,illustration3 ,cover3 ,a cylindrical projection of ,jupiter's atmosphere was made from ten color images taken by ,voyager #a during a single ten-hour rotation of the planet4 ,illustration3 ,a computer-generated mosaic of ,voyager #a pictures showing ,jupiter from directly below the south pole4 ,this view shows features as far north as #bj degrees latitude4 ,the black area at the ,pole results from missing information4 ,voyager ,encounters ,jupiter ,july #aigi ,,nasa ,national ,aeronautics and ,space ,administration ,,contents ,foreword #c ,introduction #d ,images of ,jupiter and ,its ,satellites #f ,the ,voyager ,mission #cg ,scientific ,highlights #ci ,jupiter #ci ,amalthea #ci ,io #ci ,europa #ci ,ganymede #ci ,callisto #ci ,the ,magnetosphere #dj ,scientific investigations of the ,voyager mission #dj ,illustration3 ,a ,titan_/,centaur rocket served as the launch vehicle for ,voyager and was the last planned use of this type of launch vehicle prior to the era of the ,space ,transportation ,system 7,shuttle ,orbiter74 ,foreword ,in late summer of #aigg1 the ,united ,states launched two unmanned ,voyager spacecraft on an extensive reconnaissance of the outer planets1 a decade-long odyssey that could take them to #c planets and as many as #ah planetary satellites4 ,the first encounter was with the giant ,jovian planetary system1 #fde million kilometers 7#djj million miles7 away4 ,passing by ,jupiter and its complex satellite system in #aigi1 the ,voyager spacecraft have collected and returned to ,earth an enormous amount of data and information that may prove to be a keystone in understanding our solar system4 ,this publication provides an early look at the ,jovian planetary system and contains a selected sample from the more than #cj1jjj images collected during this phase of the ,voyager mission4 ,while ,voyager achieved an impressive record of accomplishments1 full realization of the scientific value of this program must await the remaining ,voyager encounters with ,saturn and perhaps ,uranus1 and a detailed analysis of the data from all the spacecraft investigations4 ,robert ,a4 ,frosch1 ,administrator ,national ,aeronautics and ,space ,administration ,introduction ,in ,march #aigi ,voyager #a swept past ,jupiter1 photographing both the giant planet and five of its moons4 ,four months later1 a companion spacecraft1 ,voyager #b1 made a similar encounter4 ,now1 with ,jupiter receding behind them1 both spacecraft are headed toward the outer reaches of our solar system4 ,in ,november #aihj1 ,voyager #a will fly past ,saturn4 ,voyager #b1 traveling at slower speeds1 will reach the same way station in ,august #aiha4 ,beyond there1 the itinerary is less certain4 ,in ,january #aihf1 eight years after its departure from ,earth1 ,voyager #b may sail within range of ,uranus1 taking closeup pictures of that distant planet for the first time4 ,long after they have exhausted their fuel supplies and their radios have fallen silent1 both spacecraft will continue their traverse through space and beyond our solar system1 on an endless journey4 ,illustration3 ,an ,apollo #ab astronaut retrieves ,surveyor #c hardware for ,earth laboratory analysis after #cj months exposure on lunar surface4 ,illustration3 ,viking ,lander #b surveys the boulder-strewn ,utopian ,plain and reddish sky of ,mars4 ,preliminary results of the ,voyager encounters with ,jupiter are presented in this booklet4 ,as you examine the pictures1 you will be participating in a revolutionary journey of exploration4 ,living in a society where many accomplishments and products are billed as 8extraordinary10 8stupendous10 8once in a lifetime10 or 8unique10 we sometimes lose our perspective4 ,conditioned to hyperbole1 we fail to recognize those advances that are truly exceptional4 ,we need a historian's vantage point to identify the events that can literally change the course of civilization4 ,so it is that every student of history recognizes the importance of the ,renaissance1 an extraordinary time when man looked outward1 reaching beyond the traditions of the past to study his place in the natural world4 ,the results were apparent in art1 architecture1 and literature1 in new philosophic and governmental systems1 and in the staggering scientific revolution exemplified by ,galileo's first examination of the heavens with a telescope1 and in his stubborn support of the heretical assertion that the ,earth was not the center of the solar system4 ,historians writing a hundred or two hundred years from now may well look on the latter part of the twentieth century as another turning point in civilization4 ,for the first time1 we explored beyond ,earth--first the ,moon1 then the neighboring planets1 and finally the outermost planets1 the very fringe of our solar system4 ,how will the historian evaluate this period of exploration8 ,first1 perhaps1 he will describe the ,apollo program as a visionary example of great cooperative ventures that can be accomplished by many individuals1 private companies1 and government institutions4 ,he will describe the subsequent space ventures that weave a fabric of cooperation and goodwill between nations4 ,he will point out the technological advances incorporated in unmanned spacecraft1 sophisticated robots able to control their own activities and solve their own problems4 ,he will mention the revolution in microelectronics--the art of fabricating complex electrical control circuits so small the eye cannot perceive them1 a revolution accelerated by the requirement to conserve weight and generate performance in interplanetary spacecraft4 ,he will point to the introduction of new products1 particularly in areas of communication1 medical treatment1 and energy conversion4 ,illustration3 ,galileo orbiter and probe mission to ,jupiter in #aihe will expand upon the ,voyager investigations of the ,jovian system4 ,illustration3 ,a solar electric propulsion spacecraft would eject an instrumented probe toward ,halley's comet in #aihf and continue on to rendezvous with another comet1 ,tempel #b4 ,turning his