Journey Through The Solar System, Episode 07 - The Fourth Planet
Transcript
00:00Science fiction writers have long used our neighboring planet Mars as a setting for their
00:24tales about other beings. Scientists, too, theorized about the possible existence of life on Mars.
00:36Through telescopes, astronomers many years ago saw markings on the planet
00:42which some believed were canals crisscrossing the surface.
00:48A few people thought the canals had been constructed by intelligent beings.
00:53Later, we found that the markings called canals were really artifacts of perception and did not exist.
01:02But scientists were still tantalized by color changes on Mars,
01:06which some theorized might be vegetation blooming in warm months and becoming dormant during colder times.
01:52I'm Larry Ross, director of space programs at NASA's Lewis Research Center in Cleveland, Ohio.
02:01This is the seventh episode in our series of 13 programs called Journey Through the Solar System.
02:08Now we're going to see a film called Mars, The Search Begins.
02:12The film documents how fact began to replace speculation.
02:18From the earliest history of mankind, there's been a bright red speck of light in the night sky called Mars.
02:27For the last few hundred years, we've known that it's a planet, a place more or less like our own,
02:34a world in its own right. But a detailed knowledge of what Mars is like had to await
02:42the mission of Mariner 9, an unmanned spacecraft which went into orbit around the planet Mars
02:48in late 1971 and worked for almost a year.
02:55A geologist looks at a planet to first understand the processes that are going on there,
03:01the things that are affecting the development of its surface at the present time.
03:06But even more important, we tried to look back in the past to place the events that have taken place
03:14over a long period of time to understand what happened early in its development,
03:19in the middle part of the development, the things that are happening now,
03:22and to predict what might happen in the future.
03:27For a biologist, one of the great scientific opportunities of our time
03:31is the search for life on Mars. That question is so important,
03:35it will change our whole concept of life, will change our whole concept of how life originated.
03:41The question is not only whether there is life on Mars,
03:44but whether that life has a separate origin from our own life, life as we know it.
03:51When Mariner 9 was placed into an orbit around Mars,
03:55it saw a planet one-half the size of Earth blanketed by a gigantic dust storm.
04:02For almost two months, scientists could see only blurred pictures of the top of the storm,
04:07or the ice and snow of the South Pole shining dimly through the dust,
04:12and several dark spots, apparently mountain peaks, protruding up through the storm.
04:18And then the great clouds of dust receded,
04:21and the long weeks of frustration ended with one magnificent and exciting word, volcanoes.
04:32The photographs bear little witness to the violence in which these volcanic mountains were born.
04:40On Earth, the eruption of volcanoes created the atmosphere,
04:45and produced the water that fills our oceans and rivers.
04:49On Mars, the same magic of physics and chemistry created a thin alien atmosphere,
04:56and provided a source of water on a planet known to be drier than the Sahara.
05:02The exploration of Mars by early mariners photographed about 10 percent of the surface
05:09in brief encounters as they flew past the planet.
05:15But it is Mariner 9 that explores all of Mars and reveals a planet beyond speculation.
05:24The intricate spacecraft, operating at a distance of over 100 million miles,
05:28is commanded by a complex system of men and machines on Earth.
05:35Six mission experiments yield results that can be woven into a total picture of a planet.
05:42As the spacecraft orbits Mars, the density of the atmosphere is measured by radio waves
05:47as they pass through the atmosphere on their way to Earth.
05:51The thin Martian clouds are scanned in the infrared to determine if they are carbon dioxide or water.
05:59An infrared instrument continually measures the changes in surface temperatures,
06:03ranging from minus 150 degrees Fahrenheit on the night side
06:07to as high as 70 degrees at noon on the equator.
06:13The height of mountains, the depth of canyons, and the gases in the Martian atmosphere
06:17are measured by invisible radiation in the ultraviolet and infrared wavelengths.
06:24Analysis of subtle changes in the orbit of Mariner
06:28reveals that Mars has an odd bulging shape, and this shape is a new clue to its internal structure.
06:36Two television cameras photograph and map the surface of Mars.
06:41In nearly a year of operation, they transmit more than 7,000 photographs.
06:49Of these, over 1,500 are specifically taken to ensure that the entire Martian surface will be mapped.
06:58The photographs are carefully matched, precisely positioned on a globe, and skillfully fitted together.
07:11This shadow on the surface of Mars is cast by one of its two moons, Phobos, only about 13 miles long.
07:18The second moon, Deimos, is even smaller. They are the darkest objects ever photographed in space.
07:25Primitive chunks of rock battered by meteoroids, their origin is unknown.
07:32This is the face of Mars photographed by earlier mariners.
07:37Here, a visitor might think he was on our moon, but this planet too was unchanging and dead.
