,illu/ration3 ,cov]3 ,a cyl9drical      
projection ( ,jupit]'s      atmosph]e 0 
made f t5 color images tak5 by ,voyag]  
#a dur+      a s+le t5-h\r rotation ( ! 
planet4        ,illu/ration3 ,a         
comput]-g5]at$ mosaic ( ,voyag] #a      
pictures      %[+ ,jupit] f directly    
bel[ ! s\? pole4 ,?is view %[s          
features z f> nor? z #bj degrees        
latitude4 ,! black area at !      ,pole 
results f miss+ in=mation4              
,voyag]                                 
,enc\nt]s                               
,jupit]                                 
,july #aigi                             
,,nasa                                  
,national ,a]onautics &                 
,space ,adm9i/ration                    
,,cont5ts        ,=eword                
#c    ,introduction                     
#d    ,images ( ,jupit] & ,its          
,satellites                             
#f    ,! ,voyag] ,mission               
#cg    ,sci5tific ,highlights           
#ci        ,jupit]                      

#ci        ,amal!a                      
#ci        ,io                          
#ci        ,europa                      
#ci        ,ganym$e                     
#ci        ,calli/o                     
#ci        ,! ,magnetosph]e             
#dj        ,sci5tific inve/igations ( ! 
,voyag] mission                 #dj     
,illu/ration3 ,a ,titan_/,c5taur rocket 
s]v$ z ! laun* vehicle      = ,voyag] & 
0 ! la/ plann$ use ( ?is type ( laun*   
vehicle prior to ! era ( ! ,space       
,transportation ,sy/em 7,%uttle         
,orbit]74                               
,=eword      ,9 late summ] ( #aigg1 !   
,unit$ ,/ates laun*$ two unmann$ ,voyag]
  spacecraft on an ext5sive             
reconnaissance ( ! out] planets1 a      
decade-long odyssey t c\ld take !m to #c
 planets & z _m z #ah  planet>y         
satellites4 ,! fir/ enc\nt] 0 ) ! giant 
,jovian  planet>y sy/em1 #fde million   
kilomet]s 7#djj million miles7 away4    
,pass+ by ,jupit] & its complex         
satellite sy/em 9 #aigi1 ! ,voyag]      

spacecraft h collect$ & return$ to ,e>? 
an enorm\s am\nt (  data & in=mation t  
may prove to be a key/one 9 und]/&+  our
 sol> sy/em4    ,?is publication        
provides an e>ly look at ! ,jovian      
planet>y sy/em  & conta9s a select$     
sample f ! m ?an #cj1jjj images         
collect$ dur+ ?is phase ( ! ,voyag]     
mission4 ,:ile ,voyag]  a*iev$ an       
impressive record ( accompli%m5ts1 full 
realization (  ! sci5tific value ( ?is  
program mu/ await ! rema9+ ,voyag]      
enc\nt]s ) ,saturn & p]haps ,uranus1 & a
 detail$ analysis (  ! data f all !     
spacecraft inve/igations4               
,rob]t ,a4 ,fros*1 ,adm9i/rator         
,national ,a]onautics & ,space          
,adm9i/ration                           
,introduction      ,9 ,m>* #aigi ,voyag]
 #a swept pa/ ,jupit]1 photograph+ bo? !
 giant  planet & five ( its moons4 ,f\r 
mon?s lat]1 a companion spacecraft1     
,voyag] #b1 made a simil> enc\nt]4 ,n[1 
) ,jupit] rec$+ beh9d  !m1 bo?          
spacecraft are head$ t[>d ! out] rea*es 

( our sol>  sy/em4 ,9 ,novemb] #aihj1   
,voyag] #a w fly pa/ ,saturn4 ,voyag]   
#b1  travel+ at sl[] spe$s1 w rea* !    
same way /ation 9 ,augu/  #aiha4 ,beyond
 !re1 ! it9]>y is less c]ta94 ,9 ,janu>y
 #aihf1  eight ye>s aft] its dep>ture f 
,e>?1 ,voyag] #b may sail )9  range (   
,uranus1 tak+ closeup pictures ( t      
di/ant planet = !  fir/ "t4 ,long aft]  
!y h exhau/$ _! fuel supplies & _!      
radios h fall5 sil5t1 bo? spacecraft w  
cont9ue _! trav]se  ?r\gh space & beyond
 our sol> sy/em1 on an endless j\rney4  
,illu/ration3 ,an ,apollo #ab a/ronaut  
retrieves ,surveyor #c h>dw>e      =    
,e>? laboratory analysis aft] #cj mon?s 
exposure on lun>      surface4          
,illu/ration3 ,vik+ ,l&] #b surveys !   
b\ld]-/rewn ,utopian      ,pla9 & r$di% 
sky ( ,m>s4    ,prelim9>y results ( !   
,voyag] enc\nt]s ) ,jupit] are pres5t$  
9 ?is booklet4 ,z y exam9e ! pictures1 y
 w be p>ticipat+  9 a revolution>y      
j\rney ( exploration4 ,liv+ 9 a society 
:]e  _m accompli%m5ts & products are    

bill$ z 8extraord9>y10  8/up5d\s10 8once
 9 a lifetime10 or 8unique10 we         
sometimes lose our  p]spective4         
,condition$ to hyp]bole1 we fail to     
recognize ^?  advances t are truly      
exceptional4 ,we ne$ a hi/orian's       
vantage po9t  to id5tify ! ev5ts t c    
lit]ally *ange ! c\rse (  civilization4 
,s x is t e /ud5t ( hi/ory recognizes ! 
importance ( ! ,r5aissance1 an          
extraord9>y "t :5 man look$  outw>d1    
rea*+ beyond ! traditions ( ! pa/ to    
/udy 8 place  9 ! natural _w4 ,! results
 7 app>5t 9 art1 ar*itecture1  &        
lit]ature1 9 new philosophic &          
gov]nm5tal sy/ems1 & 9 !  /agg]+        
sci5tific revolution exemplifi$ by      
,galileo's fir/  exam9ation ( ! heav5s )
 a telescope1 & 9 8 /ubborn support  ( !
 h]etical ass]tion t ! ,e>? 0 n ! c5t] (
 !  sol> sy/em4    ,hi/orians writ+ a   
hundr$ or two hundr$ ye>s f n[ may well 
look  on ! latt] "p ( ! tw5tie? c5tury z
 ano!r turn+ po9t 9  civilization4 ,= ! 
fir/ "t1 we explor$ beyond ,e>?--fir/ ! 

,moon1 !n ! neighbor+ planets1 & f9ally 
! out]mo/ planets1  ! v fr+e ( our sol> 
sy/em4    ,h[ w ! hi/orian evaluate ?is 
p]iod ( exploration8 ,fir/1  p]haps1 he 
w describe ! ,apollo program z a        
vision>y example (  great coop]ative    
v5tures t c be accompli%$ by _m         
individuals1  private companies1 &      
gov]nm5t in/itutions4 ,he w describe !  
subsequ5t space v5tures t weave a fabric
 ( coop]ation &  goodwill betwe5        
nations4    ,he w po9t out !            
te*nological advances incorporat$ 9     
unmann$  spacecraft1 sophi/icat$ robots 
able to control _! own activities  &    
solve _! own problems4 ,he w m5tion !   
revolution 9  microelectronics--! art ( 
fabricat+ complex electrical control    
circuits s small ! eye _c p]ceive !m1 a 
revolution accel]at$  by ! requirem5t to
 cons]ve weight & g5]ate p]=mance 9     
int]planet>y spacecraft4 ,he w po9t to !
 introduction ( new  products1          
p>ticul>ly 9 areas ( communication1     
m$ical treatm5t1 &  en]gy conv]sion4    

