,,pioneer ,,saturn ,,encounter ,illustration3 ,,nasa ,,contents ,foreword #a ,introduction #c ,pioneer ,saturn #d ,saturn ,images #h ,science ,highlights #ba ,outward ,bound #bh ,,foreword ,the ,pioneer #aj and #aa spacecraft1 launched in #aigb and #aigc1 respectively1 were well named3 they made the first crossings of the asteroid belt and were the first to encounter ,jupiter and its intense radiation belts4 ,pioneer #aa's trajectory1 bent into a hairpin curve by ,jupiter's powerful gravitational field1 allowed it to recross the solar system to make the first flyby of ,saturn almost a billion miles from ,earth where it came within #ac1cjj miles of the cloud tops4 ,assembled in this publication is a selection of the pictures returned by ,pioneer #aa of ,saturn and its largest moon1 ,titan4 ,these images are of great beauty as well as of great scientific interest1 serving to whet our appetite for the more detailed observations to be made by ,voyager in #aihj and #aiha4 ,tracking of both ,pioneers will continue for many more years1 providing fundamental data on the nature of interplanetary space in the depths of the solar system4 ,the results of these outer-planet ,pioneer missions have far exceeded our hopes and expectations of a decade ago when the program was initiated4 ,robert ,a4 ,frosch1 ,administrator ,national ,aeronautics and ,space ,administration ,september #aigi ,,nasa ,national ,aeronautics and ,space ,administration ,ames ,research ,center ,moffett ,field4 ,california #idjce ,illustration3 ,artist's drawing of ,saturn and its rings showing the ,pioneer ,saturn spacecraft passing under the rings and nearing closest approach to the planet4 ,actual pictures could not be obtained at this time because of the high speed of the spacecraft4 ,,introduction ,we have entered into a new era of space exploration4 ,missions undertaken during the lunar exploration of the #aifj's typically lasted a matter of days with commands issued and carried out in near real time4 ,now1 a decade later1 planetary voyages may last for many years as the spiraling trajectories of the spacecraft make periodic intersections with the orbits of the planets4 ,communicating with us across the vastness of space1 these spacecraft report to us their experiences as they traverse the outer reaches of the solar system4 ,among these deep space travelers1 ,pioneers #aj and #aa are appropriately named1 for they truly are pioneering the exploration of the outer solar system4 ,launched in #aigb and in #aigc1 respectively1 they were the first spacecraft to fly by ,jupiter 7in #aigc and #aigd74 ,at ,jupiter1 ,pioneer #aa's trajectory was carefully targeted to swing it toward ,saturn for an encounter in ,september #aigi4 ,we see some of the early results in this publication4 ,other spacecraft are following along the trail blazed by ,pioneer ,saturn4 ,voyager #a passed by ,jupiter in ,march #aigi and will reach ,saturn in ,november #aihj4 ,voyager #b has also passed beyond ,jupiter and will encounter ,saturn in ,august #aiha1 with the further possibility of traveling on to ,uranus 7a #aihf encounter74 ,under development are the ,galileo orbiter and atmospheric entry probe1 destined to journey to ,jupiter where the orbiter will return more detailed information1 including high-resolution pictures of the ,galilean satellites1 and the probe will penetrate deep below the ,jovian clouds4 ,in the coming years1 each of these follow-on missions will enrich our understanding of the solar system1 greatly supplementing the observations of ,pioneers #aj and #aa4 ,but one thing will never change4 ,the ,pioneers were first4 ,thomas ,a4 ,mutch ,associate ,administrator for ,space ,science ,national ,aeronautics and ,space ,administration ,,pioneer ,,saturn ,illustration3 ,pioneer ,saturn spacecraft4 ,pioneer ,saturn has given us our first close view of the spectacular ringed planet ,saturn and its system of moons4 ,the spacecraft began its journey to the giant planets ,jupiter and ,saturn on ,april #e1 #aigc1 as ,pioneer #aa4 ,it reached ,jupiter on ,december #b1 #aigd1 passing within #db1gfj km of the ,jovian cloud tops and taking the only existing pictures of ,jupiter's polar regions4 ,jupiter's massive gravitational field was used to swing ,pioneer #aa back across the solar system toward ,saturn4 ,additional maneuvers were executed in #aige and #aigf to place the spacecraft on a