07:46But transported to the other face of Mars revealed by Mariner 9,
07:51he would see fresh evidence of a living, changing planet.
07:54The old craters here have been long since covered by immense flows of lava.
08:02Thin white clouds form and drift across the dark blue sky.
08:07In the distance, he would see the long, gentle slope of a great volcano.
08:15Intense, small dust storms scour canyon walls into sharp ribs of ancient rock.
08:20Near the poles, he would see a great series of ancient terraces,
08:25each layer composed of a mixture of dust and snow deposited by the wind.
08:30Each took thousands of years to form. Each is an episode in the history of the planet.
08:39The exciting thing that we discovered, there were many of them, but one very exciting thing
08:44that we observed in the middle of the mission, was that there was a large,
08:49large mass of dust on the Martian surface. For example, in 13 days, an area about 7 miles across
09:01discontinuously appeared, just hadn't been there before, suddenly it was there.
09:06Now that kind of change had been observed, but from the Earth and on a larger scale,
09:12for 100 years. It was called seasonal changes, and the early observers imagined
09:18that there was plant life on Mars, and that in local spring and summer, the plants grew,
09:22they darkened the landscape and heightened the coloration of the landscape.
09:28Well, we proposed before Mariner 9, my colleagues and I, that instead what was happening was that
09:35there were high winds that were uncovering the dark material, dark rocky stuff,
09:42by blowing off bright, fine particles. And the changes that we've seen on Mars
09:49happen during the course of the mission are consistent with this kind of idea.
09:53So it looks as if the seasonal changes of Mars are not due to biology, but due to weather.
10:02We calculate that the winds are maybe as much as 200 miles an hour in such a storm.
10:08And so you have to have very high winds to make that thin Martian atmosphere
10:14pick up fine particles from the surface. So while most of the time it may be nice and calm,
10:20there are storms which are much more violent than any we see on the Earth.
10:26Now if you have very fast winds picking up all this fine-grained sand, that's a source
10:33of erosion and abrasion much more serious than any windblown erosion we know about on the Earth.
10:41It breaks things up, makes things collapse. It also picks up things and denudes
10:47landscape of overlying sand and dust. It's an exceptionally dynamic environment.
10:54In some respects like the Earth, in some respects quite different. It's its own planet.
10:58There are old parts of Mars which are cratered by hunks of rock falling down into Mars and making holes.
11:09In some of those craters there are these strange black splotches. At least some of those splotches
11:16on closer inspection by Mariner 9 cameras turn out to be vast sand dune fields, another indication
11:24of windblown sand and dust on Mars. There is a similar dune field in the Mojave Desert in
11:31Southern California. That is the overall form of the two fields and the height and spacing of the
11:36larger dunes are alike. However, the complex pattern that we see here shows that the wind
11:43directions change frequently. On Mars, the wave pattern indicates a consistent wind direction.
11:54Here is an astounding feature which no one expected on Mars, an enormous rift valley
12:02almost 3,000 miles long, comparable to the largest such feature on the Earth, a sign of great
12:09geological activity. In this model, the flat surface of a large Martian plateau is cut by the Great Rift.
12:18A smooth, sloping ravine drops abruptly to the bottom of the canyon four miles below.
12:28The small peaks on the canyon floor were once part of the plateau surface.
12:34Today, this great fracture in the crust of Mars is 75 miles across.
12:41The original fault has been widened and shaped by various forms of erosion.
12:48Great landslides are triggered by quakes that shake the crustal rocks.
13:02Windblown dust strips the receding canyon wall.
13:09Some side canyons may have been deepened by running water.
13:23Melting of underground ice followed by slumping of walls further erodes the great fault.
13:39This rift valley, of which we have seen only a small part, is so huge that it would span the
13:56United States, and the Grand Canyon of Arizona would fit inside one of the smaller tributaries.
14:04And as another and even more spectacular sign of geological activity on Mars is this enormous
14:11volcano. Hundreds of miles across, it's the largest volcano in the solar system so far as we know.
14:20It's a young object because it doesn't have very many impact craters in it,
14:24meaning that geological activity on Mars has been occurring in very recent times.
14:30This is a model of the volcano. Its base measures 370 miles across,
14:37and the peak stands 15 miles above the plain.
14:49The flanks of the crater bear the familiar tortured patterns left by violent eruptions of molten rock.
14:56The walls drop steeply to a scarred blackened floor.
15:04Frozen lava lakes mark with rough circles where the interior fires of the planet forced their way to the surface and built a mountain.
15:12This is where the atmosphere of a planet is born, in searing heat that transforms solid primitive rock into thin vapors.
