Mars: The Viking Discoveries

Mars: The Viking Discoveries

Bevan M. French Chief, Extraterrestrial Materials Research Program Office of Lunar and Planetary Programs Office of Space Sciences, NASA

EP-146 October 1977

NASA National Aeronautics and Space Administration Table of Contents

The New Arrival 5

Why Mars? 5 Viking to Seek Answers 6 The Viking Spacecraft 6 A Viking's-Eye View 8 The Winds of Mars 12 The Chemistry of Mars 18 Three Chances for Life 20 From Mars to Einstein 22

What Next? 24

Appendix

Suggestions for Further Reading 32 Experiments and Activities 33

Suggested Viewing 36

Cover photo: Twilight on Mars; from Viking 1 Lander, processed by computer.

Inside front cover: Dawn on Mars; Viking 1 orbiter photo found early-morning fog filling this network of canyons on a high Martian plateau.

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock No. 033-000-00703-5 Preface

Mars: The Viking Discoveries is the For assisting the author with helpful 17th NASA educational publication to advice, comments, and criticism, we outline the results of NASA's research thank the following: Dr. Richard S. activities in space sciences. Young, Director, Planetary Biology and Prepared in a format that will be Quarantine, Office of Space Science, useful to the teacher of basic courses NASA; Loyal G. Goff, Program in Earth science, Earth-space science, Scientist, and Walter Jakobowski, astronomy, physics, and geology, they Manager, Viking Program, Office of are also written in a style that will Space Science, NASA; Dr. Harry appeal to the well-informed, Herzer, Senior Specialist, NASA intellectually curious layman. Aerospace Education Services Project The author, Dr. Bevan M. French, is and faculty associate, California State a geologist who has studied Moon University, Chico; Ms. Carolyn P. rocks and ancient terrestrial meteorite Schotter, Teacher of Earth Science, craters for more than 10 years. In 1973 Falls Church High School, Fairfax he helped discover a Brazilian impact County, Virginia; and Ms. Jeanne crater 25 miles in diameter and 150 Hewitt, Department of Geology, The million years old. He now manages George Washington University. For NASA's program for scientific research extensive editing and revision, we on meteorites, lunar samples, and express appreciation to Ms. Mary-Hill other kinds of extraterrestrial materials, French. as Chief, Extraterrestrial Materials Research Program, Office of Space October 1977 Science. His program is also helping National Aeronautics and Space NASA plan ahead for the return of Administration rocks from yet another world-Mars- Washington, D.C. so that scientists can find out directly what the Red Planet is really like.