,illu/ration3 ,galileo orbit] & probe   
mission to ,jupit] 9 #aihe      w exp&  
^u ! ,voyag] inve/igations ( ! ,jovian  
sy/em4        ,illu/ration3 ,a sol>     
electric propulsion spacecraft w\ld     
eject      an in/rum5t$ probe t[>d      
,halley's comet 9 #aihf & cont9ue on    
to r5dezv\s ) ano!r comet1 ,tempel #b4  
,turn+ 8 att5tion to ! environm5t1 !    
hi/orian w almo/  surely sugge/ t ! fir/
 widespread realization ( ! fragile     
natural balances on ,e>? came at a "t :5
 we 7 fir/ able to see  our ,e>? 9 its  
entirety4 ,! impact ( a picture ( ,e>? f
 deep  space1 a lum9\sly blue globe     
surr\nd$ by d>kness1 has probably be5  m
 p]suasive ?an l5g?y treatises describ+ 
! complex ways 9  :i* our sy/em ( rocks1
 plants1 animals1 wat]1 & air is        
int]relat$4 ,on a m practical level1 !  
hi/orian w po9t to !  new und]/&+ ( our 
t]re/rial environm5t4 ,! composition &  
/ructure ( o!r planet>y atmosph]es--on  
,v5us1 ,m>s1 &  ,jupit]--provide        
important clues to :at may happ5 9 our  

own  atmosph]e1 especially if we disrupt
 ! *emical composition4 ,/udy (  !      
primitive cru/s ( ! ,moon1 ,m>s1 &      
,m]cury p]mits u to  recon/ruct ! fir/  
billion ye>s ( ,e>? hi/ory1 a "t :5     
*emical elem5ts 7 be+ conc5trat$ 9      
activity ultimately lead+  to ! =mation 
( important ore deposits4 ,unmann$      
spacecraft missions  to ! ,sun increase 
our und]/&+ ( t mo/ fundam5tal ( all    
en]gy s\rces1 pav+ ! way = ! effici5t   
conv]sion ( sol>  en]gy into _m         
practical applications1 & releas+ u f   
dep5d5ce on ev]-decreas+ res]ves (      
fossil fuels4 ,spacecraft  circl+ ! ,e>?
 /udy ! upp] atmosph]ic processes t play
 major  roles 9 controll+ our wea!r4 ,^!
 same spacecraft look d[n on  ,e>?1 aid+
 u ) increas+ly accurate =eca/s ( wea!r 
&  crop productivity4    ,look+ beyond  
matt]s ( te*nology & ! environm5t1 !    
hi/orian  may cite ! latt] "p ( !       
tw5tie? c5tury z a "t ( explosive       
exploration1 comp>able to ! #ae? & #af? 
c5tury exploration ( !  ,e>?'s oceans & 

! di/ant l&s t b\nd$ !m4 ,9 a s5se1     
exploration--:e!r x is physical or      
intellectual--provides its own  rew>ds4 
,! ,unit$ ,/ates has always be5 a nation
 t moves =w>d1  pu%+ back ! fronti]s ( !
 ,we/1 pu%+ back ! fronti]s (  social & 
economic developm5t1 & n[ pu%+ back !   
fronti]s (  space4 ,x is arguable t ?is 
_s ( exploration is indisp5sable  to a  
vigor\s society1 & t any society t      
ceases to explore1 to  inquire1 & to    
/rive is only a few ye>s f decl9e4    ,&
 s ! hi/orian may recall ! e>ly days (  
lun> exploration1 !  ,apollo project1 ! 
l&+ ( unmann$ ,vik+ spacecraft on ,m>s1 
&  ! enc\nt]s ( ,voyag] spacecraft )    
,jupit] & ,saturn z !  fir/ /eps 9 a    
su/a9$ program ( space exploration--a   
program t  is pr(\ndly *ang+ man's      
p]spective ( himself1 ( ! ,e>?1 &  ( !  
l>g] cosmos beyond4                     
,?omas ,a4 ,mut*1 ,associate            
,adm9i/rator = ,space ,sci5ce           
,national ,a]onautics & ,space          
,adm9i/ration                           

,images ( ,jupit] & ,its ,satellites    
,! date ( ea* photograph & ! di/ance ( !
 spacecraft f    ! planet or satellite  
are includ$ ) ea* picture4              
,illu/ration3 #b_/e_/gi    #bh4d million
 km    7#ag4f million mi7        ,jupit]
 is ! l>ge/ planet 9 our sol> sy/em1 ) a
 diamet]      #aa times t ( ,e>?4       
,jupit] rotates v quickly1 mak+ "o      
full rotation 9 j "u t5 h\rs4 ,compos$  
prim>ily (      hydrog5 & helium1       
,jupit]'s colorfully b&$ atmosph]e      
displays      complex patt]ns highlight$
 by ! ,great ,r$ ,spot1 a l>ge1         
circulat+ atmosph]ic di/urbance4 ,?ree (
 ,jupit]'s #ac kn[n      satellites are 
also visible 9 ?is ,voyag] #a           
photograph4 ,!      inn]mo/ l>ge        
satellite1 ,io1 c be se5 9 front (      
,jupit] &      is di/+ui%$ by its       
bright1 orange surface4 ,to ! "r (      
,jupit] is ,europa1 also v bright b )   
fa9t] surface      m>k+s4 ,calli/o is   
b>ely visible b5ea? ,jupit]4 ,^!        
satellites orbit ,jupit] 9 ! equatorial 

plane & appe> 9 _!      pres5t position 
because ,voyag] is above ! plane4       
,illu/ration3 ,jupit]'s atmosph]e is    
und]go+ con/ant *ange1      pres5t+ an  
ev]-%ift+ face to obs]v]s4 ,! ,great ,r$
 ,spot      has und]gone ?ree major     
p]iods ( activity 9 ! la/ #ae ye>s4     
,^! images ( ,jupit]1 tak5 by ,voyag] #a
 7top7 & ,voyag] #b      7bottom7 almo/ 
f\r mon?s ap>t1 %[ t cl\d movem5t 9 !   
,jovian atmosph]e is n uni=m because w9d
 spe$s v>y at      diff]5t latitudes4 ,=
 example1 ! :ite ovals :i* appe> bel[   
! ,great ,r$ ,spot dramatically %ift$   
betwe5 ,janu>y & ,may1 !      "t int]val
 betwe5 ^! two pictures4 ,! bright      
8tongue0      ext5d+ upw>d f ! ,great   
,r$ ,spot int]act$ ) a ?91      bright  
cl\d above x t _h travel$ twice ar\nd   
,jupit] 9 f\r      mon?s4 ,eddy patt]ns 
to ! left ( ! ,great ,r$ ,spot1 :i* h   
be5 obs]v$ s9ce #aige1 appe> to be      
break+ up4        ,illu/ration3         
#a_/bd_/gi    #dj million km    7#be    
million mi7        ,illu/ration3        

#e_/i_/gi    #df4c million km    7#bh4g 
million mi7        ,illu/ration3        
#b_/be_/gi    #i4b million km    7#e4g  
million mi7        ,! ,great ,r$ ,spot  
on ,jupit] is a trem5d\s atmosph]ic     
/orm1      twice ! size ( ,e>?1 t has   
be5 obs]v$ = c5turies4 ,!      ,great   
,r$ ,spot rotates c\nt]clockwise ) "o   
revolution e      six days4 ,w9d curr5ts
 on ! top fl[ ea/ to we/1 & curr5ts     
on ! bottom fl[ we/ to ea/4 ,?is ,voyag]
 #a picture %[s !      complex fl[ &    
turbul5t patt]ns t result f ! ,great ,r$
      ,spot's int]actions ) ^! fl[s4 ,! 
l>ge :ite oval is a      simil>1 b      
small]1 /orm c5t] t has exi/$ = ab\t #dj
      ye>s4        ,illu/ration3        
#g_/c_/gi    #f million km    7#c4gb    
million mi7        ,a comp>ison ( !     
,voyag] #b photograph above ) ! prec$+  
,voyag] #a photograph %[s sev]al di/9ct 
*anges 9 ! ,jovian      atmosph]e ar\nd 
! ,great ,r$ ,spot4 ,! :ite oval b5ea? !
      ,great ,r$ ,spot 9 ! fir/ picture 
has mov$ f>!r ar\nd      ,jupit]1 & a   

diff]5t :ite oval has appe>$ "u ! ,great
 ,r$      ,spot 9 ! ,voyag] #b picture  
tak5 f\r mon?s lat]4 ,! di/urb$         
cl\d regions ar\nd ! ,great ,r$ ,spot h 
noticeably *ang$1 &      ! :ite zone we/
 ( ! ,great ,r$ ,spot has n>r[$4        
,illu/ration3 #c_/b_/gi    #d million km
    7#b4e million mi7        ,high-spe$ 
w9d curr5ts 9 ! mid-latitudes ( ,jupit] 
are %[n      9 ?is high-resolution      
,voyag] #a photograph4 ,! pale orange   
l9e      runn+ diagonally to ! upp] "r  
is ! high-spe$ nor?      temp]ate curr5t
 ) a w9d spe$ ( ab\t #abj met]s p]      
second      7#bfj miles p] h\r71 ov]    
twice z fa/ z sev]e hurricane w9ds      
on ,e>?4 ,t[>d ! top ( ! picture1 a     
weak] jet (      approximately #cj met]s
 p] second 7#fe miles p] h\r7 is        
*>act]iz$ by wave patt]ns & cl\d        
features t rotate 9 a      clockwise    
mann]4        ,illu/ration3 #c_/b_/gi   
#d million km    7#b4e million mi7      
,! l>ge br[n-color$ oval appe>+ 9 ?is   
,voyag] #a picture 0      select$ z "o (