suitable trajectory1 with the final aimpoint selected in #aigg4 ,from the many possible targeting options for the first ,saturn flyby1 two aimpoints were considered1 both of which would result in a near-equatorial flyby that would give the best mapping of the high-energy particles and the magnetic field near the planet4 ,the difference between these two aimpoints1 which came to be known as the 8inside0 and 8outside0 options1 was their relationship to ,saturn's unique ring system first discovered by ,galileo in #afaj4 ,the 8outside0 option was finally selected because it was considered to be of less risk to the spacecraft and more valuable in planning the subsequent encounter of ,saturn by ,voyager #b1 which will reach ,saturn in #aiha4 ,final targeting was completed during early #aigh1 when a series of timed rocket thrusts locked ,pioneer into the desired trajectory4 ,illustration3 ,pioneer ,saturn voyage4 ,illustration3 ,encounter trajectory4 ,on ,september #a1 #aigi1 the spacecraft1 now designated ,pioneer ,saturn1 reached ,saturn after #f years in flight4 ,it passed through the ring plane outside the edge of ,saturn's ,a-ring and then swung in under the rings from #b1jjj to #aj1jjj km below them4 ,at the point of closest approach1 it attained a speed of #aad1ajj km_/h 7#ga1ijj mi_/h7 and came within #ba1djj km of the planet's cloud tops4 ,while it was approaching1 encountering1 and leaving ,saturn1 the spacecraft took the first closeup pictures of the planet1 showing #bj to #cj times more detail than the best pictures taken from ,earth1 and made the first close measurements of its rings and several of its moons1 including the largest moon1 the planet-sized ,titan4 ,titan1 along with ,mars1 has been considered by many scientists to be the most likely place to find life in the solar system4 ,pioneer ,saturn unraveled many mysteries4 ,it determined that ,saturn has a magnetic field and trapped radiation belts1 measured the mass of ,saturn and some of its moons1 and studied the character of ,saturn's interior4 ,it confirmed the presence and determined the magnitude of an internal heat source for ,saturn4 ,its instruments studied the temperature distribution1 composition1 and other properties of the clouds and atmospheres of ,saturn and ,titan1 and took photometric and polarization measurements of ,iapetus1 ,rhea1 ,dione1 and ,tethys4 ,pioneer may also have discovered a previously unknown moon of ,saturn4 ,the spacecraft measured the mass1 structure1 and other characteristics of ,saturn's rings1 and passed safely through the outer ,e-ring1 which posed a potential hazard for ,pioneer4 ,it also discovered new rings4 ,one of these rings1 called the ,f-ring by the ,pioneer team1 lies just outside the ,a-ring4 ,the gap between the ,f-ring and the ,a-ring has been tentatively designated the ,pioneer ,division4 ,the other new ring has been called the ,g-ring1 which lies well outside the ,f-ring4 ,pioneer carries a scientific payload of #aa operating instruments2 another instrument1 the asteroid_/meteoroid detector1 was turned off in #aige4 ,two other experiments1 celestial mechanics and ,s-band occultation of ,saturn1 use the spacecraft radio to obtain data4 ,pioneer ,saturn is a spinning spacecraft1 which gives its instruments a full-circle scan #g4h times a minute4 ,it uses a nuclear source for electric power because the sunlight at ,jupiter and beyond is too weak for a solar-powered system4 ,two booms project from the spacecraft to deploy the nuclear power source about #c meters from the sensitive spacecraft instrumentation4 ,a third boom positions the magnetometer sensor about #f meters from the spacecraft4 ,six thrusters provide velocity1 attitude1 and spin-rate control4 ,a dish antenna is located along the spin axis and looks back at ,earth throughout the mission1 adjusting its view by changes in spacecraft attitude as the spacecraft and ,earth move in their orbits around the sun4 ,tracking facilities of ,,nasa's ,deep ,space ,network1 located at ,goldstone1 ,california1 and in ,spain and ,australia1 supported ,pioneer ,saturn during interplanetary flight and encounter4 ,pioneer's radio signals1 traveling at the speed of light1 took #he minutes to reach ,earth from ,saturn1 a round-trip time of almost #c hours1 somewhat complicating ground control of the spacecraft4 ,almost #aj1jjj commands were sent to the spacecraft in the #b-week