The New Arrival

Exactly 7 years after astronauts first Control Center at the NASA Jet and its relation to the other worlds we landed on the Moon, a new inhabitant Propulsion Laboratory in Pasadena, know. The discoveries did not rule out arrived on Mars. On July 20, 1976, a California. When the applause and the possibility that some form of life top-shaped object dropped from its congratulations began on Earth, Viking might exist on the distant planet. Mars orbit hundreds of kilometers above 1 already had been studying Mars for was neither entirely dry and airless like Mars and streaked. downward into the 20 minutes. Moments later, Earth's TV the Moon, nor watery and teeming with late afternoon Martian sky. About 40 screens began to show the first life like the Earth. What was Mars kilometers above the surface of the plctures of Viking 1's footpad, firmly really like, and what could it tell us planet, the thin air began to grip and planted on the soil of Mars (Figure 1). about the Earth and the Moon? slow the capsule. At an altitude of 6 A new era in our exploration of the Exploration of the solar system had kilometers, a huge parachute unfurled, Red Planet had begun. earlier been established as a top a protective shell broke away, and the NASA goal for the period after Apollo. metallic object inside began to drop to The program was aimed at a better the ground more slowly. At an altitude Why Mars? understanding of the solar system's of 1.7 kilometers, three rocket engines origin and evolution, the origin of life, fired downward, slowing the Mars has been in humanity's and the planetary processes that spacecraft even more. The parachute thoughts since astronomy began. The affect life on Earth. Because Mars, of , was cut loose, and the object settled Babylonians first began to follow the all the planets, most resembled the gently to the ground. The rocket motions of what to them was a Earth and appeared the most likely to engines immediately shut down. The wandering red light in the sky, and harbor some form of life, it was given Viking 1 Lander had arrived on Mars they named it Nergal after their god of top priority for scientific study. with no more shock than a terrestrial war. Later, the Romans, honoring their As spacecraft observed the planet skydiver landing in the center of his own war-god, gave the planet its in closer and closer detail, we target. present name. discovered that Mars is not uniform. Instantly the computer that had A century ago, as the first large The early flybys (Mariner 4 in 1964 guided the spacecraft on its journey telescopes were trained on Mars, and Mariners 6 and 7 in 1969) had sent a message to Earth that said observers saw that the planet had a produced photos of a heavily cratered essentially: "I am here. I am down reddish surface, white polar caps, an surface that looked as dead and static safely. I am beginning my work." Earth atmosphere, clouds, and changing as the surface of the Moon. But the was more than 321 million kilometers patterns of light and dark that might photographs and maps obtained from (290 million miles) away, and even at be vegetation on its surface. It seemed Mariner 9 in 1971, as it orbited Mars the incredibly fast speed of light to be an Earthlike planet on which life for about a year, showed that the (300,000 kilometers per second), it could exist, and some astronomers planet is actually a two-part world. was almost 20 minutes later, 5: 12 claimed to see long lines of canals The southern half of Mars, which the A.M., Pacific Daylight Time, before the made by intelligent beings. Fiction first Mariner spacecraft had looked at, Lander's message reached the Viking writers, therefore, needed little seems much like the surface of the encouragement to populate Mars with Moon: ancient, inactive, and still a wide variety of creatures: heavily cratered by an intense Figure 1. Mars at Close Range. Tiny philosophical canal builders, leathery meteorite bombardment that may have Martian pebbles appear in sharp detail in monsters who invaded Earth, and a occurred during the planet's earliest this first picture ever taken on the surface variety of humanoids with human traits years. of Mars. Even after being transmitted for of good and evil. The northern half of Mars is more 320 million kilometers (200 million miles), The Space Age methodically Earthlike: younger appearing, the picture is so clear that the observer removed the basis for much of this geologically active, and perhaps still seems to stand on Mars beside the Viking kind of romance about Mars. No changing. In this part of Mars the 1 Lander. One of the Lander's footpads canals could be seen at close range, Mariner 9 pictures showed huge (lower right) rests firmly on a surface made and their appearance was explained volcanoes, great fields of lava, and of fine soil and scattered rocks. Large rock as optical illusions that had affected (upper center) shows triangular faces that cracks and fractures in the crust. Most may have been cut by wind-driven sand. Earthly astronomers. The Martian surprising, and most exciting to Another rock is dotted with atmosphere proved too thin to breathe, scientists, were huge canyons and small dark pits that possibly were formed and there was very little water. These by gas escaping from once-molten lava. discoveries only increased our The picture was taken with a camera that curiosity about the real nature of Mars scanned the scene vertically, line by line, from left to right, completing the picture in about 5 minutes. winding, braided channels that elsewhere?" are basic questions that distances, there is no possibility of seemed to have been scoured by we continue to ask as we explore direct intervention if anything goes floods of running water, although no other planets. The scorched and wrong. Once the computer on the liquid water can be seen on the waterless Moon has yielded no trace Viking spacecraft was given the order surface of Mars. of life. On Earth, the records of the to land, the landing went ahead By the early 1970s Mars had been origin of life have been erased by the automatically, and the people on Earth recognized as an "in-between" world, development and activities of later could only wait and hope. partly like the Earth, partly like the plant and animal life forms. On Mars, Considering these difficulties, it was Moon, yet unique in many ways. where the environment for life is not surprising that Viking 1 was neither as harsh as the Moon's nor as actually the fourth attempt to land a generous as the Earth's we might find, spacecraft on the surface of Mars. Viking to Seek Answers still preserved, the answers to how life Two Soviet spacecraft, Mars-2 (1971) came into being. We might even find and Mars-6 (1973), apparently The Viking mission would make a life itself, answering one of our oldest crashed while attempting to land. A more thorough study to answer some speculations. Whether Viking detected third Soviet spacecraft, Mars-3 (1971) of the questions raised by Mariner 9. a humanoid or invisible microbe, the soft-landed safely but stopped For example, how old are the huge discovery of any Martian life would put operating after less than 20 seconds volcanoes that Mariner 9 had us forever in a new relationship to the on the surface. discovered on Mars? It was clear that universe around us. The Viking mission had two unique Mars, like the Earth and Moon, and important features designed to showed evidence of internal heat and make the landing successful. First, the volcanic activity. But the Moon has The Viking Spacecraft landing area was to be carefully been dead and quiet for more than 3 photographed and inspected while the billion years, since the last floods of The Viking Mission to Mars thus spacecraft stayed in orbit around lava poured across its surface to form combined two major goals: to study Mars. In addition, the actual landing the lunar "seas." The Earth, on the the atmosphere and geology of the could be postponed until an other hand, has been active for the entire planet, and to analyze its soil acceptable site was found. Viking 1 same length of time and is still active and search for life in two specific spent a month circling Mars while the today. If the volcanoes of Mars are locations. Each of the two Vikings cameras in the Orbiter portion old, then Mars may be a dead world launched toward Mars in 1975 was a photographed possible landing sites in like the Moon. If the volcanoes are double spaceship. One part, the great detail and transmitted the young (and to geologists, a few Orbiter, would circle Mars photographs back to Earth where hundred million years is "young"), then continuously, photographing the scientists examined them for rough Mars may still be an active planet like surface of Mars and analyzing its ground, boulders, and other possible the Earth. atmosphere from hundreds of hazards. The winding channels carved across kilometers above the planet. The other The Viking photographs were the Martian surface are another half, the Lander, would go down to the sharper and more detailed than mystery revealed by Mariner 9. If these surface of Mars, carrying a battery of anything obtained during the earlier channels were cut by flood waters, instruments to probe directly around Mariner missions. Landing sites that then where has all the water gone? Is the landing site. Once down, the had been considered safe because Mars now in an ice age like those that Lander would never leave. The Vikings they seemed smooth and level in the once chilled the Earth? Was Mars' would not return to Earth with a load of Mariner 9 pictures suddenly displayed water now frozen away underground, Martian rocks and soil. Instead they waiting for a slight warming to bring it would radio back to Earth their rushing forth again? The further study Figure 2. A Viking Robot Ready for Mars. discoveries about the atmosphere, A full-size worklng model of the Viklng of Mars might show us how the Earth chemistry, quakes, soil, and, perhaps, Lander sits on a simulated Martian surface had started its long history of volcanic the life of Mars. at the -NASA Jet Propulsion Laboratory. activity, and we might even learn how The landing of Viking 1 on the This spacecraft, about 1.5 meters (5 feet) climatic changes and ice ages begin surface of Mars was a complicated across and about 0.5 meters (1.5 feet) and end. and ambitious undertaking, more high, weighs about 890 kilograms (1 ton). Moreover, where there are heat and difficult in some ways than landing The soil sample collecting arm stretches liquid water, there may be life. "How astronauts on the Moon. Engineers about 3 meters (10 feet) to the lower right. did life start?" and "Is there life knew that, at the moment of landing, The cameras are the vertical cylinders, each with a vertical black slit. The disk, Mars and Earth would be so far apart top rear, is the S-band high-gain radio that communications between the antenna that transmits to Earth the camera Viking and its Earth-bound human pictures and scientific data. Equipment controllers would take about 20 and instruments are identified in the minutes for a one-way trip. At such accompanying diagram. Radar altimeter electronics number 1

Radioisotope thermoelectri

Terminal desce

radar (underside of Furlable boom Lander structure)