attention to the environment1 the historian will almost surely suggest that the first widespread realization of the fragile natural balances on ,earth came at a time when we were first able to see our ,earth in its entirety4 ,the impact of a picture of ,earth from deep space1 a luminously blue globe surrounded by darkness1 has probably been more persuasive than lengthy treatises describing the complex ways in which our system of rocks1 plants1 animals1 water1 and air is interrelated4 ,on a more practical level1 the historian will point to the new understanding of our terrestrial environment4 ,the composition and structure of other planetary atmospheres--on ,venus1 ,mars1 and ,jupiter--provide important clues to what may happen in our own atmosphere1 especially if we disrupt the chemical composition4 ,study of the primitive crusts of the ,moon1 ,mars1 and ,mercury permits us to reconstruct the first billion years of ,earth history1 a time when chemical elements were being concentrated in activity ultimately leading to the formation of important ore deposits4 ,unmanned spacecraft missions to the ,sun increase our understanding of that most fundamental of all energy sources1 paving the way for the efficient conversion of solar energy into many practical applications1 and releasing us from dependence on ever-decreasing reserves of fossil fuels4 ,spacecraft circling the ,earth study the upper atmospheric processes that play major roles in controlling our weather4 ,these same spacecraft look down on ,earth1 aiding us with increasingly accurate forecasts of weather and crop productivity4 ,looking beyond matters of technology and the environment1 the historian may cite the latter part of the twentieth century as a time of explosive exploration1 comparable to the #aeth and #afth century exploration of the ,earth's oceans and the distant lands that bounded them4 ,in a sense1 exploration--whether it is physical or intellectual--provides its own rewards4 ,the ,united ,states has always been a nation that moves forward1 pushing back the frontiers of the ,west1 pushing back the frontiers of social and economic development1 and now pushing back the frontiers of space4 ,it is arguable that this spirit of exploration is indispensable to a vigorous society1 and that any society that ceases to explore1 to inquire1 and to strive is only a few years from decline4 ,and so the historian may recall the early days of lunar exploration1 the ,apollo project1 the landing of unmanned ,viking spacecraft on ,mars1 and the encounters of ,voyager spacecraft with ,jupiter and ,saturn as the first steps in a sustained program of space exploration--a program that is profoundly changing man's perspective of himself1 of the ,earth1 and of the larger cosmos beyond4 ,thomas ,a4 ,mutch1 ,associate ,administrator for ,space ,science ,national ,aeronautics and ,space ,administration ,images of ,jupiter and ,its ,satellites ,the date of each photograph and the distance of the spacecraft from the planet or satellite are included with each picture4 ,illustration3 #b_/e_/gi #bh4d million km 7#ag4f million mi7 ,jupiter is the largest planet in our solar system1 with a diameter #aa times that of ,earth4 ,jupiter rotates very quickly1 making one full rotation in just under ten hours4 ,composed primarily of hydrogen and helium1 ,jupiter's colorfully banded atmosphere displays complex patterns highlighted by the ,great ,red ,spot1 a large1 circulating atmospheric disturbance4 ,three of ,jupiter's #ac known satellites are also visible in this ,voyager #a photograph4 ,the innermost large satellite1 ,io1 can be seen in front of ,jupiter and is distinguished by its bright1 orange surface4 ,to the right of ,jupiter is ,europa1 also very bright but with fainter surface markings4 ,callisto is barely visible beneath ,jupiter4 ,these satellites orbit ,jupiter in the equatorial plane and appear in their present position because ,voyager is above the plane4 ,illustration3 ,jupiter's atmosphere is undergoing constant change1 presenting an ever-shifting face to observers4 ,the ,great ,red ,spot has undergone three major periods of activity in the last #ae years4 ,these images of ,jupiter1 taken by ,voyager #a 7top7 and ,voyager #b 7bottom7 almost four months apart1 show that cloud movement in the ,jovian atmosphere is not uniform because wind speeds vary at different latitudes4 ,for example1 the white ovals which appear below the ,great ,red ,spot dramatically shifted between ,january and ,may1 the time interval between these two pictures4 ,the bright 8tongue0 extending upward from the ,great ,red ,spot interacted with a thin1 bright cloud above it that had traveled twice around ,jupiter in four months4 ,eddy patterns to the left of the ,great ,red ,spot1 which have been observed since #aige1 appear to be breaking up4 ,illustration3 #a_/bd_/gi #dj million km 7#be million mi7 ,illustration3 #e_/i_/gi #df4c million km 7#bh4g million mi7 ,illustration3 #b_/be_/gi #i4b million km 7#e4g million mi7 ,the ,great ,red ,spot on ,jupiter is a tremendous atmospheric storm1 twice the size of ,earth1 that has been observed for centuries4 ,the ,great ,red ,spot rotates counterclockwise with one revolution every six days4 ,wind currents on the top flow east to west1 and currents on the bottom flow west to east4 ,this ,voyager #a picture shows the complex flow and turbulent patterns that result from the ,great ,red ,spot's interactions with these flows4 ,the large white oval is a similar1 but smaller1 storm center that has existed for about #dj years4 ,illustration3 #g_/c_/gi #f million km 7#c4gb million mi7 ,a comparison of the ,voyager #b photograph above with the preceding ,voyager #a photograph shows several distinct changes in the ,jovian atmosphere around the ,great ,red ,spot4 ,the white oval beneath the ,great ,red ,spot in the first picture has moved farther around ,jupiter1 and a different white oval has appeared under the ,great ,red ,spot in the ,voyager #b picture taken four months later4 ,the disturbed cloud regions around the ,great ,red ,spot have noticeably changed1 and the white zone west of the ,great ,red ,spot has narrowed4 ,illustration3 #c_/b_/gi #d million km 7#b4e million mi7 ,high-speed wind currents in the mid-latitudes of ,jupiter are shown in this high-resolution ,voyager #a photograph4 ,the pale orange line running diagonally to the upper right is the high-speed north temperate current with a wind speed of about #abj meters per second 7#bfj miles per hour71 over twice as fast as severe hurricane winds on ,earth4 ,toward the top of the picture1 a weaker jet of approximately #cj meters per second 7#fe miles per hour7 is characterized by wave patterns and cloud features that rotate in a clockwise manner4 ,illustration3 #c_/b_/gi #d million km 7#b4e million mi7 ,the large brown-colored oval appearing in this ,voyager #a picture was selected as one of the targets to be photographed near closest approach to ,jupiter because it is probably an opening in the upper cloud deck that exposes deeper1 warmer cloud levels4 ,brown ovals 7which can also be seen in the preceding and following photographs7 are common features in ,jupiter's northern latitudes and have an average lifetime of one to two years4 ,illustration3 #f_/bh_/gi #aj4c million km 7#f4d million mi7 ,jupiter's ,equatorial ,zone is the broad1 orange band that traverses the center of this ,voyager #b picture4 ,this zone is characterized by the wispy clouds along its northern edge4 ,the brown oval was observed by ,voyager #a four months earlier1 illustrating the stability of this type of feature in the ,jovian atmosphere4 ,in contrast1 the turbulent region in the lower right of the picture1 which lies just to the left of the ,great ,red ,spot1 shows features that are relatively short lived4 ,with the exception of the cooler ,great ,red ,spot1 as colors range from white to orange to brown1 we are generally looking at deeper and warmer layers in the ,jovian atmosphere4 ,illustration3 ,this infrared image of ,jupiter was taken from ,earth and shows heat radiating from deep holes in ,jupiter's clouds4 ,bright areas in the image are higher temperature regions than the dark areas and correspond to parts of the atmosphere that are relatively free of obscuring clouds4 ,the ,great ,red ,spot appears on the left limb1 or edge of the planet1 as a dark area encircled by a bright ring1 indicating that the ,spot is cooler than the surrounding region4 ,the infrared image was recorded by the #bjj-;inch ,hale telescope on ,mount ,palomar in ,california4 ,illustration3 #a_/aj_/gi #ece1jjj km 7#ccb million mi7 ,this ,voyager #a picture was also taken the same day1 about one hour after the infrared image4 ,illustration3 #c_/e_/gi #eae1jjj km 7#cbj1jjj mi7 ,the largest aurora ever observed1 nearly #bi1jjj kilometers 7#ah1jjj miles7 long1 appears in this ,voyager #a photograph1 taken on the dark side of ,jupiter six hours after closest encounter4 ,the auroral lights are brighter than any northern lights seen on ,earth4 ,jupiter's north pole is approximately midway along the auroral arc4 ,this timed exposure of the aurora also shows what appear to be lightning storms several thousand kilometers below the aurora4 ,the strength of the lightning bolts is comparable to that of superbolts seen near cloud tops above ,earth4 ,lightning had been suspected to exist on ,jupiter1 but at lower levels in the atmosphere4 ,illustration3 #c_/d_/gi #a4b million km 7#gej1jjj mi7 ,the first evidence of a ring around ,jupiter is seen in this photograph taken by ,voyager #a4 ,this photograph was part of a sequence planned to search for such rings around ,jupiter4 ,the multiple image of the extremely thin1 faint ring appears as a broad light band crossing the center of the picture4 ,this multiple image and the elongated1 wavy motion of the background stars are due to the #aa-minute1 #ab-second exposure and the very slow natural oscillation of the spacecraft4 ,the ring1 which is in ,jupiter's equatorial plane1 is invisible from ,earth because of its thinness and transparency and because of ,jupiter's brightness4 ,the black dots in the picture are calibration points in the camera4 ,illustration3 ,because of ,voyager #a's discovery of a ring around ,jupiter1 ,voyager #b was programmed to take additional pictures of the ring4 ,these three ,voyager #b images show ,jupiter's ring in progressively higher resolution4 ,the pictures were taken when ,jupiter was eclipsed by the ,sun1 and the ring appears unusually bright because of the forward scattering of sunlight by small ring particles4 ,illustration3 #g_/aj_/gi #a4de million km 7#ijj1jjj mi7 ,in this four-picture mosaic1 the arms of the ring curving toward the spacecraft 7on the near side of the planet7 are cut off by the planet's shadow4 ,scientists estimate that the distance from the ,jovian cloud tops to the outer edge of the ring is #ee1jjj kilometers 7#ce1jjj miles74 ,illustration3 #g_/aj_/gi #a4ee million km 7#ifa1jjj mi7 ,in this picture1 which is composed of six images1 there is evidence of structure within the ring1 but the spacecraft motion during these long exposures obscured the highest resolution detail4 ,however1 there is speculation that the ring width1 estimated at #fjjj kilometers 7#djjj miles71 contains more than one ring4 ,illustration3 #g_/aj_/gi #a4de million km 7#ijj1jjj mi7 ,this photograph is an enlargement of the isolated left frame in the first picture and reveals a density gradient of very small particles extending inward from the ring4 ,the thickness of the ring has been estimated at less than one kilometer 7#j4f mile7 although the ring appears about #cj kilometers 7#ai miles7 thick in the image1 due to camera motion and finite resolution4 ,composition of the low-albedo 7dark7 particles is not known1 but particle size probably ranges from microscopic to at most a few meters in diameter4 ,if collected together to form a single body1 the total mass of the ,jovian rings would form an object with a diameter less than twice that of tiny ,amalthea4 ,illustration3 #b_/ac_/gi #bj million km 7#ab4d million mi7 ,jupiter