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PRIMITIVE METEORITES AND ASTEROIDS This page intentionally left blank
PRIMITIVE METEORITESAND ASTEROIDS PHYSICAL,CHEMICAL,AND SPECTROSCOPICOBSERVATIONS PAVINGTHEWAYTOEXPLORATION
Editedby
NEYDA ABREU AssociateProfessorofGeosciencesandMathematics
ThePennsylvaniaStateUniversity DuBoisCampus DuBois,Pennsylvania,USA
Elsevier
Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates
Copyright © 2018ElsevierInc.Allrightsreserved.
Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorageandretrieval system,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseekpermission,further informationaboutthePublisher’spermissionspoliciesandourarrangementswithorganizationssuch astheCopyrightClearanceCenterandtheCopyrightLicensingAgency,canbefoundatour website: www.elsevier.com/permissions .
Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythe Publisher(otherthanasmaybenotedherein).
Notices Knowledgeandbestpracticeinthis fieldareconstantlychanging.Asnewresearchandexperience broadenourunderstanding,changesinresearchmethods,professionalpractices,ormedical treatmentmaybecomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuch informationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers, includingpartiesforwhomtheyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors, assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproducts liability,negligenceorotherwise,orfromanyuseoroperationofanymethods,products, instructions,orideascontainedinthematerialherein.
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ISBN:978-0-12-813325-5
ForinformationonallElsevierpublicationsvisitourwebsiteat https://www.elsevier.com/books-and-journals
Publisher: CandiceJanco
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Contributors ix
Acknowledgments xi
1 . A Brief History of Spacecraft Missions to Asteroids and Protoplanets
BETH E.
CLARK,
MARIA A. BARUCCI, XIAO-DUAN ZOU, MARCELLO FULCHIGNONI, ANDREW RIVKIN, CAROLRAYMOND,MAKOTO YOSHIKAWA, LINDA T. ELKINS-TANTON, HAL LEVISON
1.1 Galileo: 951 Gaspra 2
1.2 Galileo: 243 lda 4
1.3 Galileo: Dactyl 5
1.4 NEAR-Shoemaker: 253 Mathilde 6
1.5 Deep Space 1: 9969 Braille 8
1.6 NEAR-Shoemaker: 433 Eras 9
1.7 Cassini-Huygens: 2685 Masursky 13
1.8 Stardust: 5535 Annefrank 15
1.9 Hayabusa: 25143 ltok awa 16
1.10 New Horizons: 132524 APL 19
1.11 Rosetta: 2867 Steins 20
1.12 Rosetta: 21 Lutetia 23
1.13 Dawn: 4 Vesta 25
1.14 Chang'e: 4179 Toutatis 28
1.15 Dawn: 1 Ceres 30
1.16 OSIRIS-REx: 101955 Bennu 34
1.17 H aya busa2: 162173 Ryugu 39
1.18 Lucy: Jupit er Trojans 41
1.19 Psych e: 16 Psych e 46 R eferenc es 48
Further Reading 57
2. Physical, Chemical, and Petrological Characteristics of Chondritic Materials and Their Relationships to Small Solar System Bodies
MICHAEL E. ZOLENSKY, NEYDA M. ABREU, MICHAEL A. VELBEL, ALAN RUBIN, NOEL CHAUMARD, TAKAAKI NOGUCHI, TATSUHIRO MICHIKAMI
2.1 Introduction 59
2.2 Ordin a ry Chondrites and Their Counterpart
Asteroids 6 7
2.3 Enstatite Chondrites a nd Their Counterpart
Asteroids 77
2.4 Carbonaceous Chondrit es and Their Counterpart Asteroids 80
2.5 Insolation Thermal Metamorphic of Hydrated Carbonaceous Chondrites 171
2 .6 Space W ea thering of Carbonaceous Chondrites 172
References 173
Further Reading 204
3. The Origin and Evolution of Organic Matter in Carbonaceous Chondrites and Links to Their Parent Bodies
DANIEL P. GLAVIN, CONEL M.O'D. ALEXANDER, JOSE C. APONTE, JASON P. DWORKIN, JAMIE E. ELSILA, HIKARU YABUTA
3.1 Introduction 205
3.2 Classification of Chondrites and lOPs and Postaccretion Parent Body Alteration 208
3.3 Organics in Carbonaceous Chondrites, Comets, and lOPs 212
3.4 Chemical and Spectroscopic Links Between Meteorites and Parent Bodies 248
3.5 Sample Return Missions 249
3.6 Conclusions 253 References 255
Further Reading 2 71
4. Reflectance Spectroscopy of Chondrites
EDW ARD A. CLOUTIS, MATTHEW R.M. IZA W A, PIERRE BECK
4.1 Introduction 273
4.2 Spectral Reflectance Properties of Chondrites 278
4.3 Discussion 310
4.4 Range of Spectral Properties of Chondrites 325
4.5 Chondrite-Asteroid Linkages 333
4.6 Summary and Conclusions 334
Acknowledgments 335 References 335
Further Reading 342
5. Compositional Diversity Among Primitive Asteroids
HUMBER TO CAMPINS, JULIA DE LEON , ]A VIER LICANDRO, AMANDA HENDRIX, JUAN A. SANCHEZ, VICTOR ALl-LAGOA
5.1 Introduction 345
5.2 Primitive Asteroid Locations 346
5.3 Ultraviolet Spectra of Primitive Asteroids 350
5.4 Visible and Near-Infrared Spectra 352
5 5 Mid-Infrared Spectra 357
5.6 Effects of Space We a thering on Spectral Observations of Primitive Asteroids 361
5.7 Summary 363 Acknowledgments 364 References 365 Further Reading 369
6. Linking Water-Rich Asteroids and Meteorites: Implications for Asteroid Space Missions
DRISS T AKIR, KIEREN HOW ARD, HIKARU YABUT A, MAGGIE MCADAM, CHARLES HIBBITTS, JOSHUA EMERY
6.1 Introduction 3 71
6.2 Water-Rich Asteroids 372
6.3 Water-Rich Meteorites 378
6.4 Association of Organics and Minerals in Water-Rich Small Bodies 390
6.5 Primitive Asteroid-Meteorite Matches 394
6.6 Implications for Exploration of Asteroids 399
6. 7 Future Directions 400 Acknowledgments 401 References 40 1
7. Exploring the Possible Continuum Between Comets and Asteroids
JOSEPH A. NUTH, Ill, TIMOTHY MCCOY, NATASHA JOHNSON, NEYDA M. ABREU
7.1 Introduction 409
7.2 Challenges to the Traditional View of Comets and Asteroids as Separate Entities 410