Collector head

Magnets A Viking's-Eye View deep gullies, scattered craters, and spacecraft was sterilized by heating it The safe landing of Viking 1 rugged outcrops of rock-no place to to temperatures above the boiling immediately established one basic fact land a spacecraft which had only 22 point of water. Each Lander, and all of about Mars: the planet's surface is centimeters (8 '12 inches) of ground its 1 million separate parts, had to strong enough to support a heavy clearance. While the photographs survive a number of major crises: the machine. The Lander rested firmly on were being scanned, the large radio sterilization heating, the shock and a rolling plain strewn with rocks, and telescopes at Arecibo, Puerto Rico, vibration of launch, a one-year, 400- the cameras on the Lander began and Goldstone, California, bounced million mile trip through interplanetary almost immediately to transmit back to radar waves off Mars, using the radar space, the passage through Mars' Earth the first views of the Martian reflections to measure the roughness atmosphere, and the landing on its landscape. of the planet's surface in different surface. No wonder there were Viking's cameras stood about 1.6 regions. First one landing site was heartfelt cheers from the scientists and meters (5 feet) above the ground, and rejected, and then another. Finally, a engineers when Viking 1's first pictures their view of Mars was much like what new site was located, photographed, began to appear! a person standing in the same place scanned with radar, and found The Landers are so well designed would see. The two cameras could be acceptable, and Viking 1 descended that it is often possible to fix them operated independently to provide to a perfect landing in a level rolling when things go wrong. When the panoramas covering almost a full region called the Plains of Chryse. A sampling arm on Viking 1 got stuck, a circle around the Lander. They could little more than a month later, after a carefully-planned series of commands be operated together to produce similar thorough check of a more from Earth freed it, and the cameras stereo pictures from which the shape northern region of Mars, the Viking 2 then showed that a small pin which of the surrounding surface could be Lander made an equally flawless had caused the trouble had fallen free accurately measured (Figure 4). Most landing on the Plains of Utopia. Two to the ground. Later, when the arm of the pictures were black-and-white, Landers sit on the surface of Mars, stuck again, this time in an extended but different detectors inside the while two Orbiters circle overhead, position, a different series of cameras were sometimes used to photographing the planet and relaying commands brought it safely back into provide pictures that reproduced the back to Earth the news of what the the spacecraft. Each of these "repairs" actual hues of the Martian surface. Landers find. was a carefully-planned operation. The first pictures showed firm soil The Landers on the surface of Mars Each set of commands was first tested and scattered rocks immediately are far more complex than any on a duplicate Viking Lander sitting on beneath the Lander. As the cameras automatic spacecraft launched before. a simulated Martian surface at the looked out to the horizon, they Even if the Landers had never left NASA Jet Propulsion Laboratory, and photographed a gently rolling red Earth, their design and construction the cameras on the real Viking were landscape that could almost have would still be an impressive used to check the progress of the been a desert scene in the American technological achievement. Each "repairs" at every step. Southwest. The reddish gray soil was lander looks like a cluttered six-sided With the minor troubles corrected, dotted with rocks of all sizes. The workbench with three legs (Figure 2) the Landers even took on new tasks colors of the rocks varied from dark but it contains the equivalent of two that had not been planned before the gray to light gray to slightly reddish power stations, two computer centers, landing. After digging up samples of (Figure 5). Some rocks showed up in a TV studio, a weather station, an exposed soil, the Lander's sampl~ng great detail, and many were filled with earthquake detector, two chemical arm was used to push large rocks bubbles. These rocks looked like the laboratories (one for organic and one aside and to collect samples of the lavas produced by erupting gas-rich for inorganic analyses), three separate protected soil beneath them (Figure 3). volcanoes on Earth, and scientists ~ncubatorsfor any Martian life, a scoop think that the bedrock on which both and backhoe for digging trenches and Vikings have landed is made up of collecting soil samples, and miniature ancient Martian lava flows. ra~lroadcars for delivering the samples The Viking cameras also saw wind- to the laboratories and incubators. produced features that have familiar Equipment that would normally fill counterparts in Earth's deserts. several buildings had been designed Although the atmosphere of Mars is in miniature to fit on a spacecraft less th~n,its winds are still strong enough than 3 meters (10 feet) across. to blow dust and fine sand across the Furthermore, to avoid contaminating surface. There are dunes of light- Mars with Earthly bacteria, the entire colored sand, and detailed pictures of the dunes revealed finer ripples within them (Figure 6). There are places where the wind apparently scoured out the fine soil, revealing flat masses of Figure 3. "Mr. Badger" Gets a Nudge. Controlled by scientists back on Earth, the sampling arm on the Vrkng 2 Lander reaches out to push aside a large porous rock and to collect a sample of the protected Martian soil beneath it. Because of its shape, the rock was rnformally christened "Mr. Badger" after a character in Kenneth Grahame's book, The Wind m the Wrllows. The Mart~an"Mr. Badger" is about 25 centmeters (10 ~nches)long and we~ghsseveral pounds

Figure 4. Mars in 3-0 These two images of the same scene, one taken by each camera on the Vikrng 1 Lander, can be combined, by using a pocket stereo viewer, into a single 3-drmensional view that shows the rolling Martian terrarn and the shapes of the numerous boulders. (When lookng at the images with a stereo vrewer, concentrate on a small object like a rock. Move the viewer around untrl the two rmages of the rock come together. Then you should see the landscape in R- d Figure 5. A Summer Day's Work on Mars. Traces of human exploratron already show on the red surface of Mars. Two trenches dug by the so11samplrng arm of the Vlklng 1 Lander appear as short black smudges (left), and the so11 near the bottom of the plcture that appears cracked and prtted was disturbed by the rocket exhaust blast at touchdown and by the rmpact of the footpads. The so11 sarnpkng arm and scoop 1s at rrght center, arm (lower left) holds a brush for cleanng off magnets Lrght and dark rocks can be seen. The dark rock to the rrght of the trenches 1s about 25 centrmeters (10 Inches) across. The apparent horlzon a about 100 meters (330 feet) away and may be the r~mof a small Impact crater. Boulders 1 and 2 meters (3 and 6 feet) across are vls~blein the distance.

