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00:00I'm Larry Ross, Director of Space Programs at NASA's Lewis Research Center in Cleveland,
00:13Ohio, and I'm your host for this 11th program in our 13-part series, Journey Through the
00:19Solar System.
00:49Now, let's go back to 1979 when a Pioneer spacecraft launched from Earth by the Lewis-managed
01:07Atlas-Centaur rocket made its closest approach to Saturn, the sixth planet.
01:13We received several pictures yesterday afternoon and evening, and we'd like to run through
01:19some of those now.
01:21This is the one that came in here at about 3 o'clock yesterday afternoon.
01:26This is by far the most spectacular picture we have so far.
01:33This is raw data.
01:34It has not been processed in any way.
01:37We can see the big banded planet, and of course the ring system is very prominent in this
01:44picture.
01:45Very prominent is Saturn's largest moon, Titan, in the upper right-hand corner.
01:52Titan is a very large moon, 3,600 miles in diameter, almost planet-sized.
02:01So the Pioneer Saturn mission continues to go very, very well.
02:06We're about 50 hours now from closest approach on Saturday morning.
02:10This is Pioneer Saturn mission operations.
02:14On Voyager we heard a lot of, or some, speculation about organic molecules and the possibility
02:21that within the clouds there was a belt or a zone or something where the temperature
02:25is comfortable for life, unlike this room.
02:32Are similar speculations possible or reasonable for Saturn?
02:36There almost certainly is a zone as you go down where the temperatures are comfortable
02:47for life.
02:49And even the mixture of elements is probably adequate for life.
02:53There's carbon, hydrogen, oxygen, nitrogen, et cetera, et cetera.
02:59Of course there's no solid surface for the life to cling to.
03:05And there are convection currents carrying these molecules, if there are any molecules
03:12down there, and there certainly are, if there are any organic molecules, we don't know.
03:16But let's assume there's an accidental organic molecule.
03:22It will soon be carried to some zone, probably deeper, where it's much hotter and where the
03:31molecule is dissociated.
03:33So I don't hold much chance for floating organisms in either of these planets' atmospheres.
03:39From the bulk density of the planet, the fact that it's only seven-tenths the density of
03:46water, we know that it's largely made of hydrogen.
03:50But there's a little bit of heavy stuff and it's close enough to be, the extra stuff you
03:59need is rather close to what you'd get if you just took solar material.
04:04Yes?
04:05What kind of information will you be looking for to indicate some kind of life form on
04:10the moon, Titan?
04:13On Titan?
04:16Really none, but let me now modify that simple answer.
04:23The question of life on Titan hinges on a number of factors, but mainly the temperature
04:29of the surface of Titan.
04:31If it's warm, such as above the freezing point of water, then we could say that there's a
04:39possibility of life on Titan.
04:41Now unfortunately, well, now we are a temperature measuring device, so we are relevant to how
04:48warm the surface is.
04:52Usually we can't see through the clouds, so if there are a lot of clouds in the atmosphere,
04:56we're just going to see the cold cloud tops.
04:58I have some hope that we will be able to say whether Titan has a thick atmosphere or a
05:06thin atmosphere.
05:08If it has a thick one, then there's hopes that below the clouds there's a gradually
05:15rising temperature and ultimately a warm temperature at the ground.
05:19Now Titan is particularly interesting because it's one of the planets that has a reasonable
05:24atmosphere associated with it, and it contains at least methane, which we believe may have
05:30been one of the ingredients on some of the early, in the early primitive Earth.
05:35And there are also indications, other indications, in the atmosphere of Titan that there is organic
05:42chemistry going on.
05:44So there have been some radio observations rather recently that show that the temperature
05:50at the surface is cold, not all that different from the temperature at the cloud tops, and
05:57this is sort of a suggestion that really the atmosphere isn't all that thick, and the cloud
06:03tops are not all that far above the surface, and therefore the atmosphere is thin, sort
06:10of a Mars-like atmosphere.
06:11So does that throw both a greenhouse and an inversion atmosphere model out the window
06:17that's thin?
06:18Well, these observations, these radio observations, will throw out the greenhouse model, they
06:24tend to throw it out, and they tend to throw out the possibility of life if there ever
06:29was one, because Titan is therefore much too cold.
06:33I understand one of the things that you've been looking for is the magnetosphere.
06:38So first of all, I'm talking about the magnetic field of Saturn.
06:43The Earth has a magnetic field, and because the Earth has a magnetic field, and when you
06:47take your compass, it points north, and you know where to go.
06:51Jupiter has a magnetic field also, and we expected Saturn to have a magnetic field,
06:57and you really, you need a magnetic field, a global magnetic field, in order to have
07:01radiation belts.
07:02Of course, the Earth has radiation belts, Jupiter has very strong radiation belts.