7.3 Geochemical and Mineralogical Similarities Between Comets and Asteroids 413
7.4 Geochemical and Mineralogical Differences Between Comets and Asteroids 417
7.5 Accretion of Small Bodies 420
7.6 Accretion of Large Planetary Bodies 425
7.7 Thermal Models of Small Body Evolution 427
7.8 Conclusions 429
References 4 31
Further Reading 438
8. Geotechnical Properties of Asteroids Affecting Surface Operations, Mining, and In Situ Resource Utilization Activities
KRIS ZACNY, EDW ARD B. BIERHAUS, DANIEL T. BRITT, BENTON CLARK, CHRISTINE M. HARTZELL, LESLIE GERTSCH, ANTON V. KULCHITSKY, JEROME B. JOHNSON, PHIL METZGER, DAVID M. REEVES, PAUL SANCHEZ, DANIEL J. SCHEERES
8.1 Geotechnical Properties of Asteroids Affecting Surface Operations, Mining, and In Situ Resource Utilization 439
8.2 Survey of Forces in Asteroidal Regolith 441
8.3 Dynamics of Penetrators Into Regolith on Microgravity Asteroid Surfaces 446
8.4 Discrete Element Method Simulation of Asteroid Regolith to Estimate Boulder Extraction Forces and Spacecraft Contact Pad Interactions for NASA Asteroid Redirect Mission 467
8.5 Gas Interaction With Asteroid Regolith 471
8.6 Conclusions 473
References 4 73
Further Reading 476
9. Practical Applications of Asteroidal ISRU in Support of Human Exploration jOEL C. SERCEL, CRAIG E. PETERSON, DANIEL T. BRITI, CHRISTOPHER DREYER, ROBERT JEDICKE, STANLEY G. LOVE, OTIS WALTON
9.1 Introduction 4 77
9.2 The Statistics and Accessibility of Near-Earth Object Resources 480
9.3 The Martian Moons as Asteroid-Like In Situ Resource Utilization Material Sources 485
9.4 Technologies and Approaches to Remote Discovery and Prospecting of Asteroid Resources 489
9.5 In Situ Resource Utilization for Propellants and Fluids 490
9.6 Microgravity Granular Mechanics Applied to Making Radiation Shields 496
9.7 The Asteroid Redirect Mission (ARM) or Other Future Asteroid Mission Return
Boulder as a Test Bed for Asteroid In Situ Resource Utilization Proximity Operations
Technology 502
9.8 Research Needed for Development of Asteroid In Situ Resource Utilization
Technology 506
9.9 Example of an Asteroid In Situ Resource Utilization Mission System Architecture 510
9.10 A Roadmap to Humanity's Future in Space Based on Asteroid Resources 513
References 5 21
Further Reading 524
Index 525
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Contributors NeydaM.Abreu ThePennsylvaniaState University,DuBois,PA,UnitedStates
ConelM.O’D.Alexander CarnegieInstitution ofWashington,Washington,DC,UnitedStates
VictorAli-Lagoa MaxPlanckInstitutefor ExtraterrestrialPhysics,Garching,Germany
JoséC.Aponte NASAGoddardSpaceFlight Center,Greenbelt,MD,UnitedStates; CatholicUniversityofAmerica,Washington, DC,UnitedStates
MariaA.Barucci LESIA-ObservatoiredeParis, CNRS,UniversitePierreetMarieCurie, UniversiteParisDiderot,France
PierreBeck InstitutUniversitairedeFrance, Grenoble,France
EdwardB.Bierhaus LockheedMartin,Denver, CO,UnitedStates
DanielT.Britt UniversityofCentralFlorida, Orlando,FL,UnitedStates
HumbertoCampins UniversityofCentral Florida,Orlando,FL,UnitedStates
NoelChaumard UniversityofWisconsin
Madison,Madison,WI,UnitedStates
BethE.Clark DepartmentofPhysics & Astronomy,IthacaCollege,Ithaca,NY,United States
BentonClark LockheedMartin,Denver,CO, UnitedStates
EdwardA.Cloutis UniversityofWinnipeg, Winnipeg,MB,Canada
ChristopherDreyer ColoradoSchoolofMines, Golden,CO,UnitedStates
JasonP.Dworkin NASAGoddardSpaceFlight Center,Greenbelt,MD,UnitedStates
LindaT.Elkins-Tanton SchoolofEarthand SpaceExploration,ArizonaStateUniversity, Tempe,AZ,UnitedStates
JamieE.Elsila NASAGoddardSpaceFlight Center,Greenbelt,MD,UnitedStates
JoshuaEmery UniversityofTennessee,Knoxville,TN,UnitedStates
MarcelloFulchignoni LESIA-Observatoirede Paris,CNRS,UniversitePierreetMarieCurie, UniversiteParisDiderot,France
LeslieGertsch MissouriUniversityofScience andTechnologyRolla,MO,UnitedStates
DanielP.Glavin NASAGoddardSpaceFlight Center,Greenbelt,MD,UnitedStates
ChristineM.Hartzell UniversityofMaryland, CollegePark,MD,UnitedStates
AmandaHendrix PlanetaryScienceInstitute, Tucson,AZ,UnitedStates
CharlesHibbitts JohnsHopkinsUniversity AppliedPhysicsLaboratory,Laurel,MD, UnitedStates
KierenHoward KingsboroughCommunity CollegeoftheCityUniversityofNewYork, Brooklyn,NY,UnitedStates;American MuseumofNaturalHistory(AMNH),New York,NY,UnitedStates
MatthewR.M.Izawa OkayamaUniversity, Misasa,Japan
RobertJedicke UniversityofHawai’i,Institute forAstronomy,Honolulu,HI,UnitedStates
NatashaJohnson NASA’sGoddardSpace FlightCenter,Greenbelt,MD,UnitedStates
JeromeB.Johnson CoupiInc.,Fairbanks,AK, UnitedStates
AntonV.Kulchitsky CoupiInc.,Bedford,NH, UnitedStates
JuliadeLeón InstituteofAstrophysicsofthe Canaries,Tenerife,Spain
HalLevison SouthwestResearchInstitute, Boulder,CO,UnitedStates
JavierLicandro InstituteofAstrophysicsofthe Canaries,Tenerife,Spain
StanleyG.Love NASAJohnsonSpaceCenter, Houston,TX,UnitedStates
MaggieMcAdam UniversityofMaryland,CollegePark,MD,UnitedStates
TimothyMcCoy NationalMuseumofNatural Sciences,Washington,DC,UnitedStates
PhilMetzger UniversityofCentralFlorida, Orlando,FL,UnitedStates
TatsuhiroMichikami KindaiUniversity,Higashi-Hiroshima,Japan
TakaakiNoguchi KyushuUniversity,Fukuoka, Japan
JosephA.Nuth,III NASA’sGoddardSpace FlightCenter,Greenbelt,MD,UnitedStates
CraigE.Peterson TransAstraCorp.,Lakeview Terrace,CA,UnitedStates
CarolRaymond JetPropulsionLaboratory, Pasadena,CA,UnitedStates