Figure 6. Early Morning on a Martian Desert. The variety of the Martran surface 1s captured ~n thrs panorama by the Vlkmg 1 Lander. The v~ewcovers a horizontal angle of about 100 degrees, about one- quarter of a circle. Maroan northeast 1s at the left, southeast at the rlght. The newly- rlsen Sun a just above the center of the plcture Shapes of the small sand dunes (center and left) mdrcate that the wlnds that formed them blew from upper left toward lower rrght. Large boulder (left), named "Brg Joe," measures 1 by 3 meters (3 by 10 feet) and IS only 8 meters (25 feet) from the Lander. The vertlcal white object (center) 1s the Vlklng boom that holds the weather-measuring Instruments

The Winds of Mars grayish bedrock. At other places, as firm as good farming soil on Earth. For the first time we can now streaks of dust have been deposited The soil of Mars sticks together in measure and record the weather on over and behind boulders. When about the same way, too: smaller another world. Unlike the airless Moon, Viking 1 first landed, some of these particles clump together into larger Mars has an atmosphere, winds, and piles of red dust were being eroded clods, and the walls of shallow weather patterns. and blown away by the summer trenches remain straight and show Mars' atmosphere is thinner and breezes th'at swirled around the little tendency to collapse. colder than Earth's, and scientists Lander. Seen from the surface, the two were eager to study its weather Sometimes the Viking cameras Viking landing sites have their patterns in the hope of finding general turned away from the landscape to differences. The Plains of Utopia, principles that would help us better study in detail the mechanical where Viking 2 landed, are more understand the weather of our own properties of the ground on which the rolling than the Plains of Chryse where planet. The Viking cameras often Lander rests. The cameras carefully Viking 1 sits. The Viking 1 site (Chryse) looked above the horizon to photographed the streaks produced in apparently has a larger variety of rock photograph the sky, and a battery of the soil by the rocket engines when types, while the rocks at the Viking 2 instruments recorded winds, Viking landed. Later, as the soil was locality (Utopia) are more uniform, barometric pressure, and the chemical trenched and probed and shaken to generally vesicular (bubble-rich), and composition of the atmosphere of Mars collect samples, the cameras recorded more abundant. There is bedrock (Figure 9). the appearance of marks, trenches, exposed at the Chryse site, and none Viking's first view of the sky and clods of soil on the surface visible at Utopia. produced a major surprise. Although (Figure 7). By studying these pictures. There are rippled sand dunes at the many scientists had expected that the scientists back on Earth were able to Chryse location, and none at Utopia. Martian sky would be blue like that of determine that the Martian soil is about The boulders at the Chryse site Earth, the Viking pictures showed commonly have flat, polished faces, instead that it has a creamy-pinkish apparently produced by wind-blown hue (Figure 10). The explanation is sand. that the Martian atmosphere contains a The Utopia site (Viking 2) shows an great deal of fine suspended red dust. unexplained pattern of shallow troughs that connect to form polygonal patterns. One of these troughs runs right past the Viking 2 Lander (Figure 8).

Figure 8. A Crowd of Martian Rocks. Like a throng of curious onlookers, thousands of rocks and boulders surround the Viking 2 Lander as it rests on Mars' Plains of Utopia. The field of rock and soil extends to the horizon about 3 kilometers (2 miles) away. (The horizon, actually level, appears tilted because the spacecraft is resting on the surface at a slight angle to the horizontal.) Many of the rocks display small pits and holes that may be bubbles formed when the rocks were molten lava. The rock in the lower right corner is about 25 centimeters (10 inches) across, and the large rock in the center is about 60 centimeters (2 feet) long. The small sandy trough that winds across the picture from upper left to lower right is part of an unexplained network of such channels or depress~onsthat form strange polygonal surface patterns in the Utopia region. Figure 9. " And Now, the Weather for Mars." The first interplanetary weather reports come from a small white Instrument box (upper r~ghtjmounted on the end of a long boom that holds the box about 1.3 meters (4 feet) above the Martian surface. The boom holds the box out of range of most wind disturbances caused by the 'body of the Viking Lander. instruments En the box measure the wind velocity, w~nddirectton, temperature, and atmospheric pressure. In the background are sand dunes formed by strong Martian winds. The parallel bands in the sky are not real, they were produced by the computer processing of the picture.