07:07We felt that the interior of Saturn is such that Saturn would more than likely have a
07:13magnetic field, and yet the solar storm that we're encountering as we are approaching Saturn
07:19is such that that magnetic field was masked, and so we kept getting closer and closer and
07:24closer to Saturn and no magnetic field.
07:28And early this morning, we crossed the standing bow shockwave, which results as a consequence
07:36of that magnetic field and the impact of the solar wind, which immediately told us,
07:42yes, indeed, Saturn does have a magnetic field, and we were even able to compute what the
07:46strength of that field was.
07:50On details on the wall of Saturn, on the planet Saturn itself, there is not much in the way
07:58of spots, which is a bit disappointing, because we had hoped to get precise rotation rates
08:06and thereby better information on jets and streams in the atmosphere of Saturn.
08:16The structure, however, of belts and zones is beginning to be seen and looks somewhat
08:24different from that of Jupiter, whereas from the Earth already, we knew that there are
08:31in an hemisphere, say the northern hemisphere, which is the one that we're observing best
08:36right now, on the order of five belts and five zones, so that was known from ground-based
08:43observations.
08:44It now looks that there are many more of these bright zones and dark belts, perhaps twice
08:54as many.
08:57This is Pioneer Saturn mission operations.
09:00The spacecraft has now moved to within 700,000 miles of the planet Saturn, and it's moving
09:07closer at just about 26,000 miles per hour.
09:12As we learned in the press briefing, we now believe we know what our problem with the
09:17data has been.
09:20There was a major solar event some weeks ago.
09:26Astronauts from the sun have made their way out into interplanetary space and have now
09:31enveloped our spacecraft and the planet Saturn.
09:36The most apparent result of this will be smaller pictures on our screens, and we will not be
09:43able to show as much area of the planet in each image as had been expected.
09:51As I am a radio man, I am fascinated with the radio system of Pioneer and the DSN, and
09:58I'm very impressed by the fact that all of these data are received from a distance of
10:03just about exactly one billion miles.
10:07At this distance, if you are transmitting 1,024 bits per second, at any given time there
10:14are five and a half million of those bits strung between here and Saturn, traveling
10:19at a speed of light, five and a half million.
10:23And they're spaced 182 miles apart with that output.
10:32At 7.36 a.m. this morning, the spacecraft will pass through the ring plane of Saturn,
10:42and this is probably the most dangerous part of its journey.
10:47Even though the spacecraft is going by Saturn outside of the three visible rings, the three
10:53rings that we can see from Earth, scientists are quite sure that there is a great deal
10:58of material which lies outside of the outermost visible ring, the so-called A ring.
11:03Well, Pioneer Saturn is going to be going through that, and it will take less than a
11:08second for it to penetrate the ring and move through it.
11:13If it should encounter a piece of debris, it could be the end of the mission right there.
11:18This first view is a close-up view of the equatorial region of Saturn.
11:25I think it's very interesting and has caused quite a bit of comment here in the Mission
11:29Operations Center.
11:32First of all, the block in the upper right has no meaning.
11:35That's an artifact introduced into the image as we display it here by the computers that
11:42process this spacecraft data as it comes from the spacecraft.
11:45So the part we're interested in is the portion below the middle of the screen, the lower
11:50half of the screen.
11:51What we're seeing there is a portion of the cloud tops of Saturn near the equator, and
11:59the stripes that we see to the left that move diagonally from the left up toward the upper
12:04center are a backlighted view of Saturn's rings.
12:12But the most interesting thing, perhaps, is the shadow these rings cast on the surface
12:16or the cloud tops of Saturn.
12:22Time is 9.03 on 40 seconds. Right now, 20 more seconds, and we will be able to confirm
12:29the spacecraft has survived. 15 seconds. 10 seconds.
12:375, 4, 3, 2, 1.
12:49We have a mission. The Pioneer Saturn spacecraft has survived the crossing of the rain plain.
12:57Our micrometeoroid detector on the spacecraft received two hits. Now that is the maximum
13:04number of hits it can achieve in an 80-minute period. So it could have been quite a few
13:10more hits than two, so there's no question we did go through a region that has some debris
13:16in it.
13:18And receivers reported out of lock. Receivers are out of lock. The spacecraft is behind
13:23the planet. We no longer have communications with the spacecraft.
13:28The cost of a planetary mission I like to measure in units of a beer. We all know what
13:33a beer costs. We all know what a beer means to us.
13:38The trip we're going to to Saturn now is a real cheapie. We got two flybys of Jupiter
13:42by Pioneer and now one of Saturn for two cans of beer per person.
13:49Now that's cheaper by a long shot than the cost of going to a movie today. And I can't
13:54help thinking that's worth it. Do you agree?
