,voyager #a ,encounters ,saturn ,contents ,foreword #a ,introduction #c ,the ,planet #d ,the ,rings #ab ,the ,satellites #bj ,a ,glimpse ,back #cb ,the ,voyager ,mission #cf ,,mission ,,objectives #cf ,,spacecraft ,,characteristics #cf ,,saturn ,,encounter #cf ,scientific ,highlights #ch ,,saturn #ch ,,rings #ch ,,new ,,satellites #ch ,,inner ,,satellites #ch ,,titan #ci ,,outer ,,satellites #ci ,,magnetosphere #ci ,scientific ,investigations #dj ,illustration3 ,,cover3 ,saturn and two of its moons1 ,tethys 7above7 and ,dione 7below71 were photographed by ,voyager #a on ,november #c1 #aihj1 from #ac million kilometers 7#h million miles74 ,the shadow of ,tethys is cast onto the cloudtops in the upper right corner of the image4 ,foreword ,the pictures assembled in this publication are a part of the rich and varied harvest of information returned by ,voyager #a across nearly a billion miles of interplanetary space4 ,these images are of great beauty as well as great scientific interest1 serving to remind us of the awesome and breathtaking dimensions of the solar system we inhabit4 ,voyager is providing intriguing new information which should help us to understand how the ,earth--and possibly the universe--was formed4 ,already there have been surprises and puzzles that paint a completely new picture of ,saturn and its neighborhood1 including the discovery of three new moons1 startling information about ,saturn's rings1 and observation of the unexpectedly complex structure of ,saturn's atmosphere and that of its largest moon1 ,titan4 ,it will take years for scientists to assimilate completely the information which is cascading down from ,voyager4 ,what more will this marvel of technology have to tell us before it departs the solar system to travel endlessly among the stars8 ,robert ,a4 ,frosch1 ,administrator ,national ,aeronautics and ,space ,administration ,december #aihj ,the date of each photograph and the distance of the spacecraft from the planet or satellite are included with each picture4 ,for sale by the ,superintendent of ,documents1 ,u4,s4 ,government ,printing ,office1 ,washington1 ,d4,c4 #bjdjb ,stock ,no4 #jcc-jjj-jjhag-a ,illustration3 ,voyager #a was launched from ,cape ,canaveral1 ,florida1 on ,september #e1 #aigg1 beginning its journey to ,jupiter1 ,saturn1 and beyond4 ,introduction ,no other generation has had the opportunity or the technology to reach beyond our world--to see1 to touch1 to hear the forces that shape our universe4 ,in slightly over two decades1 man has ingeniously explored five distant planets--and two dozen moons4 ,we have seen their weather and surfaces1 landed on some1 probed the atmospheres of others1 and listened to their radio noises4 ,under the planetary exploration program of the ,national ,aeronautics and ,space ,administration1 the ,voyager ,mission1 begun in #aigb1 was designed to explore ,jupiter1 ,saturn1 their satellites1 rings1 magnetic fields1 and interplanetary space4 ,two automated1 reprogrammable spacecraft1 ,voyagers #a and #b1 were launched in late summer of #aigg4 ,their goals3 the outer planets4 ,both spacecraft made astounding discoveries in the ,jupiter system in #aigi--;a thin ring1 a thick ionized sulfur and oxygen torus1 an actively volcanic satellite--these were but a few of the treasures yielded by the two ,jupiter flybys4 ,now1 ,voyager #a has completed exploration of its final target3 the ringed planet ,saturn and its enigmatic giant satellite1 ,titan4 ,true to the generally unpredictable nature of planetary exploration1 the treasures of the ,saturn system far exceeded all expectations4 ,we learned more about ,saturn in one week than in all of recorded history1 thanks to one trusty robot no larger than a compact car and to thousands of diligent and imaginative people4 ,both spacecraft carry an assortment of optical1 radiometric1 and fields and particles sensing instruments4 ,taken together1 their data present a comprehensive picture of a planetary system--and clues to what is happening1 what has happened1 and what may happen in our universe4 ,this publication presents the preliminary photographic results of ,voyager #a's encounter with ,saturn and its major satellites4 ,voyager #a transmitted over #ag1ejj images in its four months of close observations of the system4 ,many of these images have been combined to produce mosaics and color pictures4 ,hundreds have yet to be closely examined4 ,the second ,voyager spacecraft will begin its close ,saturn observations in early ,june #aiha and make its closest approach to the planet's northern hemisphere on ,august #be4 ,then1 due to its launch during a period of rare planetary alignment occurring only once every #age years1 ,voyager #b will be able to continue on to a rendezvous with the seventh planet1 ,uranus1 in ,january #aihf1 and perhaps even the eighth planet1 ,neptune1 in ,august #aihi4 ,voyager #a's primary mission is complete4 ,but its usefulness is far from over4 ,as we go about our daily business1 ,voyager #a is searching for another frontier--the edge of our solar system4 ,in #g to #ae years1 the spacecraft will cross the heliopause--the farthest reaches of our ,sun's magnetic field influence4 ,then1 high above our ecliptic plane1 ,voyager #a will continue its flight toward the