Figure 10. A Red Sky for a Red Planet. The red surface of Maw lends its color to the Martlan sky in this view from the Viking 1 Lander. Fine red dust from the soil is carried lnto the atmosphere, giving the sky a pnkish hue instead of the blue color expected by scientists. Light and dark boulders are strewq on the surface in the foreground, and light-gray ledges of 1 bedrock appear through She so11 in the middle distance. The horizon, about 100 meters (330 feet) away, may be the nm of an impact crater. Thls color ptcture was made by combining three separate prctures, each taken through a different color filter. The colafs were matched by comparing similar pictures taken of colored objects on the Viking Lander itself. Although the individual dust particles and broadcast to Earth on the first high in the atmosphere or swirl around are tiny, perhaps only 0.001 millimeter day, remained almost unchanged from the high slopes of Martian volcanoes (1125,000 inch) across, there is day to day: (Figure 11). In small valleys, apparently enough of this dust in the "Light winds from the East in the late atmospheric water freezes out during air to give the whole sky a reddish tint. afternoon, changing to light winds from the Martian night and then vaporizes Earth's sky is generally not so dusty. the Southeast after midnight. Maximum again when the sun rises, forming Only after large volcanic eruptions or winds were 15 miles per hour. local patches of white fog that vanish sandstorms do we see a reddening of Temperature ranged from minus 122" quickly in the relative warmth of the terrestrial sunsets that produces Fahrenheit just after dawn to minus 22" Martian day (Figure 12). something like the color of the Martian Fahrenheit in midafternoon. Totally unlike the Earth, however, sky. Atmospheric pressure 7.70 millibars." was the steady decline in atmospheric The sky of Mars grew even dustier (On Earth the same day, July 21, pressure recorded by the Viking several months after the Vikings 1976, the lowest temperature recorded instruments. During the Lander's first landed, and tlie spacecraft carefully was minus 100 degrees Fahrenheit at month on Mars, the atmospheric recorded the change. the Soviet Vostok Research Station in pressure dropped by about 5 percent. Astronomers have known for years the Antarctic, and the highest (On Earth, such a large drop in that huge dust storms often come temperature was plus 117" F at pressure is usually found only in the ' swirling out of the southern part of Timimoun, Algeria. The United States eye of a major hurricane.) Scientists Mars, covering the whole planet and recorded a high of 109" F. at Needles, think that the carbon dioxide (CO,) shutting off the surface from the view California and a low of 37" F. at Point which makes up most of Mars' of Earth-based telescopes. Such a Barrow, Alaska.) atmosphere was freezing out as solid storm shrouded Mars in 1971 as Some of the similarities between CO, (or "dry ice") on the cold southern Mariner 9 arrived in orbit, and the Mars' weather and Earth's were polar cap, which was then in the spacecraft was able to provide a surprising, because the atmos'phere middle of the Martian winter. The photographic record of the storm's of Mars is less than a hundredth as Viking landers thus seem able, from subsidence and the gradual dense as Earth's. Nevertheless, on two points on the surface, to detect appearance of the Martian surface both planets, the atmospheric the slow growth of an entire polar cap through the clouds of dust. These dust temperature reached its peak at about thousands of kilometers away, a feat storms usually develop as Mars 3 P.M. local time. The daily that would be impossible in the reaches the point in its orbit that is temperature variations recorded by complex water-rich atmosphere of closest to the Sun, and in the Spring of Viking showed the same pattern as Earth. 1977, these clouds arose again and records from a terrestrial desert While one group of scientists spread over the Martian surface. High "control" site at China Lake, California, followed the changes in Mars' weather, above the storms, the Viking Orbiter although the temperatures in the two an entirely different group was busy cameras photographed the shapes of places differed by more than 83" C. analyzing the chemical composition of the dust clouds and followed their (150" F.). Furthermore, the changing the atmosphere itself. The gases in a progress. With these data, scientists patterns of wind direction over the flat planet's atmosphere can come from are learning more about Martian winds Plains of Chryse on Mars were many different sources. Some gases and about the nature of the dust that duplicated by the winds blowing over may have been trapped from the they carry. the equally flat Great Plains of the original solar nebula when the planet After Viking landed, the Martian midwestern United States. formed. Others may have been weather was clear, cold, uniform, and Martian weather includes two other released by heat and chemical repetitious. The weather report, features familiar to terrestrial weather recorded by the Viking instruments watchers--clouds and fog. The air of Mars contains only about 111 000 as much water as Earth's atmosphere, but even this small amount can condense out, forming clouds that ride Figure 11. Martian Volcano Towers Above the Clouds. In this Viking 1 Orbiter photograph taken from 8,000 kilometers (5,000 miles) away, clouds cover the lower slopes of Mars' largest volcano, Olympus Mons (Mount Olympus), making it look like a satellite picture of a terrestrial hurricane. The huge mass of the volcano is 600 kilometers (375 miles) across, and the cliffs that mark its edge can be seen in the upper right corner. The summit stands 24 kilometers (15 miles) above the Martian surface, and the summit crater, visible above the clouds, is 80 kilometers (50 miles) across. The clouds in the upper left

reactions deep inside the planet. Still Earth's atmosphere. The remainder is than the chemical composition alone others may be produced by the nitrogen (2-3 percent) oxygen (0.1-0.4 would suggest. The ratio of heavy to transformation (decay) of radioactive percent), and argon (1-2 percent). The light carbon atoms (carbon-13 to elements in the planet's rocks. The discovery of nitrogen was exciting carbon-12) is 1/89, and the ratio of chemistry of an atmosphere thus because this element is an essential heavy to light oxygen atoms (oxygen- provides unique information about a component of the protein molecules 18 to oxygen-16) is 11500. These planet's origin, its history, and the which form living things. The small values are identical to those measured chemical composition of its rocks. amount of free oxygen is surprising, in our own atmosphere. However, the Earth's atmosphere is composed but this element can be formed in element nitrogen is different. The ratio almost entirely of two gases: nitrogen many ways, arid its presence does not of heavy to light nitrogen (nitrogen-15 and oxygen. Scientists believe that the prove that there is or has been plant to nitrogen-14) is 11156 on Mars, while nitrogen (78 percent of our life on Mars. the value on Earth is 11271. atmosphere) came out of the interior of More precise analyses have The carbon and oxygen ratios the Earth billions of years ago, while detected traces of the rare inert gases demonstrate a basic similarity between the oxygen (21 percent) has been krypton and xenon in the Martian air. Mars and Earth, despite the chemical produced gradually by the plant life These two gases make up only about differences in their atmospheres. One that has existed for billions of years. A 1 part per million of the Earth's explanation is that both Mars and small amount of the inert gas argon atmosphere, and scientists have not Earth formed from, similar parts of the (0.9 percent) has been formed by the yet been able to measure precisely the solar nebula which had the same decay of radioactive potassium atoms tiny amounts present in the air of Mars. isotope ratios. in the Earth's crust. Viking instruments also measured However, the isotope ratios of The composition of the Martian the ratios of different isotopes in the nitrogen provide evidence for different atmosphere was measured in two Martian atmosphere. (Isotopes are two histories of this element on the two places-at high altitudes as the atoms of the same chemical element planets. If the original nitrogen ratio on Lander descended, and on the that have different atomic weights, for Mars had been the same as on the surface. The composition was the example uranium-235 and uranium- Earth, then the light atom (nitrogen-14) same in both places, showing that the 238.) Isotope ratios of elements in the must have gradually escaped from the Martian winds keep the atmosphere as atmospheres and rocks of other atmosphere of Mars, possibly because well-mixed as Earth's. planets are important because they Mars' gravity is not as strong as The pressure of Mars' atmosphere is provide information that cannot be Earth's. only about 11125 that of Earth's and its obtained from chemical analyses From these atmospheric data, chemical composition is totally alone. Isotope measurements can scientists have calculated that the different. Most of Mars' atmosphere indicate the temperature at which ancient atmosphere of Mars, before (95 percent) is carbon dioxide, a gas rocks formed; if two different planets which makes up only 0.03 percent of have similar isotope ratios, then they may have formed from the same part of the original solar nebula. The isotope ratios measured by the Viking Lander show that the atmosphere of Mars is more Earthlike