period before closest approach4 ,continued communications should be possible through at least the mid #aihj's4 ,after the spacecraft passed ,saturn1 it headed out of the solar system1 traveling in the direction the solar system moves with respect to the local stars in our galaxy and in approximately an opposite direction from its sister spacecraft1 ,pioneer #aj4 ,both spacecraft have plaques attached to them which contain a message from ,earth for any intelligent species that may intercept the spacecraft during their endless journeys through interstellar space4 ,pioneer ,saturn ,scientific ,instruments ,instrument ,principal ,investigator ,experiment ,objective ,helium vector ,edward ,j4 ,smith ,magnetic fields magnetometer ,jet ,propulsion ,laboratory ,fluxgate ,mario ,acua ,magnetic fields magnetometer ,goddard ,space ,flight ,center ,plasma analyzer ,john ,h4 ,wolfe ,solar plasma ,ames ,research ,center ,charged particle ,john ,a4 ,simpson ,charged particle ,university of ,chicago composition ,cosmic ray telescope ,frank ,b4 ,mc,donald ,cosmic ray energy ,goddard ,space ,flight ,center spectra ,geiger tube ,james ,a4 ,van ,allen ,charged particles telescope ,university of ,iowa ,trapped radiation ,r4 ,walker ,fillius ,trapped radiation detector ,university of ,california1 ,san ,diego ,asteroid_/meteoroid ,robert ,k4 ,soberman ,asteroid_/meteoroid detector#a ,general ,electric ,co4 and astronomy ,philadelphia ,drexel ,university ,meteoroid detector ,william ,h4 ,kinard ,meteoroid detection ,langley ,research ,center ,radio transmitter ,john ,d4 ,anderson ,celestial mechanics and ,,dsn ,jet ,propulsion ,laboratory ,ultraviolet ,darrell ,l4 ,judge ,ultraviolet photometer ,university of ,southern photometry ,california ,los ,angeles ,imaging ,tom ,gehrels ,photo imaging and photopolarimeter ,university of ,arizona1 ,tucson polarimetry ,infrared radiometer ,andrew ,ingersoll ,infrared thermal ,california ,institute of structure ,technology ,radio transmitter ,arvydas ,j4 ,kliore ,s-band occultation and ,,dsn ,jet ,propulsion ,laboratory #a,not currently operational4 ,,saturn ,,images ,saturn1 called the wonder of the heavens by early astronomers1 has been studied from ,earth for many centuries4 ,when ,galileo first focused his telescope on ,saturn in #afaj1 he realized that the appearance of the planet was unusual1 but he never knew its real character because the power of his homemade telescope was far too low4 ,he thought he was looking at three globes1 one large and two small1 which seemed to change slowly in appearance4 ,in #afee1 ,huygens1 after years of observing the planet1 finally realized that these projections were actually a flat ring slightly separated from the main globe4 ,illustration3 ,first sketch of ,saturn 7,galileo1 #afaj74 ,illustration3 ,first sketch showing a division in the rings 7,cassini1 #afge74 ,in #afge1 ,cassini found the first breach in the supposedly solid1 rigid1 and opaque ring when he discovered that it was divided into two parts by a dark line1 now known as ,cassini's ,division4 ,in later years he also detected some of ,saturn's moons4 ,illustration3 ,first successful photograph of ,saturn 7,andrew ,common1 #ahhc74 7,discovering the ,universe1 ,colin ,a4 ,ronan1 ,copyright #aiga by ,colin ,a4 ,ronan1 ,basic ,books1 ,inc41 ,publishers1 ,new ,york47 ,the earliest successful photograph of ,saturn was taken in #ahhc by ,andrew ,common4 ,in #ahie1 ,james ,keeler suggested that the rings are in fact a swarm of particles in near-independent orbits4 ,these rings1 until the recent discoveries of faint ring systems around ,jupiter and ,uranus1 were considered unique in the solar system4 ,since ,galileo first used his homemade telescope to view ,saturn1 there have been many observers4 ,there have also been major advances in telescopes2 a resulting modern view of ,saturn is shown on the next page4 ,the corresponding sketch shows the nomenclature of the brightest rings4 ,now the planet has been seen for the first time not from ,earth1 but in much closer views by an instrument on a spacecraft1 the imaging photopolarimeter on ,pioneer ,saturn4 ,the instrument separately measures the strengths of the red and blue components of sunlight scattered from the clouds of ,saturn and converts this information into numbers4 ,the data are transmitted to ,earth as part of the spacecraft telemetry4 ,the signals are then