 ! t>gets to be photograph$ ne> close/  
approa* to ,jupit] because x is probably
 an op5+ 9 ! upp]      cl\d deck t      
exposes deep]1 w>m] cl\d levels4 ,br[n  
ovals      7:i* c also be se5 9 ! prec$+
 & foll[+ photographs7      are common  
features 9 ,jupit]'s nor!rn latitudes & 
h an      av]age lifetime ( "o to two   
ye>s4        ,illu/ration3 #f_/bh_/gi   
#aj4c million km    7#f4d million mi7   
,jupit]'s ,equatorial ,zone is ! broad1 
orange b& t trav]ses      ! c5t] ( ?is  
,voyag] #b picture4 ,?is zone is        
*>act]iz$ by      ! wispy cl\ds along   
its nor!rn edge4 ,! br[n oval 0         
obs]v$ by ,voyag] #a f\r mon?s e>li]1   
illu/rat+ !      /ability ( ?is type (  
feature 9 ! ,jovian atmosph]e4 ,9       
contra/1 ! turbul5t region 9 ! l[] "r ( 
! picture1      :i* lies j to ! left ( !
 ,great ,r$ ,spot1 %[s features      t  
are relatively %ort liv$4 ,) ! exception
 ( ! cool]      ,great ,r$ ,spot1 z     
colors range f :ite to orange to br[n1  
we      are g5]ally look+ at deep] &    

w>m] lay]s 9 ! ,jovian      atmosph]e4  
,illu/ration3 ,?is infr>$ image (       
,jupit] 0 tak5 f ,e>?      & %[s heat   
radiat+ f deep holes 9 ,jupit]'s cl\ds4 
,bright      areas 9 ! image are high]  
temp]ature regions ?an ! d>k      areas 
& correspond to p>ts ( ! atmosph]e t are
 relatively      free ( obscur+ cl\ds4  
,! ,great ,r$ ,spot appe>s on ! left    
limb1 or edge ( ! planet1 z a d>k area  
encircl$ by a bright      r+1 indicat+ t
 ! ,spot is cool] ?an ! surr\nd+        
region4 ,! infr>$ image 0 record$ by !  
#bjj-;in* ,hale      telescope on ,m\nt 
,palom> 9 ,cali=nia4                    
,illu/ration3 #a_/aj_/gi    #ece1jjj km 
7#ccb million mi7        ,?is ,voyag] #a
 picture 0 also tak5 ! same day1 ab\t "o
 h\r      aft] ! infr>$ image4          
,illu/ration3 #c_/e_/gi    #eae1jjj km  
7#cbj1jjj mi7        ,! l>ge/ aurora ev]
 obs]v$1 ne>ly #bi1jjj kilomet]s        
7#ah1jjj      miles7 long1 appe>s 9 ?is 
,voyag] #a photograph1 tak5 on ! d>k    
side ( ,jupit] six h\rs aft] close/     

enc\nt]4 ,! auroral      lights are     
bright] ?an any nor!rn lights se5 on    
,e>?4      ,jupit]'s nor? pole is       
approximately midway along ! auroral    
arc4      ,?is tim$ exposure ( ! aurora 
also %[s :at appe> to be      lightn+   
/orms sev]al ?\s& kilomet]s bel[ !      
aurora4 ,!      /r5g? ( ! lightn+ bolts 
is comp>able to t ( sup]bolts      se5  
ne> cl\d tops above ,e>?4 ,lightn+ _h   
be5 suspect$ to      exi/ on ,jupit]1 b 
at l[] levels 9 ! atmosph]e4            
,illu/ration3 #c_/d_/gi    #a4b million 
km    7#gej1jjj mi7        ,! fir/      
evid5ce ( a r+ ar\nd ,jupit] is se5 9   
?is      photograph tak5 by ,voyag] #a4 
,?is photograph 0 "p ( a      sequ5ce   
plann$ to se>* = su* r+s ar\nd ,jupit]4 
,!      multiple image ( ! extremely ?91
 fa9t r+ appe>s z a broad      light b& 
cross+ ! c5t] ( ! picture4 ,?is multiple
 image      & ! elongat$1 wavy motion ( 
! backgr\nd />s are due to      !       
#aa-m9ute1 #ab-second exposure & ! v sl[
 natural      oscillation ( !           

spacecraft4 ,! r+1 :i* is 9 ,jupit]'s   
equatorial plane1 is invisible f ,e>?   
because ( its ?9ness      & transp>5cy &
 because ( ,jupit]'s brightness4 ,!     
black dots      9 ! picture are         
calibration po9ts 9 ! cam]a4            
,illu/ration3 ,because ( ,voyag] #a's   
discov]y ( a r+ ar\nd      ,jupit]1     
,voyag] #b 0 programm$ to take          
additional pictures ( !      r+4 ,^!    
?ree ,voyag] #b images %[ ,jupit]'s r+ 9
      progressively high] resolution4 ,!
 pictures 7 tak5 :5      ,jupit] 0      
eclips$ by ! ,sun1 & ! r+ appe>s        
unusually      bright because ( ! =w>d  
scatt]+ ( sunlight by small r+          
p>ticles4        ,illu/ration3          
#g_/aj_/gi    #a4de million km          
7#ijj1jjj mi7        ,9 ?is f\r-picture 
mosaic1 ! arms ( ! r+ curv+ t[>d !      
spacecraft 7on ! ne> side ( ! planet7   
are cut (f by !      planet's %ad[4     
,sci5ti/s e/imate t ! di/ance f !       
,jovian cl\d tops to ! out] edge ( ! r+ 
is #ee1jjj kilomet]s      7#ce1jjj      

miles74        ,illu/ration3 #g_/aj_/gi 
#a4ee million km    7#ifa1jjj mi7       
,9 ?is picture1 :i* is compos$ ( six    
images1 !re is evid5ce      ( /ructure  
)9 ! r+1 b ! spacecraft motion dur+ ^!  
long exposures obscur$ ! highe/         
resolution detail4 ,h[ev]1      !re is  
speculation t ! r+ wid?1 e/imat$ at     
#fjjj      kilomet]s 7#djjj miles71     
conta9s m ?an "o r+4                    
,illu/ration3 #g_/aj_/gi    #a4de       
million km    7#ijj1jjj mi7        ,?is 
photograph is an enl>gem5t ( ! isolat$  
left frame 9 !      fir/ picture &      
reveals a d5sity gradi5t ( v small      
p>ticles      ext5d+ inw>d f ! r+4 ,!   
?ickness ( ! r+ has be5      e/imat$ at 
less ?an "o kilomet] 7#j4f mile7 al?\gh 
! r+      appe>s ab\t #cj kilomet]s 7#ai
 miles7 ?ick 9 ! image1 due to          
cam]a motion & f9ite resolution4        
,composition ( ! l[-alb$o      7d>k7    
p>ticles is n kn[n1 b p>ticle size      
probably ranges      f microscopic to at
 mo/ a few met]s 9 diamet]4 ,if collect$

      toge!r to =m a s+le body1 ! total 
mass ( ! ,jovian r+s      w\ld =m an    
object ) a diamet] less ?an twice t (   
t9y      ,amal!a4        ,illu/ration3  
#b_/ac_/gi    #bj million km    7#ab4d  
million mi7        ,jupit] & two ( its  
planet-siz$ satellites1 ,io at left &   
,europa at "r1 are visible 9 ?is ,voyag]
 #a picture4 ,jupit]'s      f\r l>ge/   
satellites--,io1 ,europa1 ,ganym$e &    
,calli/o--7      discov]$ 9 #afaj by    
,galileo ,galilei4 ,! two out] ,galilean
      satellites are ,ganym$e &         
,calli/o1 n %[n 9 ?is picture4 ,all     
f\r satellites probably =m$ ab\t f\r    
billion ye>s ago b      _! surfaces v>y 
9 age trem5d\sly4 ,io & ,europa h y\ng]1
      m active surfaces ?an ,ganym$e &  
,calli/o4 ,l our ,moon1 !               
satellites keep ! same face t[>d        
,jupit]4 ,9 ?is picture1 !      sides ( 
! satellites t always face away f !     
planet are      visible4                
,illu/ration3 ,amal!a1 ,jupit]'s inn]mo/
 satellite1 0      discov]$ 9 #ahib4 ,x 