Figure 12. Foggy Morning in a Martian Valley. White patches of early-morning fog and mist fill a rugged network of Martian canyons and spill out onto the surrounding high, rust-colored plateau. The clouds are probably formed by water vapor that has frozen out of the air during the previous Martian night. In the sunlight, the water vaporizes again, becoming briefly visible as mist before being absorbed into the dry atmosphere. This part of Mars, called Labyrinthus Noctis (The Labyrinth of the Night) was photographed at dawn by the Viking I Orbiter; the view covers an area about 100 kilometers (62 miles) on a side. The color picture was made by superimposing three separate black-and- white images taken through color filters. the nitrogen was lost, might have been about 5 per cent of the soil is four or five times as dense as it is magnetic material and that it is an iron now. This early atmosphere also might oxide like magnetite (Fe,,OJ, the have contained enough water to form mineral that forms terrestrial a layer several meters deep over the lodestones. This result makes Mars whole surface of the planet. Here was seem rather Earthlike; the lunar soil, by another indication that the winding contrast, has only about 1 per cent of channels on Mars actually had been magnetic material, and it is all metallic carved by water, although the iron. atmospheric analyses could not tell us More precise measurements of the where this water had vanished. soil were made with an instrument that bombarded a soil sample with X-rays and then measured the secondary X- The Chemistry of Mars rays given off by the atoms in the Martian soil. While the atmosphere of Mars was The composition of the Martian soil, giving up its secrets, other scientists as determined by the bombardment with other instruments began to test experiment, is approximately the same the solid matter of the planet, to see at both landing sites, even though the what could be deciphered from the two sites are about 5000 kilometers rocks and windblown dust around the (3100 miles) apart. spacecraft. The chemical elements detected, On the eighth day of Viking 1's and their amounts (in weight percent), Figure 13. The Ancient Crust of Mars. residence on Mars, a long arm are: silicon (Si) 21, iron (Fe) 13, Mars shows a battered and heavily- reached out from the spacecraft, and aluminum (Al) 3, magnesium (Mg) 5, cratered Moon-like surface in this picture a small scoop at the end of the arm calcium (Ca) 4, sulfur (S) 3, chlorine taken from the Viking 1 Orbiter from began to dig a small trench in the (CI) 0.7, titanium (Ti) 0.5, and 18,000 kilometers (1 1,200 miles) away. loose soil about two meters away from potassium (K) less than 0.25. The flat c~rcularplain at top left is Argyre, where the Lander stood (Figure 7). a large impact basin about 800 kilometers Scientists calculate that, to balance (500 miles) in diameter and located in the Continually guided by a computer these elements, oxygen (0) makes up southern part of Mars. This basin, aboard the Lander, the arm carefully another 42 per cent of the soil, leaving surrounded by a rugged range of pushed the scoop through the trench about 8 percent made up of elements mountains, may have been formed by a and then retreated slowly back to the (e.g.; sodium, hydrogen) that cannot huge meteorite impact billions of years Lander, bringing with it the first sample be detected by this method. ago. Smaller, younger craters cover the of Martian soil ever to be analyzed. This composition corresponds Martian surface outside the basin. The air Within the Lander, the soil sample was approximately to that of a terrestrial or is clear and cloudless over Argyre, but the sieved automatically, divided, and sent lunar basalt lava, but there are some brightness of the distant Martian horizon on its way for several different kinds of striking differences. The Martian soil (top right) suggests that clou8s are present there. The parallel white streaks analysis. contains less aluminum than a above the horizon are also cloud layers, One test of the soil did not require a terrestrial basalt and less titanium than perhaps composed of frozen Copthese chemical laboratory. Several magnets a lunar basalt. clouds are about 25 to 30 kilometers (15 were mounted on the scoop, and The unusually large amount of iron to 20 miles) above the surface of Mars. another magnet had been placed on detected confirms the long-held theory the outside of the Lander. These that the red dust of Mars is a red iron Figure 14. A View Down a Volcano's magnets trapped and held magnetic oxide similar to terrestrial rust. The red Throat. From 6,000 kilometers (3,700 particles in the soil and windblown color and the small amount (about 5 miles) up, the cameras of the Viking 1 dust. By simply examining these per cent) of magnetic material suggest Orbiter provide a vertical view of Arsia Mons, one of Mars' largest volcanoes. The magnets with the Viking cameras now volcano reaches about 19 kilometers (12 and then, the amount of magnetic miles) above the surrounding Martian material in the Martian soil could be terrain, more than twice as high as Earth's measured. Early results suggest that Mount Everest. The crcular central area in its summit is about 120 kilometers (75 miles) across. Around this summit crater, the slopes of the volcano are covered with lava flows that produce distinctive braided patterns seen clearly at the bottom of the picture. At left and right, small craters and canyons cut into the main cone of the volcano; these features may be the sources of vast amounts of lava that spilled out to flood the surrounding plains. that the iron must be present in two or know what life looks like?" It was not CO, to the confined atmosphere more distinct m~nerals,only one of possible to build, on one small above the soil sample. The sample whlch is magnetic. spacecraft, enough instruments to was then illuminated with simulated The chemical analyses rndicate that detect all the poss~bleforms of life that Martian sunlight. If any Martian life- the Martian soil cannot be made of sclentrsts could imagine to exist on forms converted the CO, into organic fresh basalt lava alone. The presence Mars. Before bullding the instruments, compounds, the compounds could be of water (perhaps as much as 1 per the scientists had to make some detected by their radioactivity. cent) in the soil, the large amount of decrsrons about what the instruments Lrving terrestrial organisms give off iron, and the unusually large amount of should look for. gases. Plants give off oxygen, animals sulfur, all indicate that the soil is a The Viking experiments were give off carbon dioxide, and both mrxture of original basalt lava with designed around two assumpt~ons. exhale water. A second experiment on other compounds that have formed as First, rt was assumed that Martian life each Lander, the gas exchange the rock has been changed or would be like Earth life, whrch is based experiment was designed to detect "weathered" by contact with the on the element carbon and thr~vesby this kind of activity. Nutrients and atmosphere of Mars. The soil could be transforming carbon compounds. water were added to the soil, and the a mixture of iron-rich clay minerals and Second, the example of Earth shows chemical composition of the gas other compounds such as Iron that where there are large life forms above the soil was continuously hydroxide and magnesium sulfate. (like human beings and elephantsj, analyzed for changes that might The soil of Mars is much more there are also small ones (like Indicate biological act~vity. similar to Earth's soil than to the soil of bacteria), and that the small ones are A third experiment on each Lander the Moon. The lunar soil, as we have far more abundant, w~ththousands or was based on the fact that terrestrial learned from the samples returned by m~llionsof them ~nevery gram of soil. animals (including humans) consume the Apollo missions, is waterless, To have the best possible chance of organic compounds and glve off unweathered, and formed by the detecting life, an Instrument should carbon dioxide. The labeled release contrnuous bombardment of large and look for the most abundant kind of Irfe. experiment added a variety of radio- small meteorites. Martian so11seems If a Martian verslon of Vrking were sent active nutrients to the soil, then waited almost terrestrial, it contains water, it to Earth to look for life, it might easrly to see if any rad~oactrveCO, (der~ved seems to be weathered, and it is land in a place where there were from consumption of this "food") would continually blown about and neither elephants nor humans, but it be given off. redistributed by the wind. would be very unltkely to land in a Several soil samples were place where there were no bacteria rn processed by all three instruments on the soil. each Lander. The results? Puzzling. Three Chances for Life The Vik~ngInstruments were There is definitely some form of act~vity designed, therefore, to detect carbon- In the Martian soil, but it is not yet A major goal of the Viking missions based MartIan microbes or s~milar clear whether this activity 1s caused by was to determine whether the soil of creatures living ~nthe soil. The three Martian life or by some unusual Mars was dead like the soil of the laboratories in each Lander were chemical characterist~cof the soil Moon or teeming with mlcroscoplc life essentially incubators, des~gnedto itself. like the soils of Earth. Soil samples warm and nourish any life, living or Viking has glven us some chemical brought into the Lander were divided dormant, in the Martiansoil and to information about the Martian soil, but and sent to three separate biological detect with sensitive instruments the laborator~esto be tested in different chemical products of the organisms' ways for the presence of life. activrty. Searching for life on Mars raises a One characteristic of terrestrial basic problem, best summed up as: organisms such as plants is that they "How do you look for life if you don't transform carbon dioxide (CO,) in the surrounding air into the organlc compounds which make up their roots, branches, and leaves. Accordingly, one Viking biological experiment, designated carbon assimilat~on(or pyrolytic release) added radioactive Figure 15. Landslides Fill Martian "Grand Canyon". This Viking I Orbiter picture, taken from a range of 2.000 kilometers (1,240 miles) shows a small segment of the Valles Marineris ("Mariner Valley"), a huge gash that runs east-west for almost 5,000 kilometers (3,000 miles) along the equatorial region of Mars. This part of the canyon is more than 50 kilometers (30 miles) across and 2 kilometers (1.3 miles) deep. The aprons of debris on the canyon floor show how the canyon widens as its walls collapse and produce immense landslides. The large apron in the center has overridden and partly covered an older landslide deposit to the left. The lines in the deposits indicate the direction in which the material flowed after breaking away from the canyon walls. Whife streaks in the middle of the canyon are features produced by winds blowing along the length of the canyon. Upper walls of the canyon provide a cross-sectional view through the different rock layers that cover this part of Mars; hard, resistant rocks (lava flows) at the top overlie less durable rubble (wind-blown dust or volcanic ash) below. Dark circle near center is photographic flaw.