converted by computer into shades of gray on photographic film1 and the two components plus a synthesized green image can be recombined into a color image that approximates the planet's true color4 ,some of the resulting images are shown on the pages following the ,earth-based view4 ,these pictures were produced by a scientific team from the ,university of ,arizona4 ,these images1 while helping to unravel some of the mystery surrounding the planet1 have created even more interest regarding it4 ,we are really just beginning to know ,saturn4 ,it is up to future spacecraft to more completely reveal her secrets and solve her mysteries4 ,illustration3 ,high-quality contemporary ,earth-based view of ,saturn 7,photo3 ,catalina ,observatory1 ,university of ,arizona74 ,illustration3 ,nomenclature of bright rings4 ,,outer 7,a7 ,,ring ,,cassini ,,division ,,middle 7,b7 ,,ring ,,crepe 7,c7 ,,ring ,illustration3 ,pioneer ,saturn image of ,saturn and its rings from a distance of #h1djj1jjj km 7,august #bb1 #aigi1 #aj days before closest approach74 ,resolution has not yet reached ,earth-based quality4 ,faint banding is visible on the disk of the planet4 ,the silhouette of the rings can be seen in front of the planet4 ,slightly above this silhouette is the shadow of the rings on the disk4 ,beyond the disk1 structure can be seen in the rings4 ,the rings have a distinctly different appearance in this and subsequent images than in ,earth-based pictures because they are illuminated from below rather than from above as we view them from ,earth4 ,the ,a-ring and ,c-ring are bright1 and between them the ,b-ring is dark4 ,the ,cassini ,division at the inner edge of the ,a-ring is also bright1 but is blended with the ring at this distance4 ,illustration3 ,pioneer ,saturn image of ,saturn and its rings from a distance of #e1ejj1jjj km 7,august #bf1 #aigi1 #f days before closest approach74 ,resolution of features is beginning to be approximately equal to that of ,earth-based pictures4 ,belts on the planet are becoming more distinct1 and considerable structure can be seen in the rings4 ,the small blue spot at the bottom of the planet is due to incomplete data and will be corrected by further processing4 ,a notch appears at the top left of the planet1 which may be a data transmission problem or the shadow of one of ,saturn's moons4 ,illustration3 ,pioneer ,saturn image of ,saturn and its rings from a distance of #b1hjj1jjj km 7,august #bi1 #aigi1 #gb hours before closest approach74 ,the ,cassini ,division at the inner edge of the ,a-ring is clearly resolved and is bright4 ,the ,a-ring is dark outside the ,cassini ,division because it has more particulate matter there4 ,polar belts are becoming more visible on the face of the planet4 ,irregularities that appear in the ring silhouette and shadow are due to stepping anomalies in the imaging photopolarimeter and will be removed in further processing4 ,the small round image that appears above the planet is the moon ,titan4 ,illustration3 ,these pictures of ,saturn and its rings were taken by ,pioneer ,saturn from a distance of #b1ejj1jjj km 7,august #bi1 #aigi1 #eh hours before closest approach74 ,the imaging photopolarimeter gathers data using the red and blue components of the light reflected from ,saturn4 ,these two views are from the two color components 7upper1 blue2 lower1 red74 ,the banded structure on the planet is particularly evident in the upper image4 ,because the spacecraft is nearing the planet1 the rings are partially outside the field of view of the instrument4 ,the speck of light below the planet is ,saturn's moon ,rhea1 which is #adej km in diameter1 about one-half the size of ,earth's moon4 ,illustration3 ,saturn and its rings3 red components4 ,illustration3 ,this image was produced by combining the two images on the facing page1 adding a synthesized green component1 and adjusting the intensity of each to obtain an approximation to ,saturn's true color4 7,the same process was used in all of the ,pioneer color images of ,saturn shown here47 ,although not evident on this reproduction1 scientists believe that1 from detailed study of both the uncombined and the combined images1 they can begin to see evidence of jet streams in ,saturn's upper atmosphere4 ,the slight blue edge is an artifact from the computer-enhancement procedure4 ,illustration3 ,pioneer ,saturn view showing the structure of ,saturn's