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00:00Saturn is the great ringed planet.
00:28Until the Voyager missions, we did not know simple facts
00:33such as the approximate number of rings circling the huge planet.
00:40I'm Larry Ross, Director of Space Programs at NASA's Lewis Research Center in Cleveland, Ohio,
00:46and I'm your host for this program, Voyager 2, Saturn Encounter,
00:51which is the 12th in our 13-part series, Journey Through the Solar System.
01:21Saturn is the sixth planet from the sun and is the second largest planet in the solar system.
01:44As we saw in our previous program, the Pioneer spacecraft gave us our first good views of Saturn,
01:50but the pictures did not have enough resolution to show the planet's rings and moons
01:55as clearly as the later Voyager pictures did.
01:59In late 1980, the Voyager 1 spacecraft made its close encounter with Saturn.
02:05About 10 months later, the Voyager 2 spacecraft also flew by the great ringed planet.
02:11Voyager 2 produced thousands of pictures of Saturn and its rings and moons
02:17from different angles and distances than did the first Voyager spacecraft.
02:22Now let's see the saga of Voyager 2 as the story unfolded in late August 1981.
02:29The spacecraft has journeyed a billion miles from Earth in four years.
02:34The beauty and complexity of the ringed planet and its family of satellites
02:38was first revealed by Voyager 1 in its November 1980 encounter.
02:44Now, Voyager 2 will closely explore specific targets in Saturn's realm.
02:54We join Voyager 2 on its approach as the spacecraft, cameras, and other instruments
02:59scan the planet and most of its 17 known moons.
03:05Good morning. At 8 o'clock this morning, Voyager will be 1,700,000 miles.
03:12That's 2,700,000 kilometers from the cloud tops of Saturn,
03:17and it's closing in on the planet at 26,500 miles per hour,
03:21which works out to 11.9 kilometers a second.
03:25And that makes it still just under a billion miles from Earth,
03:29965 million miles away.
03:33The young lady right there.
03:37I have two questions. First for Dr. Smith.
03:40On the screen yesterday afternoon on the limb of Saturn,
03:45I saw a lot of white flecks on the image of Saturn.
03:50Do you have any idea what those were?
03:54Well, there are, particularly at the higher latitudes,
03:57a large number of these small white features
04:02that are similar to many that we saw on Jupiter.
04:04They may be small convective elements,
04:07like a large aggregation of thunderheads or cumulus-type clouds.
04:13The resolution was probably something in the order of 100 kilometers or so,
04:17so that gives you an idea of the scale of those features.
04:20It's similar to what we've seen in Jupiter's atmosphere as well.
04:24Good afternoon. At 2.30, Voyager is a little over 900,000 miles
04:30away from the Saturn atmospheric surface,
04:34and going about 28,500 miles an hour towards Saturn.
04:39All is working well. We have been watching recently,
04:42and will continue to see for a little while longer,
04:44some photopolarimetry of Saturn.
04:46Actually, what we're seeing are the backup photographs
04:48that go along with the photopolarimetry scans.
04:50These are going north to south across the surface of the planet,
04:54and we're looking for the information we get
04:58from the photopolarimeter instrument,
05:01quite a bit of which has to do with the nature of the particles,
05:04the size and characteristics of the particles
05:06that make up the high haze layers and the upper portions of the clouds.
05:12Saturn's rings are targeted for special study
05:15throughout Voyager 2's approach.
05:18Sections of the braided F ring are studied from different points of view
05:22to create three-dimensional pictures of the strands of the ring.
05:30Dark, spoke-like features in the B ring are photographed
05:34as they move around the planet.
05:41There we go, coming around the racetrack.
05:46Briefly in front of the planet, then coming around again.
05:50Okay, now there are at least a few places where we think we see,
05:53this is going a bit too quickly,
05:55but where we think we see, right in here,
05:58instantaneously, almost instantaneously,
06:01the production of a radial spoke.
06:03There's another one right there.
06:05Wasn't there before, suddenly appears.
06:08Right there, momentarily radial.
06:12If you see them, it will be startling.
06:14The spoke-like features of the B ring,
06:16discovered by Voyager 1,
06:18are an important focus of study during this encounter.
06:21These members of the Voyager imaging team
06:24want to glean all they can from Voyager 2's photographs
06:27during 14 hours of the spoke's movement around Saturn.
06:31Another phenomena they want to look for
06:33are possible additional satellites that might be embedded in the rings.
06:37Two deep gaps in the Cassini division
06:40at one in the outer part of the C ring
06:42might be just the spots for such satellites.
