SATURN IN THE 21ST CENTURY TheCassiniOrbitermission,launchedin1997,hastransformedourunderstandingoftheoriginsandworkingsof Saturn. Drawing from new discoveries and scientific insights from the mission, this book provides a detailed overviewoftheplanetasrevealedbyCassini.Chaptersbyeminentplanetaryscientistsandresearchersfromacross the world comprehensively review the current state of knowledge regarding Saturn’s formation, interior, atmo- sphere, ionosphere, thermosphere, and magnetosphere. Specialized chapters discuss the planet’s seasonal varia- bility; the circulation of strong zonal winds; the constantly changing polar aurorae; and the Great Storm of 2010–2011, the most powerful convective storm ever witnessed by humankind. Documenting the latest research on the planet, from its formation to how it operates today, this is an essential reference for graduate students, researchers,andplanetaryscientists. KEVIN H. BAINES is Senior Scientist at the Space Science and Engineering Center at the University of Wisconsin–Madison, and Principal Scientist at Caltech/Jet Propulsion Laboratory, Pasadena. He has over 35 years of experience in the development, planning, data analysis, and publication of science results from NASA and ESA planetary orbital missions. Specializing in the 3D nature of planetary atmospheres as gleaned from spacecraft-borne visual-to-near-infrared spectral imagers, he has been a NASA-selected scientist on the Cassini–Huygens and Galileo orbiter missions to Jupiter and Saturn and was the leader of the NASA science teamonESA’sVenusExpressorbitermission. F. MICHAEL FLASAR isSpaceScientistatthePlanetarySystemsLaboratoryattheNASAGoddardSpaceFlight Center. He has devoted 45 years to the study of solar system planets and their atmospheres, particularly from thermal-infrared spectroscopy and radio-occultation data. Hehas been aninvestigator onthe Voyagermission to the giant planets, the Galileo mission to Jupiter, the Mars Global Surveyor mission, and the Cassini–Huygens missiontoSaturn.HeisarecipientofNASAGoddardSpaceFlightCenter’sJohnC.LindsayMemorialAwardfor SpaceScienceandheisafellowoftheAmericanGeophysicalUnion. NORBERT KRUPP isScientistattheMaxPlanckInstituteforSolarSystemResearch,Göttingen,Germany.Hehas 25 years of experience in data analysis and the development of space instrumentation. His main interest is the understandingofprocessesdrivingtheglobalconfigurationanddynamicsofparticlesaroundplanets,includingthe interactionwithmoons,rings,andneutralclouds.Hehasbeeninvolvedinseveralspacemissions,includingMars Express, Venus Express, Ulysses, Bepi Colombo, Juice, Galileo, Cassini–Huygens, and Europa Clipper. On Cassini, he co-led the magnetosphere and plasma science working group MAPS, and is Co-Investigator of theMIMIinstrument. TOM STALLARD is Associate Professor in Planetary Astronomy at the University of Leicester. He is a world- leading planetary astronomer who has observed the gas giants of our solar system from many of the largest telescopesaroundtheworld.Focusingontheinvestigationofauroraeoftheseplanets,hehasalsobeenextensively involvedinanalyzingspacecraftdata,includingimagesofSaturn’sauroratakenbytheCassinispacecraft.Hehas