DavidM.Reeves NASALangleyResearch Center,Hampton,VA,UnitedStates
AndrewRivkin TheJohnsHopkinsUniversity AppliedPhysicsLaboratory,Laurel,MA, UnitedStates
AlanRubin UniversityofCalifornia Los Angeles,LosAngeles,CA,UnitedStates
PaulSanchez UniversityofColorado,Boulder, CO,UnitedStates
JuanA.Sánchez PlanetaryScienceInstitute, Tucson,AZ,UnitedStates
DanielJ.Scheeres UniversityofColorado, Boulder,CO,UnitedStates
JoelC.Sercel TransAstraCorp.,LakeviewTerrace,CA,UnitedStates
DrissTakir SETIInstitute,MountainView,CA, UnitedStates
MichaelA.Velbel MichiganStateUniversity, EastLansing,MI,UnitedStates;Smithsonian Institution,Washington,DC,UnitedStates
OtisWalton GrainflowDynamics,Inc.,Livermore,CA,UnitedStates
HikaruYabuta HiroshimaUniversity,Hiroshima,Japan
MakotoYoshikawa JapanAerospaceExplorationAgency(JAXA),Sagamihara,Kanagawa, Japan
KrisZacny HoneybeeRobotics,Pasadena,CA, UnitedStates
MichaelE.Zolensky NASAJohnsonSpace Center,Houston,TX,UnitedStates
Xiao-DuanZou PlanetaryScienceInstitute, Tucson,AZ,UnitedStates
Acknowledgments PrimitiveAsteroidsandMeteoriteswas bornasacollaborationamongmembersof NASA’sAsteroidRedirectMission(ARM) FormulationAssessmentandSupportTeam (FAST).Assuch,weownagreatdebtof gratitudetoDanielD.MazanekandDavid M.ReevesatNASA’sLangleyResearch Center,toPaulA.AbellattheJohnsonSpace Center,toMicheleGatesatNASAHeadquarters,andtocountlessotherswho workedindevelopingthismission.Inmany ways,ARMallowedforasteroidexploration andminingtomoveintothetangiblerealm. ARMbroughttogetheradiverseandvery passionategroupofscientistsandengineers whohavemadethestudyofmeteorites,asteroids,andhowtogetusthereintotheir lives’ work.Mostoftheleadingauthorsin thisvolume’schaptersareformermembers oftheARMFAST.Thepresentworkisan efforttointegrate findingsrelevanttoeachof ourcommunitiestothegoalofexploration, withaparticularemphasisonwater-rich asteroids.
Whileorganizinganddevelopingthis book,Ioftenfoundmyselfmusingaboutthe factthatallofmycoauthorshavemuchmore experienceandquali ficationsthanIdo that everyoneoftheirnamesoughttobeonthe coverofthisvolumeinsteadofmine.My admirationandrespectfortheirworkand theircommitmenttospaceexploration hasonlygrownthroughthiseffort.Iam incrediblygratefulandhumbledforthe opportunitythatthisvolumegavemeto learnfromthisextraordinaryteam.Iwould alsoliketothankThePennsylvaniaState
University,ourDuBoiscampus,andthe DuBoisEducationalFoundation.
Therewasalsoagreatdealofwork behindthescenes.Theproposalforthisbook receivedverymanyvaluablecommentsand suggestionsfromthreeanonymous reviewers.Inaddition,ourAcquisitionsEditorMarisaLaFleur,ourEditorialProject ManagersBriannaGarciaandHilaryCarr, ourCopyrightsCoordinatorNarmatha MohanandourPublishingServicesManager DivyaKrishnaKumarhaveworkedtirelesslytoguideusthroughtheElsevierpublicationprocess,answerallmannerof questions,andkeepusontrackforthe durationofthisprocess.Iamextremely gratefulfortheirpatienceandattentionto detail.
Personally,Ihavehadthegoodfortuneto receivethewisecounselandfriendshipof manyveryaccomplishedandgenerous mentors:RalphHarvey,LindsayKeller,Joe Nuth,RhondaStroud,LaurieLeshin,Keiko Nakamura-Messenger,NicholaGutgold, RichardBrazier,PingjuanWerner,Brian Weiner,andDaveDraper.Iwouldliketo thankourcolleague,ChristineFloss,whowe losttoosoon.Youaresodearlymissed.
IwouldalsoliketothankmyPlanetary Sciencecolleaguesformanyinsightfulconversationsandcollaborationsovertheyears: EveBerger,JanaBerlin,GretchenBenedixBland,PhilBland,EmmaBullock,Tom Burbine,PaulBurger,KarenStockstillCahill, NancyChabot,LysaChizmadia,Barbara Cohen,HaroldConnollyJr.,CariCorrigan, KatherineCrispin,LauraCrossey,Jemma
Davidson,JamesDay,BradDeGregorio, TashaDunn,DentonEbel,VeraFernandes, JonFriedrich,LindaWelzenbachFries,Marc Fries,JamesGaier,JulianeGross,Victoria Hamilton,ChrisHerd,RogerHewins,Jim Karner,AlfredKracher,TiborKremic,Zita Martins,AmyMcAdam,HapMcSween, AndreasMorlok,JeffNettles,AnnNguyen, FransRietmeijer,KevinRighter,Minako Righter,RhiannonRose,SaraRussell,Bill Satterwhite,CeciliaSatterwhite,Devin Schrader,JohnScott,ZachSharp,Steven Singletary,CarolineSmith,EricTonui,Allan Treiman,MarkTyra,MichaelWeisberg,Tom Zega,KarenZiegler,andMishaZolotov.
Iwouldliketothankmywonderful familywhohasbeenasourceofunconditionalsupport.Iamdeeplygratefultomy husband,ErichSchienke,whohasalways beenasoundingboardformyideasand projects.Iamsoverythankfulforhisacademicperspectiveontheethicaldimensions ofscienti ficresearch,engineeringdesign, andinnovation.Overtheyears,ourconversationsandsharedreadinglistshave
informedmyviewsontheroleofnear-Earth asteroids,onsustainableuseofmineral resources,andtheroleofinnovationonthe asteroidalmineralresourcesupplychain. ErichwasalsoinchargeofoursonKonrad’ s centrallineandIVinfusionseverynightand caredforKonrad’smanymedicalneeds whileItraveledtotheFASTmeetingsand conferences.KonradwaspartofthedevelopmentofthisbookfromtheFASTapplicationthatIsubmittedfromthebackofan ambulance,theteleconsthatIattendedfrom thebathroomofhisroomatBoston Children’sHospital,tothebookteammeetingsthatIranfromthebackofmycaratthe parkinglotatHersheyHospital.IthankOtto SchienkeandRosemaryNazareneforall theirhelpandkindness.Finally,Ithankmy parentsHermelindaZambranodeAbreu andJoseAbreuVergaraandmysister AlibethAbreudeLeonforyearsandyears ofpatience,support,andadvice.Sinsu ayuda,apoyo,ycariñonadadeestose hubieselogrado. “Soydesierto,selva,nieve, yvolcan.”