is s small & close to ,jupit] t x is    
extremely difficult to obs]ve f ,e>?4   
,amal!a's surface is      d>k & r$1 q   
unlike any ( ! ,galilean satellites4 ,! 
?ree      ,voyag] #a pictures & ! "o    
,voyag] #b picture foll[+ 7se5          
aga9/ ! disk ( ,jupit]7 reveal a small1 
elongat$ object1 ab\t      #bfe         
kilomet]s 7#afe miles7 long & #aej      
kilomet]s 7#ij miles7 9      diamet]4   
,amal!a keeps its long axis po9t$ t[>d  
,jupit] z x      orbits ar\nd ! planet e
 #ab h\rs4        ,illu/ration3         
#c_/d_/gi    #a4be million km           
7#ghj1jjj mi7        ,illu/ration3      
#c_/d_/gi    #fie1jjj km    7#dcj1jjj   
mi7        ,illu/ration3 #c_/e_/gi      
#dbe1jjj km    7#bfd1jjj mi7            
,illu/ration3 #g_/i_/gi    #efj1jjj km  
7#cej1jjj mi7        ,amal!a 0 obs]v$   
end-on 9 ! ,voyag] #b picture1 :i* has  
be5 comput]-process$ to enhance ! image4
        ,illu/ration3 #c_/d_/gi         
#cgg1jjj km    7#bcd1jjj mi7        ,io1
 ,jupit]'s inn]mo/ ,galilean satellite1 

displays great div]sity      9 color &  
brightness4 ,?is ,voyag] #a f\r-picture 
mosaic %[s      ,io's complex coloration
 ( r$-orange1 black1 & :ite regions1 &  
! two major topographic features3       
volcanic regions1 ! mo/      prom95t (  
:i* is ! 8ho(pr9t0 7volcanic deposition 
feature7      9 ! c5t]-"r1 & !          
int]volcanic pla9s t are      relatively
 featureless4 ,io's vivid color+ is     
probably due to its      composition (  
sulfur-ri* mat]ials t h be5 br\ght to ! 
surface by volcanic activity4           
,illu/ration3 #c_/e_/gi    #abi1fjj km  
7#hj1ejj mi7        ,! bright area at ! 
upp] "r 9 ?is ,voyag] #a picture ( ,io  
appe>s to be a cald]a 7collaps$ volcano7
 t is v5t+ cl\ds      ( gases4 ,! cl\ds 
may cond5se to =m extremely f9e p>ticles
      t scatt] light & appe> blue4      
,because ! infr>$      spectromet]      
discov]$ sulfur dioxide on ,io1 sci5ti/s
 believe      ?is gas may be ! ma9      
compon5t ( ! cl\ds4 ,sulfur dioxide     
cl\ds w\ld rapidly freeze & sn[ back to 

! surface4 ,x is also      possible t   
d>k areas 9 ! floors ( ! cald]as are    
pools (      encru/$ liquid sulfur4     
,illu/ration3 #c_/e_/gi    #ff1jjj km   
7#da1jjj mi7        ,evid5ce ( erosion 9
 ,io's s\!rn pol> region is visible 9   
?is      ,voyag] #a high-resolution     
image4 ,! picture has be5               
comput]-enhanc$ to br+ out surface      
detail :ile suppress+      bright m>k+s4
 ,a depress$ segm5t ( ! cru/1 b\nd$ by  
faults1 is se5 ne> ! t]m9ator 9 ! upp]  
"r portion (      ! image4 ,at ! l[]    
c5t] are complicat$ sc>ps 7slopes7 &    
portions ( isolat$ elevat$ t]ra9 t      
geologi/s int]pret z      8isl&s0 left  
beh9d z ! sc>ps erod$4 ,sci5ti/s        
speculate      t sulfur dioxide 7z a    
subsurface liquid7 may be a det]m9ant 9 
! creation ( ^! features4               
,illu/ration3 #c_/d_/gi    #hfb1jjj km  
7#edj1jjj mi7        ,io's surface1 less
 ?an t5 million ye>s old1 is q "y       
comp>$ to ! o!r ,galilean satellites &  
to o!r t]re/rial      bodies1 su* z     

,m]cury & ! ,moon4 ,! surface is compos$
 (      l>ge am\nts ( sulfur & sulfur   
dioxide fro/1 bo? ( :i*      acc\nt =   
mo/ ( ! surface color4 ,?is picture 0   
tak5 by      ,voyag] #a4 ,mat]ial       
deposit$ by ! volcano 7see foll[+       
pictures7 c be se5 z a :ite r+ ne> !    
c5t] ( ,io4        ,illu/ration3 ,! fir/
 active volcanic eruptions o!r ?an on   
,e>? 7 discov]$ on ,io4 ,^! volcanoes   
are extremely explosive      ) ejection 
velocities ( m ?an "o kilomet] p] second
 7#bbjj      miles p] h\r71 :i* is m    
viol5t ?an ,etna1 ,vesuvius1 or         
,krakatoa on ,e>?4 ,bo? pictures bel[ 7 
tak5 by ,voyag] #a4        ,illu/ration3
 #c_/d_/gi    #dej1jjj km    7#bhj1jjj  
mi7        ,9 ?is picture1 ! plume      
visible on ! "r edge ext5ds m      ?an  
#ajj kilomet]s 7#fj miles7 above !      
surface4        ,illu/ration3 #c_/d_/gi 
#dii1jjj km    7#caj1jjj mi7        ,!  
same volcano is %[n 9 ?is picture1      
photograph$ "o h\r &      #eb m9utes    
e>li]4        ,illu/ration3 #c_/d_/gi   

#dij1jjj km    7#cjd1jjj mi7            
,special color recon/ruction by means ( 
ultraviolet1 blue1 gre51      & orange  
filt]s all[$ sci5ti/s to /udy ! am\nt ( 
gas &      du/ & ! size ( ! du/ p>ticles
 t erupt$ f !      volcano on ,io %[n 9 
?is ,voyag] #a image4 ,! region t is    
bright] 9 ! ultraviolet 7blue area7 is  
ab\t #baj kilomet]s 7#acj      miles7   
high1 ov] twice ! height ( ! d5s]1      
bright yell[      core4 ,! v5t area is  
visible on page #ah z a d>k r+ 9 !      
upp] left region ( ,io4                 
,illu/ration3 #g_/aj_/gi    #a4b million
 km    7#gej1jjj mi7        ,( ! eight  
active volcanoes discov]$ on ,io by     
,voyag] #a1 six (      ! sev5 volcanoes 
sight$ by ,voyag] #b 7 /ill active4 ,!  
giant volcano obs]v$ by ,voyag] #a ov] !
 8ho(pr9t0 region 7see      page #ah7 _h
 become inactive4 ,sci5ti/s1 !re=e1     
believe t      ! satellite is und]go+   
cont9u\s volcanic activity1 mak+        
,io's surface ! mo/ active 9 ! sol>     
sy/em4 ,?is ,voyag] #b      photograph1 

:i* %[s ?ree active volcanoes1 0 "o ( ! 
la/      ( an ext5sive sequ5ce (        
8volcano wat*0 pictures plann$ z a      
result ( ,voyag] #a's volcano discov]y4 
,! black dots are      calibration po9ts
 on ! cam]a4        ,illu/ration3       
#g_/h_/gi    #a4b million km            
7#gej1jjj mi7        ,europa1           
approximately ! same size & d5sity z our
 ,moon1 is !      brighte/ ,galilean    
satellite4 ,! surface displays a complex
 array      ( /reaks1 indicat+ t ! cru/ 
has be5 fractur$4 ,9      contra/ to its
 icy neighbors ,ganym$e & ,calli/o1     
,europa has v      few impact crat]s4 ,!
 relative abs5ce ( features & l[        
topography indicate t ! cru/ is "y &    
probably w>m a few      kilomet]s bel[ !
 surface4 ,! w>m? is probably due to a  
comb9ation ( radioactive & tidal heat+4 
,! tidal heat+      )9 ,europa is       
e/imat$ to be t5 p]c5t t ( ! /rong]     
tidal heat+ effect )9 ,io4 ,! regions t 
appe> blue 9 ?is      ,voyag] #b image  
are actually :ite4        ,illu/ration3 