star ,alpha ,ophiuchus4 ,eventually1 ,voyager #a will be too distant to communicate with ,earth and will silently drift in space forever4 ,andrew ,j4 ,stofan1 ,acting ,associate ,administrator for ,space ,science ,national ,aeronautics and ,space ,administration ,the ,planet ,illustration3 #aa_/e_/hj #i million km 7#e4e million mi7 ,saturn is the sixth planet from the ,sun and second largest in our solar system4 ,like ,jupiter1 it is a giant sphere of gas--mostly hydrogen and helium--with a possible core of rocky material4 ,various features in ,saturn's cloudtops are visible in the accompanying color-enhanced image of the planet's northern hemisphere3 small-scale convective cloud features 7similar to1 but much larger than1 thunderstorms in ,earth's atmosphere7 are visible in the brown belt2 an isolated convective cloud with a dark ring is visible in the light brown zone2 and a longitudinal wave is visible in the light blue region4 ,illustration3 #i_/ag_/hj #gf million km 7#dg million mi7 ,as ,voyager #a approached ,saturn1 a series of dark and light cloud bands 7belts and zones7 became apparent in the planet's northern hemisphere through a high altitude atmospheric haze4 ,the planet's shadow obscures the rings behind and immediately to the east of the disk4 ,in addition1 the shadow of the rings on the planet's disk can be seen just north of the rings themselves as they cross in front of the planet4 ,six of ,saturn's #ae known satellites are visible4 ,saturn's largest moon1 ,titan 7considerably larger than ,earth's moon71 is clearly visible in the upper left corner4 ,the smaller satellites ,dione1 ,tethys1 and ,rhea are shown in the lower left corner 7upper1 middle1 and lower1 respectively74 ,two of the innermost moons1 ,mimas and ,enceladus1 appear to the right of the planet 7,mimas is the one closer to the planet74 ,these six moons orbit ,saturn in the equatorial plane and appear in their present positions because ,voyager is above that plane4 ,illustration3 #aj_/ah_/hj #cd million km 7#ba million mi7 ,the ,north ,temperate ,belt is visible as the violet-colored belt in this false-color photograph4 ,in this image1 features which are especially bright in ultraviolet light appear as turquoise and violet1 while ultraviolet-dark areas appear orange4 ,notice in particular the three spots 7two bright orange and one pale violet7 at mid-northern latitudes4 ,the bright spots are similar to those shown at much higher resolution in later images4 ,the distinct color difference between the ,north ,equatorial ,belt and ,saturn's other belts and zones may be due to a thick haze layer covering the northern portion of the belt4 ,it is not yet understood why the southern hemisphere of the planet 7below the rings7 appears bluer than the northern hemisphere4 ,color spots in the rings are artifacts of image processing4 ,illustration3 #aj_/cj_/hj #ah million km 7#aa million mi7 ,saturn's soft1 velvety appearance and previously unseen detail in its mysterious rings became visible as ,voyager #a approached the planet4 ,for example1 a gap in the dark ,c-,ring is now visible1 and material can be seen within the relatively wide ,cassini ,division 7long believed to be empty71 which separates the ,b-,ring 7middle7 from the ,a-,ring 7outer74 ,the ,encke ,division appears near the outer edge of the ,a-,ring4 ,detail can be seen within the shadow cast by the rings upon the planet3 the broad1 dark band near the equator is the shadow of the ,b-,ring2 the thinner1 brighter line just to the south is the shadow of the less dense ,a-,ring4 ,three of ,saturn's moons1 ,tethys 7outer left71 ,enceladus 7inner left71 and ,mimas 7right7 are also visible in this computer mosaic of ,voyager #a images4 ,illustration3 #aa_/f_/hj #h4e million km 7#e4c million mi7 ,an unusual red oval cloud feature1 similar to 7but smaller than7 ,jupiter's ,great ,red ,spot1 was discovered in the southern hemisphere of ,saturn4 ,the oval1 #fjjj kilometers 7#djjj miles7 in length1 is located at #ee degrees south latitude4 ,the difference in color between the red oval and the surrounding bluish clouds in these two false-color images indicates that material within the oval contains a substance that absorbs more blue and violet light than the bluish clouds4 ,voyager scientists first observed the oval in ,august #aihj1 and the feature has retained its appearance since its discovery4 ,illustration3 #aa_/f_/hj #h million km 7#e million mi7 ,in this photograph1 the shadow of the satellite ,dione is seen as a dark circle on the face of the planet4 ,illustration3 #aa_/aj_/hj #c4e million km 7#b4b million mi7 ,a ribbon-like wave structure and small convective features marking a westward jet stream above the wave are visible in this photograph of ,saturn's cloudtops4 ,the view1 extending from #dj degrees to #fj degrees north latitude1 shows features #fe kilometers 7#dj miles7 in diameter4 ,measurements in images such as this one indicate that ,saturn has fewer east-to-west wind currents than does ,jupiter4 ,illustration3 #aa_/ab_/hj #ddb1jjj km 7#bfe1jjj mi7 ,numerous small cloud features were photographed as ,voyager #a passed above ,saturn's southern hemisphere4 ,at these polar latitudes1 the large-scale light and dark bands break down into small-scale features1 seen