06:46That same set of pictures, incidentally,
06:49is the one that we use to look for embedded satellites
06:52in the gaps, in these clear regions,
06:57in the Cassini division in the outer edge of ring C.
07:00And the ones that Len Tyler pointed out
07:03are in fact the very ones that we're looking into.
07:05The ones he sees as free space
07:07that we also judge to be almost completely free of material.
07:11And it's within those regions that we're looking for
07:13these embedded satellites, which we would calculate
07:16ought to be in the vicinity of 30 kilometers in diameter.
07:20Well, a progress report on that
07:23is that Terrell has now completed
07:27one third of both rings in the Cassini division
07:31and the outer edge of ring C
07:34very, very carefully, where he believes
07:36he can see anything down to 5 kilometers,
07:40certainly, and possibly a little bit smaller.
07:43And that assumes that the particle is even a little on the
07:46dark side of average for the rings.
07:49And nothing in that one third.
07:52Cozzi, within the Cassini division only,
07:56has looked at the remaining two thirds
07:59of the Cassini division, not quite as carefully.
08:03His limit is probably something of the order of 10 kilometers,
08:07but still quite a bit smaller than,
08:10the limit is quite a bit smaller than what we were looking for,
08:13a 30-kilometer satellite.
08:16Cozzi did not find any satellite
08:20larger than 10 kilometers in either of the gaps
08:24in the Cassini division.
08:26And we now find ourselves at a point
08:29where we had hoped not to be.
08:33Included in this image of Saturn
08:36are actually four satellites.
08:38Three of them show up quite readily.
08:40Tethys, Dione, and Rhea.
08:43And this is the shadow of Tethys up here.
08:46But if you look very carefully,
08:49you'll see a little bright spot right here.
08:51That's Mimas, and its shadow is seen up here.
08:55This is used in false color
08:59because it gives us a little more contrast
09:02to the features that we're looking at.
09:04Colors that go into this are ultraviolet, violet, and green.
09:08And again, indicate the way Saturn might appear
09:11if our eyes were sensitive to the shorter wavelength part
09:15of the spectrum.
09:17Once again, we see this high-velocity jet,
09:20this looping feature,
09:23indicative of that high-velocity jet,
09:25blowing toward the east about 150 meters per second.
09:28Down below is a much weaker jet toward the west
09:32at about 15 meters per second.
09:34And then these anticyclonic features
09:36that are caught up in the shear in between.
09:39This brownish spot moving along
09:42at about something like 30 meters per second
09:46toward the east.
09:49Note that when we look at these objects into the UV,
09:55this brownish spot tends to have a slightly brighter center,
09:58and these two features show up quite well.
10:01And that's in contrast to the green image,
10:05black and white green image,
10:07that I'll show you in just a moment.
10:09Note the position of these two features.
10:13This is about the same latitude as this one,
10:16and so they're moving along more rapidly
10:19than this feature, which is almost standing still
10:22in between this strong jet that's moving toward the east
10:26and the weaker one that's moving toward the west.
10:29So the next black and white image now
10:34shows this region with somewhat higher resolution.
10:37This picture was taken about two days later.
10:40This one, in fact, on the 21st of August.
10:42And now you can just barely see those two features
10:45that showed up so well in ultraviolet.
10:48The pictures Voyager 2 sent back this morning
10:51were part of a sequence of photos shot 10 hours apart.
10:54Scientists were hoping they would show motion on the planet.
10:57Such motion would help them measure wind velocities
11:00and help them understand more about various weather conditions on Saturn.
11:04First, some photos of a region in the northern hemisphere
11:07which shows up as a great brown spot.
11:10Voyager 2 took photos of it Sunday night and again this morning.
11:13The two sets of photos showed a great deal of motion in the spot.
11:17They found that the spot is what is called an anticyclone,
11:20meaning a high-pressure region which moves in a clockwise direction.
11:25Imaging scientists Andy Ingersoll and Gary Hunt were, in their words,
11:29delighted with what they saw of the great brown spot,
11:32calling it their most important discovery of this morning.
11:35Oh, very nice.
11:37And not only have you got the flow around it,
11:39there's also something occurring right at the very edge.
11:42Yeah. This is an intriguing image, all this ribbed stuff.
11:49Notice also that we've got one of the points,
11:51which is almost a characteristic of anything that has a large flow.
11:54The internal part is generally symmetric in its flow,
11:58but you always get the barrier, the points being set up at the edge.
12:01You can just see, without even getting a time sequence,
12:06you can see these rotations this way.