ring system in detail never before seen4 ,the image was taken from a distance of #idc1jjj km 7,august #ca1 #aigi1 about #dd hours before encounter74 ,the moon ,tethys1 seen at the top of the image1 is #abjj km in diameter4 ,there is a very faint unidentified ,saturnian moon at the lower right1 just off the tip of the bright ,a-ring 7may not be visible in this print74 ,the newly defined ,f-ring appears faintly just outside the bright edge of the ,a-ring4 ,the region between the ,a-ring and the ,f-ring has been tentatively named the ,pioneer ,division4 ,this print has been processed to enhance detail of the main rings4 ,illustration3 ,a color print of a version of the same image as shown on the facing page4 ,the blue dot at the outer edge of the ,c-ring is an artifact4 ,this image has not been computer processed to the same extent as the facing image4 ,tethys1 for example1 is only faintly visible1 and the ,f-ring cannot be seen4 ,illustration3 ,close-up image from ,pioneer ,saturn of ,saturn from a distance of #djj1jjj km 7,september #a1 #aigi1 a few hours before closest approach74 ,inset shows the location of the image on the planet4 ,the part of the disk shown is about #be1jjj by #gj1jjj km4 ,the sawtooth pattern is an artifact4 ,the vertical stripe on the disk is due to a gain change in the instrument4 ,the image has not had its final corrections for shape4 ,the rings and their shadows cut diagonal swaths across the image with the upper swath being the shadow4 ,the rings1 seen from the unlit side1 are visible in the foreground4 ,the ring shadow shows clearly that ,saturn's rings have two major divisions3 the ,cassini ,division dividing the outer ,a-ring from the middle ,b-ring1 and a second division 7previously controversial7 dividing the ,b-ring from the inner ,c-ring4 ,these divisions show as parallel pinstripes in the broad black band of the rings' shadow1 with the upper stripe being the ,cassini ,division4 ,some shearing in the bands and belts on ,saturn's disk is beginning to appear1 although the low contrast on the planet 7due to its high-altitude haze7 does not make this highly evident4 ,illustration3 ,post-encounter image of ,saturn from a distance of #hej1jjj km 7,september #b1 #aigi1 #ae hours after encounter74 ,as planned1 during the encounter ,saturn's gravitational field turned the spacecraft's trajectory behind the planet and out toward the edge of the solar system at approximately a right angle to the inbound trajectory4 ,thus1 the planet is now illuminated from the side1 and the view is of a crescent ,saturn with the terminator on the right of the picture4 ,the rings appear dim when compared with the previous inbound pictures because of the different angle between the sun1 the rings1 and the spacecraft4 ,when this picture was taken1 the spacecraft1 as seen from ,earth1 was about to pass behind the sun1 and solar activity was interfering with spacecraft communications4 ,the image quality1 therefore1 is not as good as for pictures taken inbound4 ,with this farewell image from ,pioneer1 ,saturn waits for the ,voyager spacecraft in #aihj and #aiha4 ,illustration3 ,this image of cloud-covered ,titan is one of the 8firsts0 for the ,pioneer ,saturn mission4 ,titan is the largest of ,saturn's moons4 ,because of its great distance from ,earth1 however1 ,titan can be seen only as a point of light in ,earth-based pictures4 ,the ,pioneer trajectory could not be adjusted to allow passage close to ,titan1 and imaging of the planet from the spacecraft was at the outer range of capability of the imaging instrument4 ,thus1 the fuzzy edges and contrast variations on the moon should not be construed as surface features4 ,titan was imaged in the spirit of exploration and discovery4 ,with this image1 which is now a part of recorded history1 our visual information on ,titan is materially increased1 but is still only roughly equal to ,galileo's information on ,saturn itself in #afaj at the time that he prepared his first sketch4 ,better images of ,titan will be obtained by the ,voyager spacecraft4 ,,science ,,highlights ,pioneer ,saturn has already greatly expanded our knowledge of ,saturn1 its rings and moons4 ,we now know that ,saturn1 in many ways1 represents an intermediate case between ,jupiter1 the largest planet in the solar system1 and ,earth4 ,the composition of ,saturn's interior is essentially the same as ,jupiter's1 