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00:00Well I think that exploring peace is a cultural activity. It's been just science for science
00:13sake. And this is an important point for both the scientists and for the public to realize.
00:18When Armstrong stepped out on the moon, a million people watched him in real time and the moon all
00:27of a sudden a familiar place. When Mariner's 4, 6, 7 and 9 photographed Mars, it was grasped
00:37away from science fiction and put into the role of science. It was a real place, although
00:42very strange, remains very strange. When Mariner 10 went to Mercury and photographed it for
00:48the first time, Mercury entered from the domain of obscurity, just nobody even knew it was
00:55there really, into at least a real place with features, with a surface and a character
01:02of its own. As a consequence, in this last decade really, the volume of space that exists in
01:12the mind of man all over the world, millions and millions of men, has expanded.
01:19Mercury, as seen through the best Earth telescope. Venus, in 62, these were the best photos of
01:31the planets we had. Mars, we had no knowledge of what features lay on their surfaces. We didn't
01:39know their ages, had they formed at different times. The last 13 years has changed that.
01:46Mars has changed that.
01:47Mars has changed that.
01:48Mars has changed that.
01:53Mars had changed that.
01:54Mars has changed that.
01:56Mars has changed that.
02:00THE END
02:30There's been a celebration of US and Soviet rockets to the planets.
02:35Beginning with a Russian mission to Venus in 1961, it accelerated to a crescendo in the spring of 1974 when there were six rockets simultaneously travelling out from Earth.
02:46The planetary exploration was paralleled by Apollo, man on the moon.
02:53Apollo began from a political decision to get a man on the moon before the Russians did, specifically by 1970.
03:00They did that. Now, with the rationalisation of hindsight, their trips to the moon have turned out to be the key to understanding the planets.
03:08The US National Aeronautics and Space Administration, NASA, has evolved two major scientific objectives for its research in space.
03:22One, to seek out how life began.
03:25Secondly, to seek the origin of the solar system.
03:28The prime tools of planetary exploration are precision television cameras.
03:34These are two about to fly to Mars.
03:43They're made by craftsmen, each contributing something of his own design to the component he makes.
03:49Sculptors carving from solid lumps of metal.
04:03The cameras are on their last test before being fitted to the spacecraft.
04:08In a vacuum chamber, they're being checked to see their optics will not go out of focus in the temperature changes they'll experience when they're launched into space.
04:16They'll send their pictures back as a set of numbers, each number representing one of 256 possible levels of brightness.
04:33A computer converts each number to an appropriate dot of grey, and half a million dots build up a picture.
04:41A photograph can only show ten shades of grey, so the numbers hold much more information than the picture you're looking at now.
04:53This picture can be reprocessed so as to reveal only the fine detail.
04:58These are some of the thousands of pictures from the mission to Mercury.
05:08With the arrival of the pictures, analysis begins.
05:13This machine compares two pictures of the same object taken at different times during a mission.
05:19It allows contours of a mountain to be plotted directly.
05:32The thousands of pictures are all individually studied and their information blended together in maps.
05:40NASA has created an information explosion.
05:44These maps are a complete contrast to the fuzzy blobs of 13 years ago.
05:50Then there were hundreds of theories of the origin.
05:53Some saying the planets were the debris left after our sun had collided with other stars.
05:58Some that the planets and sun condensed from a cloud of gas.
06:03The trouble was not finding a theory, but finding one which was not totally improbable.
06:08NASA's philosophy has been to visit as many planets as possible to find the facts.
06:16To find out what theory has to explain.
06:20What story origin can we tell after 14 years of exploration?
06:29The search begins before men landed on the moon.
06:33The question then was, what was the cause of the craters there?
06:36Most people were sure they were volcanoes.
06:44But 15 years ago, in a field of volcanic craters in the Arizona desert, a study was begun.
06:53It was to prove this crater was not volcanic at all.
06:56That it was caused by the impact of a meteorite 24,000 years ago.
07:09The scientist who's made the most intensive study of meteor crater and the expert on impact events is Dr. David Roddy.
07:16It's really quite surprising to me that as early as the mid-1950s, meteor crater was still considered to be a volcanic crater by a certain part of the scientific community.
07:27Enough to blow your mind, but there were serious papers still being written at that time.