12:10More questions were raised about another phenomenon in the northern hemisphere region,
12:14this one, the ribbon-shaped configuration in the lower left-hand corner of this photo.
12:18Scientists are saying it is an eastward jet of wind blowing at about 300 miles an hour.
12:24Now, there you are. There's a little spotty here,
12:27and there's the convection on the north side again.
12:31Ingersoll and Hunt had wanted to find out whether the ribbon was causing the great spot
12:35or affecting it in some other way,
12:37but this morning's series of photos didn't answer that question.
12:42Voyager scientists like Ingersoll and Hunt will spend the next several months
12:46poring over these pictures, mapping and measuring the surface of Saturn,
12:50becoming even more familiar with its various features.
12:53But right now, they are like excited campers,
12:55getting their first glimpses of snapshots they took on their summer vacation.
12:59From the Interactive Room in Mission Control, Bill Griffith, NASA News Net.
13:05In the press conference this morning,
13:07one unusual new set of pictures was put out,
13:11that having to do with the small moon Hyperion.
13:15The pictures available so far show that this is indeed a very irregular object.
13:20That in itself is fairly significant.
13:23And the way it looked in the pictures we have so far,
13:27it didn't seem to have its axis lined up right with its spin directions.
13:32But to talk about all of that and what this all may be
13:35and how it all may be disentangled, we hope,
13:38we have Joe Viverka, a member of the imaging team.
13:41Joe, what about it? Is this an oddball object?
13:45First of all, it's awfully big to be so irregular.
13:48Isn't this a little unusual?
13:50Well, it certainly is an oddball object.
13:52I guess we don't know all the ways in which it's strange yet,
13:55but we're going to find out as we get a closer and closer look.
13:58I think it's true that the first views we got from Voyager 2 were rather surprising
14:04because, in fact, we were looking at the end which faces away from Saturn.
14:10And what we saw was a very rectangular cross-section.
14:16This is, I guess, the first picture we got.
14:19And the resolution here is something like 32 kilometers per line pair.
14:24And to the best of our estimates, the spin axis is in this direction.
14:31Not lined up with the long axis.
14:33And what we're probably looking at, in this case,
14:36is something that may have the shape of a chocolate bar.
14:39And you would normally expect that the long end of the chocolate bar would point at the planet
14:43and that the flat end of it would lie in the orbital plane.
14:46This one came in at noon, yes.
14:48Is there some change of aspect between the two?
14:51We're essentially going around towards the trailing side.
14:54And, as I said, we're about maybe 40 degrees away from the anti-Saturn point.
15:01One of the most interesting satellites of Saturn is Iapetus,
15:04the most distant large satellite from the planet.
15:06I'm here with Dave Morrison and Jeff Placia, who are Voyager imaging scientists.
15:10We're looking now at pictures of the dark and light sides of the satellite.
15:14And, gentlemen, what do we know about why there is this dark side and the light side?
15:18The light side is clearly waterized.
15:21We know that from ground-based observations.
15:23And we suspect that that is representative of the bulk composition of the whole object.
15:28But the simplest idea would then be that the dark material was somehow just a surficial thing
15:34laid down over the leading hemisphere,
15:36the hemisphere that faces forward as Iapetus goes around Saturn.
15:40But that's precisely what we're looking for.
15:43Can these pictures tell us about whether we have a surficial dark layer
15:48or whether that's produced externally by stuff falling in
15:52or whether it's somehow related to the activity itself?
15:55And, particularly, we want to look at the individual craters
15:59and see how they relate to the light and dark.
16:02The dark and light sides of Iapetus have nothing to do with the angle of light from the sun
16:07but rather the intrinsic reflective surface of Iapetus.
16:11Morrison describes the difference in reflectivity of the dark and light areas
16:15as that of bright snow versus asphalt.
16:18The leading theory to explain what happened on Iapetus
16:21is that the dark material came from elsewhere,
16:24namely from the outermost satellite of Saturn, Phoebe,
16:27and that it was chipped off of Phoebe in fine dust from impacts over billions of years
16:33and this dust drifted inward,
16:35and Iapetus, on its leading side, as it went around the orbit, collected that dust.
16:41So it just painted the front of Iapetus dark and the back stayed light.
16:46Part of the light surface of Iapetus is splattered with craters.
16:50Part is quite smooth, as if an eruption of methane snow might have filled up the craters.
16:56The light side also has curious streaks that scientists had not seen before.
17:01Another new discovery in these pictures is a large crater with a dark floor,
17:05which may hold more clues to the ongoing geologic activity of Iapetus.
17:11The cameras of Voyager 2 have taken a series of photos of the satellite
17:15through different colored filters.