differing only in the size and extent of the various internal layers4 ,measurements for ,saturn are consistent with a central core of molten heavy elements 7probably mostly iron7 which is the approximate size of the entire ,earth1 but about three times more massive4 ,surrounding the central core is an outer core of highly compressed hot1 liquefied volatiles such as methane1 ammonia1 and water4 ,this outer core is equivalent to approximately nine ,earth masses4 ,these core regions1 however1 represent a very small fraction of the planet1 which is composed primarily of the very lightest gases1 hydrogen and helium1 and is almost #ajj times the mass of the ,earth4 ,because of the high pressure in ,saturn's interior1 the hydrogen is transformed to its liquid metallic state4 ,above this metallic hydrogen shell are liquid molecular hydrogen and ,saturn's gaseous atmosphere and clouds1 which make up the rest of the planet4 ,electrical currents set up within the metallic hydrogen shell produce ,saturn's magnetic field1 which was measured by ,pioneer4 ,in spite of ,saturn's large size1 the magnetic field at the cloud tops is only slightly weaker than the field at the ,earth's surface4 ,saturn is unique in that its magnetic axis is nearly aligned with its rotation axis1 unlike ,earth and ,jupiter4 ,saturn's magnetic field is also much more regular in shape than the fields of the other planets4 ,at large distances from ,saturn1 the magnetic field is deformed by the inward pressure of the solar wind4 ,near the noon meridian 7close to the inbound ,pioneer trajectory71 the solar wind causes a compression of the field2 in the dawn meridian 7close to the outbound trajectory71 the field is swept back and presumably forms a long magnetic tail4 ,in both cases1 ,pioneer ,saturn crossed the outer boundary of the magnetic field several times as the field moved in and out1 responding to changing solar wind pressure4 ,pioneer also observed inward and outward boundaries4 ,the magnetic envelope surrounding ,saturn is intermediate in size and energetic particle population between those of the ,earth and ,jupiter1 the only two other planets known to be strongly magnetized4 ,the three other planets investigated thus far 7,venus1 ,mars1 and ,mercury7 and ,earth's moon have little or no magnetism4 ,virtually all our knowledge of ,saturn's magnetic environment has been obtained by ,pioneer4 ,the spacecraft found rings of particulate material and several small moons near the rings1 which strongly affect ,saturn's trapped radiation4 ,these features provide important diagnostic capabilities4 ,a unique finding is the nearly total absence of radiation belt particles at distances closer to the planet than the outer edge of the visible rings4 ,the inner region of the thick magnetic envelope of ,saturn1 called the magnetosphere1 contains trapped high-energy electrons and protons1 with some evidence for heavier nuclei4 ,the overall form of the magnetosphere is simple and compact1 more similar to that of ,earth than of ,jupiter4 ,the unique measuring capabilities of the ,pioneer ,saturn radiation detectors led directly to the discovery of a diffuse new ring of particulate matter in the region from about #aj to #ae planetary radii 7#a ,saturn radius #fj1jjj km7 from ,saturn4 ,this ring has been tentatively designated as the ,g-ring4 ,the ,g-ring clearly causes particle absorption near the equatorial region4 ,moreover1 ,pioneer discovered another region inside #g or #h planetary radii in which the radiation belt particles were subjected to a strong loss or absorption1 presumably caused by the presence of an extensive cloud of plasma corotating with the planet4 ,inside about #aj planetary radii1 the trapped radiation shows a high degree of axial symmetry around ,saturn and is consistent with the centered dipole magnetic field observed by ,pioneer4 ,saturn's rings annihilate all trapped radiation at the outer edge of the ,a-ring1 leaving a shielded region close to the planet in which the radiation intensity is the lowest so far encountered in this mission4 ,this shielding prevents the further buildup of electron intensities at lower altitudes1 which otherwise would have been present and would have made ,saturn a strong radio source observable from ,earth4 ,pioneer found that several of ,saturn's moons absorb trapped particles from the radiation belts1 producing prominent