07:31But with the advent of the space program and the large amount of research that's been dumped into those kinds of areas,
07:39we've come to a point where we have enough physical data in which we can tell quite clearly the specific diagnostic criteria
07:47that tells us whether this is a volcanic crater or whether this is a meteorite impact crater.
07:52The laboratory experiments that led to understanding what happened during an impact were done by Don Gault with this gun.
08:06It fires small aluminium spheres.
08:10They simulate meteorites at speeds upwards of 20,000 miles an hour.
08:15The complexity of the gun is because the impact takes place in a vacuum.
08:18The angle of the gun can be varied.
08:24For the experiment we're about to see, it's a vertical impact into this box of sand.
08:34It's filmed with a high-speed camera expanding one second into five minutes.
08:48Experiments and Roddy's fieldwork established how impact craters form.
09:00How they can be distinguished from volcanoes.
09:03It was Roddy who instructed the astronauts and these are the actual diagrams he used.
09:08The meteorite would vaporize and the floor of the basin would be flung into the air as large chunks of rock.
09:15A cone of surface material would flop over upside down forming a raised rim
09:22and the blocks of rock would rain back creating an outer ring of secondary craters.
09:31The features were recognizable in the moon craters seen from Earth.
09:35So before man went to the moon, telescopes had confirmed that a few of those craters down there were caused by impact.
09:55The astronauts produced two very important results.
10:00The first was how many impacts the moon had received.
10:05In this dramatic piece of film, the lunar exploration module of Apollo 17
10:10is just skimming over the tops of the lunar mountains on its last orbit before landing.
10:15On board, the last man on the moon.
10:21Incidentally, the only geologist to go there, Harrison Schmidt.
10:25This bombardment was unbelievably intense.
10:28It's something that is almost beyond the comprehension of people, even geologists to a large degree.
10:33The surface of that moon, the light-colored surface you can see on a full moon, even now,
10:41was saturated with craters, with impacts capable of forming craters, say, 100 kilometers in diameter.
10:48Saturated.
10:49Every point on that surface was hit with that size of an impact.
10:53After this time, after about around 4 billion years ago,
10:58there was a period when there were a number of very large impacts.
11:03impacts large enough to form basins up to 1,000 kilometers in diameter.
11:09Now, this appears to be a very distinct and different period of bombardment.
11:13We don't understand why, but it is distinct.
11:17The moon had been pulverized to a depth of six miles.
11:21The bombardment ended with impacts of an incredible size.
11:26The imbrium almost split the moon in two.
11:29The second thing they did was to bring back rocks so that the events on the moon could be dated.
11:39The man who pioneered the chemical techniques necessary was Jerry Wasserberg.
11:44Well, since we're mostly investigating extraterrestrial materials and we have to worry about terrestrial contamination,
11:52in some cases, the total sample just weighs a millionth of a gram.
11:57So, we have had to develop manipulative procedures and standards of cleanliness,
12:03which permit us to handle these materials, a single grain at a time,
12:06frequently much smaller than a grain of salt,
12:09and analyze that rather than our own droppings.
12:16Wasserberg's team measure how long it is since a rock was last molten, since it solidified.
12:23Moon rocks are a mixture of the powdered remnants of earlier rocks,
12:26rocks that can be of such different ages that dating the whole sample would give meaningless numbers.
12:32That's why the natural cement is shattered so that some of the individual sand-like grains come free.
12:44Nothing in this laboratory is ordinary.
12:47That's not paper, but a very special plastic.
12:50The air is filtered, all surfaces covered with unchippable paint.
12:54Everything is wrapped till needed.
13:02Just those pieces which might be individual crystalline grains are sieved through,
13:06and finally they're picked out by hand.
13:17Each of the little grains is going to be dated from its content of lead, thorium and uranium.
13:24The ratios of those three trace elements give the age since it solidified.
13:36Dissolved in acid, the grain goes into an ion exchange column
13:39that allows the chemicals through at different speeds.
13:43Experience tells them when the lead comes through.
13:45By catching just the right drip, he catches the millionth of a millionth of a gram of lead he's looking for.
14:03That drop is gingerly put onto a heated wire.
14:06Gingerly, for to get that drop has taken three days' work.