alsoappearedonnumeroustelevisionandradioprogramstodiscussrecentscienceadvances.Hispublicoutreach hasincludedinvolvementinBBCStargazingliveeventsandhewasawardedthehonorarytitleof“HokuKolea” forhisextensiveworkwiththeMaunaKeavisitors’center. Cambridge Planetary Science SeriesEditors: FranBagenal,DavidJewitt,CarlMurray,JimBell,RalphLorenz,FrancisNimmo,SaraRussell BooksintheSeries † 1. Jupiter:ThePlanet,SatellitesandMagnetosphere EditedbyBagenal,DowlingandMcKinnon 978-0-521-03545-3 † 2. Meteorites:APetrologic,ChemicalandIsotopicSynthesis Hutchison 978-0-521-03539-2 † 3. TheOriginofChondrulesandChondrites Sears 978-1-107-40285-0 † 4. PlanetaryRings Esposito 978-1-107-40247-8 † 5. TheGeologyofMars:EvidencefromEarth-BasedAnalogs EditedbyChapman 978-0-521-20659-4 † 6. TheSurfaceofMars Carr 978-0-521-87201-0 † 7. VolcanismonIo:AComparisonwithEarth Davies 978-0-521-85003-2 † 8. Mars:AnIntroductiontoitsInterior,SurfaceandAtmosphere Barlow 978-0-521-85226-5 9. TheMartianSurface:Composition,MineralogyandPhysicalProperties EditedbyBell 978-0-521-86698-9 † 10. PlanetaryCrusts:TheirComposition,OriginandEvolution TaylorandMcLennan 978-0-521-14201-4 † 11. PlanetaryTectonics EditedbyWattersandSchultz 978-0-521-74992-3 † 12. ProtoplanetaryDust:AstrophysicalandCosmochemicalPerspectives EditedbyApaiandLauretta 978-0-521-51772-0 13. PlanetarySurfaceProcesses Melosh 978-0-521-51418-7 14. Titan:Interior,Surface,AtmosphereandSpaceEnvironment EditedbyMüller-Wodarg,Griffith,LellouchandCravens 978-0-521-19992-6 15. PlanetaryRings:APost-EquinoxView(SecondEdition) Esposito 978-1-107-02882-1 16. Planetesimals:EarlyDifferentiationandConsequencesforPlanets EditedbyElkins-TantonandWeiss 978-1-107-11848-5 17. Asteroids:AstronomicalandGeologicalBodies Burbine 978-1-107-09684-4 18. TheAtmosphereandClimateofMars EditedbyHaberle,Clancy,Forget,SmithandZurek 978-1-107-01618-7 19. PlanetaryRingSystems:Properties,StructureandEvolution EditedbyTiscarenoandMurray 978-1-107-11382-4 20. Saturninthe21stCentury EditedbyBaines,Flasar,KruppandStallard 978-1-107-10677-2 † Reissuedasapaperback SATURN IN THE 21ST CENTURY Editedby KEVIN H. BAINES UniversityofWisconsin–Madison F. MICHAEL FLASAR NASAGoddardSpaceFlightCenter NORBERT KRUPP MaxPlanckInstituteforSolarSystemResearch TOM STALLARD UniversityofLeicester UniversityPrintingHouse,CambridgeCB28BS,UnitedKingdom OneLibertyPlaza,20thFloor,NewYork,NY10006,USA 477WilliamstownRoad,PortMelbourne,VIC3207,Australia 314–321,3rdFloor,Plot3,SplendorForum,JasolaDistrictCentre,NewDelhi–110025,India 79AnsonRoad,#06–04/06,Singapore079906 CambridgeUniversityPressispartoftheUniversityofCambridge. ItfurtherstheUniversity’smissionbydisseminatingknowledgeinthepursuitof education,learning,andresearchatthehighestinternationallevelsofexcellence. www.cambridge.org Informationonthistitle:www.cambridge.org/9781107106772 DOI:10.1017/9781316227220 ©CambridgeUniversityPress2019 Thispublicationisincopyright.Subjecttostatutoryexception andtotheprovisionsofrelevantcollectivelicensingagreements, noreproductionofanypartmaytakeplacewithoutthewritten permissionofCambridgeUniversityPress. Firstpublished2019 PrintedintheUnitedKingdombyTJInternationalLtd.PadstowCornwall AcataloguerecordforthispublicationisavailablefromtheBritishLibrary. LibraryofCongressCataloging-in-PublicationData Names:Baines,KevinHays,editor.