Figure 16. The Vanished Rivers of Mars. Cameras in the Viking I Orbiter photographed this maze of wandering channels that cut across the terrain west of the Viking 1 landing site. The surface slopes downward, dropping about 3 kilometers (2 miles) in elevation from left to right. Flood waters once poured across this region from left to right, cutting through a high ndge (right) to pour out into the plains to the east. Older craters were cut, filled, and eroded by this flood. Younger craters, formed after the flood, show sharp outlines. The fate of these torrents is unknown; the water may now be frozen as ice in the polar caps or as permafrost in the Martian soil. Rows of dark circles are photographic flaws. we still do not know enough about its oxygen- and carbon-rich materials that definite answers about the chemicals, nature to predict what reactions will originally had been produced in the the minerals, and, perhaps, any life occur when water and nutrients are soil by ultra-violet light. forms in the red soil of Mars. added to it in Viking's biological Finally, the labeled release laboratories. The Martian soil may experiment showed a rapid release of contain many unusual and unexpected radioactive CO, that at first seemed to From Mars to Einstein chemicals, possibly formed by the be caused by biological activity. But repeated blasts of ultraviolet radiation the release quickly slowed down, Late in November, 1976, Mars from the Sun that penetrate the th~n suggesting that some chemical in the passed behind the Sun, and atmosphere of Mars and blanket the soil was being rapidly used up, communications between Earth and surface of the planet. Earth's soils are whereas a biological reaction should Viking were cut off until mid- not affected in this way, because the have continued as the organisms grew December, when Mars appeared on Sun's ultraviolet light is absorbed by and multiplied. the other side of the Sun. As Mars our denser atmosphere, and the One problem with a biological passed behind the Sun, the Viking chemistry of Martian soil could very interpretation of these reactions is that spacecraft carried out a major well be unpredictably different from analyses of Martian soil by another experiment to study, not Mars, but the the soils of our own planet. Even if Viking instrument have detected none basic nature of the universe itself. Martian soil is completely lifeless, it is of the organic carbon molecules that The spacecraft s'ignals from Mars , possible that some reactions with the make up living things. It is hard to made it possible for scientists on Earth added water and nutrients are understand how these chem~cal to carry out the most accurate test imitating biological activity. reactions could be caused by Earthlike ever performed of Einstein's Theory of Because of these uncertainties, microbes that leave no other trace, scientists are being cautious in their living or dead, in the Martian soil. interpretations of the biological At the moment, we know that there experiments, even though many of the are reactive ingredients in the soil of results resemble those from tests Mars, but it will take more experiments made on terrestrial soils rich ~nliving and more examination of the Viking Figure 17. Islands in the Stream The organisms. data before we know just what they raised rims of these Martian craters seem The carbon assimilation experiment are. As this work goes on, the to have acted as barriers to floods of showed that a small amount of CO, separate Viking experiments support water that poured across the surface of had been converted into carbon and reinforce each other, each one Mars in the past. The upstream (lower left) sides of all the craters seem eroded, with compounds, but this conversion could providing data to help interpret the streamlined islands left on the downstream have been accomplished by some results of another. The chemical (upper right) side. A curiously shaped reducing agent in the soil, such as analyses of the soil, made by X-ray ejecta deposit still preserved around the metallic iron. methods, are used to help interpret the uppermost crater may have been above In the gas exchange experiment, puzzling results of the biological the level of the floods. Th~sspectacular both oxygen and CO, were given off experiments. The instrument that has scenery, photographed by the Viking 1 when water was added to the soil. looked in vain for organic carbon Orbiter from 1600 kilometers (1000 miles) However, these reactions could have molecules has also measured the above Mars, is located near the Viking 1 been caused by the decomposition of landing site on the Plains of Chryse. (Small amount of such inorganic gases as dark rings in the picture were caused by a water and sulfur dioxide in the soil. flaw in the camera.) When these data are combined and evaluated, we may have some more Figure 18. The Source of the Flood? This strange Martian valley, more than 50 kilometers across, shows a striking change from a chaotic, hilly floor at its head (right) to a narrower and more streamlined shape (left). One explanation is that water, frozen below the Martian surface, suddenly melted and ran out, causing the ground to collapse and producing a short-lived torrent that eroded the downstream part of the valley. Such "collapsed terrain" is common in this part of Mars; numerous large and small impact craters can also be seen. A smaller valley, possibly produced by a smaller flood, is visible near the large impact crater at the top of the picture. This picture was taken by the Viking 7 Orbiter from a distance of 2300 kilometers (7900 miles). (The small dark rings in the picture are caused by a flaw in the camera.)