14:09Finally, that wire is heated in a mass spectrometer,
14:18which flings the atoms down a tube where a magnet sorts them out and electronics count them.
14:23From here, it's arithmetic to calculate the ages.
14:30They're reaching back through long periods of time.
14:34A thousand million years is given a technical name, one eon.
14:40The measurements show that all the material in the solar system is the same age,
14:44precisely 4.6 eons.
14:47The cratering began between this and four eons ago, when it ended suddenly.
14:55The final big impacts were at four eons.
14:58Then came floods of lava rising from the interior of the moon.
15:05Since then, very little change at all.
15:07Ten or so craters like Copernicus and Tycho.
15:10This is what the moon would have looked like four eons ago, after the bombardment.
15:21Then the lavas flooded out.
15:25And since then, very little change apart from the dozen or so craters and the lavas changing to lighter gray.
15:32The next question was, is that bombardment something particular to the moon, or had it happened to the earth as well?
15:45We couldn't know, until recently our oldest rock was from Minnesota.
15:50The oldest so far from Greenland, so we couldn't tell, because on earth we don't have rocks old enough to record the bombardment.
15:58So the question still was, was the cratering record special to the moon, or perhaps waiting to be read on the other planets?
16:08If it was, would it be the same story, or a different one?
16:12The space missions were to answer that.
16:15But first, what's the scale of the solar system?
16:18Suppose the sun to be seven feet six inches across.
16:21At this scale, Mercury, a pea.
16:33And it's 36 million miles from the sun, a hundred yards.
16:40Next planet, Venus, a walnut.
16:42It's 67 million miles, which is 190 yards.
16:49Earth and moon, only 240 yards.
17:02Mars, 142 million miles becomes only 400 yards, a quarter of a mile.
17:10Massive Jupiter, a nine-inch cabbage.
17:15Now we move out to a different area of the solar system.
17:19486 million miles are represented by 1,500 yards.
17:27From here on, distances are vast.
17:29Saturn would be at a mile and a half.
17:32Uranus, three miles.
17:34Neptune, four miles.
17:37Pluto, seven.
17:411971, the Mariner 9 spacecraft arriving to be launched to go into orbit around Mars
17:47and map it systematically.
17:51There'd been three previous flights to Mars, flyby missions.
17:55They'd seen moon-like craters as they zipped past, taking their strips of photographs.
18:00There were suggestions Mariner 9 should be cancelled.
18:03The answer was already known.
18:05Mars had craters.
18:06What was the point of looking at another moon?
18:12But they did go.
18:13In fact, it was to have been preceded by Mariner 8.
18:17A member of the TV team was Bruce Murray.
18:20Mariner 9 was the geologist mission and Mariner 8 was the meteorologist and the astronomers mission.
18:25Except fate has a nasty way of interfering.
18:29Mariner 8 ended up in the Atlantic Ocean.
18:31There was a failure of the launch vehicles.
18:34And so these things have to be done very quickly because there's only a few weeks that one can launch
18:38at any particular opportunity to Mars.
18:40We had to go with one space vehicle, Mariner 9, and had to somehow compromise the two.
18:45As it turned out, Mariner 9 proved to be an extraordinary exploration mission.
18:52I think it was the most astounding mission perhaps the United States had flown to date in many ways
18:57because of the nature of the discoveries that were found.
18:59There's been a profound and I think irreversible cultural change brought about by the very act
19:19of space exploration and by having it well photographed in a means that the photographs
19:24could speak for themselves, not be interpreted through the jargon of science.
19:29As Mariner 9 approached Mars, a tremendous dust storm broke out, covering the whole planet with
19:43dust 50 kilometers up into the air. As the spacecraft came in, all that the television team could see
19:49were these four dark spots, christened Groucho, Chico, Harpo and Zeppo.
19:55Embarrassed and to fill in time, the team turned the cameras onto the two Martian satellites,
20:04Deimos, the outer satellite, 10 miles in diameter,
20:07and Phobos 20 miles across, both battered by billions of years in space.
20:21The storm lasted 30 days. Then as the dust started to settle, the spots became darker and darker.
20:28There was mounting curiosity about what they could be.
