceandtransport,LNEAIII,2008.A.Ulla&M.Manteiga(editors).29 Lopez-Valverdeetal.VenusupperatmosphereobservedbyVenusExpress andevenmicroscopicphysicsintheupperatmosphere.ThedensityandtemperatureprolesfromSPICAVandVERAaresupplyingnewresultswithunprecedenteddetailoftheverticalvariation,thedynamicsatglobalscale,andtheextensionoftheclouddeckanditsimpactonthethermalbudget.NodoubtthesenewdatafromVEXinthemesosphereandthermospherewilltriggermodelingeortstounderstandtheminthenearfuture.Someoftheseeortsarealreadyon-going,withthedevelopmentofanumberofglobalcirculationmodels,andtheoertocreateaclimatedatabasesimilartothesuccessfulonewearebuildingonMarsnowadays[78].RoutineoperationsofVEXaregrantedbyESAuntil2009.ExtensionoftheVEXlifetimebeyond2009ishighlydesirable.NotonlyVenusisunderadierentsegmentofthesolarcycle,butanumberofstudieswouldbebenetedfromit.Oneisthecorrelationbetweendierentinstruments,asmentionedabove.AsecondoneisthepossibilitytomodifytheVEXorbit,byusingsomefuelonboard,whichwouldsupplynewgeographicalperspectivesofVenus.Mostimportant,thescienticvalueofthenewmeasurementsmeritsuchanextension.Thepresentdatabasepromisealreadytokeepusactivelyanalyzingthedataandtestingourmodellingtoolsforalongtime.Also,thesistermissionMarsExpressisalsooperativeonMarsatpresent,andwithsimilarinstrumentation,andthismultipliesthescienticbenetfromeachofthesemissions.Thisisauniqueopportunityforcomparativeplanetology,andkeepingbothrunningwouldbeahighpriorityforESAandtheEuropeanscienticcommunity.Acknowledgments:ThisworkhasbeencarriedoutunderprojectESP2004-01556.References[1]Laur,H.2005,COSPARInformationBulletin162,31[2]Mertens,C.J.,Schmidlin,F.J.,Goldberg,R.A.etal.2004GRL31,L03105,doi:10.1029/2003GL018605[3]Albee,A.L.,Palluconi,F.D.,Arvidson,R.E.1998,Science279,1671[4]Saunders,R.S.,Arvidson,R.E.andBadhwar,G.D.2004,SpaceSci.Rev.110,1[5]Chicarro,A.F.2006,HighlightsAstron.14,ProceedingsoftheIAUXXVIGeneralAssembly2006,CUP,2007,334[6]Crisp,D.,Allen,M.,Anicidh,V.G.etal.2002,ASPConferenceProceedings,Vol.272,\TheFutureofSolarSystemExploration(2003-2013)",AstronomicalSocietyofthePacic,5[7]Taylor,F.W.etal.1999,\TheVenusianEnvironment",ESATechnicalReport[8]Titov,D.V.,Svedhem,H.andTaylor,F.W.2006,\TheAtmosphereofVenus:CurrentKnowledgeandFutureInvestigations"SpringerPhysicsandAstronomy,London[9]Svedhem,H.,Titov,D.V.,Taylor,F.W.etal.2007,Nature450,629[10]Ingersoll,A.P.2007,Nature450,617[11]Mendillo,M.,Nagy,A.andWaite,J.H.2000,Editors,\Atmospheresinthesolarsystem:Comparativeaeronomy",Geophysicalmonograph.AGU,Washington30LNEAIII,2008.A.Ulla&M.Manteiga(editors). 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