here as waves and eddies4 ,illustration3 #aa_/g_/hj #g4e million km 7#d4f million mi7 ,two brown ovals1 approximately #aj1jjj kilometers 7#fjjj miles7 across1 were discovered in ,saturn's northern hemisphere1 at about #dj degrees and #fj degrees latitude4 ,the polar oval 7upper left7 has a structure similar to ,saturn's red oval located in the southern polar latitudes4 ,detail within the ovals is not visible at this resolution1 so it is not yet known if they are rotating features similar to the many spots in ,jupiter's atmosphere4 ,the ,rings ,illustration3 #aa_/ab_/hj #gag1jjj km 7#ddd1jjj mi7 ,the rings of ,saturn have amazed and intrigued astronomers for over #cjj years4 ,now that we have seen them up close1 they are even more astonishing4 ,although they stretch over #fe1jjj kilometers 7#dj1jjj miles71 they may be only a few kilometers thick4 ,the ring particles--from a few microns to a meter 7three feet7 in size--have been described as icy snowballs or ice-covered rock4 ,voyager scientists continue to pore over their data1 searching for answers to the puzzles of the rings4 ,the rings were named in order of their discovery1 so the labels do not indicate their relative positions4 ,from the planet outward1 they are known as ,d1 ,c1 ,b1 ,a1 ,f1 and ,e4 ,illustration3 #aj_/be_/hj #bd million km 7#ae million mi7 ,extraordinarily complex structure is seen across the entire span of ,saturn's ring system4 ,the sequence 7taken approximately every #ae minutes as ,voyager #a approached ,saturn7 proceeds from top to bottom in each column and shows radial 8spokes0 rotating within the ,b-,ring4 ,the spokes may be caused by a combination of magnetic and electrostatic forces4 ,illustration3 #aa_/f_/hj #h million km 7#e million mi7 ,over #ie individual concentric features can he counted2 the final count in higher resolution images may be anywhere from #ejj to #ajjj separate rings4 ,a few of the ringlets shown in this computer-assembled mosaic are not concentric circles but are instead elliptical4 ,ring particles are probably ice or ice covered rock4 ,illustration3 ,the classic features of the rings are illustrated in the diagram4 ,d-,,ring ,c-,,ring ,b-,,ring 8,,spoke0 ,,cassini ,,division ,,encke ,,division ,a-,,ring ,f-,,ring ,illustration3 #aa_/h_/hj #f million km 7#c4g million mi7 ,the ,cassini ,division is filled with numerous ringlets4 ,discovered by ,cassini in #afge1 this area between the ,a- and ,b-,rings had long been thought devoid of material4 ,the ,voyager observation of well-defined rings within the ,cassini ,division was an unexpected discovery4 ,illustration3 #aa_/ab_/hj #gdj1jjj km 7#dfj1jjj mi7 ,saturn's ring system1 viewed from below1 appears dramatically different from its appearance on the sunlit side4 ,this computer-processed image shows the ,f-,ring circling outside the ,a-,ring1 the ,a-,ring with its ,encke ,division1 the multiple ringlets in the ,cassini ,division1 and the optically thick ,b-,ring1 seen here in magenta hues 7the coloration is an artifact of processing and is not real74 ,the ,b-,ring appears dark from below the ring plane because it is dense enough to reflect most of the sunlight1 causing it to appear very bright when seen from the sunward side4 ,the opaline brightness of the ,cassini ,division here indicates a great deal of sunlight being scattered through this region4 ,the ,encke ,division may really be empty1 since it appears dark from both above and below4 ,illustration3 #aa_/ab_/hj #gbj1jjj km 7#dej1jjj mi7 ,outbound and above the ring plane1 ,voyager #a gave us this view of ,saturn's rings eight hours after its closest approach to the planet4 ,the unique lighting accentuates the many hundreds of bright and dark ringlets comprising the ring system4 ,the ,c-,ring 7dark gray area7 seems to blend into the brighter ,b-,ring as the concentric features radiate out from the planet4 ,the dark spoke-like features seen in images taken during the approach to ,saturn now appear as bright streaks1 indicating that they may be composed of small particles4 ,illustration3 #aa_/ab_/hj #gej1jjj km 7#dgj1jjj mi7 ,two narrow1 braided rings in the ,f-,ring are evident in this view1 as well as a broader1 very diffuse component about #ce kilometers 7#bj miles7 across4 ,a totally unexpected discovery1 the braided rings trace distinctly separate orbits intertwining each other4 ,the 8knots0 may be local clumps of ring material or tiny moons4 ,it is difficult to explain this complicated structure using only the gravitational forces known to be affecting the particles of this ring4 ,it is possible that additional1 electrostatic forces may also influence these particles4 ,illustration3 #aa_/h_/hj #g million km 7#d4c million mi7 ,brightness variations in the ,f-,ring may be due to clumping in the ring material4 ,the features are seen at the top and again near the left edge of the ring in this image4 ,the 8gap0 in the ring 7left center7 is not real but is the location of a reseau mark on the camera's vidicon tube4 ,these bright features in the ,f-,ring appear to move at the orbital rate of the ring particles and may be larger bodies or thicknesses in the rings4 ,saturn's thirteenth and fourteenth satellites1 which orbit on either side of the ,f-,ring1 may act like 8sheepdogs10 herding the ,f-,ring particles between them4 ,less than #ajj kilometers 7#fj miles7 wide1 the ,f-,ring is located outside of the ,a-,ring4 ,satellite #ad1 discovered by ,voyager #a1 is seen just inside the ,f-,ring4 ,the ,satellites ,illustration3 ,in only twelve hours1 ,saturn's satellites grew from names in ancient mythology into dazzling worlds with personae of their own4 ,as ,voyager #a sailed through the ,saturn system1 it returned photographs of ,mimas1 ,enceladus1 ,tethys1 ,dione1 and ,rhea--all part of a class of intermediate-sized icy bodies heretofore unstudied by planetary spacecraft4 ,all but ,enceladus show heavily cratered surfaces1 evidence of aeons of meteorite bombardment4 ,enceladus hints at internal processes1 as yet unidentified1 which may have erased from its surface the evidence of early bombardment--but we must await ,voyager #b's arrival next ,august to better understand this body4 ,illustration3 #aa_/i_/hj #d4e million km 7#b4h million mi7 ,the surface of giant ,titan1 now dethroned from its seat as the solar system's largest satellite 7,jupiter's ,ganymede is larger71 remains an enigma1 shrouded beneath thick layers of haze4 ,illustration3 #aa_/ab_/hj #bb1jjj km 7#ad1jjj mi7 ,tiny moons--three new ones and three confirmed from previous sightings--may tell us much about ring dynamics since gravitational forces from satellites probably influence the ring structure4 ,two of these tiny moons are on the verge of collision in the same orbit1 while several others appear to bound the ,a- and ,f-,rings4 ,iapetus1 whose two hemispheres differ dramatically in brightness1 was photographed in its orbit1 almost #c4f million kilometers 7#b4b million miles7 from the planet4 ,illustration3 #aa_/ab_/hj #dbe1jjj km 7#bfd1jjj mi7 ,mimas1 ,saturn's innermost large satellite1 has an impact crater covering more than one quarter the diameter of the entire moon4 ,nowhere else in the solar system has such a disproportionately large feature been seen4 ,in fact1 it is believed that any impact larger than this would probably have shattered ,mimas into two or more fragments4 ,the crater has a raised rim and central peak1 typical of large impact structures on terrestrial planets4 ,additional smaller craters1 #ae to #de kilometers 7#aj to #cj miles7 in diameter1 can be seen scattered across the surface1 particularly along the terminator4 ,mimas is one of the small1 low density ,saturnian satellites implying that it is composed primarily of ice4 ,illustration3 #aa_/ab_/hj #acj1jjj km 7#hj1jjj mi7 ,mimas' other side shows a uniformly and heavily cratered surface--a record of the bombardment that occurred throughout the solar system in its early history #d4e billion years ago4 ,a long1 narrow trough about #e kilometers 7#c miles7 wide crosses from northeast to southwest4 ,mimas' surface is very reflective 7about #fj percent71 indicating that it consists largely of ice1 which has been chipped and pulverized by aeons of meteoritic bombardment4 ,such a surface on a small1 low mass moon would probably resemble light1 powdery snow4 ,features as small as #c kilometers 7#b miles7 across are visible4 ,illustration3 #aa_/ab_/hj #fej1jjj km 7#djj1jjj mi7 ,enceladus appears to be largely devoid of craters or other major surface relief1 suggesting that perhaps internal processes may have erased such structures4 ,this satellite will be seen better by ,voyager #b when it flies past ,saturn in ,august #aiha4 ,illustration3 #aa_/ab_/hj #a4b million km 7#gej1jjj mi7 ,this heavily cratered surface of ,tethys faces toward ,saturn and includes a large valley about #gej kilometers 7#ejj miles7 long and #fj kilometers 7#dj miles7 wide4 ,the craters are the result of impacts1 and the valley appears to be a large fracture of unknown origin4 ,tethys has a diameter of #ajej kilometers 7#fej miles71 about one-third that of ,earth's ,moon4 ,the smallest features visible in this picture are about #bd kilometers 7#ae miles7 across4 ,illustration3 #aa_/ab_/hj #gjj1jjj km 7#dce1jjj mi7 ,dione reveals two distinctly different hemispheres4 ,the photograph shows ,dione's trailing side4 ,bright radiating patterns are probably rays of debris thrown out of impact craters2 other bright areas may be topographic ridges and valleys4 ,illustration3 #aa_/ab_/hj #afb1jjj km 7#aja1jjj mi7 ,dione's other hemisphere 7mosaic7 also has many impact craters--the record of cosmic collisions4 ,the largest crater is less than #ajj kilometers 7#fj miles7 in diameter and includes a well-developed central peak4 ,sinuous valleys 7seen near each pole7 are probably the result of crustal fracturing in the moon's icy crust4 ,dione's diameter is only #aajj kilometers 7#gjj miles71 much smaller than any of ,jupiter's icy moons4 ,illustration3 #aa_/ac_/hj #hj1jjj km 7#ej1jjj mi7 ,craters stand shoulder-to-shoulder on the surface of ,saturn's satellite ,rhea1 seen in this mosaic of the highest-resolution pictures of the north polar region4 ,rhea is #aejj kilometers 7#iej miles7 in diameter and is the most heavily cratered ,saturn moon4 ,the largest crater1 made by the impact of cosmic debris1 is about #cjj kilometers 7#aij miles7 in diameter4 ,illustration3 #aa_/ab_/hj #abh1jjj km 7#gi1ejj mi7 ,impact craters on the ancient surface of ,rhea closely resemble those on ,mercury and ,earth's ,moon4 ,many of the craters have central peaks formed by rebound of the floor during the explosive formation of the crater4 ,some craters are old and degraded by later impacts4 ,many have sharp rims and appear relatively fresh1 while others are very shallow and have subdued rims1 indicative of their antiquity4 ,white areas on the edges of several of the craters are probably fresh ice exposed on steep slopes or possibly deposited by volatiles leaking from fractured regions4 ,surface features as small as #b4e kilometers 7#a4e miles7 in diameter are visible4 ,illustration3 #aa_/i_/hj #d4e million km 7#b4h million mi7 ,titan is a large1 bizarre satellite4 ,it is larger 7almost #eabj kilometers or #cahj miles in diameter7 than the planet ,mercury and possesses a dense atmosphere of unique composition4 ,voyager #a's cameras show ,titan's surface to be totally obscured by a thick layer of atmospheric haze4 ,in the full-disk photograph1 only two features are visible3 a faint boundary between the southern and darker northern hemispheres and a dark 8hood0 overlying ,titan's north polar region4 ,illustration3 #aa_/ab_/hj #dce1jjj km 7#bgj1jjj mi7 ,this hood and greater detail in the haze layers are shown in the higher resolution photograph4 ,illustration3 #aa_/aj_/hj #d4f million km 7#b4h million mi7 ,little detail can be seen in this distant view of ,hyperion1 the satellite which orbits just beyond ,titan4 ,voyager #b will observe ,hyperion at a closer range4 ,illustration3 #aa_/ab_/hj #c4b million km 7#a4i million mi7 ,saturn's satellite ,iapetus displays a large1 circular feature about #bjj kilometers 7#abj miles7 across with a dark spot in its center4 ,the circular feature is probably a large impact structure outlined by dark material1 possibly thrown out by the impact4 ,the satellite's leading hemisphere is to the left1 and the trailing hemisphere1 which is four to five times brighter1 is to the right4 ,iapetus' diameter is #adej kilometers 7#ijj miles74 ,illustration3 #aa_/ab_/hj #agg1jjj km 7#aaj1jjj mi7 ,two satellites 7,saturn's tenth and eleventh7 revolve in nearly identical orbits #aea1jjj kilometers 7#id1jjj miles7 from ,saturn's center4 ,the satellites are each #ajj to #bjj kilometers in diameter1 larger than the distance separating their orbits1 and they are currently approaching one another at a rate which promises collision in about two years4 ,such a collision1 however1 will probably be averted by orbital changes induced by the satellites' mutual gravitational interactions as they near one another4 ,the trailing co-orbital satellite1 seen in this photograph1 has a very irregular outline 7the ,sun is shining from the left74 ,this color composite was produced from three exposures taken over a period of more than six minutes4 ,during this period1 a thin shadow1 cast by a previously unknown ring1 moved across the satellite causing the 8rainbow0 pattern shown here4 ,illustration3 #aj_/be_/hj #be million km 7#af million mi7 ,two smaller satellites--,saturn's thirteenth and fourteenth moons--were discovered on ,october #be1 #aihj1 in images taken to study the dark 8spokes0 within ,saturn's ,b-,ring4 ,the smaller1 inner satellite has a diameter of about #ejj kilometers 7#cjj miles7 and is visible just outside the ,a-,ring1 near the bottom of the picture4 ,it travels in an orbit between the ,a-,ring and the ,f-,ring 7not visible in this photograph74 ,the second satellite1 seen to the left1 travels just outside the ,f-,ring and is about #fjj kilometers 7#djj miles7 in diameter4 ,scientists believe the dimensions of the narrow ,f-,ring may be determined by these two satellites1 which orbit on either edge of the ring4 ,a ,glimpse ,back ,illustration3 #aa_/ac_/hj #a4e million km 7#icj1jjj mi7 ,looking back at the ,saturn system as it soared upward and outward1 ,voyager #a continued its observations for nearly five weeks after closest ,saturn approach4 ,the spacecraft photographed the planet's sunlit crescent1 the ring shadows falling on the planet1 and ,saturn's dark hemisphere illuminated by 8ringshine40 ,it searched for lightning and auroras on the planet's dark side and looked for 8sun dogs0 resulting from ammonia crystals in the atmosphere4 ,it continued temperature and composition measurements and searched for new satellites out to the orbit of ,mimas4 ,it measured the flow of plasma in ,saturn's magnetosphere and now1 its journey far from over1 ,voyager #a proceeds toward the outer boundary of our solar system1 as it seeks to probe the space among the stars of our galaxy1 the ,milky ,way4 ,illustration3 #aa_/af_/hj #e4c million km 7#c4c million mi7 ,departing ,saturn1 ,voyager #a photographed the planet from a unique perspective1 clearly showing ,saturn's shadow on the rings4 ,illustration3 #aa_/ab_/hj #bej1jjj km 7#aej1jjj mi7 ,during a #dj-minute period on the day of encounter1 the spacecraft was itself in the planet's shadow4 ,at this time1 the wide-angle camera acquired a photograph of this shadow line1 revealing ring material in a region very close to the planet1 where no material had been previously observed4 ,this inner ring1 the ,d-,ring1 is roughly #fjjj kilometers 7#djjj miles7 wide and extends to within about #fjjj kilometers of ,saturn's cloudtops4 ,the ,voyager ,mission ,only once every #age years are the outer planets aligned in their orbits so that we can take advantage of gravity-assist trajectories to achieve encounters with ,jupiter1 ,saturn1 ,uranus1 and ,neptune on one mission4 ,the gravity-assist technique uses one planet's gravity field and motion through space to alter the spacecraft's flight path and propel it outward toward the next planet4 ,voyager #a's trajectory1 which was selected to best view ,titan1 has now propelled the spacecraft out of the ecliptic plane1 while ,voyager #b's path will remain in this plane to provide future encounters with ,uranus and possibly with ,neptune4 ,,mission ,,objectives ,the ,voyager ,project was approved in ,june #aigb and had as its mission objectives3 ,exploration of the ,jupiter and ,saturn planetary systems1 including their atmospheres1 rings1 satellites1 and magnetospheres ,comparative analyses of the two systems ,investigation of the interplanetary medium between ,earth and ,saturn ,a fourth objective1 added in #aigf1 was to preserve the possibility of extending the mission to include an investigation of the planet ,uranus and the interstellar medium4 ,with the completion of ,voyager #a's ,saturn flyby1 it is now clear that these objectives will be achieved4 ,,spacecraft ,,characteristics ,two identical spacecraft were developed for the #aigg launch opportunity4 ,these marvelous machines were cleverly designed to survive the rigors of long voyages in outer space and to deliver high-quality scientific information required for detailed understanding of planetary systems4 ,the spacecraft are both complex--automatically responding to their ,earth-bound monitors that remotely control them via radio commands--and highly autonomous--capable of caring for themselves in many areas through a system of sensors1 computers1 and spare equipment4 ,each spacecraft functions on about #djj watts of electrical power which is provided by nuclear generators4 ,broadcasts of data across a billion miles to ,earth are accomplished with a spacecraft transmitter power of only about #be watts1 the amount of energy required by a small household light bulb4 ,voyager's scientific payload was carefully chosen to observe ,saturn over a wide range of wave-lengths and to measure magnetic fields1 charged particles1 and plasma waves4 ,,saturn ,,encounter ,illustration3 ,voyager #a approached within #abd1jjj kilometers 7#gg1jjj miles7 of ,saturn's cloudtops4 ,six of the satellites that were photographed are shown in their approximate positions at closest approach by the spacecraft4 ,,titan ,,dione ,,tethys ,,mimas ,,enceladus ,,rhea ,voyager #a's ,saturn encounter period began on ,august #bb1 #aihj1 at a range of #aji million kilometers 7#fh million miles7 from the planet4 ,even at this great distance1 ,voyager's images were better than any from ,earth-based telescopes4 ,during the long encounter period1 which extended through ,december #ai1 #aihj1 continuous observations of ,saturn's realm were carried out by ,voyager's instruments4 ,voyager #a's flight path through the ,saturn system demanded navigation of the highest precision to meet three critical targets3 7#a7 a close #djjj-kilometer 7#bcjj-mile7 flyby and occultation at ,titan1 7#b7 a precise1 three-minute time period when the spacecraft was emerging from occultation at the same time ,earth was in a position to receive the spacecraft signals passing through the gap between ,saturn and its rings1 and 7#c7 a flight path through the ,e-,ring at ,dione's orbit to assure safe passage through a zone clear of potentially dangerous material4 ,to assure these targets were achieved1 small trajectory trim maneuvers were executed on ,october #aa1 #aihj1 and again on ,november #f1 #aihj1 as ,voyager #a sped toward ,saturn4 ,illustration3 ,voyager spacecraft and scientific instruments4 ,,high-,,gain ,,antenna 7#c4g-meter diameter7 ,,low-,,energy ,,charged ,,particle ,,cosmic ,,ray ,,plasma ,,imaging ,,ultraviolet ,,spectrometer ,,infrared ,,interferometer ,,spectrometer ,,photopolarimeter ,,optical ,,calibration ,,target ,,planetary ,,radio ,,astronomy ,,and ,,plasma ,,wave ,,antenna 7#b7 ,,radioisotope ,,thermoelectric ,,generator 7#c7 ,,magnetometer ,,boom ,by ,october #bd1 #aihj1 when ,voyager #a was about #cj million kilometers 7#ai million miles7 from ,saturn1 the spacecraft's narrow-angle camera could no longer capture the planet in a single picture4 ,thus1 a period of multiple images or mosaics began4 ,by ,november #b1 #aihj1 even four-picture mosaics could no longer cover the rapidly growing scene4 ,voyager #a's pace of operations reached an exciting peak during the near-encounter phase from ,november #aa through ,november #ac1 #aihj4 ,while still about #a4f million kilometers 7#a million miles7 from closest approach to ,saturn1 ,voyager #a encountered ,titan on ,november #aa1 #aihj1 and then dipped below the ring plane as it accelerated rapidly toward ,saturn4 ,on ,november #ab1 #aihj1 ,voyager #a came within #abd1jjj kilometers 7#gg1jjj miles7 of the cloudtops of ,saturn's southern hemisphere1 where ,saturn's gravity altered the spacecraft's course1 hurtling the spacecraft upward past the ring plane4 ,close observation of ,saturn's other major satellites and its rings were made during this