20:35Then the Marx Brothers heads broke through. Immediately two geologists, Mazursky and McCauley,
20:42guessed they were volcano tops. The others were skeptical.
20:46When the dust did finally clear, there was no doubt.
20:57Groucho turned out to be the biggest volcano known in the solar system, 17 miles high,
21:02more than twice the height of Everest.
21:04Hal Mazursky, leader of the Mariner 9 TV team, now heads the committee selecting the site for the two
21:13Viking spacecraft that will land on Mars in 1976.
21:19Viking will search for life. It'll analyze the Martian soil for microbes and radio its answer back.
21:26Mazursky has to decide where they'll land and search.
21:37What is the best place on Mars to land these very few spacecraft? We only have two.
21:41We've got a very complicated, very large planet. So we only have two chances to find the right information.
21:48The interesting thing about the volcanoes is that's where the atmosphere comes from.
21:51That's where water vapor comes from. That's the clue in the search for life.
21:56Well, that was our first requirement, that the planet be hot in the interior and the juice coming out of the volcanoes.
22:03The second problem is what happened to that water vapor after it came out.
22:08And we looked carefully at the pictures and we found that in this region,
22:13there were a number of great stream channels that started in this country.
22:18They start in great masses of collapsed debris. And one of the ideas is that Mars warmed up
22:23and melted the subsurface ice, caused the collapse of the great masses of debris.
22:29Then the water flowed out downhill into the northern lowland. So our Viking landing site is obviously here,
22:36right at the mouth of these largest streams on Mars.
22:39In addition to the great conglomeration of channels that flows into the northern lowland,
22:45in other parts of Mars, we have quite different kinds of channels.
22:48In this region, in the smooth uplands, is quite a different kind of stream channel.
22:55There are dozens of little tributaries that come together. And here it looks as though we have
23:02to have had water falling out of the Mars atmosphere and hitting the surface, collecting
23:07together into these little streams and flowing down this sinuous channel. All through the central
23:13upland of Mars, in every sloping surface, there are hundreds of little tiny micro channels, just
23:20a hundredth of the size of the ones we've been talking about. And this map was prepared for the
23:26Soviet Union. They tried to land on Mars earlier this year. And their landing site was right in the middle
23:33of this region that has dozens of these little tiny micro channels in it. They didn't successfully land,
23:38that was their fourth attempt. The lesson to us is that Mars is difficult to land on,
23:44so we really have to be prepared for our try in about a year and a half. What we found out from
23:49detailed examination of these three different kinds of channels is that some of them are very old,
23:55they have many craters that have struck them, and the sides are eroded and degraded. Others look
24:02brand spanking new and fresh. So we think that not only did the Mars climate have to have been different
24:09one time in order to form stream and have water flow on the surface, but it has to have been that way
24:15dozens of times in the past. Do I think that the most probable explanation of the stream channels
24:22is that water rained and flowed on the surface? The answer is yes. I think of the various choices we have,
24:27that's easily the best one. A wind tunnel experiment at the University of Santa Clara, California.
24:37Ronald Greeley is trying to explain a unique feature on the Mars surface.
24:42He's looking for an explanation of a long black plume that stretches 60 miles.
24:47It obviously begins from a crater.
24:55And in the bottom of the crater he finds an intense dark spot. His theory is that this might be a volcanic
25:02source. So he set up in the wind tunnel a model crater into which he could introduce sand.
25:07He would let it drift downwind and film the pattern that would result.
25:28The plumes match. That suggests that there's at least one active volcano on Mars throwing its cinders
25:35across the surface. Jack McCauley was senior geologist on the Mariner 9 team.
25:43He's been trying to understand this Martian feature, here dimly seen through the dust,
25:48but 40 days later seen to be two deep rugged valleys.
25:54All the geologists were excited to see something familiar in the cliff edge,
25:58the big bite of a landslide, but dramatically bigger than any landslide on earth. These cliffs are four miles high.
26:10This model of the canyons was made by NASA. Its accuracy has been approved by NASA's higher brass.
26:17This is what it would be like to swoop down into that vast canyon system,
26:21so deep the Alps would get lost down there.
26:28Barely reaching halfway up the cliffs.
26:35It's called the Caprates Canyon. It's 3,000 miles long. It's 150 miles wide.