and two of its planet-sized satellites1 ,io at left and ,europa at right1 are visible in this ,voyager #a picture4 ,jupiter's four largest satellites--,io1 ,europa1 ,ganymede and ,callisto--were discovered in #afaj by ,galileo ,galilei4 ,the two outer ,galilean satellites are ,ganymede and ,callisto1 not shown in this picture4 ,all four satellites probably formed about four billion years ago but their surfaces vary in age tremendously4 ,io and ,europa have younger1 more active surfaces than ,ganymede and ,callisto4 ,like our ,moon1 the satellites keep the same face toward ,jupiter4 ,in this picture1 the sides of the satellites that always face away from the planet are visible4 ,illustration3 ,amalthea1 ,jupiter's innermost satellite1 was discovered in #ahib4 ,it is so small and close to ,jupiter that it is extremely difficult to observe from ,earth4 ,amalthea's surface is dark and red1 quite unlike any of the ,galilean satellites4 ,the three ,voyager #a pictures and the one ,voyager #b picture following 7seen against the disk of ,jupiter7 reveal a small1 elongated object1 about #bfe kilometers 7#afe miles7 long and #aej kilometers 7#ij miles7 in diameter4 ,amalthea keeps its long axis pointed toward ,jupiter as it orbits around the planet every #ab hours4 ,illustration3 #c_/d_/gi #a4be million km 7#ghj1jjj mi7 ,illustration3 #c_/d_/gi #fie1jjj km 7#dcj1jjj mi7 ,illustration3 #c_/e_/gi #dbe1jjj km 7#bfd1jjj mi7 ,illustration3 #g_/i_/gi #efj1jjj km 7#cej1jjj mi7 ,amalthea was observed end-on in the ,voyager #b picture1 which has been computer-processed to enhance the image4 ,illustration3 #c_/d_/gi #cgg1jjj km 7#bcd1jjj mi7 ,io1 ,jupiter's innermost ,galilean satellite1 displays great diversity in color and brightness4 ,this ,voyager #a four-picture mosaic shows ,io's complex coloration of red-orange1 black1 and white regions1 and the two major topographic features3 volcanic regions1 the most prominent of which is the 8hoofprint0 7volcanic deposition feature7 in the center-right1 and the intervolcanic plains that are relatively featureless4 ,io's vivid coloring is probably due to its composition of sulfur-rich materials that have been brought to the surface by volcanic activity4 ,illustration3 #c_/e_/gi #abi1fjj km 7#hj1ejj mi7 ,the bright area at the upper right in this ,voyager #a picture of ,io appears to be a caldera 7collapsed volcano7 that is venting clouds of gases4 ,the clouds may condense to form extremely fine particles that scatter light and appear blue4 ,because the infrared spectrometer discovered sulfur dioxide on ,io1 scientists believe this gas may be the main component of the clouds4 ,sulfur dioxide clouds would rapidly freeze and snow back to the surface4 ,it is also possible that dark areas in the floors of the calderas are pools of encrusted liquid sulfur4 ,illustration3 #c_/e_/gi #ff1jjj km 7#da1jjj mi7 ,evidence of erosion in ,io's southern polar region is visible in this ,voyager #a high-resolution image4 ,the picture has been computer-enhanced to bring out surface detail while suppressing bright markings4 ,a depressed segment of the crust1 bounded by faults1 is seen near the terminator in the upper right portion of the image4 ,at the lower center are complicated scarps 7slopes7 and portions of isolated elevated terrain that geologists interpret as 8islands0 left behind as the scarps eroded4 ,scientists speculate that sulfur dioxide 7as a subsurface liquid7 may be a determinant in the creation of these features4 ,illustration3 #c_/d_/gi #hfb1jjj km 7#edj1jjj mi7 ,io's surface1 less than ten million years old1 is quite young compared to the other ,galilean satellites and to other terrestrial bodies1 such as ,mercury and the ,moon4 ,the surface is composed of large amounts of sulfur and sulfur dioxide frost1 both of which account for most of the surface color4 ,this picture was taken by ,voyager #a4 ,material deposited by the volcano 7see following pictures7 can be seen as a white ring near the center of ,io4 ,illustration3 ,the first active volcanic eruptions other than on ,earth were discovered on ,io4 ,these volcanoes are extremely explosive with ejection velocities of more than one kilometer per second 7#bbjj miles per hour71 which is more violent than ,etna1 ,vesuvius1 or ,krakatoa on ,earth4 ,both pictures below were taken by ,voyager #a4 ,illustration3 #c_/d_/gi #dej1jjj km 7#bhj1jjj mi7 ,in this picture1 the plume visible on the right edge extends more than #ajj kilometers 7#fj miles7 above the surface4 ,illustration3 #c_/d_/gi #dii1jjj km 7#caj1jjj mi7 ,the same volcano is shown in this picture1 photographed one hour and #eb minutes earlier4 ,illustration3 #c_/d_/gi #dij1jjj km 7#cjd1jjj mi7 ,special color reconstruction by means of ultraviolet1 blue1 green1 and orange filters allowed scientists to study the amount of gas and dust and the size of the dust particles that erupted from the volcano on ,io shown in this ,voyager #a image4 ,the region that is brighter in the ultraviolet 7blue area7 is about #baj kilometers 7#acj miles7 high1 over twice the height of the denser1 bright yellow core4 ,the vent area is visible on page #ah as a dark ring in the upper left region of ,io4 ,illustration3 #g_/aj_/gi #a4b million km 7#gej1jjj mi7 ,of the eight active volcanoes discovered on ,io by ,voyager #a1 six of the seven volcanoes sighted by ,voyager #b were still active4 ,the giant volcano observed by ,voyager #a over the 8hoofprint0 region 7see page #ah7 had become inactive4 ,scientists1 therefore1 believe that the satellite is undergoing continuous volcanic activity1 making ,io's surface the most active in the solar system4 ,this ,voyager #b photograph1 which shows three active volcanoes1 was one of the last of an extensive sequence of 8volcano watch0 pictures planned as a result of ,voyager #a's volcano discovery4 ,the black dots are calibration points on the camera4 ,illustration3 #g_/h_/gi #a4b million km 7#gej1jjj mi7 ,europa1 approximately the same size and density as our ,moon1 is the brightest ,galilean satellite4 ,the surface displays a