dips in the intensity4 ,the effectiveness of absorption at the moons ,tethys and ,enceladus is particularly astonishing1 and supports the idea that radiation belt particles are drifting inward slowly across the moons' orbits4 ,a precipitous decrease in particle intensity1 lasting only for about #ab seconds1 was observed over a wide range of energies for both protons and electrons at a distance near #b4ec ,saturn radii1 #bc minutes after ,pioneer crossed the ,saturn ring plane inbound4 ,at about the same time1 an anomaly was also observed in the magnetic field measurements4 ,these phenomena have been tentatively interpreted as indicating the presence of a nearby massive body absorbing the trapped radiation and perturbing ,saturn's magnetic field4 ,the estimated radius of this object lies in the range of #ajj to #cjj km1 based on the effectiveness with which it absorbed the high-energy radiation4 ,the total radiation dose received at ,saturn was equivalent to only #b minutes in the ,jovian radiation belts because ,saturn's radiation belts were so much weaker4 ,in addition to images of ,saturn1 the brightness1 color1 and polarization of the reflected light were also measured by the imaging photopolarimeter on ,pioneer ,saturn4 ,these measurements are used to study the cloud layers of ,saturn and ,titan and to model the vertical structure of the atmospheres of these two bodies4 ,in the scans that made the images1 the banded structures of ,saturn and of the rings were obtained in fine detail4 ,these are essential in studying the atmosphere1 rings1 and moons4 ,a new ,saturnian ring1 which has been tentatively designated the ,f-ring1 was discovered in the images4 ,it is narrower than #ejj km in width1 but is important because it forms an outside barrier to the bright ,a- and ,b-rings4 ,the gap between the ,f- and ,a-rings has been designated the ,pioneer ,division by the ,pioneer team4 ,a small moon1 which either was previously unknown or had been previously discovered from ,earth but lost again1 was found in the ,pioneer ,saturn images4 ,after its initial discovery1 this new moon continued on its #ag-;hour orbit around the planet and passed near ,pioneer as the spacecraft entered the ring system4 ,it is quite conceivable that this moon is the same one that perturbed the radiation belt particles and produced the anomaly in the magnetic field measurements4 ,infrared observations obtained during the ,saturn flyby revealed the temperatures in the atmospheres of ,saturn and the rings and in the atmosphere of ,titan4 ,it was found that ,saturn has a temperature of about #ajj ,k 7about #bhj;,f below zero7 and1 according to these observations1 has an internal heat source of enough strength that the planet emits approximately #b4e times as much energy as it absorbs from the sun4 ,the equatorial yellowish band observable in many of the images was found to be several degrees colder than the planet at other latitudes and is probably a zone of high clouds resembling similar zones on ,jupiter4 ,as expected1 the rings were extremely cold1 #fe to #ge ,k 7about #ccj;,f below zero71 at the time of encounter4 ,the temperature differences between the illuminated and unilluminated sides of the rings1 and the rate of cooling as the ring particles go into ,saturn's shadow1 suggest that the ring particles are at least several centimeters in diameter and the rings themselves are many particle diameters thick4 ,the very minor perturbation to ,pioneer's trajectory1 as it passed under the visible rings1 indicates that the rings probably consist of ices4 ,as ,pioneer passed through ,saturn's ring system1 very sensitive meteoroid detectors observed the impact of five particles on the spacecraft1 particles that were about #aj micrometers 7#j4jjje inch7 in diameter4 ,two impacts occurred while the spacecraft was above the rings and three while the spacecraft was below the rings4 ,no impacts were detected going through the ring plane1 but the ,pioneer instrument cannot detect individual impacts that occur less than #gg minutes apart4 ,this characteristic would have prevented detection of ring particles because of the impacts detected just before both ring plane crossings4 ,it is uncertain whether the micrometeoroids detected by ,pioneer ,saturn were stray ring particles deflected out of ,saturn's ring plane or whether they were particles from interplanetary space drawn