17:17These allow scientists to reconstruct a color picture of Iapetus
17:20and to get better information on the reflectivity of its surface.
17:23But still, they want to know more.
17:26We are looking for a single explanation for almost everything,
17:29and that's because this is the first chance to look at it,
17:31and probably there is no single explanation,
17:34and there are different phenomena taking place.
17:37I'm focusing on what produces the dark stuff,
17:40and that may have nothing to do with what's producing some of the geological features that we're seeing.
17:45Yeah. The thing we really need to constrain are a lot of craters
17:48where we can see the floors if they're dark or if they're bright,
17:51and we just haven't been lucky enough to see it.
17:53But this is it. This is it.
17:55This is the highest resolution picture we're going to get of Iapetus in our lifetimes, probably.
18:00Reporting from the interactive room at JPL, I'm Carol Ackroyd, NASA News Net.
18:06And there's the outer edge of the A ring and the very narrow F ring that we can see.
18:11Very faintly. One of its satellites in that picture.
18:14And Dione. Now, Dione is one of the satellites, icy satellites,
18:18we visited very closely with Voyager 1,
18:21but actually we will not be looking at it as closely with Voyager 2.
18:25There are several, though, that we will be visiting more closely with Voyager 2,
18:29for instance, Enceladus and Tethys.
18:31Now, Iapetus also we're seeing for the first time with resolution of something on the order of 15 miles.
18:37This is the one that has this curious marking.
18:40One side is many times brighter than the other.
18:42I heard that some material on the dark side is 10 times darker than that on the light side.
18:46It's at roughly 10 to 1 brightness ratio. That's right. It's a remarkable object.
18:50This is Tethys. Tethys has a 500-mile-long canyon on it.
18:53We didn't image it very well on Voyager 1.
18:55With Voyager 2, we'll be able to resolve things as small as...
18:58Now, a little bit down at the bottom.
18:59One can begin to see the canyon right at the edge of the image. That's right.
19:04And there is Hyperion.
19:07That's where we just began to see today and discover that it doesn't look right at all.
19:11It just doesn't look right at all. That's right.
19:14After the... Of course, right now we're still approaching closest approach.
19:18After we go by, we'll then see Saturn in the south pole.
19:22Yes, we'll be looking at the dark side of the rings, the side that's unilluminated,
19:25and we'll be looking at the south polar region of Saturn.
19:28Going on to the satellites now.
19:32Here is our three views of Hyperion.
19:37There have been all kinds of descriptions given for it,
19:41from a peanut to various other things.
19:45It is obviously very irregular.
19:50The scale is not the same in each of these images.
19:55It reflects the approach to Titan,
19:58this being taken at a distance of about 1.2 million,
20:010.7 million, and 0.5 million.
20:04So it's growing in size as the spacecraft gets closer.
20:08But the best description that I could give it right now
20:12is it sort of looks like a thick hamburger patty or whatever.
20:16And here, you're looking into the edge of it.
20:19I wish I had a little model or something I could show you.
20:24One important science objective is the photopolarimeter observation
20:28of the occultation of a star by the rings.
20:32Light from the star, Delta Scorpii,
20:35is measured as it flashes through the rings in the shadow of Saturn.
20:40The two-and-a-quarter-hour experiment provides information
20:43on the number of ringlets, their densities, and widths.
20:48Now, that entire measurement lasts about two-and-a-half hours.
20:52And I think we're just now seeing the beginning of this sequence.
20:55But they have obviously found the star.
20:57They're starting to make the measurement.
20:59And they're getting in the data they expected.
21:01It's a fantastic experiment when you think of the fact that the ring system,
21:05the distance from the inner edge to the outer edge of the ring system,
21:08is tens of thousands of miles.
21:10It's comparable to the distance around the Earth.
21:12Yet, we will measure detail there at the size of a city block.
21:16And as you pointed out, we've already seen thousands of rings,
21:19of small ring features.
21:20This map may show us a lot more even than thousands.
21:24Yes.
21:25The fact is that the planetary program really has...
21:28I guess one way to look at today, today is the day of challenge,
21:31where we're going to be challenged by our new views of Saturn.
21:35I think it's fair to say that everything we're seeing today,
21:38basically everything we're seeing today, will be new.
21:41I'd like to start off with the first slide showing a filtered view,
21:49actually a mosaic of several images just showing a filtered view
21:55of the very high latitudes on Saturn.
21:57There's a notch out of the north polar limb here.
22:02But one can see the enormous amount of structure
22:06that's up at the very, very high latitudes.
22:08Here we see some of these complex features.
