Pioneer : Saturn Encounter (1979)

for I'm Larry Ross director of space programs at NASA's Lewis Research Center in Cleveland Ohio and I'm your host for this 11th program in our 13p part series Journey Through the solar system [Music] now let's go back to 19 1979 when a Pioneer spacecraft launched from Earth by the Lewis managed Atlas Centaur rocket made its closest approach to Saturn the sixth planet we received uh several pictures uh yesterday afternoon and evening and we'd like to run through some of those now uh this is the one you that came in here at about 3:00 yesterday afternoon this is are by far the most spectacular picture uh we have so far this is raw data it has not been processed in any way uh we can see the the big banded planet and the of course the ring system is very prominent in this picture also prominent is uh Saturn's largest moon Titan in the upper right hand corner uh Titan is a very large Moon 300 uh 3,600 miles in diameter almost Planet size so the Pioneer Saturn Mission continues to go very very well we're about 50 hours now from closest approach on Saturday morning this is Pioneer Saturn Mission operations on Voyer we heard a lot of uh or some speculation about organic molecules and uh the possibility that within the clouds there's a belt or zone or something where the temperature is comfortable for life unlike this room up here our Sim similar speculations possible or reasonable for Saturn there almost certainly is a Zone as you go down where the temperatures are um comfortable uh for life and even the mixture of elements is probably adequate for life there's carbon hydrogen oxygen nitrogen Etc um of course there's no solid surface for the life to cling to and there are convection currents carrying these molecules if there are any molecules down there and there certainly are if there are any organic molecules we don't know but uh let's assume there's a accidental organic molecule uh it will soon be carried to some Zone probably deeper where it's much hotter and where the molecule is dissociated so I don't hold much chance for floating organisms in either of these planet's atmospheres from the bulk density of the planet the fact that it's only 7/10 the density of water we know that it's largely made of hydrogen but there's a little bit of heavy stuff and it's close enough to be um the the extra stuff you need is rather close to what you'd get if you just solar material yes what kind of information will you be looking for to indicate some kind of life form on the moon Titan on Titan really none but let me now modify that simple answer the uh question of life on Titan hinges on a number of factors but mainly the temperature of the surface of Titan if it's warm such as above the freezing point of water then we could say that there's a possibility of Life un tighten now unfortunately well now we are a temperature measuring device so we are relevant to how warm the surface is uh unfortunately we can't see through the clouds so if there are a lot of clouds in the atmosphere we're just going to see the cold Cloud tops I have some hope that we will be able to say whether Titan has a thick atmosphere or a thin atmosphere if it has a thick one then there's hopes that below the clouds there's a gradually Rising temperature and ultimately a warm temperature at the ground now Titan is particularly interesting because uh it's one of the planets that has a reasonable atmosphere associated with it and it contains at least methane which we believe may have been one of the ingredients on some of the early uh in the early primitive Earth and there are also indications other indications in the in the atmosphere of Titan that there is organic chemistry going on actually there have been some radio observations rather recently that uh show that the temperature at the surface is cold not all that different from the temperature at the cloud tops and this is an uh sort of a suggestion that really the atmosphere isn't all that thick the cloud tops are not all that far above the surface and therefore uh the atmosphere is thin sort of a Mars like atmosphere so does that throw both a greenhouse and a inversion atmosphere model out the window thin these observations these radio observations will throw out the greenhouse model they tend to throw throw it out and they tend to throw out the possibility of life if there ever was one because Titan is there for much too cold I understand one of the things that you've been looking for is the magnetosphere well first of all I'm talking about the magnetic field of Saturn the Earth has a magnetic field and because the Earth has a magnetic field and when you take your your compass it Points North and you know where to go uh Jupiter has a magnetic field also and we expected Saturn to have a magnetic field and you really you need a magnetic field a global magnetic field in order to have radiation belts of course the Earth has has radiation belts Jupiter has very strong radiation belts we felt that the interior of Saturn is such that Saturn would more than likely have a