26:43Macaulay believes it began from a fault crack. There are networks of cliffs near the canyon.
26:52They're very similar to fault cracks on earth, the result of tension pulling the surface apart.
26:59He believes that there was erosion of the exposed cliff faces, as here in the Arizona desert,
27:06this cliff is retreating as wind and water wear it away.
27:14To get some sense of scale, Caprates is more than a hundred times bigger than this,
27:20the Grand Canyon.
27:24The Grand Canyon, after its initial opening, is being widened by erosion.
27:29On earth, the erosion is primarily by water, but helped by the wind.
27:33On Mars, the erosion is by wind alone. A fierce sand blasting by the thin wind at 400 miles an hour.
27:56One of the members of the TV team of Mariner 10 is a British scientist, Dr John Guest.
28:02It's interesting on Mars that the volcanoes
28:09tend to form some kind of a pattern. We have these four major volcanic structures running
28:16in this direction. They're in a straight line and must represent a fundamental structure in the
28:22Martian crust. And then we have this great Caprates chasm running through here,
28:30another major structure in the crust. The planet is splitting apart there, forming a great tectonic fracture.
28:41Possibly the kind of thing that one could imagine if one was seeing incipient plate tectonics,
28:50where one plate is beginning to break away from another point. The earth was about 200 million years ago.
28:59I think we've seen a sort of revolution in the earth sciences with this increased knowledge of the
29:05planets because the other planets appear to have preserved a period of their history, which is before
29:14a period that we can recognize on earth. Quite unexpected by the scientists, they saw the beginnings
29:21of continental drift as it may have happened on earth two eons ago. Mars, and so it turned out, each of the other
29:29planets seemed to be a snapshot of some stage in the earth's early history. That's a curious thread in this story.
29:38So Mariner 9 was worth sending. It did more than confirm that there was a cratering record on Mars.
29:45That record on Mars was like that on the Moon.
29:50One feature that was seen on the maps that had been too big to see on the photographs
29:54was an enormous crater like the big imbrium basin on the Moon, the Hellas basin.
30:041973 Mariner 10.
30:24Venus was to be visited on the way to Mercury. No one has seen the surface of Venus because it's
30:32continuously covered in cloud. A haze of sulfuric acid droplets floating in a dense atmosphere of
30:39carbon dioxide. At the edge of the planet Mariner 10 could just pick out a layered structure in the acid
30:46clouds. But when photographed through ultraviolet filters, a pattern showed up.
30:55During the approach Mariner 10 took mosaics of pictures every two hours.
31:02Bruce Murray and his team processed them all so that they would be the same scale.
31:06Then they filmed the 40 pictures assembling what's known in the business as Bruce Murray's creaky movie.
31:17It shows four days of weather condensed into six seconds.
31:24The surface temperature of Venus is 480 degrees centigrade, enough to melt lead.
31:30The temperature is due to the mighty Venus atmosphere allowing heat in but not letting it escape, a runaway greenhouse.
31:39The interesting evolutionary question is why are the atmospheres of Venus, Earth and Mars so different?
31:46Scientists can see the surface with radar. They claim to recognize craters that might be volcanoes.
31:52It's from that surface that the atmosphere would have evolved. The atmosphere came out when the solid core melted.
32:02The temperature then of the bare surface would have been just about 80 to 90 degrees.
32:11As the carbon dioxide and water accumulated, the greenhouse effect quickly raised that temperature
32:17to 300 degrees so no water could possibly condense and the carbon dioxide continued to build the thick hot atmosphere we see today.
32:28On Mars it was different. So far from the sun, its temperature was below the freezing point of carbon dioxide and water.
32:36Both froze instantly. So Mars' atmosphere is there but frozen down.
32:42Mariner 9's monthly observation of the Mars South Pole showed it was made out of a mixture of water ice and solid carbon dioxide.
32:55During the first two months of the spring it shrank rapidly as the carbon dioxide evaporated.
33:05It left only the permanent water ice which didn't shrink during the summer.
33:12On Earth our atmosphere started to come out when the Earth's bare surface had a temperature of three degrees just above freezing point.
33:20The water condensed beginning the sea.