14:04This is Pioneer-Saturn mission operations. A minute and a half now from the receipt of
14:13telemetry for the second ring crossing. Four seconds. We're through the time. The telemetry
14:29continues to look good. Four minutes now after the nominal time. Pioneer-Saturn seems
14:39to be safely through the ring plane and still in business.
14:49This is Pioneer-Saturn mission operations. The spacecraft is now 760,000 miles away from
14:57Saturn and moving away at about 25,400 miles per hour.
15:04Yesterday, during a press briefing yesterday afternoon, some of the findings from yesterday's
15:13encounter at Saturn were announced. These include the possibility of the discovery of
15:20a new moon at Saturn, also the discovery of a new ring and the so-called Pioneer Division
15:27or perhaps the Pioneer Gap between this new ring and the outside of the A ring, which
15:35is the outermost ring which is visible through Earth telescopes. We also announced major
15:42structural features have been discovered in the Saturn's atmosphere and also made the
15:51first ever temperature measurements of Saturn's rings.
15:55There are a few anomalies, but we've learned to live with it. And so these pictures that
16:00I will be showing you will not at all be perfect. There will be some missed scan lines in there
16:05and so forth, but we have the bookkeeping. We know exactly where each element is and
16:09in our computers eventually, that is sometime this fall, we can release pictures that will
16:14be appreciably better than what you're seeing here.
16:18Saturn has been called the most beautiful planet in the solar system and perhaps this
16:23picture is a good example of why.
16:31This is a close-up of two views actually of the rings, an image and then a mirror image
16:38as the imaging instrument stepped back across the rings. And this is the picture that gave
16:47us our first glimpse of the new ring system, the new outer ring at Saturn and the Pioneer
16:56Division between that ring and the outside of the A ring.
17:01Here's an enlargement of the previous view. The planet appears oblate. It is oblate. The
17:12diameter quite a bit larger at the equator than it is down through the pole.
17:17Another close-up view of the cloud tops at Saturn. This is the image that was made at
17:24very near the closest approach point to Saturn. There's a great deal of data and information
17:31contained in this image that may not be readily apparent on your screen, but there's data
17:37here that will be studied by scientists for years to come.
17:42Coming out the other side of the planet now, we have another view of Saturn in cross-light
17:48with the sun lighting the planet from the side.
17:54The Pioneer Saturn spacecraft is on its way out of the solar system, but will be tracked
18:02for a number of years yet to come, returning valuable data on the interplanetary medium,
18:11on the solar wind. This is Pioneer Saturn mission operations.
18:19With that sort of preview, maybe we can show, call up the Titan image or one of the Titan
18:24images from last night. It doesn't have a lot of obvious features on it. I think you'll
18:32agree, but if you've heard the model builders talking, they haven't predicted a lot of obvious
18:37features. The other thing to notice is that this is really raw data. It's been processed,
18:44but only in the sense that it's been squashed back together again to make it look round.
18:48It gets very elongated when it goes for a long time in one direction and a shorter time
18:53in another direction.
18:55And the good news is that Titan is there. The bad news is that we barely saw it. We
19:01were counting on, first of all, twice as much data at the high telemetry rate. Secondly,
19:09we were counting on no data dropouts. So we have a good deal less data and we were
19:16counting on lots of data in order to average it and beat down the noise. And I'd say we've
19:23said the temperature of Titan is 75 degrees Kelvin, plus or minus five, which is about
19:28the temperature you'd expect for an object in equilibrium with the sun at that place
19:34in the solar system. And as you can see, there's no prayer of measuring a day-night
19:40temperature difference with these data.
19:44We are not looking at the surface. We are looking at the cloud tops or some point high
19:50in the atmosphere, and we cannot say what the temperature of the surface is.
19:56Do I gather that based on the data that you did get back with Titan, there is not insufficient
20:01temperature data with respect to the surface to ascertain whether indeed there is an atmosphere
20:06that could be hospitable as life form?
20:10I think there's plenty of other data, Earth-based data, that tend to rule out the possibility
20:18of high surface temperatures and therefore rule out life. But I'll leave the door open
20:24I'll leave the door open a crack. And I will certainly agree with you, my data do not have
20:31much to say about the surface temperature.
20:35So, perhaps a summary of Saturn, or rings first. I guess I've summarized the significance
20:41of the Titan data for you already. I think we can say that our eclipse data, just as
20:47we go behind the planet, just at the end on the right there, are consistent with other
20:53analyses that imply that the rings are centimeter sized.
20:59And the preliminary indications are that the masses are not high, that they are more consistent
21:08with the hypothesis of the rings being made of ices rather than something heavy,
21:15containing a lot of iron.
21:18On the planet itself, I think we've at least confirmed that these yellow bands are correlated
21:26with cloud heights, the various colored bands on Saturn are correlated with cloud heights,
21:33by which I mean different colored bands are at different heights.