CHAPTER ABriefHistoryofSpacecraft MissionstoAsteroidsand Protoplanets BethE.Clark 1,MariaA.Barucci2,Xiao-DuanZou3, MarcelloFulchignoni2,AndrewRivkin4,CarolRaymond5, MakotoYoshikawa 6,LindaT.Elkins-Tanton 7,HalLevison8
1DepartmentofPhysics & Astronomy,IthacaCollege,Ithaca,NY,UnitedStates; 2LESIA-ObservatoiredeParis,CNRS,UniversitePierreetMarieCurie,UniversiteParis Diderot,France; 3PlanetaryScienceInstitute,Tucson,AZ,UnitedStates; 4TheJohnsHopkins UniversityAppliedPhysicsLaboratory,Laurel,MA,UnitedStates; 5JetPropulsionLaboratory, Pasadena,CA,UnitedStates; 6JapanAerospaceExplorationAgency(JAXA),Sagamihara, Kanagawa,Japan; 7SchoolofEarthandSpaceExploration,ArizonaStateUniversity,Tempe, AZ,UnitedStates; 8SouthwestResearchInstitute,Boulder,CO,UnitedStates
Therearehundredsofthousandsofknownasteroids,yetonly14havebeenvisited byspacecraftthusfar,and9ofthoseweretargetsofopportunity.Theremaining fi ve asteroids(Braille,Eros,Itokawa,Vesta,andCeres)werevisitedbyfourmissionsdedicatedtoasteroidresearch(DeepSpace1,NearEarthAsteroidRendezvous Shoemaker [NEAR-Shoemaker],Hayabusa,andDawn,respectively).Infact,ofthese fi veasteroids, VestaandCeresareperhapsbetterde fi nedasprotoplanetsbecauseoftheirsizesand theemergingevidencefortheirphysicalandchemicalevolution.TwomorenearEarthasteroids(NEAs)willbevisitedin2018,followedbyevenmorevisitsin2023 and2030.Thisasteroidmissionchronologyislistedin Table1.1 .Thischapterwilltell thestoryoftheseasteroidmissionsandvisiteachoftheminturntobriefl yreview someoftheexcitingscienceresults.Thestorybeginswithasteroid951Gaspraandcontinuesdownthelistin Table1.1 ,accordingtothetargetasteroidnamepresentedin chronologicalorder.
1.ABRIEFHISTORYOFSPACECRAFTMISSIONS
TABLE1.1 Past,Present(LightGray),andFuture(DarkGray)MissionstoAsteroids YearAgencyMissionAsteroidTargetSpectralClass 1991NASAGalileo951GaspraS 1993NASAGalileo243IdaandDactylS 1996NASANEAR-Shoemaker253MathildeC 1999NASADeepSpace19699BrailleQ 2000NASANEAR-Shoemaker433ErosS 2000NASACassini2685MasurskyUnknown 2002NASAStardust5535AnnefrankS 2005JAXAHayabusa25143ItokawaS 2006NASANewHorizons132524APLS
2008ESARosetta2867SteinsE 2010ESARosetta21LutetiaMorC 2011NASADawn4VestaV 2012CNSAChang’e24179ToutatisS 2015NASADawn1CeresC 2018NASAOSIRIS-REx101955BennuB 2018JAXAHayabusa2162173RyuguC 2023NASALucyJupitertrojansD 2030NASAPsyche16PsycheM
1.1GALILEO:951GASPRA The Galileo spacecraftwaslaunchedbyNASAin1989onatrajectorytoJupiterandtheGalileanmoons.Thespacecraftwasequippedwithanorbiterandanentryprobetomeasurethe atmosphereofJupiter.Onepartofthespacecraftwaskeptrotatingat3revolutionsperminute forstability,andthispartheldsixscientificinstruments,includingseveralformeasuring electromagnetic fieldsandparticles.Thespacecraftwaspoweredbytworadioisotope thermoelectricgenerators(RTGs),harnessingtheenergyfromthedecayofplutonium-238at about500W.LearningabouttheRTGsonGalileo,thepublicgrewveryalarmedandconsideredthemanunacceptablelaunchrisk.Antinucleargroupssoughtacourtinjunctiontoprohibitthelaunch,butthiswasnotsuccessful.ThespacecraftwaslaunchedbytheSpaceShuttle Atlantis,ontheSTS-34missionfromKennedySpaceCenter,onOctober18,1989.
Thespacecraftpayloadconsistedof10scienceinstruments,plustheatmosphericprobe. Theinstrumentsusedfornonparticlesand fieldmeasurementsincludedacamera system,aNear-InfraredMappingSpectrometer(NIMS),anultravioletspectrometer,anda photopolarimeter-radiometer.Themainsciencecamerawasasolidstateimaging(SSI)camera,makingGalileooneofthe firstspacecraftmissionstouseacharge-coupleddevice(CCD)
forimaging.TheNIMSwassensitivefrom0.7to5.2microns.Themissionwasalmost crippled,however,whenthehigh-gainantenna(HGA)onboardfailedtoopenuptoitsoperationalconfiguration,andtheprojectwasthereafterseverelyrestrictedintermsofthevolume ofdatathatcouldbetransmittedtoEarth.Thisproblemwaslargelyovercomebycarefuluse ofdatacompression,thelow-gainantenna(LGA),datastoragebuffers,andfrequentdownlinkwiththeDeepSpaceNetwork,allowing Galileo tocompleteitsmainmissionandachieve mostofitsscienceobjectives.ThespacecraftarrivedatJupiter,itsmaintarget,inDecemberof 1995andbecamethe firstspacecrafttoorbitJupiter.Intotal,themissionoperatedforalmost 14years,sendingunprecedentedcoverageoftheJupitersystembacktoEarth.
OnitswaytoJupiter, Galileo flew(at8km/s)towithin1600kmofmain-beltasteroid951 GaspraonOctober29,1991,obtainingthe firsteverclose-upimagesofanasteroidsurface. BecauseofthelossoftheHGA,thedataweredownlinkedslowlyovera13-monthperiod. The firstimages,obtainedbytheSSIcamera,wererelayedtoEarthinearlyNovember 1991,andconsistedoffourimagestakenatwavelengthsof0.40,0.56,0.89,and0.99microns fromarangeof16,065kmat164m/pixel(Beltonetal.,1992).Playbackofalltheimaging dataobtainedduringthe flybywascompletedinNovemberof1992,andintotal,951Gaspra appearsin57imagesandin7color filters(Helfensteinetal.,1994).Shapemodelsof951 Gaspraindicateabodywithdimensionsof18.2 10.5 8.9kmindiameter,andimages ofthesurfacerevealascarcityofcraterslargerthan1.5kmindiameter(Fig.1.1).