magnetic field and yet the solar storm that we're encountering as we uh are approaching Saturn is such that that magnetic field was masked and so we kept getting closer and closer and closer to Saturn and no magnetic field and uh early this morning we crossed the standing bow shock wave which results as a as a consequence of of that magnetic field and the impact of the solar wind which immediately told us yes indeed Saturn does have a magnetic field and we were even able to compute what the strength of that field was at on details on the ball of Saturn on the planet Saturn itself there is not much in the way of spots which is a bit disappointed disappointing because we had hoped to uh get precise rotation rates and thereby a better information on uh Jets and streams in the atmosphere of Saturn the structure however of belts and zones is beginning to be seen and look somewhat different from that of Jupiter whereas from the earth already uh we knew that there are in in hemisphere say the northern hemisphere which is the one that we're observing best right now on the order of five uh belts and five zones so that was known from groundbased uh observations it now looks that there many more of these bright zones and dark belts uh perhaps twice as many this is Pioneer Saturn Mission operations the uh spacecraft has now moved to within 700,000 mil of uh the planet Saturn and it's moving closer at uh just about 26,000 Mi per hour uh as we learned in the Press briefing we now believe we know what our problem with the data has been uh there was a major solar event uh uh some weeks ago uh particles from the Sun have made their way out into interplanetary space and have now enveloped our spacecraft and the planet Saturn the most uh apparent result of this will be smaller pictures on our screens and we will not be able to show as much area of the planet in each image as uh had been expected since I I'm a radio man I I'm kind fascinated with uh the radio system of uh Pioneer and the DSN and I'm very impressed by the fact that all of these data I received from a distance of just about exactly uh 1 billion miles at this distance uh if you are transmitting 1,24 bits per second at any given time there are 5 and a half million of those bits strung between here and Saturn all traveling at a speed of light 5 and a half million and they're spaced 182 miles apart with that a quit at uh uh at 7:36 a.m. this morning the spacecraft will pass through the ring plane at Saturn and this is probably the most dangerous part of its Journey even though the spacecraft is going by Saturn outside of the three visible Rings the the three rings that we can see from earth scientists are quite sure that there is a great deal of material which lies outside of the outermost visible ring the soal called a-ring well paner Saturn is going to be going through that and uh it will take less than a second for it to uh penetrate the the ring and move through it but if it should encounter a piece of debris uh it could be the end of the mission right there uh this first view is is a close-up view of the equatorial region of Saturn I think it's very interesting and has caused quite a bit of comment here in the mission Operation Center uh first of all the Block in the upper right has no meaning that's an artifact introduced uh into the image as we display it here by the computers that uh process the spacecraft data that comes from the spacecraft so the part we're interested in is the portion uh below the middle of the screen the lower half of the screen and what we're seeing there is a portion of the cloud tops of Saturn uh near the equator and the stripes that we see to the left uh that move diagonally from the left up toward the upper Center uh are a backlighted view of Saturn's rings but the most interesting thing perhaps is the shadow of these Rings cast on the surface or the cloud tops at Saturn time is 9:03 and 40 seconds right now 20 more seconds and uh we will be able to confirm the spacecraft has survived 15 seconds 10 seconds five 4 3 2 [Music] one this we have a mission the Pioneer Saturn spacecraft has survived the crossing of the rain plane we our micr meteoroid detector on the spacecraft received two hits uh now that is the maximum number of hits it can achieve in an 80 SEC or 80 minute period so it could have been a quite a few more hits than two so uh there's no question we did go through a a region that has some debris in it and receivers rep ported out of lock receivers are out of lock the spacecraft is behind the planet we no longer have communications with the spacecraft the cost of a planetary emission I like to measure in units of a beer we all know what a beer costs we all know what a beer means to us the trip we're going to to Saturn now is a real cheapy we got two flybys of Jupiter by Pioneer and now one of Saturn for two cans of beer per person now that's cheaper than buy a long shot than the cost of going to a movie today and I can't help thinking that's worth it do you agree right this is Pioneer Saturn Mission operations a minute