|Flasar,F.Michael,editor.|Krupp,Norbert,editor.|Stallard,Tom,editor. Title:Saturninthe21stcentury/editedbyKevinH.Baines(UniversityofWisconsin,Madison), F.MichaelFlasar(NASA-GoddardSpaceFlightCenter),NorbertKrupp (MaxPlanckInstitutefortheStudyofSocieties,Cologne),TomStallard(UniversityofLeicester). Description:Cambridge:CambridgeUniversityPress,2019.| Series:Cambridgeplanetaryscienceseries;20|Includes bibliographicalreferencesandindex. Identifiers:LCCN2017054700|ISBN9781107106772 Subjects:LCSH:Saturn(Planet)|Saturn(Planet)–Geology. Classification:LCCQB671.S24452018|DDC523.46–dc23 LCrecordavailableathttps://lccn.loc.gov/2017054700 ISBN978-1-107-10677-2Hardback CambridgeUniversityPresshasnoresponsibilityforthepersistenceoraccuracyof URLsforexternalorthird-partyinternetwebsitesreferredtointhispublication anddoesnotguaranteethatanycontentonsuchwebsitesis,orwillremain, accurateorappropriate. Contents ListofContributors pagesix 6 GlobalConfigurationandSeasonal ListofReviewers xiii VariationsofSaturn’sMagnetosphere 126 , , NORBERT KRUPP PETER KOLLMANN 1 IntroductiontoSaturninthe21stCentury 1 . , DONALD G MITCHELL MICHELLE KEVIN H. BAINES, F. MICHAEL THOMSEN, XIANZHE JIA, ADAM MASTERS , FLASAR NORBERT KRUPP AND TOM AND PHILIPPE ZARKA STALLARD 7 Saturn’sAurorae 166 2 TheOriginandEvolutionofSaturn, , . , TOM STALLARD SARAH V BADMAN withExoplanetPerspective 5 , ULYANA DYUDINA DENIS GRODENT SUSHIL K. ATREYA, AURE´LIEN CRIDA, AND LAURENT LAMY , . TRISTAN GUILLOT JONATHAN I 8 Saturn’sIonosphere 196 , LUNINE NIKKU MADHUSUDHAN , , LUKE MOORE MARINA GALAND AND OLIVIER MOUSIS . , . ARVYDAS J KLIORE ANDREW F NAGY 3 TheInteriorofSaturn 44 ’ AND JAMES O DONOGHUE . , , JONATHAN J FORTNEY RAVIT HELLED 9 Saturn’sVariableThermosphere 224 , . NADINE NETTELMANN DAVID J . , . DARRELL F STROBEL TOMMI T , . , STEVENSON MARK S MARLEY WILLIAM KOSKINEN AND INGO MU¨LLER-WODARG . B HUBBARD AND LUCIANO IESS 10 Saturn’sSeasonallyChangingAtmosphere: 4 Saturn’sMagneticFieldandDynamo 69 ThermalStructure,Composition . , ULRICH R CHRISTENSEN HAO andAerosols 251 , . CAO MICHELE K DOUGHERTY AND KRISHAN . , LEIGH N FLETCHER THOMAS KHURANA . , , K GREATHOUSE SANDRINE GUERLET 5 TheMysteriousPeriodicitiesofSaturn . . JULIANNE I MOSES AND ROBERT A WEST CluestotheRotationRateofthePlanet 97 11 TheGlobalAtmosphericCirculation . , . JAMES F CARBARY MATTHEW M ofSaturn 295 , . , , HEDMAN THOMAS W HILL XIANZHE JIA . , . ADAM P SHOWMAN ANDREW P , WILLIAM KURTH LAURENT LAMY AND , INGERSOLL RICHARD ACHTERBERG GABRIELLE PROVAN AND YOHAI KASPI vii viii Contents 12 Saturn’sPolarAtmosphere 337 14 TheFutureExplorationofSaturn 417 KUNIO M. SAYANAGI, KEVIN H. BAINES, KEVIN H. BAINES, SUSHIL K. ATREYA, ULYANA DYUDINA, LEIGH N. FRANK CRARY, SCOTT G. EDGINGTON, FLETCHER, AGUST´IN SA´NCHEZ-LAVEGA THOMAS K. GREATHOUSE, HENRIK MELIN, AND ROBERT A. WEST OLIVIER MOUSIS, GLENN S. ORTON, 13 TheGreatSaturnStormof2010–2011 377 THOMAS R. SPILKER AND AGUST´IN SA´NCHEZ-LAVEGA, GEORG ANTHONY WESLEY , . , FISCHER LEIGH N FLETCHER ENRIQUE GARCI´A-MELENDO, BRIGETTE HESMAN, Index 442 SANTIAGO PE´REZ-HOYOS, KUNIO M. Colorplatescanbefoundbetweenpages210 SAYANAGI AND LAWRENCE A. SROMOVSKY and211