Gaspradoesshowalargenumberofsmallcratersinthehighestresolutionimagingfrom Galileo,andthesurfaceisfurthercharacterizedbyseverallarge flatareasandconcavities, givingGaspraaveryangularappearance(Figs.1.1and1.2).Itisuncertainwhetherthese concavitiesand flatareasresultedfromimpactsorwhethertheyaresurfacefacetsthat were firstexposedwhenGasprabrokeoffitsparentasteroid.
FIGURE1.1 Thispictureofasteroid951Gaspraisamosaicoftwoblack-and-whiteimagestakenbytheGalileo spacecraftatarangeof5300km,10minbeforeclosestapproachonOctober29,1991.
FIGURE1.2 Best(highestspatialresolution)colorcompositeimageofasteroid951Gaspraobtainedbythe Galileospacecraft.
951Gaspraisclassi fiedbasedonground-basedtelescopicobservationsasanS-type asteroid(TholenandBarucci,1989),oneofthemostabundantasteroidclassesintheinner mainasteroidbelt.ThesurfacemineralogyofS-typeasteroidsisrichinolivine,pyroxene, andiron nickelmetal,consistentwithordinarychondrites(OCs)and/orstony-ironmeteorites(Chapmanetal.,1975;Clark,1993).
Analysesofthe Galileo imagesacrossthephaseanglerangeof33 51degreesplacethegeometricalbedoofGaspraat0.22 0.06at0.55microns,consistentwithground-basedtelescopic measurementsandwithidentificationintheS-class(Helfensteinetal.,1994;TholenandBarucci,1989).Colorvariationsofabout 5%(accompaniedbysubtlealbedovariations)are detectedoverthespectralrangeoftheSSIcameraandaresystematicwithrespecttolongitude (Fig.1.2).Somecolorvariationscorrelatedwithfreshercratermorphologyhintatspaceweatheringeffects.Thisisbecausesimplegrain-sizeeffectscannotfullyexplaintheincreasein redness,decreasein1-micronabsorptionbanddepth,anddecreaseinalbedothatareobserved inareasnotaffectedbyrecentcratering(Beltonetal.,1992;Clark,1993;Helfensteinetal.,1994).
1.2GALILEO:243IDA Asteroid243Idawasthesecondasteroidtobevisitedbyspacecraft,asGalileo flewbyin 1993onitswaytoJupiter.243IdaisamemberoftheKoronisfamilyoftheinnermain asteroidbelt.The firstimagesofIdarevealaveryirregularlyshapedobject,withellipsoid dimensionsmeasuring59.8 25.4 18.6kmindiameter.Thisworksouttoameanradius of15.7kmandavolumeof16,100 1900km3 (Beltonetal.,1996)(Fig.1.3).Over18different timeperiods,theSSIrecorded96imagesofasteroidIda,providingcoverageof95%ofthe
1.3GALILEO:DACTYL
AsteroidIdawithitsmoonDactyl,the firstasteroidmoontobediscovered.
asteroidsurface.TheSSIcameraobtainedmulticolorimagesinfourpassbandsatspatial resolutionsupto105m/pixel(Beltonetal.,1996).
243Ida’ssurfacehasbeenexposedtocrateringprocesseslongenoughtohavereached equilibrium,meaningthatthesurfaceisdisturbedbynewimpactsatthesamerateasolder craterserodeaway(duetometeoriteandmicrometeoritebombardment),atleastforcraters withdiametersuptoabout1km(Beltonetal.,1994).ThisindicatesthatIdamayhavea substantialregolith,uptoapproximately100mdeep(Chapman,1996).Severaldozenlarge (40 150macross)boulders(orblocks)havebeendescribedonIda,presumablydepositedby impactejection.Ejectablocksareconsideredtobeevidenceofayoungersurfacebecausethey areexpectedtobeeasilybrokendownbyimpactprocessesatthesurface.Thus,itisprobable thattheejectablockson243Ida’ssurfaceeitherformedorwereexposedrecently(Leeetal., 1996).
243IdaandotherbrightmembersoftheKoronisfamilyareS-typeasteroids.Theobserved spectralsimilaritiesofKoronisfamilymembersandtheobserveddistributionofspinstatesin thisfamilyhavebeeninterpretedtoindicateayoungagefortheKoronisfamily,relativeto theageofthesolarsystem(Binzel,1988).AnalysisofthedatareturnedfromtheGalileo flyby (e.g., Chapman,1996)pointedtoS-typeasteroidslike243IdaasthesourceoftheOCs.
1.3GALILEO:DACTYL Assomeofthe firstimagesof243IdawerebeameddowntoEarth,linebyline,usingthe LGAonboardthespacecraft,itbecameveryclearthatIdawasnotaloneinspace(Fig.1.3). Astheimagesformedinfrontoftheireyes,investigatorsfromtheGalileoscienceteamwere astonishedto findthatasmall,irregularlyshapedmoonhoveredcloseto243Ida(Belton etal.,1996).Thisdiscoveryisthe firstconfirmeddetectionofanasteroidsatellite.Subsequently namedDactyl(aftertheDactyls creaturesthatinhabitedMountIdainGreekmythology), theorbitdeterminationofIda’ssmallsatellitepermittedveryprecisemassanddensity
FIGURE1.3
determinationoftheasteroid(see Burns,2002).Dactylissmall,relativetoIda,androughly sphericalwithadiameterof1.4km.
MeasurementsofDactyl’sorbitallowedcalculationsof243Ida’smassas4.2 0.6 1019 g and2.6 0.5g/cm3 for243Ida’sbulkdensity(Beltonetal.,1996).243Ida’sbulkdensityis lowcomparedwiththeaveragedensityofOCs,whichrangesfrom3.0to3.8g/cm3 (WilkisonandRobinson,2000;Carry,2012).243Ida’sdensitywouldimplythat243Idahas moderatetolowFe Nimetalcontent,unlessthebulkporosityisunusuallyhigh.OCsare dividedintoseveralgroupsbasedontheirFecontent,whichaffectstheirbulkdensities suchthattheHchondriteshavethehighestdensitiesandthehighestvolumesofFe Nimetal. 243IdaandDactylaresimilarenoughincolorandbrightnesscharacteristicsthatacommon originisindicated.Infact,thereisageneralconsensusthatthesetwobodies(IdaandDactyl) originatedfromthecatastrophicbreakupoftheKoronisparentbody.Itisalsopossiblethatthe formationofasteroid satellitesystemsmayberelativelycommoninsuchevents.Afterthe discoveryofDactyl,moreasteroidswerediscoveredtohavemoonsusingground-basedopticalandradartelescopes.Thesecondasteroidmoonwasdiscoveredaround45Eugeniain 1998(Merlineetal.,2002).Morethan320minorplanetsarenowknowntohavesatellites.