complex array of streaks1 indicating that the crust has been fractured4 ,in contrast to its icy neighbors ,ganymede and ,callisto1 ,europa has very few impact craters4 ,the relative absence of features and low topography indicate that the crust is young and probably warm a few kilometers below the surface4 ,the warmth is probably due to a combination of radioactive and tidal heating4 ,the tidal heating within ,europa is estimated to be ten percent that of the stronger tidal heating effect within ,io4 ,the regions that appear blue in this ,voyager #b image are actually white4 ,illustration3 #g_/i_/gi #bdj1jjj km 7#aej1jjj mi7 ,europa's surface is probably a thin ice crust overlying water or softer ice 7slush7 about #ajj kilometers 7#fj miles7 thick that covers a silicate interior4 ,the tectonic processes on ,europa's surface create patterns that are drastically different from the fault systems seen on ,ganymede's surface1 where pieces of the crust have moved relative to each other4 ,on ,europa1 the crust evidently fractures1 but the pieces remain roughly in their original position4 ,this ,voyager #b picture is composed of three images4 ,illustration3 #g_/i_/gi #bdj1jjj km 7#aej1jjj mi7 ,long linear fractures or faults which crisscross ,europa's surface in various directions are over #ajjj kilometers 7#fjj miles7 long in some places4 ,large fractures are #bjj to #cjj kilometers 7#abe to #ahe miles7 wide1 wider than the crust is thick4 ,also visible are somewhat darker mottled regions that appear to have a slightly pitted appearance4 ,no large craters 7more than five kilometers in diameter7 are identifiable in this ,voyager #b picture1 indicating that this satellite has a very young surface relative to ,ganymede and ,callisto1 although perhaps not as young as ,io's surface4 ,scientists believe that the surface is a thin ice crust overlying water or softer ice and that the fracture systems are breaks in the crust4 ,resurfacing processes1 such as the production of fresh ice or snow along the cracks and cold glacier-like flows1 have probably removed evidence of impact events 7cratering74 ,europa1 therefore1 appears to have many properties similar to ,ganymede and ,io4 ,illustration3 #g_/i_/gi #bdj1jjj km 7#aej1jjj mi7 ,complex narrow ridges1 seen as curved bright streaks #e to #aj kilometers 7#c to #f miles7 wide and typically #ajj kilometers 7#fj miles7 long1 characterize the surface topography of this view of ,europa4 ,the dark bands also visible in this ,voyager #b photo are #bj to #dj kilometers 7#ab to #be miles7 wide and up to thousands of kilometers long4 ,the fractures on the icy surface are filled with material from beneath1 probably as a result of internal tidal flexing which continually heats the thin outer ice crust4 ,a few features are suggestive of degraded impact craters4 ,illustration3 #c_/d_/gi #b4f million km 7#a4f million mi7 ,ganymede1 ,jupiter's largest satellite1 is about one and one-half times the size of our ,moon but only about half as dense and is composed of about #ej percent water or ice and the rest rock4 ,the bright surface of ,ganymede is a complex montage of ancient1 relatively dark and cratered terrain1 grooved terrain that resulted from a dramatic history of tectonic movement in the icy crust1 and bright young ray craters that expose fresh ice4 ,this photograph was taken by ,voyager #a4 ,illustration3 #g_/g_/gi #a4b million km 7#gej1jjj mi7 ,the dark1 cratered1 circular feature in this ,voyager #b photograph is about #cbjj kilometers 7#bjjj miles7 in diameter and is on the side of ,ganymede opposite to that shown in the previous picture4 ,this region is apparently the largest piece of ancient1 heavily cratered crust left on ,ganymede4 ,the light branching bands are ridged and grooved terrain which are younger than the more heavily cratered dark regions4 ,despite the dramatic surface appearance1 ,ganymede is relatively devoid of topographic relief due to the consequences of glacier-like 8creep0 in the icy crust4 ,illustration3 #g_/h_/gi #cab1jjj km 7#aid1jjj mi7 ,several different types of terrain common to ,ganymede's surface are visible in this ,voyager #b picture4 ,the boundary of the largest region of dark ancient terrain 7also shown in the previous photo7 can be seen to the right1 revealing the light linear features that may be the remains of shock rings from an ancient impact4 ,the broad light regions are the typical grooved structures contained within the light regions on ,ganymede4 ,on the lower left is another example of what might be evidence of large-scale lateral faulting in the crust2 the band appears to be offset by a linear feature perpendicular to it4 ,these are the first clear examples of lateral faulting seen on any planet other than ,earth4 ,illustration3 #g_/h_/gi #cac1jjj km 7#aid1ejj mi7 ,this color reconstruction of part of ,ganymede's northern hemisphere1 taken by ,voyager #b1 encompasses an area about #acjj kilometers 7#hjj miles7 across4 ,it shows part of a dark1 densely cratered region that contains numerous craters1 many with central peaks4 ,the large bright circular features have little relief and are probably the remnants of old1 large craters that have been annealed by the flow of icy material near the surface4 ,the gradually curving lines that press through the dark region suggest the presence of a large impact basin to the southwest1 which has been obliterated by the subsequent formation of younger grooved terrain4 ,illustration3 #c_/e_/gi #afe1jjj km 7#ajc1jjj mi7 ,a broad1 north-south strip of grooved terrain on ,ganymede1 offset by a traversing fault in the upper part of the picture1 is shown in this ,voyager #a photograph4 ,there are several other perpendicular fault lines farther down on the fault4 ,within the major light stripes1 the more closely spaced1 shallow grooves run parallel to the boundaries of the stripes4 ,the larger striped features divide the cratered terrain into isolated polygons several hundred to about #ajjj kilometers 7#fjj miles7 across4 ,illustration3 #c_/e_/gi #ade1jjj km 7#ij1jjj mi7 ,the grooved terrain at higher resolution emphasizes numerous interwoven linear features in this ,voyager #a picture1 near the terminator on ,ganymede4 ,this suggests an early period in ,ganymede's history when the crust was active and mobile1 resembling ,earth's plate tectonics in some ways4 ,the causes of the extreme differences in crustal evolution between ,callisto and ,ganymede are under investigation4 ,combinations of radioactive heating and a greater degree of tidal heating for ,ganymede are possibilities4 ,illustration3 #g_/i_/gi #ajj1jjj km 7#fb1jjj ml7 ,this mosaic of ,ganymede1 composed of photographs taken by ,voyager #b1 shows numerous impact craters1 many with bright ray systems4 ,the rough terrain at the lower right is the outer portion of a large1 fresh impact basin that postdates most of the other terrain4 ,the dark patches of heavily cratered terrain 7right center7 are probably ancient mixtures of ice and rock formed prior to the grooved terrain4 ,the large rayed crater at the upper center is about #aej kilometers 7#ie miles7 in diameter4 ,illustration3 #g_/h_/gi #he1jjj km 7#ec1jjj mi7 ,curved troughs and ridges in this high-resolution ,voyager #b photograph of ,ganymede are the distinctive characteristics of an enormous1 ancient impact basin4 ,the basin itself has been eroded by later geologic processes2 only the shock ring features are preserved on the ancient surface4 ,near the bottom of the picture these curved markings are perforated with the younger1 grooved terrain4 ,illustration3 #g_/g_/gi #b4c million km 7#a4d million mi7 ,callisto1 only slightly smaller than ,ganymede1 has the lowest density of all the ,galilean satellites1 implying that it has large amounts of water in its bulk composition4 ,its surface is darker than the other ,galilean satellites1 although it is still twice as bright as our ,moon4 ,this ,voyager #b image shows ,callisto to have the most heavily cratered and1 therefore1 the oldest surface of the ,galilean satellites1 probably dating back to the period of heavy meteoritic bombardment ending about four billion years ago4 ,illustration3 #c_/f_/gi #cej1jjj km 7#bag1jjj mi7 ,the prominent concentric ring structure shown in this ,voyager #a four-picture mosaic of ,callisto is believed to be a large impact basin1 similar to ,mare ,orientale on the ,moon and ,caloris ,basin on ,mercury4 ,the bright circular spot is about #fjj kilometers 7#cfj miles7 across1 and the outer ring is about #bfjj kilometers 7#aefj miles7 across4 ,this is the first recognized basin in the ,jovian system and supports the assumption that ,callisto's surface is old4 ,the lack of high ridges1 ring mountains1 or a large central depression suggests that the impacting body caused melting1 some flow1 and shock waves1 and that the refreezing occurred in time to preserve the concentric shock rings4 ,illustration3 #g_/g_/gi #cij1jjj km 7#bde1jjj mi7 ,callisto is the most heavily cratered planetary body in our solar system4 ,in this ,voyager #b nine-frame mosaic1 a special computer filter was used to provide high contrast in the surface topography4 ,the impact structure visible at the upper right edge of the satellite is smaller than the largest one found by ,voyager #a but more detail is obvious2 it is estimated that #ae concentric rings surround the bright center4 ,many hundreds of moderate-sized craters are also visible1 a few with bright ray patterns4 ,the limb is smooth1 which is consistent with ,callisto's icy composition4 ,illustration3 #c_/f_/gi #bjj1jjj km 7#abe1jjj mi7 ,this high-resolution image of ,callisto1 photographed by ,voyager #a1 shows details of the large ring structure surrounding the remains of the ancient impact basin visible on page #ce4 ,the surface area shown in this image is at the right edge and slightly above the center of the picture on page #ce4 ,the relatively undisturbed region on the right shows the shoulder-to-shoulder large impact craters typical of most of ,callisto's surface4 ,a decrease in crater density toward the center of the structure 7to the left7 is evident1 and is caused by the destruction of very old craters by the large impact that formed the ring ,the ,voyager ,mission ,the ,voyager mission is focused on the exploration of the ,jupiter and ,saturn systems4 ,the alignment of these large planets permits the use of a gravity-assist trajectory in which the gravity field of ,jupiter and ,jupiter's motion through space may be used to hurl the spacecraft on to ,saturn4 ,in #aigg1 a rare alignment 7once every #agf years7 of our four outer planets--,jupiter1 ,saturn1 ,uranus1 and ,neptune--may permit a gravity-assist trajectory to ,uranus and even to ,neptune for ,voyager #b4 ,voyagers #a and #b began their journeys in the late summer of #aigg1 catapulted into space by a ,titan_/,centaur launch vehicle from ,cape ,canaveral1 ,florida4 ,with them went the hopes and dreams of thousands of people who had worked to create them and their mission4 ,the ,voyager spacecraft are unique in many respects4 ,since their journeys are taking them far from the ,sun1 the ,voyagers are nuclear powered rather than solar powered4 ,the ,voyagers are the fastest man-made objects ever to have left ,earth4 ,in fewer than ten hours1 they had crossed the ,moon's orbit4 ,this compares to about three days for an ,apollo flight and one day for the ,mariner and ,viking spacecraft4 ,their launches marked the end of an era in space travel--the end of the planned use of ,titan_/,centaur launch vehicles4 ,with the advent of the ,space ,shuttle in the #aihjs1 future spacecraft will be launched from the ,shuttle ,orbiter4 ,voyager #a was launched #af days after its sister ship1 but because of a different trajectory1 it arrived at ,jupiter four months ahead of ,voyager #b4 ,both spacecraft spent more than nine months crossing the asteroid belt1 a vast ring of space debris circling the ,sun between the orbits of ,mars and ,jupiter4 ,during their #af- and #bj-month journeys to ,jupiter1 the spacecraft tested and calibrated all of their instruments1 exercised their