#g_/i_/gi    #bdj1jjj km    7#aej1jjj   
mi7        ,europa's surface is probably
 a ?9 ice cru/ ov]ly+ wat] or      s(t] 
ice 7slu%7 ab\t #ajj kilomet]s 7#fj     
miles7 ?ick t cov]s      a silicate     
int]ior4 ,! tectonic processes on       
,europa's surface      create patt]ns t 
are dra/ically diff]5t f ! fault        
sy/ems se5 on ,ganym$e's surface1 :]e   
pieces ( ! cru/ h      mov$ relative to 
ea* o!r4 ,on ,europa1 ! cru/ evid5tly   
fractures1 b ! pieces rema9 r\ghly 9 _! 
orig9al position4      ,?is ,voyag] #b  
picture is compos$ ( ?ree images4       
,illu/ration3 #g_/i_/gi    #bdj1jjj km  
7#aej1jjj mi7        ,long l9e>         
fractures or faults :i* crisscross      
,europa's surface 9      v>i\s          
directions are ov] #ajjj kilomet]s 7#fjj
 miles7 long 9 "s      places4 ,l>ge    
fractures are #bjj to #cjj kilomet]s    
7#abe to #ahe miles7      wide1 wid] ?an
 ! cru/ is ?ick4 ,also visible are      
some:at      d>k] mottl$ regions t appe>
 to h a slightly pitt$      appe>ance4  

,no l>ge crat]s 7m ?an five kilomet]s 9 
diamet]7      are id5tifiable 9 ?is     
,voyag] #b picture1 indicat+ t ?is      
satellite has a v "y surface relative to
 ,ganym$e &      ,calli/o1 al?\gh p]haps
 n z "y z ,io's surface4 ,sci5ti/s      
believe t ! surface is a ?9 ice cru/    
ov]ly+ wat] or      s(t] ice & t !      
fracture sy/ems are breaks 9 ! cru/4    
,resurfac+ processes1 su* z ! production
 ( fre% ice or sn[      along ! cracks &
 cold glaci]-l fl[s1 h probably remov$  
evid5ce ( impact ev5ts 7crat]+74        
,europa1 !re=e1 appe>s to      h _m     
prop]ties simil> to ,ganym$e & ,io4     
,illu/ration3 #g_/i_/gi    #bdj1jjj km  
7#aej1jjj mi7        ,complex n>r[      
ridges1 se5 z curv$ bright /reaks #e to 
#aj      kilomet]s 7#c to #f miles7 wide
 & typically #ajj kilomet]s 7#fj        
miles7 long1 *>act]ize ! surface        
topography ( ?is view (      ,europa4 ,!
 d>k b&s also visible 9 ?is ,voyag] #b  
photo are #bj      to #dj kilomet]s 7#ab
 to #be miles7 wide & up to ?\s&s (     

kilomet]s long4 ,! fractures on ! icy   
surface are fill$ )      mat]ial f      
b5ea?1 probably z a result ( int]nal    
tidal      flex+ :i* cont9ually heats ! 
?9 out] ice cru/4 ,a few      features  
are sugge/ive ( degrad$ impact crat]s4  
,illu/ration3 #c_/d_/gi    #b4f million 
km    7#a4f million mi7        ,ganym$e1
 ,jupit]'s l>ge/ satellite1 is ab\t "o &
 "o-half      times ! size ( our ,moon b
 only ab\t half z d5se & is      compos$
 ( ab\t #ej p]c5t wat] or ice & ! re/   
rock4 ,!      bright surface ( ,ganym$e 
is a complex montage ( anci5t1          
relatively d>k & crat]$ t]ra91 groov$   
t]ra9 t result$      f a dramatic hi/ory
 ( tectonic movem5t 9 ! icy cru/1 &     
bright "y ray crat]s t expose fre% ice4 
,?is photograph 0      tak5 by ,voyag]  
#a4        ,illu/ration3 #g_/g_/gi      
#a4b million km    7#gej1jjj mi7        
,! d>k1 crat]$1 circul> feature 9 ?is   
,voyag] #b photograph is      ab\t #cbjj
 kilomet]s 7#bjjj miles7 9 diamet] & is 
on ! side (      ,ganym$e opposite to t 

%[n 9 ! previ\s picture4 ,?is region    
is app>5tly ! l>ge/ piece ( anci5t1     
heavily crat]$ cru/      left on        
,ganym$e4 ,! light bran*+ b&s are ridg$ 
& groov$      t]ra9 :i* are y\ng] ?an ! 
m heavily crat]$ d>k      regions4      
,despite ! dramatic surface appe>ance1  
,ganym$e is      relatively devoid (    
topographic relief due to ! consequ5ces 
(      glaci]-l 8creep0 9 ! icy cru/4   
,illu/ration3 #g_/h_/gi    #cab1jjj km  
7#aid1jjj mi7        ,sev]al diff]5t    
types ( t]ra9 common to ,ganym$e's      
surface are      visible 9 ?is ,voyag]  
#b picture4 ,! b\nd>y ( ! l>ge/         
region ( d>k anci5t t]ra9 7also %[n 9 ! 
previ\s photo7      c be se5 to ! "r1   
reveal+ ! light l9e> features t      may
 be ! rema9s ( %ock r+s f an anci5t     
impact4 ,! broad      light regions are 
! typical groov$ /ructures conta9$ )9   
! light regions on ,ganym$e4 ,on ! l[]  
left is ano!r example      ( :at might  
be evid5ce ( l>ge-scale lat]al fault+ 9 
!      cru/2 ! b& appe>s to be (fset by 

a l9e> feature      p]p5dicul> to x4 ,^!
 are ! fir/ cle> examples ( lat]al      
fault+ se5 on any planet o!r ?an ,e>?4  
,illu/ration3 #g_/h_/gi    #cac1jjj km  
7#aid1ejj mi7        ,?is color         
recon/ruction ( "p ( ,ganym$e's nor!rn  
hemisph]e1      tak5 by ,voyag] #b1     
encompasses an area ab\t #acjj kilomet]s
 7#hjj      miles7 across4 ,x %[s "p ( a
 d>k1 d5sely crat]$ region t            
conta9s num]\s crat]s1 _m ) c5tral      
peaks4 ,! l>ge bright      circul>      
features h little relief & are probably 
! remnants      ( old1 l>ge crat]s t h  
be5 anneal$ by ! fl[ ( icy      mat]ial 
ne> ! surface4 ,! gradually curv+ l9es t
 press      ?r\gh ! d>k region sugge/ ! 
pres5ce ( a l>ge impact bas9      to !  
s\?we/1 :i* has be5 oblit]at$ by !      
subsequ5t      =mation ( y\ng] groov$   
t]ra94        ,illu/ration3 #c_/e_/gi   
#afe1jjj km    7#ajc1jjj mi7        ,a  
broad1 nor?-s\? /rip ( groov$ t]ra9 on  
,ganym$e1 (fset by      a trav]s+ fault 
9 ! upp] "p ( ! picture1 is %[n 9       

?is ,voyag] #a photograph4 ,!re are     
sev]al o!r p]p5dicul>      fault l9es   
f>!r d[n on ! fault4 ,)9 ! major light  
/ripes1 ! m closely spac$1 %all[ grooves
 run p>allel to      ! b\nd>ies ( !     
/ripes4 ,! l>g] /rip$ features divide   
! crat]$ t]ra9 into isolat$ polygons    
sev]al hundr$ to ab\t      #ajjj        
kilomet]s 7#fjj miles7 across4          
,illu/ration3 #c_/e_/gi    #ade1jjj km  
7#ij1jjj mi7        ,! groov$ t]ra9 at  
high] resolution emphasizes num]\s      
int]wov5 l9e> features 9 ?is ,voyag] #a 
picture1 ne> !      t]m9ator on         
,ganym$e4 ,?is sugge/s an e>ly p]iod 9  
,ganym$e's      hi/ory :5 ! cru/ 0      
active & mobile1 resembl+ ,e>?'s        
plate tectonics 9 "s ways4 ,! causes ( !
 extreme diff]5ces      9 cru/al        
evolution betwe5 ,calli/o & ,ganym$e are
 "u      inve/igation4 ,comb9ations (   
radioactive heat+ & a great]      degree
 ( tidal heat+ = ,ganym$e are           
possibilities4        ,illu/ration3     
#g_/i_/gi    #ajj1jjj km    7#fb1jjj ml7