inward toward ,saturn by its strong gravitational field4 ,close to the point of closest approach to ,saturn1 the spacecraft's radio transmissions were affected by ,saturn's ionosphere4 ,the manner in which the radio signals were absorbed indicates that ,saturn has an extensive ionosphere composed of ionized atomic hydrogen with a temperature of about #abej ,k in its upper regions4 ,this high temperature requires an extensive energy source other than the sun4 ,this phenomenon was also observed at ,jupiter4 ,pioneer measured ultraviolet glow throughout the ,saturnian system4 ,this ultraviolet glow is due to the scattering of the light from the sun by atomic hydrogen4 ,the observations of ultraviolet emission from an extensive cloud of hydrogen gas surrounding ,saturn's visible rings are especially interesting4 ,the rings themselves are presumably the source of this hydrogen4 ,on the planet's disk1 the ultraviolet observations show significant latitude variations1 suggesting the possibility of aurora near ,saturn's polar regions4 ,a similar extensive cloud of hydrogen was also seen partially surrounding ,titan's orbit4 ,these very preliminary findings by ,pioneer ,saturn represent only a small fraction of what will ultimately be learned about ,saturn and its environment as the spacecraft data are analyzed in greater detail over the weeks and months ahead4 ,illustration3 ,schematic of the solar wind interaction with ,saturn's magnetosphere4 ,the solar wind arrives from the direction of the sun1 is deflected at ,saturn's bow shock1 and flows around ,saturn in the magnetosheath 7orange region71 as indicated by the arrows4 ,the sizes of the magnetosheath and radiation belts change in response to the external solar-wind pressure1 becoming smaller when the external pressure is larger and vice versa4 ,illustration3 ,diagram of ,saturn's inner trapped radiation belts4 ,the energetic particle fluxes generally become more intense closer to ,saturn4 ,decreases in particle flux at the locations of ,saturn's moons are due to the sweeping up of the energetic particles caused by particles striking the moons and being absorbed by them4 ,also1 there are decreases in particle flux at the outer edge of the rings1 where the energetic particles are also absorbed1 so that a region free of trapped radiation is created from the outer edge of the rings to ,saturn4 ,illustration3 ,infrared radiometer image of ,saturn and its rings4 ,brightness in the image is related to temperature1 with the brightest areas at about #ajj ,k 7about -#bhj;,f74 ,the left version shows contrast in the colder regions 7the rings74 ,the right version shows contrast in the warmer regions 7the planet74 ,the image contains many separate scans from top to bottom4 ,each scan is displaced to the right from the one before by the motion of the spacecraft4 ,the spacecraft was below the ring plane during most of the #c-;hour observation period and was much closer to the planet at the end of the period 7right of image7 than at the start 7left of image74 ,thus1 the images are quite distorted4 ,the small-scale pattern is instrument noise4 ,in the left image1 the warm infrared radiation from the planet is seen through ,cassini's ,division between the ,a- and ,b-rings4 ,the brightness level in the right image implies that ,saturn emits heat at a rate that is #b4e times the rate that it absorbs energy from the sun4 ,,outward ,,bound ,illustration3 ,after increasing our knowledge of the ,saturnian system manyfold1 the spacecraft is now outward bound4 ,it carries a message1 engraved on a plaque1 from ,earth to any inhabitants of another star system who might discover the spacecraft4 ,with its journey far from over1 ,pioneer ,saturn travels on--to the outer reaches of space4 ,the ,pioneer ,project is managed by the ,ames ,research ,center for the ,national ,aeronautics and ,space ,administration4 ,the spacecraft was built by ,,trw ,systems1 ,redondo ,beach1 ,california4 ,national ,aeronautics and ,space ,administration ,ames ,research ,center ,moffett ,field1 ,california #idjce ,official ,business ,penalty for ,private ,use1 #cjj ,postage and ,fees ,paid ,national ,aeronautics and ,space ,administration ,,nasa-#dea ,illustration3 ,,nasa ,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 --,added a ,table of ,contents4 --,in the text versions only1 text in italics is delimited by underscores4