and a half now from the receipt of telemetry for the second ring Crossing 4 seconds we're through the time the Telemetry uh continues to look good four minutes now after the uh uh nominal time pioner Saturn seems to be safely through the ring plane and still in business this is Pioneer Saturn Mission operations the spacecraft is now 760,000 miles away from Saturn and uh moving away at about 25,000 400 miles hour uh yesterday uh we uh during a press briefing yesterday afternoon uh some of the findings from yesterday's encounter at uh Saturn were announced these include the possibility of the discovery of a new moon at Saturn also the discovery of a new ring and the so-called Pioneer division or perhaps the Pioneer Gap uh uh between this new ring and the outside of the a-ring which is the outermost ring which is visible through Earth telescope we also announced major structural features uh have been discovered in the Saturn's atmosphere uh and also made the first ever temperature measurements of Saturn's ring there are a few anomalies but we've learned to live with it and so these pictures that I will be showing you will not at all be perfect there will be some some missed uh scan lines in there and so forth but we have the bookkeeping we know exactly where each element is and in our computers eventually that is sometime this fall we can release pictures that will be appreciably better than what you're seeing here Saturn has been called the most beautiful planet in the solar system and uh uh perhaps this picture is a good example of why this is a closeup of uh two views actually of the Rings uh an image and then a mirror image as the Imaging instrument Ste back across the Rings and this is the picture that uh uh I gave us our first glimpse of the new ring system the the new outer ring at Saturn and the Pioneer division between that ring and the outside of the a ring uh here's a an enlargement of the previous View the planet appears oblate it is oblate uh the diameter quite a bit larger at the equator than it is down through the pole another closeup view of the cloud tops at Saturn this is the image that was made uh at very near the closest approach point to Saturn there's a great deal of uh data an information contained in this image that may not be readily apparent on your screen but there's data here that will be studied by scientists for years to come uh coming out the other side of the planet now uh we have another view of Saturn in Cross light with the sun uh lighting the planet from the side the the Pioneer Saturn spacecraft is on its way out of the solar system uh but we be tracked for a number of years Yet to Come returning valuable data on the interplanetary medium the solar wind this is Piner Saturn Mission operations uh with that sort of preview maybe we can show uh call up the Titan image or one of the Titan images from last night uh it doesn't have a lot of uh obvious features on it I think you'll agree but if you've heard the model Builders talking they haven't predicted a lot of obvious features the other uh thing to notice is that this is really raw data it's been processed but only in the sense that it's been squashed back together again to make it look round it gets very elongated when it when it goes for a long time in One Direction and a shorter time in another Direction and the good news that Titan is that Titan is there the bad news is that we barely saw it we were counting on first of all twice as much data because at at the high Telemetry rate secondly we are counting on no data dropouts so we have good deal less data and uh we we're counting on lots of data in order to average it and beat down the noise and I'd say we've said the temperature Titan is 75 degrees Kelvin plus or minus 5 which is about the temperature you'd expect for an object in equilibrium with the Sun at that place in the solar system and uh as you can see there's no prayer of measuring a day night temperature difference with these data we are not looking at the surface we are looking at the cloud tops or some point high in the atmosphere and we cannot say what the temperature of the surfaces do I gather that based on the data that you did get back with with Titan there is not insufficient temperature data with respect to the surface to ascertain whether indeed there is an atmosphere that could be hospitable to some life form I think there's plenty of other data earth-based data that tend to rule out the possibility of high surface temperatures and therefore rule out life there's but I'll leave the door open a crack I will certainly agree with you my data do not have much to say about the surface temperature so perhaps summary of Saturn or rings first I guess I've summarized the significance of the Titan data for you already I think we can say that our Eclipse data just as we go behind the planet just at the end on the right there are consistent with other analyses that imply that the Rings are centimet size and uh the the prary indications are that the uh masses are not high that they are more consistent with uh