        ,?is mosaic ( ,ganym$e1 compos$ 
( photographs tak5 by ,voyag] #b1       
%[s num]\s impact crat]s1 _m ) bright   
ray sy/ems4 ,!      r\gh t]ra9 at ! l[] 
"r is ! out] portion ( a l>ge1      fre%
 impact bas9 t po/dates mo/ ( ! o!r     
t]ra94 ,!      d>k pat*es ( heavily     
crat]$ t]ra9 7"r c5t]7 are probably     
anci5t mixtures ( ice & rock =m$ prior  
to ! groov$      t]ra94 ,! l>ge ray$    
crat] at ! upp] c5t] is ab\t #aej       
kilomet]s 7#ie miles7 9 diamet]4        
,illu/ration3 #g_/h_/gi    #he1jjj km   
7#ec1jjj mi7        ,curv$ tr\ghs &     
ridges 9 ?is high-resolution ,voyag] #b 
photograph ( ,ganym$e are ! di/9ctive   
*>act]i/ics ( an      enorm\s1 anci5t   
impact bas94 ,! bas9 itself has be5     
erod$ by      lat] geologic processes2  
only ! %ock r+ features are pres]v$     
on ! anci5t surface4 ,ne> ! bottom ( !  
picture ^! curv$      m>k+s are p]=at$ )
 ! y\ng]1 groov$ t]ra94                 
,illu/ration3 #g_/g_/gi    #b4c million 
km    7#a4d million mi7        ,calli/o1

 only slightly small] ?an ,ganym$e1 has 
! l[e/      d5sity ( all ! ,galilean    
satellites1 imply+ t x has l>ge         
am\nts ( wat] 9 its bulk composition4   
,its surface is d>k] ?an      ! o!r     
,galilean satellites1 al?\gh x is /ill  
twice z bright      z our ,moon4 ,?is   
,voyag] #b image %[s ,calli/o to h ! mo/
      heavily crat]$ &1 !re=e1 ! olde/  
surface ( ! ,galilean      satellites1  
probably dat+ back to ! p]iod ( heavy   
meteoritic      bomb>dm5t end+ ab\t f\r 
billion ye>s ago4        ,illu/ration3  
#c_/f_/gi    #cej1jjj km    7#bag1jjj   
mi7        ,! prom95t conc5tric r+      
/ructure %[n 9 ?is ,voyag] #a           
f\r-picture mosaic ( ,calli/o is believ$
 to be a l>ge impact      bas91 simil>  
to ,m>e ,ori5tale on ! ,moon & ,caloris 
,bas9 on      ,m]cury4 ,! bright circul>
 spot is ab\t #fjj kilomet]s 7#cfj      
miles7 across1 & ! out] r+ is ab\t #bfjj
 kilomet]s 7#aefj      miles7 across4   
,?is is ! fir/ recogniz$ bas9 9 !       
,jovian      sy/em & supports !         

assumption t ,calli/o's surface is old4 
,! lack ( high ridges1 r+ m\nta9s1 or a 
l>ge c5tral      depression sugge/s t ! 
impact+ body caus$ melt+1 "s      fl[1 &
 %ock waves1 & t ! refreez+ occurr$ 9 "t
 to      pres]ve ! conc5tric %ock r+s4  
,illu/ration3 #g_/g_/gi    #cij1jjj km  
7#bde1jjj mi7        ,calli/o is ! mo/  
heavily crat]$ planet>y body 9 our sol> 
sy/em4 ,9 ?is ,voyag] #b n9e-frame      
mosaic1 a special comput]      filt] 0  
us$ to provide high contra/ 9 ! surface 
topography4      ,! impact /ructure     
visible at ! upp] "r edge ( !           
satellite is small] ?an ! l>ge/ "o f\nd 
by ,voyag] #a b      m detail is obvi\s2
 x is e/imat$ t #ae conc5tric r+s       
surr\nd ! bright c5t]4 ,_m hundr$s (    
mod]ate-siz$ crat]s      are also       
visible1 a few ) bright ray patt]ns4 ,! 
limb is      smoo?1 :i* is consi/5t )   
,calli/o's icy composition4             
,illu/ration3 #c_/f_/gi    #bjj1jjj km  
7#abe1jjj mi7        ,?is               
high-resolution image ( ,calli/o1       

photograph$ by ,voyag] #a1      %[s     
details ( ! l>ge r+ /ructure surr\nd+ ! 
rema9s (      ! anci5t impact bas9      
visible on page #ce4 ,! surface area %[n
      9 ?is image is at ! "r edge &     
slightly above ! c5t] (      ! picture  
on page #ce4 ,! relatively undi/urb$    
region on !      "r %[s ! %\ld]-to-%\ld]
 l>ge impact crat]s typical (      mo/ (
 ,calli/o's surface4 ,a decrease 9 crat]
 d5sity t[>d !      c5t] ( ! /ructure   
7to ! left7 is evid5t1 & is caus$ by    
! de/ruction ( v old crat]s by ! l>ge   
impact t =m$      ! r+                  
,! ,voyag] ,mission      ,! ,voyag]     
mission is focus$ on ! exploration ( !  
,jupit] &  ,saturn sy/ems4 ,! alignm5t (
 ^! l>ge planets p]mits ! use (  a      
gravity-assi/ trajectory 9 :i* ! gravity
 field ( ,jupit] &  ,jupit]'s motion    
?r\gh space may be us$ to hurl !        
spacecraft on to  ,saturn4 ,9 #aigg1 a  
r>e alignm5t 7once e #agf ye>s7 ( our   
f\r  out] planets--,jupit]1 ,saturn1    
,uranus1 & ,neptune--may p]mit a        

gravity-assi/ trajectory to ,uranus &   
ev5 to ,neptune = ,voyag] #b4           
,voyag]s #a & #b began _! j\rneys 9 !   
late summ] ( #aigg1  catapult$ into     
space by a ,titan_/,c5taur laun* vehicle
 f ,cape  ,canav]al1 ,florida4 ,) !m w5t
 ! hopes & dreams ( ?\s&s (  p :o _h    
work$ to create !m & _! mission4    ,!  
,voyag] spacecraft are unique 9 _m      
respects4 ,s9ce _! j\rneys  are tak+ !m 
f> f ! ,sun1 ! ,voyag]s are nucle> p[]$ 
r ?an sol> p[]$4 ,! ,voyag]s are ! fa/e/
 man-made objects  ev] to h left ,e>?4  
,9 few] ?an t5 h\rs1 !y _h cross$ !     
,moon's orbit4 ,?is comp>es to ab\t ?ree
 days = an ,apollo flight &  "o day = ! 
,m>9] & ,vik+ spacecraft4 ,_! laun*es   
m>k$ !  end ( an era 9 space travel--!  
end ( ! plann$ use (  ,titan_/,c5taur   
laun* vehicles4 ,) ! adv5t ( ! ,space   
,%uttle 9  ! #aihjs1 future spacecraft w
 be laun*$ f ! ,%uttle ,orbit]4         
,voyag] #a 0 laun*$ #af days aft] its   
si/] %ip1 b because ( a  diff]5t        
trajectory1 x arriv$ at ,jupit] f\r     