33:23The carbon dioxide would have begun to heat that surface with a greenhouse effect but, a very big but,
33:29it didn't get far enough to boil the sea because the hot liquid water converted the carbon dioxide into carbonate rocks,
33:36into massive beds of limestone and chalk.
33:41If it hadn't been for the liquid water, all the carbon dioxide would have stayed free.
33:47Venus and Earth have the same amount of carbon dioxide.
33:51The nitrogen, a one percent trace in the initial volcanic gases,
33:55accumulated as a thin remnant of what was potentially our massive atmosphere.
33:59Earth's temperature had Earth's initial temperature been just five degrees centigrade higher,
34:06that is, had we been at 89 million miles from the sun instead of 93, the greenhouse effect would have
34:13boiled away the water and our Earth would be as hostile as Venus.
34:18So Venus shows us Earth as it might have been.
34:20After Venus, Mariner 10 continued on to Mercury.
34:28This was all we knew then of Mercury's surface.
34:31There were different views among the team of what they would see.
34:35Some thought it would be cratered like the Moon.
34:39One thought that Mercury was small because the sun had boiled its surface off
34:44and he was expecting to see a blasted wreck.
34:46Others that Mercury had an atmosphere whose violent action would have scoured the original craters away.
34:54We switched the cameras of the spacecraft on about a week before we encountered the planet.
35:01The first thing we saw was just a small disc with a white spot on it and very little else.
35:07But nevertheless, we started discussing what it might be that we were seeing and going to see.
35:12And then every day after that, at midday, we'd switch the cameras on again.
35:16And then about two days before the near encounter, we thought we were recognizing craters on the surface.
35:23At that time, we had a suspicion that we were looking at a planet that may well look like the Moon.
35:29And then the spacecraft got closer.
35:31We swooped past the planet at about 11 kilometers per second, taking pictures all the time.
35:36And this great flood of data came back, covering everything that could be seen by the spacecraft.
35:42It was almost as if somebody had arrived with a great lorry load of pictures and dumped them in our office.
35:50The surface was exactly like the Moon, difficult even for an expert to tell the difference.
35:56It meant that Mercury's skin is the same as the Moon, a light silicate.
36:00But Mercury is the densest of all the planets.
36:06It couldn't be light silicates all through.
36:09Beneath that crust must lie a massive iron core, at least 80% of the planet's diameter.
36:17At some time, the whole planet had melted.
36:20And as slag rises and floats on the iron in a blast furnace,
36:24so the surface had formed on top of the molten interior.
36:29That surface was cold before the bombardment ended.
36:32It had to be solid to preserve this cratering record.
36:36So Mercury melted and stopped there, a snapshot of what Earth was like sometime before four eons ago.
36:44As Mariner 10 left Mercury, it saw on the other face a huge impact, half in shadow.
36:50It's filling your screen now.
36:54The curved ring of mountains is the crater rim surrounding the lava-filled interior.
37:00Mercury had had its gigantic impact too.
37:05Again, the crater record showed what had happened to the Moon had happened to Mercury.
37:11Oh, I think the neatest thing that happened was when the Mercury photographs came back,
37:15because when we, and even Mars for that matter, because we were seeing cratering on not just the Earth
37:22and the Moon, but on Mars and on Mercury. And I think we can very, very safely predict
37:26we'll see cratering throughout the entire solar system.
37:30The most fundamental and most interesting thing to me is that we are working on a particular process
37:37that we know should be operable throughout not just our solar system, but throughout our galaxy,
37:43throughout all of space as far as we're concerned.
37:491972, Pioneer 11 out from Earth passes the Moon heading for Jupiter.
38:13As the spacecraft approached, the coloured bands and the red spot could be seen.
38:32Pioneer 11 confirmed what Pioneer 10 had discovered on the first visit to Jupiter a year earlier.
38:38The planet was giving out two and a half times as much heat as it received from the Sun.
38:47The explanation most favoured was that the heat is produced because Jupiter is still contracting
38:52out of the original cloud of gas. So the snapshot is not so much a planet, but of a forming Sun.
39:00Scientists see suggestive parallels between Jupiter and the origin of the solar system.
39:05There is one theory beginning to be discussed in scientific circles. It's very tentative yet,
39:10but it does explain the cratering record and why planets near the Sun are dense and those far away
39:16made of light materials. It's thought the planets evolved from one cloud of gas.