the uh uh hypothesis of the Rings being made of IES rather than something heavy uh containing a lot of iron on the planet itself I think we've at least confirmed that these yellow bands are correlated with Cloud Heights the various colored bands on Saturn are correlated with Cloud Heights by which I mean different colored bands are at different Heights and then we come to this Exquisite fine feature uh the eering a very narrow eing which lies near or on the inside of the earring which we have not been able to observe uh but I have little doubt that the earring exists and then this morning we heard then of the discovery of the g- ring uh between approximately 10 and 15 radi now I know the ladies and gentlemen of the press are probably a little bit uh perplexed by some of the complicated figures that we show you so I thought I'd start with a simple one this is it now this is my summary of the hard information we had hard scientific information we had about Saturn's magnetic field prior to the Pioneer 11 Mission so we know that we can now turn this blank page begin to uh concentrate on the fact that Saturn does indeed have a magnetic field and and we know what its properties are and uh to paraphrase William Gilbert who started this business originally back in the 1600s might say Saturn is indeed a giant magnet what we've shown here is a the Pioneer Rock uh which we uh presume lies in or near the ring plane this is the Pioneer spacecraft which at this time was about 10 minutes after having crossed the ring plane and was moving inward towards periapsis it seems clear that uh referring to this as the Pioneer Rock was perhaps somewhat misleading as you've heard the energetic particles have given us some idea about the size of this thing which uh we nearly missed and several hundred kilometers is probably more comparable in cross-section to the greater San Francisco Oakland area so uh calling it a rock is perhaps not really the appropriate thing far as we know what wasn't there we went under it about 10 minutes after clossing the ring plane and I would say along with the others that we were damn lucky what this shows we'll just keep it at this for the moment is how using trajectory information we can learn things about the interior of the planet uh first we show here just a core uh an interc cor to Saturn which will produce a nearly spherical gravitational field it will be slightly flattened and we show again very schematically a trajectory flying through that uh gravitational field now we can add in a uh region of uh metallic hydrogen and uh that can be shown by here we add metallic hydren on top of the core this will change the gravitational field flatten it uh even more and we'll get a uh slightly different trajectory as a result of that metallic hydrogen region and then finally we show the uh outer envelope of Saturn uh the liquid hydrogen region and we show in a very exaggerated way the shape of the surface or the uh the geid we have a figure of the uh interior uh this is built up by an in core uh I guess I have no control over how fast this this accumulat so we can we can let it go all the way out to the surface but anyway that inner core you see is made up of molten rock and iron uh this model that we show here is uh essentially correct uh it consists of about three Earth masses but is of about the same size as the Earth so we have have a density of about uh three times what we have in the earth and a body of about the same size made up of rock and iron but uh higher density by about a factor of three because it's inside of Saturn uh then we have an outer core where um uh substances water methane and ammonia have settled out of the uh upper regions of Saturn formed a uh outer core consisting of about nine Earth masses and the boundary of that uh outer core is about 23% of the total planetary radius then on top of that is the uh metallic hydrogen region which is consistent with the diagram that Ed Smith showed and uh the boundary of that uh makes up about 58% of the radius on top of that a uh liquid hydrogen region and then on the very top a uh gaseous atmosphere which we estimate to be about 300 km deep yeah I just want to make a few closing remarks and that is that first of all in the last two weeks I think our our knowledge on Saturn is increased by at least a thousandfold conservatively and uh so I think you know two weeks ago we didn't know very much about Saturn I think we know a lot now we got a lot of questions and hopefully a lot of these will be answered as we analyze the data further but I think we've learned awful lot in the last two weeks compared to what we've known in the last 370 years or so truly great strides were made by the Pioneer missions but the Voyager spacecraft which followed the Pioneers to Saturn gave us even clearer pictures and much more information during our next program we will see planetary data received by scientists at NASA's jet propulsion laboratory in California until then this is Larry Ross saying goodbye from NASA's leou Research Center including the have [Music] la e