mon?s ahead ( ,voyag]  #b4 ,bo?         
spacecraft sp5t m ?an n9e mon?s cross+ !
 a/]oid  belt1 a va/ r+ ( space debris  
circl+ ! ,sun betwe5 ! orbits (  ,m>s & 
,jupit]4 ,dur+ _! #af- & #bj-mon?       
j\rneys to ,jupit]1 !  spacecraft te/$ &
 calibrat$ all ( _! in/rum5ts1 ex]cis$  
_! scan plat=ms1 & measur$ p>ticles &   
fields 9  int]planet>y space4 ,z !      
spacecraft ne>$ ! planet1 ! cam]as  %[$ 
! dramatic visible *anges t _h tak5     
place 9 ! five  ye>s s9ce ,jupit] _h be5
 photograph$ by ,pione] #aa4 ,& = !     
fir/ "t1 we got a close look at "s (    
,jupit]'s moons3 ,amal!a1  ,io1 ,europa1
 ,ganym$e1 & ,calli/o4    ,t>get$ = !   
close/ look at ,io1 ,voyag] #a flew ! m 
haz>d\s  c\rse1 pass+ betwe5 ,jupit] &  
,io1 :]e ! radiation environm5t  is !   
mo/ int5se4 ,voyag] #b's flight pa? gave
 ,jupit] & its  int5se radiation a mu*  
wid] b]?4 ,unlike ,voyag] #a1 :i*       
enc\nt]$ ! five inn]mo/ satellites z x 0
 leav+ ,jupit]1  ,voyag] #b enc\nt]$ !  
satellites z x 0 approa*+ ! planet1  ?us

 provid+ closeup photography ( opposite 
sides ( ! satellites4                   
,illu/ration3 ,m>* #e1 #aigi4 ,voyag]   
#a's unique flight pa?      all[$       
sci5ti/s to /udy at close range #e (    
,jupit]'s #ac kn[n      satellites4 ,ea*
 is %[n at its close/ po9t to !         
trajectory (      ,voyag] #a's outb\nd  
flight away f ,jupit]4 ,close/ approa* 0
      #bhj1jjj kilomet]s 7#agd1jjj      
miles7 f ,jupit]4        ,illu/ration3  
,july #i1 #aigi4 ,voyag] #b's close/    
approa* to      ,jupit] 0 #fde1jjj      
kilomet]s 7#djj1jjj miles7 f ! planet4  
,voyag] #b enc\nt]$ ! satellites on its 
inb\nd j\rney to      ,jupit]1 :i*      
enabl$ ! spacecraft to photograph !     
opposite      sides ( ! satellites4     
,arriv+ at ,jupit] f slightly diff]5t   
angles1 bo? spacecraft  measur$ ! l>ge1 
d\ghnut-%ap$ r+ ( *>g$ sulfur & oxyg5   
ions1 call$ a torus1 encircl+ ! planet  
at ab\t ! orbit ( ,io4  ,!n1 bo?        
spacecraft disappe>$ beh9d ,jupit]1 out 
( view ( ,e>?  & ,sun1 = ab\t two h\rs4 

,dur+ ?is "t1 measurem5ts 7 tak5  on !  
planet's d>k side4 ,ea* spacecraft took 
ov] #ae1jjj photographs  ( ,jupit] & its
 satellites4        ,illu/ration3       
,voyag] spacecraft & sci5tific          
in/rum5ts4    ,f ! mom5t ( laun*1 !     
,voyag] spacecraft h be5 monitor$ by  a 
worldwide track+ sy/em ( n9e giant      
ant5nas /rategically locat$  ar\nd ! _w 
9 ,cali=nia1 ,spa91 & ,au/ralia to      
ensure con/ant  radio contact ) !       
spacecraft z ! ,e>? rotates4 ,radio     
contact  ) ,voyag]s #a & #b has n be5   
in/antane\s1 h[ev]4 ,:5 ,voyag]  #a flew
 pa/ ,jupit]1 radio signals betwe5 ,e>? 
& ! spacecraft took  #cg m9utes2 :5     
,voyag] #b arriv$1 ! signals took #eb   
m9utes because  by !n ! planet 0 f>!r f 
,e>?4    ,! pictures 9 ?is book 7 tak5  
by a %utt]$ television-type  cam]a4 ,ea*
 picture is compos$ ( #fdj1jjj dots1 :i*
 7 conv]t$  into b9>y numb]s be=e be+   
radio$ to ,e>?4 ,:5 ! signals  rea*$    
,e>?1 !y 7 reconv]t$ by comput] into    
dots &  reassembl$ into ! orig9al image4

 ,mo/ ( ! color pictures are  compos$ ( 
?ree images1 ea* "o tak5 ?r\gh a diff]5t
 color  filt]3 blue1 orange1 or gre54 ,!
 images 7 comb9$ & !  orig9al color 0   
recon/ruct$ by comput]4 ,! comput]      
elim9at$  _m ( ! imp]fections t crept   
into ! images1 & enhanc$ "s  ( ! images 
by emphasiz+ diff]5t colors4    ,design$
 to provide a broad spectrum ( sci5tific
 inve/igations at  ,jupit]1 ! sci5ce    
in/rum5ts inve/igat$ atmosph]es1        
satellites1  & magnetosph]es4 ,!        
sci5tific inve/igations = ! ,voyag]     
mission & _! ,jovian enc\nt] objectives 
are %[n 9 ! table on  page #dj4    ,aft]
 _! close/ approa*es to ,jupit]1 bo?    
spacecraft fir$ _!  ?ru/]s1 ret>get+ =  
_! next goal1 ! ,saturn sy/em4          
,sci5ti/s w /ill be /udy+ ! weal? ( new 
in=mation ab\t  ,jupit] :5 ,voyag] #a   
rea*es ,saturn 9 ,novemb] #aihj1 &      
,voyag] #b  foll[s 9 ,augu/ #aiha4 ,aft]
 ,voyag] #a enc\nt]s ,saturn1 ,voyag] #b
 may  be ret>get$ to fly pa/ ,uranus 9  
#aihf4 ,^u completion ( _!  planet>y    

missions1 bo? spacecraft w se>* = ! out]
 limit (  ! sol> w9d1 t b\nd>y some:]e 9
 our "p ( ! ,milky ,way  :]e ! influ5ce 
( ! ,sun gives way to o!r />s ( !       
galaxy4  ,voyag]s #a & #b w cont9ue to  
/udy int]/ell> space until !  spacecraft
 signals c no long] be receiv$4         
,sci5tific ,highlights      ,"s ( ! mo/ 
important in=mation ga!r$ by ,voyag]s #a
 & #b on  ! ,jovian sy/em is pres5t$    
pictorially 9 ?is book & is  supplem5t$ 
"h ) brief summ>ies ( ! major           
discov]ies1  obs]vations1 & !ories4     
,jupit]    ,! atmosph]e ( ,jupit] is    
colorful1 ) cl\d b&s ( alt]nat+  colors4
 ,a major *>act]i/ic ( ! atmosph]e is ! 
appe>ance (  regul>ly spac$ features4   
,ar\nd ! nor!rn edge ( ! equator1 a     
tra9 ( plumes is obs]v$1 :i* has bright 
c5t]s repres5tative (  cumulus          
convection simil> to t se5 on ,e>?4 ,at 
bo? nor!rn &  s\!rn latitudes1 cl\d     
spots are obs]v$ spac$ almo/ all ! way  
ar\nd ! planet1 sugge/ive ( wave        
int]actions4 ,! cl\d /ructures  9 !     

nor!rn & s\!rn hemisph]es are di/9ctly  
diff]5t4  ,h[ev]1 ! velocities betwe5 ! 
bright zones & d>k belts appe>  to be   
symmetric ab\t ! equator1 & /able ov] _m
 decades4 ,?is  sugge/s t su* long-liv$ 
& /able features may be controll$ by  ! 
atmosph]e f> b5ea? ! visible cl\ds4 ,!  
,great ,r$ ,spot  possesses ! same      
meteorological prop]ties ( int]nal      
/ructure &  c\nt]clockwise rotation z ! 
small] :ite spots4 ,! color ( !  ,great 
,r$ ,spot may indicate t x ext5ds deep  
into ! ,jovian  atmosph]e4 ,cl\d-top    
lightn+ bolts1 simil> to ^? on ,e>?1 h  
also be5 f\nd 9 ! ,jovian atmosph]e4 ,at
 ! pol> regions1 auroras  h be5 obs]v$4 
,a v ?9 r+ ( mat]ial less ?an "o        
kilomet]  7#j4f mile7 9 ?ickness & ab\t 
#fjjj kilomet]s 7#djjj miles7 9 radial  
ext5t has be5 obs]v$ circl+ ! planet    
ab\t #ee1jjj kilomet]s  7#ce1jjj miles7 
above ! cl\d tops4      ,amal!a         
,amal!a is an elongat$1 irregul>ly %ap$ 
satellite ( r$di% color4  ,x is #bfe    
kilomet]s 7#afe miles7 long & #aej      