passage4 ,from ,earth to ,saturn1 ,voyager #a has traveled in the ecliptic plane1 the plane in which the major planets orbit4 ,now1 having completed its final planetary flyby1 ,voyager #a is rising above this plane on a trajectory that will eventually carry it above and out of the solar system1 probably before the end of this century4 ,as it proceeds1 the spacecraft will return information about the solar wind and magnetic fields in the far1 unexplored reaches of our solar system and will observe cosmic rays emitted from the distant stars among which ,voyager will ultimately cruise4 ,scientific ,highlights ,some of the most important information gathered by ,voyager #a on the ,saturn system is presented pictorially in this publication and is supplemented here with brief summaries of the major discoveries1 observations1 and theories4 ,,saturn ,saturn's atmosphere appears similar to ,jupiter's1 with alternating dark belts and bright zones1 circulating storm regions1 and other dark and light cloud markings4 ,saturn's belt and zone system extends to higher latitudes than those on ,jupiter1 and all of the features are muted by a thick atmospheric haze1 perhaps #gj kilometers 7#dj miles7 deep4 ,wind speeds up to #aejj kilometers per hour 7#ijj miles per hour7 occur at the equator--four to five times faster than any ,jovian winds4 ,temperatures near the cloudtops range from #hf to #ib kelvins 7-#cje to -#bid ,fahrenheit7--nearly #fj degrees colder than at ,jupiter4 ,saturn still radiates about #b4h times as much heat as it receives from the ,sun4 ,the coolest temperatures are found at the center of the equatorial zone4 ,auroral emissions have been seen near ,saturn's poles1 and auroral-type emissions have been seen in ultraviolet light near the illuminated limb of the planet4 ,lightning bolts have not been seen on ,saturn1 but radio emissions typical of lightning discharges have been recorded4 ,the source of these discharges is believed to be the rings rather than ,saturn's atmosphere4 ,,rings ,hundreds of tiny ringlets--a few of them elliptical rather than circular--comprise the classic ,a-1 ,b-1 and ,c-,rings1 once thought to be uniform disks of material4 ,the ,f-,ring1 which was first sighted by ,pioneer #aa in #aigi1 was observed to be three separate1 intertwined ringlets4 ,the existence of a ,d-,ring between the ,c-,ring and the planet has been confirmed by observations during ,voyager #a's passage through ,saturn's shadow4 ,the tenuous ,e-,ring1 previously observed from ,earth only when ,saturn's rings could be viewed edge-on 7every #ae years71 has also been observed during shadow passage4 ,at least one other ring has been found between the ,e- and ,f-,rings in ,voyager images4 ,long1 radial1 spoke-like features in the ,b-,ring were dark when viewed upon approach and bright when observed after encounter when the spacecraft looked back toward the planet and the ,sun4 ,,new ,,satellites ,voyager #a photographed six tiny moons1 some that had never been seen before4 ,satellites #aj and #aa1 dubbed the 8co-orbitals10 share an orbit #ia1jjj kilometers 7#eg1jjj miles7 above ,saturn's cloudtops4 ,the leading satellite has a diameter of about #afj kilometers 7#ajj miles71 while the trailing satellite has an irregular shape1 approximately #aje by #fe kilometers 7#fe by #dj miles74 ,little is known about satellites #ab1 #ac1 #ad1 and #ae aside from their orbits and periods4 ,satellite #ab orbits at the same distance from ,saturn as ,dione1 at a point about #fj degrees ahead of ,dione4 ,satellites #ac and #ad1 outside and inside the ,f-,ring 7respectively71 appear to 8herd0 this thin ring between them4 ,satellite #ae appears to limit the outer edge of the ,a-,ring in a similar manner4 ,,inner ,,satellites ,mimas1 ,enceladus1 ,tethys1 ,dione1 and ,rhea represent a body size not previously explored by spacecraft4 ,they are larger than ,jupiter's ,amalthea and ,mars' ,phobos and ,deimos1 yet smaller than ,mercury1 our ,moon1 or ,jupiter's large satellites4 ,their diameters range from #cij kilometers 7#bdj miles7 for ,mimas to #aecj kilometers 7#iej miles7 for ,rhea1 and they are probably composed primarily of water ice4 ,with the exception of ,enceladus1 all of these moons have heavily cratered surfaces1 looking much like the ,moon and ,mercury4 ,mimas displays an impact crater whose diameter is one-fourth that of the satellite--such an impact must have nearly shattered the icy satellite4 ,tethys has a valley #gj kilometers 7#dj miles7 wide that stretches #hjj kilometers 7#ejj miles7 across the satellite1 an apparent crustal fracture resulting from seismic activity4 ,several sinuous valleys1 some of which appear to branch1 are visible on ,dione's surface4 ,both ,dione and ,rhea have bright1 wispy streaks on their already highly reflective surfaces1 perhaps caused by ice thrown out of craters by meteorite impacts4 ,of the five inner moons1 ,enceladus appears the smoothest1 but we will have to wait for ,voyager #b to photograph the satellite at greater resolution in #aiha4 ,since the maximum intensity of the ,e-,ring occurs near ,enceladus' orbit1 ,enceladus may be a source of ,e-,ring particles4 ,,titan ,titan is now known to be smaller than ,jupiter's ,ganymede4 ,its diameter is less than #eabj kilometers 7#cahj