scan platforms1 and measured particles and fields in interplanetary space4 ,as the spacecraft neared the planet1 the cameras showed the dramatic visible changes that had taken place in the five years since ,jupiter had been photographed by ,pioneer #aa4 ,and for the first time1 we got a close look at some of ,jupiter's moons3 ,amalthea1 ,io1 ,europa1 ,ganymede1 and ,callisto4 ,targeted for the closest look at ,io1 ,voyager #a flew the more hazardous course1 passing between ,jupiter and ,io1 where the radiation environment is the most intense4 ,voyager #b's flight path gave ,jupiter and its intense radiation a much wider berth4 ,unlike ,voyager #a1 which encountered the five innermost satellites as it was leaving ,jupiter1 ,voyager #b encountered the satellites as it was approaching the planet1 thus providing closeup photography of opposite sides of the satellites4 ,illustration3 ,march #e1 #aigi4 ,voyager #a's unique flight path allowed scientists to study at close range #e of ,jupiter's #ac known satellites4 ,each is shown at its closest point to the trajectory of ,voyager #a's outbound flight away from ,jupiter4 ,closest approach was #bhj1jjj kilometers 7#agd1jjj miles7 from ,jupiter4 ,illustration3 ,july #i1 #aigi4 ,voyager #b's closest approach to ,jupiter was #fde1jjj kilometers 7#djj1jjj miles7 from the planet4 ,voyager #b encountered the satellites on its inbound journey to ,jupiter1 which enabled the spacecraft to photograph the opposite sides of the satellites4 ,arriving at ,jupiter from slightly different angles1 both spacecraft measured the large1 doughnut-shaped ring of charged sulfur and oxygen ions1 called a torus1 encircling the planet at about the orbit of ,io4 ,then1 both spacecraft disappeared behind ,jupiter1 out of view of ,earth and ,sun1 for about two hours4 ,during this time1 measurements were taken on the planet's dark side4 ,each spacecraft took over #ae1jjj photographs of ,jupiter and its satellites4 ,illustration3 ,voyager spacecraft and scientific instruments4 ,from the moment of launch1 the ,voyager spacecraft have been monitored by a worldwide tracking system of nine giant antennas strategically located around the world in ,california1 ,spain1 and ,australia to ensure constant radio contact with the spacecraft as the ,earth rotates4 ,radio contact with ,voyagers #a and #b has not been instantaneous1 however4 ,when ,voyager #a flew past ,jupiter1 radio signals between ,earth and the spacecraft took #cg minutes2 when ,voyager #b arrived1 the signals took #eb minutes because by then the planet was farther from ,earth4 ,the pictures in this book were taken by a shuttered television-type camera4 ,each picture is composed of #fdj1jjj dots1 which were converted into binary numbers before being radioed to ,earth4 ,when the signals reached ,earth1 they were reconverted by computer into dots and reassembled into the original image4 ,most of the color pictures are composed of three images1 each one taken through a different color filter3 blue1 orange1 or green4 ,the images were combined and the original color was reconstructed by computer4 ,the computer eliminated many of the imperfections that crept into the images1 and enhanced some of the images by emphasizing different colors4 ,designed to provide a broad spectrum of scientific investigations at ,jupiter1 the science instruments investigated atmospheres1 satellites1 and magnetospheres4 ,the scientific investigations for the ,voyager mission and their ,jovian encounter objectives are shown in the table on page #dj4 ,after their closest approaches to ,jupiter1 both spacecraft fired their thrusters1 retargeting for their next goal1 the ,saturn system4 ,scientists will still be studying the wealth of new information about ,jupiter when ,voyager #a reaches ,saturn in ,november #aihj1 and ,voyager #b follows in ,august #aiha4 ,after ,voyager #a encounters ,saturn1 ,voyager #b may be retargeted to fly past ,uranus in #aihf4 ,upon completion of their planetary missions1 both spacecraft will search for the outer limit of the solar wind1 that boundary somewhere in our part of the ,milky ,way where the influence of the ,sun gives way to other stars of the galaxy4 ,voyagers #a and #b will continue to study interstellar space until the spacecraft signals can no longer be received4 ,scientific ,highlights ,some of the most important information gathered by ,voyagers #a and #b on the ,jovian system is presented pictorially in this book and is supplemented here with brief summaries of the major discoveries1 observations1 and theories4 ,jupiter ,the atmosphere of ,jupiter is colorful1 with cloud bands of alternating colors4 ,a major characteristic of the atmosphere is the appearance of regularly spaced features4 ,around the northern edge of the equator1 a train of plumes is observed1 which has bright centers representative of cumulus convection similar to that seen on ,earth4 ,at both northern and southern latitudes1 cloud spots are observed spaced almost all the way around the planet1 suggestive of wave interactions4 ,the cloud structures in the northern and southern hemispheres are distinctly different4 ,however1 the velocities between the bright zones and dark belts appear to be symmetric about the equator1 and stable over many decades4 ,this suggests that such long-lived and stable features may be controlled by the atmosphere far beneath the visible clouds4 ,the ,great ,red ,spot possesses the same meteorological properties of internal structure and counterclockwise rotation as the smaller white spots4 ,the color of the ,great ,red ,spot may indicate that it extends deep into the ,jovian atmosphere4 ,cloud-top lightning bolts1 similar to those on ,earth1 have also been found in the ,jovian atmosphere4 ,at the polar regions1 auroras have been observed4 ,a very thin ring of material less than one kilometer 7#j4f mile7 in thickness and about #fjjj kilometers 7#djjj miles7 in radial extent has been observed circling the planet about #ee1jjj kilometers 7#ce1jjj miles7 above the cloud tops4 ,amalthea ,amalthea is