kilomet]s 7#ij miles7  wide4 ,j l ! l>ge
 ,galilean satellites1 ,amal!a is 9     
syn*ron\s rotation1 ) its long axis     
always ori5t$ t[>d ,jupit]4  ,at lea/ "o
 significant color v>iation has be5     
detect$ on its  surface4      ,io       
,eight active volcanoes h be5 detect$ on
 ,io1 ) "s plumes  ext5d+ up to #cbj    
kilomet]s 7#bjj miles7 above ! surface4 
,ov] !  f\r-mon? int]val betwe5 !       
,voyag] #a & #b enc\nt]s1 ! active      
volcanism appe>s to h cont9u$4 ,sev5 ( !
 volcanoes 7  photograph$ by ,voyag] #b1
 & six 7 /ill erupt+4    ,! relative    
smoo?ness ( ,io's surface & its volcanic
 activity  sugge/ t x has ! y\nge/      
surface ( ,jupit]'s moons4 ,its surface 
is compos$ ( l>ge am\nts ( sulfur &     
sulfur dioxide fro/1 :i*  acc\nt = !    
prim>ily yell[-orange surface color4 ,! 
volcanoes  seem to eject a suffici5t    
am\nt ( sulfur dioxide to =m a          
d\ghnut-%ap$ r+ 7torus7 ( ioniz$ sulfur 
& oxyg5 atoms ar\nd  ,jupit] ne> ,io's  
orbit4 ,! ,jovian magnetic field l9es t 

g ?r\gh  ! torus all[ p>ticles to       
precipitate into ! pol> regions (       
,jupit]1 result+ 9 int5se ultraviolet & 
visible auroras4      ,europa           
,europa1 ! brighte/ ( ,jupit]'s         
,galilean satellites1 may h a  surface (
 ?9 ice cru/ ov]ly+ wat] or s(t] ice1 ) 
l>ge-scale fracture & ridge sy/ems      
appe>+ 9 ! cru/4 ,europa  has a d5sity  
ab\t ?ree times t ( wat]1 sugge/+ x is a
  mixture ( silicate rock & "s wat]4 ,v 
few impact crat]s are  visible on !     
surface1 imply+ a cont9ual resurfac+    
process1  p]haps by ! production ( fre% 
ice or sn[ along cracks & cold  glaci]-l
 fl[s4      ,ganym$e    ,ganym$e1 l>ge/ 
( ,jupit]'s #ac satellites1 has bright  
8"y0 ray  crat]s2 light1 l9e> /ripes    
resembl+ ! out] r+s ( a v  l>ge1 anci5t 
impact bas92 groov$ t]ra9 ) _m faults2 &
  regions ( d>k1 heavily crat]$ t]ra94  
,among ! ,galilean  satellites1 ,ganym$e
 probably has ! greate/ v>iety (        
geologic  processes record$ on its      
surface & may be ! be/ example =  /udy+ 

! evolution ( ,jupit]'s inn] satellites4
 ,imb$d$ )9  ,jupit]'s magnetosph]e1    
,ganym$e is subject$ to ! influ5ces ( ! 
corotat+ *>g$-p>ticle plasma & an       
int]action may exi/ )  ?is plasma4 ,no  
atmosph]e has be5 detect$4      ,calli/o
    ,! icy1 dirt-lad5 surface ( ,calli/o
 appe>s to be v anci5t &  heavily       
crat]$4 ,! l>ge conc5tric r+s indicate !
 rema9s (  sev]al enorm\s impact bas9s1 
creat$ by huge meteors cra%+ into  !    
surface1 & s9ce eras$ by ! fl[ ( ! cru/4
 ,calli/o's  d5sity 7less ?an twice t ( 
wat]7 is v close to t (  ,ganym$e1 yet  
!re is little or no evid5ce ( ! cru/al  
motion &  int]nal activity t is visible 
on ,ganym$e4      ,! ,magnetosph]e      
,p]haps ! l>ge/ /ructure 9 ! sol> sy/em 
is ! magnetosph]e  ( ,jupit]4 ,?is is ! 
region ( space :i* is fill$ ) ,jupit]'s 
magnetic field & is b\nd$ by !          
int]action ( t magnetic field  ) ! sol> 
w9d1 :i* is ! ,sun's outw>d fl[ ( *>g$  
p>ticles4 ,! plasma ( electrically *>g$ 
p>ticles t exi/s 9  ! magnetosph]e is   

flatt5$ into a l>ge disk m ?an #d4h     
million  kilomet]s 7#c million miles7 9 
diamet]1 is c\pl$ to ! magnetic  field1 
& rotates ar\nd ,jupit]4 ,! ,galilean   
satellites are locat$  9 ! inn] regions 
( ! magnetosph]e :]e !y are subject$ to 
int5se radiation bomb>dm5t4 ,x appe>s t 
,io is a s\rce ( !  sulfur & oxyg5 ions 
:i* fill ! magnetosph]e4 ,ano!r         
magnetosph]ic int]action is ! electrical
 connection betwe5 ,io &  ,jupit] along 
! magnetic field l9es t leave ,jupit] & 
int]sect  ,io4 ,?is magnetic flux tube 0
 exam9$ by ,voyag] #a & a fl[ (  ab\t   
five million amp]es ( curr5t 0 measur$1 
:i* 0  consid]ably m ?an anticipat$4    
,voyag] also discov]$ a new  l[-frequ5cy
 radio emission com+ f ,jupit]1 :i* is  
possibly  associat$ ) ! ,io torus4      
,sci5tific inve/igations ( ! ,voyag]    
mission     ,inve/igation               
,typical ,jovian enc\nt] objectives     
,imag+ sci5ce                           
,high-resolution reconnaissance ov] l>ge
                                  phase 

angles2 atmosph]ic dynamics2            
geologic /ructure ( satellites   ,infr>$
 radiation             ,atmosph]ic      
composition1 !rmal                      
/ructure & dynamics2 satellite surface  
composition & !rmal prop]ties           
,photopol>imetry                        
,atmosph]ic a]osols2 satellite surface  
texture & sodium cl\d   ,radio sci5ce   
,atmosph]ic & ionosph]ic /ructure1      
con/itu5ts1 & dynamics   ,ultraviolet   
spectroscopy       ,upp] atmosph]ic     
composition &                           
/ructure2 auroral processes2            
di/ribution ( ions & neutral atoms 9    
! ,jovian sy/em   ,magnetic fields      
,planet>y magnetic field2 magnetosph]ic 
/ructure2 ,io flux tube curr5ts         
,plasma p>ticles                        
,magnetosph]ic ion & electron           
di/ribution2 sol> w9d int]action )      
,jupit]2 ions f satellites   ,plasma    
waves                   ,plasma electron
 d5sities2 wave-p>ticle                 
int]actions2 l[-frequ5cy wave emissions 

,planet>y radio a/ronomy                
,pol>ization & spectra ( radio          
frequ5cy emissions2 ,io radio modulation
                                        
process2 plasma d5sities   ,l[-en]gy    
*>g$ p>ticles   ,di/ribution1           
composition1 & fl[ (                    
en]getic ions & electrons2              
satellite-en]getic p>ticle int]actions  
,cosmic ray p>ticles                    
,di/ribution1 composition1 & fl[ (      
high-en]gy trapp$ nuclei2 en]getic      
electron spectra        ,illu/ration3 ,a
 comput]-g5]at$ mosaic ( ,voyag] #a     
pictures      %[+ ,jupit] f directly    
above ! nor? pole4 ,?is view %[s        
features to ab\t #bj degrees s\?        
latitude4 ,! black area at !      pole  
results f miss+ in=mation4              
,illu/ration3 ,,nasa      ,national     
,a]onautics & ,space ,adm9i/ration      
,jet ,propulsion ,laboratory            
,cali=nia ,in/itute ( ,te*nology        
,pasad5a1 ,cali=nia    ,,jpl #djj-bd    
#g_/gi                                  

,transcrib]'s ,notes      --,reta9$     
publication in=mation f ! pr9t$ edition3
 ?is e,book    is public-doma9 9 !      
c\ntry ( publication4    --,sil5tly     
correct$ a few palpable typos4          
--,mov$ captions ne>] ! relevant images2
 tweak$ image ref]5ces    )9 captions   
accord+ly4    --,add$ a ,table (        
,cont5ts4    --,9 ! text v]sions only1  
text 9 italics is delimit$ by           
und]scores4