miles71 which implies a density twice that of water ice4 ,a dense1 hazy atmosphere at least #djj kilometers 7#bej miles7 thick obscures the surface4 ,voyager #a determined that ,titan has a nitrogen-rich atmosphere 7as does ,earth71 but with concentrations of hydrocarbons such as methane 7natural gas71 ethane1 acetylene1 ethylene1 and deadly hydrogen cyanide4 ,the haze layers merge into a darkened hood over the north pole4 ,at the poles1 liquid nitrogen lakes may form4 ,the surface temperature is probably near #ajj kelvins 7-#bhj ,fahrenheit71 only slightly warmer than the boiling point of liquid nitrogen4 ,titan has no appreciable magnetic field and therefore possesses no large liquid conducting core4 ,it does1 however1 supply a small amount of charged particles to ,saturn's magnetosphere4 ,the southern hemisphere is somewhat brighter than the northern1 perhaps as a result of seasonal effects4 ,,outer ,,satellites ,of the three known outer satellites1 ,voyager #a studied from a distance only ,hyperion and ,iapetus4 ,tiny ,phoebe1 in its retrograde 7clockwise7 orbit1 will be studied by ,voyager #b in the summer of #aiha4 ,hyperion and ,iapetus are most likely composed of water ice1 although their masses and densities are uncertain4 ,iapetus has one bright and one dark hemisphere4 ,the dark side1 which faces forward as ,iapetus circles ,saturn1 reflects about one-fifth as much light as the trailing1 bright side4 ,,magnetosphere ,although it is only about one-third the size of ,jupiter's magnetosphere1 ,saturn's magnetosphere is still an enormous structure1 extending nearly two million kilometers from the planet toward the ,sun4 ,the size of the magnetosphere fluctuates rhythmically as the flow of charged particles in the solar wind increases or decreases in intensity4 ,the magnetosphere can be pushed inside ,titan's orbit1 so that at times the satellite finds itself outside of the magnetosphere altogether4 ,charged particles in the planet's magnetosphere are dragged along by the magnetic field1 circling the planet at ,saturn's rotation rate of #aj hours1 #ci minutes4 ,these charged particles whiz by ,titan at a dizzying rate of more than #bjj kilometers 7#abj miles7 per second4 ,titan leaves a motorboat-like wake in its orbital path4 ,extending from the orbit of ,titan inward to the orbit of ,rhea1 an enormous cloud of uncharged hydrogen atoms forms a doughnut-shaped torus of ultraviolet-emitting particles4 ,because of their neutrality1 these atoms are not towed around by ,saturn's magnetic field4 ,close to the planet1 ,saturn's rings act as an effective shield or absorber of charged particles4 ,the rings themselves are apparently substantially affected in this process1 however1 as evidenced by their 8spokes0 of fine particles and the lightning-like electrical discharges attributed to the rings4 ,scientific ,investigations ,,investigation ,,saturn ,,encounter ,,objectives ,imaging science ,planetary meteorology2 satellite geology2 ring structure and dynamics ,infrared ,atmospheric composition1 thermal structure interferometry and dynamics2 satellite surface composition and thermal properties2 ring composition ,radio science ,atmospheric and ionospheric structure1 constituents1 and dynamics at ,saturn and ,titan2 ring particle size ,ultraviolet ,upper atmospheric composition and structure2 spectroscopy auroral processes2 distribution of ions and neutral atoms in the ,saturn system ,magnetic fields ,planetary magnetic field2 magnetospheric structure ,plasma particles ,magnetospheric ion and electron distribution2 solar wind interaction with ,saturn2 ions from satellites ,plasma waves ,plasma electron densities2 wave-particle interactions2 low-frequency wave emissions ,planetary radio ,polarization and spectra of radio-frequency astronomy emissions2 plasma densities ,low-energy charged ,distribution1 composition1 and flow of particles energetic ions and electrons2 satellite-energetic particle interactions ,cosmic ray particles ,distribution1 composition1 and flow of high-energy trapped nuclei2 energetic electron spectra 8,notre voyageur connaissait merveilleusement les lois de la gravitation1 et toutes les forces attractives et rpulsives4 ,il s'en servait si propos1 que tantt l'aide d'un rayon de soleil1 tantt par la commodit d'une comte1 il allait de globe en globe1 lui et les siens1 comme un oiseau voltige de branche en branche40 8,our voyager knew marvelously the laws of gravitation1 and all attractive and repulsive forces4 ,he used them in such a timely way that1 once with the help of a ray of sunshine1 another time thanks to a cooperative comet1 he went from globe to globe1 he and his kin1 as a bird flutters from branch to branch40 ,,voltaire--,micromgas1 ,histoire ,philosophique1 #ageb4 ,illustration3 ,,nasa ,national ,aeronautics and ,space ,administration ,jet ,propulsion ,laboratory ,california ,institute of ,technology ,pasadena1 ,california ,,jpl #djj-ajj #ab_/hj ,transcriber's ,notes --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,silently corrected a few palpable typos4 --,moved captions nearer the relevant images2 tweaked image references within captions accordingly4 --,added a ,table of ,contents4 --,in the text versions only1 text in italics is delimited by underscores4