15:23Today, the crater looks dead, frozen into a rigid page in a textbook on the evolution of a planet.
15:31This is not an old volcano. To a geologist, it is young, and no one can say if it is alive or dead.
15:41In this volcanic field near Flagstaff, Arizona, there are hundreds of volcanic vents, some as old as two million years.
15:50The youngest of these, Sunset Crater, is similar to the small volcanoes we see on Mars,
15:58and the lava flows are the same as those we see on the flanks of the larger volcanoes.
16:06I'm standing beside the basaltic lava flow that comes out of Sunset Crater,
16:10and the great jumble of blocks that you see here are caused by the fact that the lava comes out as a liquid,
16:17but it chills on the outside, and the interior of the flow keeps moving,
16:23and it breaks up the outer edge into this great mass of jumbled blocks.
16:27It's very similar in size and form to the lava flows that we see on Nix Olympica on Mars.
16:37In many Mars photographs, we see long, sinuous ridges that go across the great lava plains.
16:44We're sitting on a feature that's very much like those.
16:48We think the way this feature formed is that the still liquid lava down in the center of the flow
16:54keeps exerting pressure, it lifts the top up, finally breaks it, and then squeezes out through the frozen crust.
17:04And here is something which no one guessed would exist on Mars at all.
17:09This is one of hundreds of little channels.
17:13This is actually not so little.
17:15This is a few hundred miles long.
17:17Channels which look for all the world as if they've been cut by running water.
17:21Here's a close-up of the inside of one of those channels,
17:25and it has the characteristic patterns of terrestrial stream beds.
17:29The trouble is there isn't any liquid water on Mars.
17:33The pressure on Mars is so small,
17:36that it can't keep a lid on liquid water.
17:40If this is due to running water on Mars,
17:42it must have been made at a time when the Martian climate was very different from what it is today.
17:48At a time when Mars had much more Earth-like conditions.
17:56This is a model of a section of a three-mile-wide channel north of the Martian equator
18:02that seems to be formed by a broad flow of liquid water.
18:06It is similar to drainage channels on Earth that are fed by rainfall.
18:12Parts of this channel also show evidence of wind erosion and softening of contours.
18:19The islands appear to be similar to sandbars formed by rivers on Earth.
18:25They might be heavy gravel, or perhaps solid rock.
18:29I personally don't see any escape from the idea that running water is what carved out those channels.
18:37But if that is the case,
18:39I don't see any escape from the idea that running water is what carved out those channels.
18:46But if that is the case,
18:48then we must imagine that Mars was one time, not so long ago, very different from Mars today.
18:54Right now, we have a Martian atmosphere which is thin, the surface which is cold.
18:59But when those channels were cut, if they were cut by water, and I think they are,
19:03then you must have had a much thicker atmosphere, much warmer conditions,
19:06and a lot more water around than you have today.
19:10Volcanic eruptions are the source of water on Mars.
19:15With each eruption of lava, water vapor is spilled out in the atmosphere.
19:19It is stored in two different ways.
19:25The first way is in the residual polar caps.
19:28This is the north pole of Mars, and the cap shrinks down to about five degrees.
19:34It starts at the end of winter, almost 50 degrees across.
19:38And we think that polar cap is very thin carbon dioxide ice.
19:42It shrinks very quickly to this little residual cap,
19:45and we're still debating as to whether that's water ice, carbon dioxide, or dry ice,
19:50or a mixture of the two.
19:52The second way that it's stored is in these regions where the frost has disappeared from the surface,
19:58but we think it's still stored underground as permafrost,
20:02that is, water frozen into the pores of the rocks.
20:06We were able to photograph several different kinds of clouds with Mariner 9.
20:12This photograph is of one of these clouds.
20:15It's the edge of the north polar hood.
20:18It covers the whole northern region of the planet, and this is the southern edge of the hood.
20:23Here you see an ice rim crater and the clouds that form downwind.
20:29By measuring the temperatures and the elevation,
20:33we're able to understand the composition of these clouds.
20:37This particular cloud, the temperature was critical,
20:40and we know that it was made of dry ice or carbon dioxide ice crystals.
20:47Near the great volcanoes, we saw clouds that were much lower and much warmer.
20:52We also got spectral lines that proved that these clouds were composed of water ice crystals.
20:59Just as the study of the climate of Mars should, I think, help us understand the climate of the Earth,
21:07I think the study of the biology of Mars will help us understand the biology of the Earth.
21:13The big question for the biologists is what is life?
21:18What do we mean when we say life?
21:21We're really only familiar with one form of life, terrestrial life.
21:26Terrestrial life, life on Earth, carries a trademark revealed by biochemical analysis.