22:12This brown spot that we've been looking at quite recently,
22:15now taking on morphology very similar to a spiral galaxy.
22:19And we're seeing material actually flowing out
22:22and forming rather curious patterns.
22:26Here is that high-velocity jet
22:32showing somewhat of a Rossby-like structure,
22:35Rossby wave-like structure.
22:37And associated with it are some cyclonic,
22:41that is the equivalent of low-pressure areas,
22:45in a system that's not altogether different from the Earth.
22:49This is the first view of Titan that we've released
22:54for the Voyager 2 encounter.
22:56It's not by any means our highest resolution image,
22:59and we'll perhaps release another at somewhat higher resolution.
23:05One can still see that it's a rather uninspiring orange ball,
23:10but there is this north-south demarcation with a line
23:14which still is in there fairly close to the equator of Titan.
23:22High-resolution photographs of the planet and satellites
23:26are assembled from mosaics of images
23:28covering separate areas of each target.
23:32From a distance of about 58,000 miles,
23:35Voyager 2's cameras compose a four-image mosaic of Tethys.
23:40Well, even though we're still,
23:42we're last night a million kilometers away from Tethys,
23:47we did record a feature of rather curious appearance,
23:52a very, very large crater on one face of Tethys,
23:57a face that was not seen by Voyager 1.
24:01The crater is huge.
24:02In fact, it is the largest crater so far seen in the Saturnian system.
24:06It's about 400 kilometers,
24:08that is something in the order of 300 miles in diameter.
24:12We see a central peak.
24:14We see a ring of mountains that surround the impact feature.
24:20The central peak is caused by the rebound of material
24:25up from the center after the impact,
24:27and then as that central peak slumps back down,
24:30it pushes up the mountain chain,
24:33the mountain ridge that surrounds the impact crater of the planet.
24:38Well, there's an enormous amount of detail that's beginning to show up,
24:41and we expected this.
24:43This approach to Saturn with Voyager 2
24:45giving us a good high-resolution view
24:48down on the illuminated ring system.
24:54Early in the approach by Voyager 1,
24:57we had estimated that there were hundreds of rings,
25:00and by the time we got through,
25:02that estimate grew up to perhaps something like 1,000.
25:05And why don't we take a look at the Zoom movie of Saturn?
25:08I think it's a good way of seeing
25:10how dramatically the weather patterns have changed.
25:12You can see, particularly in the northern hemisphere,
25:14these bright cloud features bursting out.
25:16They're giant storm systems.
25:18Dark feature also on other clouds.
25:20We can run it forwards and backwards.
25:22If you stop it about there, Al,
25:24in fact, you can see that there are a large number
25:26of very bright patches in the region
25:28between about 20 and 40 degrees.
25:30In the northern hemisphere.
25:32In the northern hemisphere.
25:34A large amount of detail is showing up there.
25:36And even if you look right towards the pole,
25:38you can start to see that the banding continues
25:40right on the way up towards the pole.
25:42So there's a lot of detail and a lot of change
25:45in the basic meteorology of Saturn.
25:47We cannot see much in the southern hemisphere.
25:49The suggestion of spots is because
25:51we haven't got the optimum viewing.
25:53We'll see that better after encounter.
25:55The data from the Voyager 2 Saturn encounter
25:58are still being analyzed by scientists.
26:00The rings were resolved into thousands
26:02of nearly concentric features,
26:04now thought to be shaped by the gravitational effects
26:07of the Saturn moon.
26:09Large bolts of lightning,
26:11as energetic as the total output
26:13of an Earth-based nuclear power plant,
26:15were detected in the Saturn B ring plane.
26:19Clouds in Saturn's atmosphere
26:21were clocked moving at speeds
26:23of 1,770 kilometers per hour.
26:27Saturn pictures were made by scanning instruments
26:30aboard Voyager.
26:32The pictures were converted to an electronic number code
26:35and the numbers were transmitted to Earth
26:37by radio waves.
26:39Computers then used the numbers
26:41to reconstruct the images.
26:58During our next and final program in the series,
27:01we will look at what we know
27:03and what we expect to learn
27:05about the three outer planets,
27:07Uranus, Neptune, and Pluto.
27:09We will also talk briefly about comets, asteroids,
27:12and our hopes for the further exploration of space.
27:16Until next time, this is Larry Ross saying goodbye
27:19from NASA's Lewis Research Center in Cleveland, Ohio.
27:36NASA Jet Propulsion Laboratory
27:40California Institute of Technology
28:06NASA Jet Propulsion Laboratory
28:10California Institute of Technology