1.4NEAR-SHOEMAKER:253MATHILDE LaunchedonFebruary17,1996,theNEAR-Shoemakerspacecraftwasthe firstDiscovery Programmission,anditincorporatedapayloaddesignedtoconductthe firstdetailedorbital investigationofanasteroid,NEA433Eros(Veverkaetal.,2000).TheNEAR-Shoemakercraft wasaroboticspaceprobedesignedbytheJohnsHopkinsUniversityAppliedPhysicsLaboratory.Thespacecraftcarriedan X-ray/gamma-rayspectrometer,amultispectralimaging(MSI) camera fittedwitha CCDimaging detector,anear-infraredimagingspectrograph(NIS),a laserrangefinder,anda magnetometer.Aradioscienceexperimentwasalsoperformedusing thespacecrafttrackingsystemtomapthe gravity fieldoftheasteroid.Thetotalmass oftheinstrumentswas56kg,andtheyrequired80Wpower.AtlaunchfromCapeCanaveral,thespacecraftweighedabout800kg.
Onthewayto433Eros,NEAR flewwithin1212kmofmain-beltasteroid253Mathildeon June27,1997(Veverkaetal.,1997).Thedataobtainedduringthe flybyinclude534frames fromtheMSIcamera(Fig.1.4);however,toconservepowertheMSIwastheonlyinstrument turnedon.Thehighestresolutionimageswere160m/pixel,obtainedduringclosest approach.253Mathildehasameandiameterof53 2.6km(Veverkaetal.,1997).253 Mathildewasobservedataphaseanglerangeof40 136degrees,allowingcraterstostand outinreliefacrossthesurface.Themostprominentcrater,namedKaroo,isapproximately 33kmindiameter,presentingevidenceofaremarkablysevereimpactthatdoesnotseem tobeaccompaniedbylarge-scalefracturing(Veverkaetal.,1997).Twootherlargecraters, Ishikari(29.3km)andDamodar(20km)(Fig.1.5),havediametersthatrivaltheasteroid’ s averageradius(Veverkaetal.,1999).Theimpactsappeartohavespalledlargevolumes offtheasteroid,assuggestedbytheangularedgesofthecraters(Veverkaetal.,1999).No differencesinbrightnessorcolorwerevisibleinthecraters,andtherewasnoappearance oflayering,sotheasteroid ’sinteriormustbeveryhomogeneous.Thereareindicationsofmaterialmovementalongthedownslopedirection.
FIGURE1.4 Asteroid253MathildeasimagedbytheNEAR-Shoemakerspacecraft.
FIGURE1.5 Aviewofa20-kmcrateron253Mathilde.
253Mathildewasclassifiedbasedonground-basedspectrophotometryasaC-typecarbonaceousasteroid(Chapmanetal.,1975).AnalysisoftheMSIimagesplacetheasteroid’ sgeometricalbedoat0.047 0.005at0.55microns,consistentwithacompositionsimilartothe darkestcarbonaceouschondrite(CC)meteorites,suchastheCMchondrites(Clarketal., 1999).Afterclosestapproach,whenthespacecraftwasreceding,multicolorhemispherical coveragewasobtainedatabout500m/pixelresolution,usingMSI’ssevencolor filters, coveringthespectralrangeof0.4 1.1microns.Thesedataalsoindicateasurfacespectrum consistentwithlow-albedoCCsanddonotshowmarkeddeviationsincoloracrossthesurfaceinthelow-resolutioncolormosaics.
253Mathildeisknowntohaveaveryslowrotationperiodof17.4days(Mottolaetal., 1995),andtheNEAR flybywastoofasttoobservetheasteroidrotatemorethanafew
degrees.However,theMSIimagesallowedashapedetermination,withuncertaintiesdominatedbytheunseenhemisphere(Veverkaetal.,1997).Theresultingvolumetogetherwith radiotrackingdatathatprovidedanestimateofthemassof253Mathildeyieldmeandensity valuesbetween1.1and1.5g/cm3.Thisislessthanhalfoftheaveragedensitymeasuredfor CMmeteorites,indicatingthatMathilde’sinteriorstructuremaybeporousandunderdense (Veverkaetal.,1997).Subsequentstudieshaveestimatedthattomatchthedensityof253 Mathildewithaknowntypeofgroupofchondrites,253Mathildewouldhavetohavea porositygreaterthan40%(BrittandConsolmagno,2000).
1.5DEEPSPACE1:9969BRAILLE The firstlaunchofNASA’ s NewMillenniumProgram ,dedicatedtotestingadvancedtechnologies,was DeepSpace1 (DS1).Themainobjectiveofthemissionwastechnologydemonstration,includingautonomousnavigationandsolarelectricpropulsion.Itstargetwasthe Mars-crossingasteroid9969Braille,andthe flybyonJuly29,1999wasapartialsuccess.Technicaldifficultiesledtoa flybydistanceof26kmfor9969Brailleratherthantheplanneddistanceof240m.Aspartofanextendedmission,thespacecraftwasthentargetedtoward Comet19P/Borrelly(RaymanandVarghese,2001).
TheonlyinstrumentreturningdataduringtheBrailleencounterwastheMiniature IntegratedCameraandImagingSpectrometer(MICAS).Twomedium-resolutionCCD imageswerereturnedbyMICASbeforeclosestapproachataphaseangleof98degrees (Fig.1.6),aswellasthree1.25 2.6 mmspectraataphaseangleof82degrees(Fig.1.7).
Theinfrared(1.25 2.6 m m)spectrafrom DS1 indicatea2-m mabsorptionand1.6- mm re fl ectancepeak,typicalofsilicateasteroidsandsimilartopyroxeneminerals. Buratti etal.(2004) favoredaQ-typeinterpretationfor9969Braille ’sspectrum,withOCsthe mostlikelyanalog. Lazzarinetal.(2001) alsofoundastrongspectralsimilaritytotheLtypeOCsfrom0.45to0.82 m mspectroscopy,withappropriateasteroidclassesranging fromtheVtypetoQtype.However,thegeometricalbedoreportedfor9969Braille
FIGURE1.6 ImagesofBraille(leftandcenter)andsuperresolutioncombinationofthetwo(right)takenbythe MiniatureIntegratedCameraandImagingSpectrometerinstrumentonDeepSpace1. ImagecourtesyofNASA/JPLCaltech.
FIGURE1.7 Acombinationofground-basedandMiniatureIntegratedCameraandImagingSpectrometer (MICAS)dataforBraille,showingthespectralshapeofBraillefrom0.4to2.6 mm. FigurereproducedfromBuratti,B.J., Britt,D.T.,Soderblom,L.A.,Hicks,M.D.,Boice,D.C.,Brown,R.H.,Meier,R.,Nelson,R.M.,Oberst,J.,Owen,T.C.,Rivkin, A.S.,Sandel,B.R.,Stern,S.A.,Thomas,N.,Yelle,R.V.,2004.9969Braille:deepSpace1infraredspectroscopy,geometric albedo,andclassification.Icarus167,129 135.