an elongated1 irregularly shaped satellite of reddish color4 ,it is #bfe kilometers 7#afe miles7 long and #aej kilometers 7#ij miles7 wide4 ,just like the large ,galilean satellites1 ,amalthea is in synchronous rotation1 with its long axis always oriented toward ,jupiter4 ,at least one significant color variation has been detected on its surface4 ,io ,eight active volcanoes have been detected on ,io1 with some plumes extending up to #cbj kilometers 7#bjj miles7 above the surface4 ,over the four-month interval between the ,voyager #a and #b encounters1 the active volcanism appears to have continued4 ,seven of the volcanoes were photographed by ,voyager #b1 and six were still erupting4 ,the relative smoothness of ,io's surface and its volcanic activity suggest that it has the youngest surface of ,jupiter's moons4 ,its surface is composed of large amounts of sulfur and sulfur dioxide frost1 which account for the primarily yellow-orange surface color4 ,the volcanoes seem to eject a sufficient amount of sulfur dioxide to form a doughnut-shaped ring 7torus7 of ionized sulfur and oxygen atoms around ,jupiter near ,io's orbit4 ,the ,jovian magnetic field lines that go through the torus allow particles to precipitate into the polar regions of ,jupiter1 resulting in intense ultraviolet and visible auroras4 ,europa ,europa1 the brightest of ,jupiter's ,galilean satellites1 may have a surface of thin ice crust overlying water or softer ice1 with large-scale fracture and ridge systems appearing in the crust4 ,europa has a density about three times that of water1 suggesting it is a mixture of silicate rock and some water4 ,very few impact craters are visible on the surface1 implying a continual resurfacing process1 perhaps by the production of fresh ice or snow along cracks and cold glacier-like flows4 ,ganymede ,ganymede1 largest of ,jupiter's #ac satellites1 has bright 8young0 ray craters2 light1 linear stripes resembling the outer rings of a very large1 ancient impact basin2 grooved terrain with many faults2 and regions of dark1 heavily cratered terrain4 ,among the ,galilean satellites1 ,ganymede probably has the greatest variety of geologic processes recorded on its surface and may be the best example for studying the evolution of ,jupiter's inner satellites4 ,imbedded within ,jupiter's magnetosphere1 ,ganymede is subjected to the influences of the corotating charged-particle plasma and an interaction may exist with this plasma4 ,no atmosphere has been detected4 ,callisto ,the icy1 dirt-laden surface of ,callisto appears to be very ancient and heavily cratered4 ,the large concentric rings indicate the remains of several enormous impact basins1 created by huge meteors crashing into the surface1 and since erased by the flow of the crust4 ,callisto's density 7less than twice that of water7 is very close to that of ,ganymede1 yet there is little or no evidence of the crustal motion and internal activity that is visible on ,ganymede4 ,the ,magnetosphere ,perhaps the largest structure in the solar system is the magnetosphere of ,jupiter4 ,this is the region of space which is filled with ,jupiter's magnetic field and is bounded by the interaction of that magnetic field with the solar wind1 which is the ,sun's outward flow of charged particles4 ,the plasma of electrically charged particles that exists in the magnetosphere is flattened into a large disk more than #d4h million kilometers 7#c million miles7 in diameter1 is coupled to the magnetic field1 and rotates around ,jupiter4 ,the ,galilean satellites are located in the inner regions of the magnetosphere where they are subjected to intense radiation bombardment4 ,it appears that ,io is a source of the sulfur and oxygen ions which fill the magnetosphere4 ,another magnetospheric interaction is the electrical connection between ,io and ,jupiter along the magnetic field lines that leave ,jupiter and intersect ,io4 ,this magnetic flux tube was examined by ,voyager #a and a flow of about five million amperes of current was measured1 which was considerably more than anticipated4 ,voyager also discovered a new low-frequency radio emission coming from ,jupiter1 which is possibly associated with the ,io torus4 ,scientific investigations of the ,voyager mission ,investigation ,typical ,jovian encounter objectives ,imaging science ,high-resolution reconnaissance over large phase angles2 atmospheric dynamics2 geologic structure of satellites ,infrared radiation ,atmospheric composition1 thermal structure and dynamics2 satellite surface composition and thermal properties ,photopolarimetry ,atmospheric aerosols2 satellite surface texture and sodium cloud ,radio science ,atmospheric and ionospheric structure1 constituents1 and dynamics ,ultraviolet spectroscopy ,upper atmospheric composition and structure2 auroral processes2 distribution of ions and neutral atoms in the ,jovian system ,magnetic fields ,planetary magnetic field2 magnetospheric structure2 ,io flux tube currents ,plasma particles ,magnetospheric ion and electron distribution2 solar wind interaction with ,jupiter2 ions from satellites ,plasma waves ,plasma electron densities2 wave-particle interactions2 low-frequency wave emissions ,planetary radio astronomy ,polarization and spectra of radio frequency emissions2 ,io radio modulation process2 plasma densities ,low-energy charged particles ,distribution1 composition1 and flow of energetic ions and electrons2 satellite-energetic particle interactions ,cosmic ray particles ,distribution1 composition1 and flow of high-energy trapped nuclei2 energetic electron spectra ,illustration3 ,a computer-generated mosaic of ,voyager #a pictures showing ,jupiter from directly above the north pole4 ,this view shows features to about #bj degrees south latitude4 ,the black area at the pole results from missing information4 ,illustration3 ,,nasa ,national ,aeronautics and ,space ,administration ,jet ,propulsion ,laboratory ,california ,institute of ,technology ,pasadena1 ,california ,,jpl #djj-bd #g_/gi ,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