21:38And then we come to this exquisite fine feature, the F-ring, a very narrow F-ring,
21:44which lies near or on the inside of the E-ring, which we have not been able to observe,
21:50but I have little doubt that the E-ring exists. And then this morning we heard, then,
21:55of the discovery of the G-ring between approximately 10 and 15 radii.
22:01Now, I know the ladies and gentlemen of the press are probably a little bit perplexed
22:07by some of the complicated figures that we show you, so I thought I'd start with a simple one.
22:12This is it.
22:16Now, this is my summary of the hard information we had, hard scientific information we had
22:23about Saturn's magnetic field prior to the Pioneer 11 mission.
22:27So we know that we can now turn this blank page and begin to concentrate on the fact
22:34that Saturn does indeed have a magnetic field and we know what its properties are.
22:39And to paraphrase William Gilbert, who started this business originally back in the 1600s,
22:45I'd say Saturn is indeed a giant magnet.
22:50What we've shown here is the Pioneer rock, which we presume lies in or near the ring plane.
22:59This is the Pioneer spacecraft, which at this time was about 10 minutes after having crossed
23:07the ring plane and was moving inward towards periapsis.
23:12It seems clear that referring to this as a Pioneer rock was perhaps somewhat misleading.
23:19As you've heard, the energetic particles have given us some idea about the size of this thing,
23:26which we nearly missed, and several hundred kilometers is probably more comparable
23:32in cross section to the greater San Francisco-Oakland area.
23:37So calling it a rock is perhaps not really the appropriate thing.
23:41As far as we know, it wasn't there.
23:44We went under it about 10 minutes after crossing the ring plane,
23:48and I would say, along with the others, that we were damn lucky.
23:53What this shows, we'll just keep it at this for the moment,
23:57is how, using trajectory information, we can learn things about the interior of the planet.
24:03First we show here just a core, an inner core to Saturn,
24:09which will produce a nearly spherical gravitational field.
24:12It will be slightly flattened.
24:14And we show, again, very schematically, a trajectory flying through that gravitational field.
24:19Now we can add in a region of metallic hydrogen,
24:24and that can be shown by here.
24:28We add metallic hydrogen on top of the core.
24:31This will change the gravitational field, flatten it even more,
24:35and we'll get a slightly different trajectory as a result of that metallic hydrogen region.
24:41And then finally we show the outer envelope of Saturn, the liquid hydrogen region,
24:49and we show in a very exaggerated way the shape of the surface or the geoid.
24:57We have a figure of the interior.
25:03This is built up by an inner core.
25:07I guess I have no control over how fast this accumulates,
25:10so we can let it go all the way out to the surface.
25:13Anyway, that inner core you see is made up of molten rock and iron.
25:18This model that we show here is essentially correct.
25:24It consists of about three Earth masses, but is of about the same size as the Earth.
25:30So we have a density of about three times what we have in the Earth,
25:34and a body of about the same size made up of rock and iron,
25:38but higher density by about a factor of three because it's inside of Saturn.
25:45Then we have an outer core where substances of water, methane, and ammonia
25:54have settled out of the upper regions of Saturn
25:57and formed an outer core consisting of about nine Earth masses.
26:03And the boundary of that outer core is about 23% of the total planetary radius.
26:11Then on top of that is the metallic hydrogen region,
26:14which is consistent with the diagram that Ed Smith showed,
26:18and the boundary of that makes up about 58% of the radius.
26:25On top of that, a liquid hydrogen region,
26:29and then on the very top, a gaseous atmosphere,
26:32which we estimate to be about 300 kilometers deep.
26:36I just want to make a few closing remarks,
26:39and that is that, first of all, in the last two weeks,
26:42I think our knowledge on Saturn has increased by at least 1,000-fold conservatively.
26:49So I think two weeks ago we didn't know very much about Saturn.
26:53I think we know a lot now.
26:54We've got a lot of questions,
26:55and hopefully a lot of these will be answered as we analyze the data further.
26:59But I think we've learned an awful lot in the last two weeks
27:01compared to what we've known in the last 370 years or so.
27:06Truly great strides were made by the Pioneer missions,
27:09but the Voyager spacecraft, which followed the Pioneers to Saturn,
27:13gave us even clearer pictures and much more information.
27:17During our next program,
27:18we will see planetary data received by scientists
27:21at NASA's Jet Propulsion Laboratory in California.
27:25Until then, this is Larry Ross saying goodbye
27:28from NASA's Lewis Research Center in Cleveland, Ohio.
27:32NASA Jet Propulsion Laboratory
27:34California Institute of Technology
28:01NASA Jet Propulsion Laboratory
28:04California Institute of Technology