(0.34)byBurattietal.wasnotedas “unusuallyhigh” andperhapsindicatesarelatively freshsurfaceormaterialthatdiffersfromthatrepresentedintheEarthlycollectionofmeteorites. Oberstetal.(2001) usedspacecraftdataandground- basedphotometrytoestimate asizeof2.1 1 1kmindiameterforBraille,withphotometricpropertiesandgeometric albedosimilartoasteroid(4)Vesta.
1.6NEAR-SHOEMAKER:433EROS Basedonground-basedtelescopicobservations,theAmorNEA433Erosisspectrally classi fiedasanS-typeasteroid,meaningthesurfacemineralogyisdominatedbysilicates suchaspyroxeneandolivine,and,possibly,metallicFe Ni(Chapmanetal.,1975;Chapman, 1996).Duringopposition,Erosisarelativelybrightasteroidinthesky(reachingupto eighthand,rarely,seventhvisualmagnitude accordingtoephemeriscalculations).With ameaneffectivediameterofapproximately17km,ErosisthesecondlargestNEA,making itanimportantmemberoftheNEApopulation.Inaddition,dynamicalstudiesshowthat
asanAmor(Mars-crosserasteroid),Erosisexpectedtoremaininitscurrentorbitforonlyafew hundredmillionyearsbeforetheorbitis perturbed bygravitationalinteractions,atwhich pointErosmayevolveintoan Earth-crosser (Micheletal.,1996).
TheNEAR-Shoemakerspacecraftapproachedasteroid433Erosfororbitinsertioninearly Januaryof1999.However,aspacecraftpropulsionanomalyoccurredandsuddenlythe first Erosencounterbecamea flybywithahurriedlypreparedobservationsequencecarriedout overthewinterholidaysin1998.TheclosestapproachwasonDecember23,1998,when thespacecraft flewwithin3800kmoftheasteroid.Fortunately,observationsthatwere veryimportantforthesubsequentplanningoftheorbitalmissionwereobtainedduring the flyby,allowingestimatesofthemass,shape,andspinstateofasteroid433Eros.After ayearlongnavigationaltourbacktowardEros,NEAR-Shoemakerwasinsertedsuccessfully intoorbitaround433ErosonFebruary14,2000.
Themajorityofthe433Erosimagingdatawereobtainedfroma200-kmterminatororbitat aphaseangleofabout90degreesandaspatialresolutionofabout25m/pixel.During approach,however,thenear-infraredspectrometer(NIS)obtainedspectrafrom0.8to2.4 micronsatspatialresolutionsofabout1kmperspectrumatphaseanglesassmallas1 degree.Becauseshadowsareminimized,lowphaseangleconditionsareidealforspectral mapping.
Theorbitalpathof433Erosrangesfrom1.13to1.73AU,crossingthepathofMars,andthe orbitalperiodis1.76Earthyears 433Eros’ rotationpoleisinclined88degreestothenormal ofitsorbitalplane,suchthatwhenNEAR flewbyinDecemberof1998,thesouthernlatitudes oftheasteroidwereinsunlight.ByFebruaryof2000,thesunilluminatedthenorthern latitudesandthenorthpolarregion.Bycombiningcoverageofthesouthernhemisphere obtainedduringtheDecember1998 flybywiththatofthenorthernhemisphereobtained in2000,thescienceteamwasabletoconstructacompletethree-dimensionalmodelofthe shapeof433Eros(Thomasetal.,2001;Zuberetal.,2000).433Erosisahighlyirregularly shapedbody,withdimensions34 13 13kmindiameter,achallengingshapeforshape modeling,cartography,orglobalmosaics(see Fig.1.8).Since2001, Gaskelletal.(2008) haveemployedatechniquethatcombinesstereoandphotoclinometryanalysisofimaging datatopublishaverywidelyusedshapemodelofErosthatcapturesthesmallesttopographicreliefvisibleinimagingdata(Gaskelletal.,2008).
VisibleonthesurfaceofErosarecraters,blocks,ridges(alsocalled “dorsa”),slumps, slides,andremnantscarsofoldercraters(e.g.,CharloisRegio).Manyoftheselandforms areconsistentwiththeideathattheregolithonErosispartlymobile itmovesaroundon thesurface,propelled,byacombinationofgravitationalandnongravitationalforces(Cheng etal.,2007;Veverkaetal.,2001).Oneofthemostsurprisinglandformsfoundon433Erosare theso-called “ponds ” ofrelatively fine-grained,sorted,regolithmaterialsthatoccupy gravitationallowareas,clusteredwithin30degreesof433Eros’ equator(see Fig.1.9).These ponddepositsappeartobesmoothdowntoaspatialresolutionof1.2cm/pixel.Such depositshadnoprecedentinanylunarorasteroidalimageseverobtainedbyspacecraft. Robinsonetal.(2001) findthatthecolorpropertiesofponddepositsaredistinctlydifferent fromthoseoftheambientsurroundings.Thepondsarerelativelyblue,relativelybright,and showadeeper1-micronabsorptionbandduetoolivineandpyroxene.Thesecolorproperties maybeexplainedbyasimplegrain-sizeeffectorbyaseparationoffreshermaterialfroma moreweatheredbackgroundorevenbyaconcentrationofsilicate-richmaterialfromsilicate
FIGURE1.8 Adramatichighphaseangleviewofasteroid433EroscapturedbytheNEAR-Shoemakerspacecraft in2000. ImagebyNASA/JHU-APL/CornellUniversity.
FIGURE1.9 Thesmooth “ponds” of finematerialsonasteroid433Erosmaybeevidenceofelectrostaticlevitation anddownslopemovementand/orseismicshakingcausedbyimpactsintoafracturedsurface(Robinsonetal.,2001; Richardsonetal.,2005).Thepondsshownherearelocatedonalowsurfacegravity “ nose ” oftheasteroid.(A)MET 155888598,179.04W,2.42S,0.55m/pixel.(B)MET155888731,183.88W,3.21S,0.63m/pixel. Reproducedfrom Richardson,J.E.,Melosh,H.J.,Greenberg,R.J.,O’Brien,D.P.,2005.Theglobaleffectsofimpact-inducedseismicactivityon fracturedasteroidsurfacemorphology.Icarus179,325 349;NASA/JHU-APL/CornellUniversity.
plusmetallicironregolith(wherelessmetallicironresultsinbrighter,bluermaterial) (Robinsonetal.,2001;Rineretal.,2008).Robinsonetal.discusspossibleformationscenarios thatcouldexplainthemorphology,color,andlocationsofthesedeposits.Theirfavored explanationiselectrostaticlevitationfollowedbydownslopemovement,resultingin
concentrationsof finerparticlesingravitationallows.Asubsequentstudyby Richardson etal.(2005) favorsimpact-inducedseismicshakingofafracturedsurface. Richardsonetal. (2005) alsopresentevidencethattheponds(andthecraters)on433Erosareconsistent withanexposureageof400 200Myrandlessthanameterofmobilizedregolithatthe surfaceof433Eros.