39:24Ninety-eight percent would have been hydrogen and helium, but there would be traces of iron,
39:29silicon, rock forming materials. In the gas there would be chemistry going on as atoms bang together,
39:37creating many compounds.
39:43The molecules stuck together to form tiny grains. They grew quickly to the size of a small pebble.
39:52But they didn't get any bigger. Because of the gravity,
39:55they started to settle to the plane of the nebula, a flat sheet, exactly like Saturn's rings.
40:03They couldn't fall inward to the Sun, because like the rocks in Saturn's rings,
40:07they would be orbiting around it.
40:09So in a few million years, much of the gas would condense to a flat disk. But this disk didn't have
40:23a uniform composition. What grains can condense depends on how close to the proto-Sun they are.
40:30Close to the Sun, just the rocky material would condense. Iron and silica by the orbit of Mercury.
40:37Next, perhaps, iron sulfide, say by the orbit of Venus.
40:44And further out, water ice. Further out still, carbon dioxide ice.
40:51Beyond Jupiter, the hydrogen and helium would condense.
40:55Only the small amount of rocky material had condensed out at the center.
41:00Towards the edge, everything had solidified.
41:02What happened next was that the disk broke up because it was gravitationally unstable.
41:09The pebbles condensed to lumps about five kilometers in diameter, each weighing about a hundred tons.
41:16Rather like the asteroids. Now, these bodies started collecting each other up through collision.
41:22It's this history of impact we may be reading in the cratering record.
41:33So, in the end, the planets formed.
41:35Those near the Sun, the inner planets, were the trivial amounts of rocky silicon, iron and aluminium oxides.
41:50The outer planets, big. Cold enough to condense all the ices and gases of the gas cloud.
41:56At this stage, the inner planets were still moving in the hydrogen and helium.
42:04It's presumed that the Sun became super hot and its solar wind increased tenfold.
42:11That blew the uncondensed gas away.
42:13And that's how we find the solar system today.
42:19The interesting feature that comes out of this picture
42:22is that the most volatile substances we find on the Earth
42:26are the substances that condensed somewhat farther away from the Sun than where the Earth is now.
42:31In fact, these are substances that were coming down.
42:33Gene Schumacher has been trying to understand how planets finally formed.
42:38Water ice is particularly important to us. Carbon dioxide ice is another.
42:42These materials were condensing out about two to three times as far away from the Sun
42:46as where our Earth is now.
42:48But those particles, those planetesimals, which grew out of particles condensed to that distance,
42:53were very close to Jupiter and they were perturbed very greatly.
42:57In fact, most of them fell on Jupiter, but a small fraction fell on the Earth.
43:02And that's where the water and the carbon dioxide that's now on our Earth,
43:07making up the oceans and contributing to rocks in the crust.
43:12That's where most of that material came from.
43:13The substances, carbon, oxygen, hydrogen, that we now find on the Earth,
43:19actually were perturbed by Jupiter from a distance about three times as far away as we are
43:25and fell on the Earth last, sort of plating the Earth
43:28and giving us the substances that have now formed life.
43:32That's why I'm able to stand here and talk to you today because of old Jupiter that was formed out there.
43:38One of the major problems which we have in the origin of the solar system is to know
43:42the particular types of material from which the solar system was constructed.
43:46And now many of my colleagues and I are obsessed with attempting to identify
43:55those particular mineral species which were present in the interstellar medium, dust grains,
44:01which were then aggregated to form the solid bodies of the solar system.
44:04And the hunt is on.
44:06I don't know how lucky we'll be in finding them, but I think it's quite clear that when the work done here
44:11by Lee and Papanastasiou clearly have identified relics of the interstellar medium that we can now
44:18handle in our hands, sort of with tweezers in the clean room.
44:23Now, which stellar objects fed the solar system?
44:27What are the true materials which are identifiable as an interstellar grain is what the great hunt is now.
44:35I thought last week for sure we were going to find one this Monday.
44:40I'm not that sure today, but next Monday we'll still be looking.
44:45During the last two eons, the Moon has had a dozen or so impacts about the size of London.
44:52We now know these impacts aren't special to the Moon, but are universal.
44:57So the Earth should have had some too.