21:33All living things on Earth are composed of combinations of molecules,
21:38some as simple as water, which is fundamental to life as we know it,
21:42others of great complexity.
21:46One of these combinations, protein, forms the enzymes that direct the complex chemistry of life.
21:54Another, nucleic acids, are genes contained in chromosomes, the basic unit of life.
22:02These combinations of molecules distinguish living things from nonliving systems.
22:08One other element needed to make a living system work is a method of reproduction.
22:15DNA is a molecule containing the genetic message, the blueprint for future generations.
22:24This genetic code is the same for all living creatures, for all life,
22:29which means that there is really only one form of life on Earth.
22:33If there is life on Mars, then there will be a simply fabulous expansion of the perspective of the biologists.
22:41Because all the organisms on the Earth, even though they seem to be different, are fundamentally the same.
22:46Their chemistry is all identical, and they're just wrapped in different kinds of wrapping.
22:52Us bacteria, and us people, and us plants, us protozoa, we're all the same on the inside.
23:00Now the question is, are Martian organisms the same on the inside as us?
23:05Is life everywhere, does it have to be the same as us?
23:10Or are we just one example of a vast array of possible kinds of biochemistries?
23:17Well, there's no way for us ever to answer that question,
23:19no way for us to determine the generality of life on Earth, except by looking for life elsewhere.
23:27And the nearest candidate planet is surely Mars.
23:33We're not quite sure how to search for life on Mars.
23:36We do the obvious.
23:38Microorganisms, the small creatures, are always associated with higher forms of life.
23:43So it's microorganisms we're searching for.
23:46A small microbe could adapt itself possibly to the cold Martian winter,
23:52to the dry Martian summer, to hostile Martian atmosphere,
23:56or even to the sub-zero temperatures of the Martian night.
24:01This is a full-scale model of the lander spacecraft.
24:05This device contains a 10-foot extendable boom.
24:09It reaches out, picks up a soil sample, and returns it to an instrument inside the spacecraft,
24:15which will then perform three life search experiments.
24:20The first experiment will assume that Martian life is similar to Earth life.
24:25It uses Martian soil and Martian atmosphere.
24:30The soil is soaked in a liquid containing a large quantity of water
24:34with a mixture of foodstuffs used by microscopic life on Earth.
24:39If Martian life forms eat the nutrients, they should excrete gases in the process,
24:45as do microorganisms on Earth.
24:48This will change the gases in the test cell.
24:52Any changes will be detected and will be evidence of life processes.
24:59The second experiment is half Martian and half Earth.
25:04The soil sample is moistened with only a little water
25:08containing foodstuffs that scientists think exist on Mars.
25:12The foodstuffs are tagged with radioactive carbon-14.
25:17If life processes take place, then carbon gases released in the process
25:22will contain the radioactive tracer and can be detected.
25:28The third experiment is based on Martian conditions.
25:32It uses Martian soil, Martian atmosphere with scarcely any moisture
25:38to which is added radioactive carbon gases,
25:41and simulated Martian sunlight minus the ultraviolet radiation.
25:48If Martian life forms are growing and multiplying in the Martian soil,
25:52it is assumed they would use some of the Martian atmosphere in the process.
25:57The atmosphere, tagged with carbon-14,
26:00should be metabolized into the bodies of the life forms.
26:04After allowing time for life processes to take place,
26:08heat will be used to break down solids into gases.
26:18Detection of carbon-14 in those gases will be evidence of a life process.
26:27It always happens in the history of science that as your perspective broadens,
26:31you learn more about what you left at home as well as what you went out to seek.
26:37And so it may be that in the long term the greatest boon to science and to mankind
26:44from the exploration of Mars will come in terrestrial biology.
26:48It's just a speculation on my part, but I think there's a good chance that that will be the case.
26:56We have seen the planet Mars in one sense for the first time through the eyes of Mariner 9,
27:02and it was not quite what we had expected.
27:06How can a planet bear the scars of great raging floods and the gentle tracing of rain
27:12when liquid water on its surface vanishes into thin vapor or congeals into solid ice?
27:19The possibility now of large amounts of frozen water on Mars
27:24may hold the answer to one of man's basic questions.
27:28Has life developed only on Earth, or is there life elsewhere?
27:35The possibility of life on other planets intrigues us all.
27:39The search for life on Mars continued in 1976
27:43when two Viking spacecraft launched by the Titan Centaur landed on the Red Planet.
27:49We will review the results of those missions during our next episode, Life on Mars?
27:55Until then, this is Larry Ross saying goodbye from NASA's Lewis Research Center in Cleveland, Ohio.
28:05NASA Jet Propulsion Laboratory, California Institute of Technology
28:35NASA Jet Propulsion Laboratory, California Institute of Technology