Clarketal.(2001) combineimagingandspectroscopyobservationsof433Eros’ largest crater,Psyche,a5.3kmcrater,toinvestigatesurfaceprocessesinanareaofhighalbedo contrast.Psycheandothercratersexhibitdistinctivebrightnesscontrastpatternsthatare bestexplainedbydownslopemotionofdarkregolithmaterialoverlyingasubstrateof brightermaterial.Atspatialscalesof620mperspectrum,craterwallmaterialsexhibitalbedo contrastsof32% 40%,withassociatedcolorcontrastsofonly4% 8%.Severalpossible causesareexaminedin Clarketal.(2001),andtheonlymechanismsthatexplainallthe observationsareanenhancementofadarkspectrallyneutralcomponent(suchastroilite orcarbon)and/orlunar-likeopticalmaturation(spaceweathering).Forafullexploration ofspaceweatheringonasteroidsurfaces,see Clarketal.(2002). Rineretal.(2008) alsopresent acomprehensivestudyofthecolorimagingpropertiesofErosand findthatbrightmaterials, averageregolith,anddarksoilsallfallonaspectralmixinglinethatisconsistentwithspace weatheringeffects.
McCoyetal.(2001) attemptedtosynthesizemineralogicalandchemicalresultsfromthe X-ray/gamma-rayspectrometer,themultispectralimager,andthenear-infraredspectrometerontheNEAR-Shoemakerspacecraft.Theseworkersfoundthatthebestmatchfor433 ErosisanOCmeteoritethathasbeenalteredatthesurfaceoftheasteroidorperhapsaprimitiveachondritethatwasderivedfromOCmaterial(McCoyetal.,2001).
OnFebruary12,2001,whenNEAR-Shoemakerhadsuccessfullycompleteditsyearof investigating433Erosfromorbit,themissionendedwithagentlecontrolleddescentof thespacecraftdowntothesurfaceof433Eros,returningextremelyhighspatialresolution imagesuptothelastmomentofpossiblecontactwiththeEarth(Veverkaetal.,2001).In all,70descentimageswereobtained.Thepictureswereobtainedwhenthespacecraftwas ascloseas120m,revealingfeaturesassmallas1cmacross.Descentimagemosaicsreveal alandingareawithveryfewsmallcratersandanabundanceofejectablocks(someboulders mayshowevidenceoffracturing seethemosaicofthelastfourimagesin Fig.1.10).
Thedescenttrajectorywasdesignedtomaximizethenumberofimagesreturnedfrom altitudesbelow5km,whileminimizingtheimpactvelocity.Todownlinkthedata,the HGAhadtomaintainconstantcontactwiththeEarth.BecausetheNEAR-Shoemaker spacecrafthad fixedradioantennas,thislimitedthepossibilitiesforpointingthecamera. Simulationsshowedthatdescenttrajectoriestolandingsitesalongthesmalleraxisof433 Eroswerelesssensitivetospacecraftorbitdeterminationtimingerrorsthantothoseon thelongaxis,hencethelongitudeofthetouchdownsitewasselectedsothatthespacecraft couldmaintaincontinuousEarthcontactwiththeimagerpointedat433Erosduringdescent (Veverkaetal.,2001).
Dr.JosephVeverkatellsthedescentstory: “Beforethedescent,theNEARspacecraftwasin anear-circular34kmby36kmretrogradeorbit.Ade-orbitburnof2.57m/sperformedon12 Februaryat15:14UTCchangedtheorbitinclinationfrom180degreesto135degreesrelative to433Eros’ equator.Fouradditionalbrakingmaneuverswerepre-programmedtoexecuteat fixedintervalsduringthe4.5-hcontrolleddescent.ThetimeofimpactfromDopplertracking
FIGURE1.10 Thelastfourframesobtainedduringdescentandlandingatasteroid433Eros.Notethatthelast frameisonlyabouthalfaslargeasthepreviousframe thisisbecausethespacecraftlikelytoucheddownduringthe lastimageframeexposure,buryingandobscuringthecameraapertureintothesurfacematerial.Imagenumbersare indicatednearesttherelevantframe. ReproducedfromVeverka,J.,Farquhar,B.,Robinson,M.,Thomas,P.,Murchie,S., Harch,A.,Antreasian,P.G.,Chesley,S.R.,Miller,J.K.,OwenJr,W.M.,Williams,B.G.,Yeomans,D.,Dunham,D.,Heyler,G., Holdridge,M.,Nelson,R.L.,Whittenburg,K.E.,Ray,J.C.,Carcich,B.,Cheng,A.,Chapman,C.,BellIII,J.F.,Bell,M.,Bussey, B.,Clark,B.E.,Domingue,D.,Gaffey,M.J.,Hawkins,E.,Izenberg,N.,Joseph,J.,Kirk,R.,Lucey,P.,Malin,M.,McFadden,L., Merline,W.J.,Peterson,C.,Prockter,L.,Warren,J.,Wellnitz,D.,2001.ThelandingoftheNEAR-Shoemakerspacecrafton asteroid433Eros.Nature413,390 393;NASA/JHU-APL/CornellUniversity.
wasdeterminedtobe19:44:16UTC.Post-landinganalysisindicatedaverticalimpactvelocity of1.5to1.8m/sandatransverseimpactvelocityof0.1ms-11ms-1 to0.3m/s.Thetouchdown sitewasdeterminedtobeat35.78S,279.58W,about500mfromthenominalsite.” (Veverka etal.,2001).
However,since2001,therehasbeenarenewedefforttodeterminetheexactlocationofthe landingsiteusingreconstructedpointinginformation,andasaresult,thelocationofthe final landingsitehasbeenupdatedandpinpointedtobeinacraterat41.626S,80.421E (x ¼ 0.82 0.01,y ¼ 4.85 0.01,z ¼ 4.37 0.01),about200msouthofthepreviousestimate(Barnouinetal.,2012).
1.7CASSINI HUYGENS:2685MASURSKY TheCassini Huygensmission,launchedin1997towardtheSaturnsystem,wasajoint effortofNASA,theEuropeanSpaceAgency(ESA),andtheItalianSpaceAgency(ASI). TheCassini Huygensspacecraftwasequippedwith18instruments,12ontheCassiniorbiter and6ontheHuygensprobe(foradetaileddescriptionoftheinstrumentpanoplies,seethe specialissuesof SpaceScienceReviews 104(2002)and114 115(2004)).