44:59What would an impact be like if we had one in the Atlantic tomorrow?
45:03The order of magnitude calculations would suggest that if you had a vertical impact in, say,
45:11the central part of the Atlantic Ocean, you could expect a tidal wave, initial wave around the crater,
45:18that is what you'd call the crater rim, which would be transit, of course, that would be on the order of
45:23probably 10 to 20,000 feet high, which is a speculation in terms of the actual height of it,
45:29but the numbers are impressive if you can make the direct analog calculations, which are reasonable,
45:34and we're only interested in ballpark.
45:37And imagining a wave in a transient body, such as water, moving up to, say, even a couple of miles in height,
45:44and then imagine the tidal effects that you'd have from that quite clearly.
45:48If we were to have an event such as this, the tidal waves from that would extend all the way across
45:53the ocean, and, of course, they would wash the seaboards of both the continent,
45:58Great Britain, and, of course, the North American coast.
46:03This is not a statement to cause one concern, but there are bodies of this size passing the Earth.
46:09The so-called Apollo asteroids, for example, are in Earth-intersectoring trajectories.
46:14They have diameters on the order of several miles to 12, 13, 15 miles across.
46:18These are super bodies. If we would have a collision with such a body of this size,
46:24I think one would expect both atmospheric effects and terrestrial effects that would truly modify
46:30the entire climactic pattern and the life ecological systems that we see at this present time.
46:37Ten years ago, an asteroid, Icarus, passed within four million miles of the Earth.
46:42Forty years ago, Hermes came closer than the Moon.
46:48Now geologists are beginning to find some Earth structures are best explained as impact craters.
46:55It's something new in geological interpretation.
46:58About a hundred craters have been positively identified and a new one is being discovered every year.
47:03But instead of the 50-mile basins, think of those big ones thousands of miles across,
47:10the enormous impacts of four eons ago.
47:15Did we have one?
47:16Suppose an impact happened on Earth as large as the one that produced the Caloris Basin on Mercury,
47:25or the Imbrium Basin on the Moon, or the Hellas Basin on Mars, for example.
47:32That would mean that the size of the impact was a thousand to maybe even two thousand kilometers in diameter.
47:38That the depth was a hundred or two hundred, maybe even three hundred kilometers deep initially before it started to rebound.
47:46But what happened, a lot of things would happen obviously.
47:50Obviously it would be kind of tough on anybody living around there.
47:52But what would happen that might have lasting consequences is that the material,
47:58which had originally been two hundred or maybe even three hundred kilometers deep,
48:02is now brought to which becomes a surface.
48:06If the pressure on top of it is relieved.
48:10Now the rocks of the Earth are very sensitive to this,
48:12and different reactions take place at different pressures and temperatures.
48:15And so by taking material that's originally very deep and then bringing it immediately to the surface
48:20on a large scale may trigger some reactions, some chemical reactions, which otherwise would not happen.
48:27It's possible something like this was the beginning point necessary to start the growth of continents.
48:34What space has done for geologists is to give them a new perspective into the past,
48:39put in context the small piece of Earth's history they knew.
48:44For us, we have become increasingly aware of our fragility,
48:48of the knife edge of chance on which our continents and our atmosphere depended.
48:54There's no economic value to go to the Moon.
48:56There's no economic value of going to Mars.
48:59It's not utilitarian in that sense.
49:01It's cultural.
49:02It affects the minds of people.
49:04And if material necessity were enough, the United States would be a very happy and passive place.
49:09It's not.
49:10And so the parallel issue of our times is a framework, a reference, a set of values,
49:15a perspective on one man's existence.
49:18That's where space exploration is important, not in material necessity.
49:32The state's framework beneath global design is important.
49:38こんな effective солI, a level of experience to try to find a way where things meet naturally.
49:40That's very central to Northaola.
49:41That's where space exploration is important.
49:42From learning certainalles that come at our fullest speed to drive duos apples and Premise.
49:44So the TIPE found the different waves in America saying that our resources are important.
49:48By missing around elements, we have survived through meteorologically near the travel universe right for the time that we willroll it.
49:50Where is this space exploration is becoming more person, and that's the third base Оч dari question like us.
49:52So that's a way of chance of one of the maritimeir forces of mankind.