General Relativity. The theory, which Landers will operate for a year or two, explains gravitation and the sending back photographs and other relationships between space and time, information from Mars. Each Lander predicts that light waves (or radio has a long-lived nuclear power source, waves) will be slowed down as they and each Orbiter gets electricity from pass close to a large and massive large solar cell arrays backed up by object like the Sun. Precise two nickel-cadmium batteries. measurement of the delay in radio Scientists are eager to use the transmrssion from the Viking Lander instruments to follow the spacecraft as Mars went behind the weather patterns at Chryse and Utopia Sun would test whether the General through the Martian fall and winter, Relativity Theory was correct or and into the spring when the time of whether some competing theory was a planet-wide dust storms is thought to better explanatron of how our universe begin. A complete weather record of works. the Martian year, which is two Earth- On the day of the experiment, years long, would be a unique November 25, 1976, Mars was about document that could lead to better 321 million kilometers (200 million understanding the weather and climate ' miles) from Earth, and the radio on Earth and other worlds. signals took about 42 minutes to make Geologists are also eager for a long the round-trip. But the timing and period of Viking data. The Viking signalling devices used in Viking Landers carry seismometers to aetect commun~cationsare so accurate that "Marsquakes" so that scientists can the transmission time could be determine whether Mars is active like measured to one ten-millionth the Earth or dead and quiet like the Figure 19. Splat? The crater Yuty, 18 (0.0000001) of a second. With such Moon. Unfortunately, the instrument on kilometers (1 1 miles) in diameter, looks accuracy, rt was not difficult to Viking 1 did not operate. entirely different from the numerous craters determine that the radio signals from Since Viking 2 landed in September, that cover the Moon and Mercury. The Mars had been delayed by a full two 1976, ~tssensitive seismometer has high central peak inside this crater, and ten-thousandths (0.0002) of a been steadily recording the tlny the scalloped blanket of ejected material second-exactly the delay predicted vibrations caused by the wind and the around it, make Yuty look like a large-scale by the Theory of General Relativity. mechanical devices on the spacecraft. verslon of a crater formed by throwing a This Viking relativity experiment was A distinctive "event" in early pebble into thick mud. One possible also the most accurate measurement November, 1976, may have been a explanation for this resemblance is that large quantities of frozen water beneath of distance ever made; the 321 -million- quake with a Richter magnitude of 6.4, the Martian surface were instantaneously kilometer Earth-Mars distance was fully as large as the major San melted by the heat produced by a large determined with an accuracy of about Fernando earthquake that struck the meteorite impact. As a result, huge "mud 1.5 meters (5 feet)! Los Angeles area in 1971. avalanches," made of water and broken Overhead, the two Orbiters continue rock, poured out of the crater to form the to take pictures of the surface of Mars curiously-shaped blanket around it. This What Next? and to measure the amount of water view was taken by the Viking 1 Orbiter vapor in the Martian air and the from a range of 1877 kilometers (1 165 temperatures of the Martian surface. miles). (Yuty is named for a village in Although most of the Vikrng Honduras.) excitement was concentrated in the Even before the Landers touched first few months after the landings, it is down, the Orbrters had provided new Figure 20. Cracks in the Martian Crust? likely that the Viking Orbiters and high-resolution photographs of the This part of Mars, west of the Argyre major features of Mars: circular basins Basin, is cut by numerous parallel and mountains (Figure 13), huge fractures (faults) thar run for hundreds of volcanoes (Figure 14), great canyons k~lometersthrough circular craters and flat and landslides (Figure 15), mazes of plains alike. The dominant set of fractures (top left) runs from lower left to upper right, but other fractures run in other directions (see lower right). The fractures may be the surface effects of slow movements in the interior of the planet. The small fan-shaped channels (top center) may have been cut by running water at some time in the past. The light- colored region (top right) is part of a frost deposit associated with Mars' south polar cap.

winding, water-cut channels (Figures beneath the polar ice is composed of 16, 17, and 18), and craters with layer upon layer of what may be curiously scalloped deposits around windblown dust. Here under the polar them (Figure 19). Large areas of Mars cap may be preserved the records of are covered with strange patterns of the changing climates of Mars during fractures and joints in the bedrock thousands or millions of years in the (Figure 20), and with unexplained past. Some individual layers, as much polygonal mark~ngsthat resemble, on as 50 meters thick and covering a large scale, the permafrost or hundreds of square kilometers, may "patterned ground" of Earth's Arctic have been deposited by huge regions. sandstorms far more violent than any On September 30, 1976, the orbit of observed on Mars today. the Viking 2 Orbiter was shifted so that When the Orbiters finish their task, the spacecraft could swing over the much of Mars will be photographed, polar regions of Mars. This maneuver mapped, and studied in great detail, made it possible to study in detail the and future missions to Mars will be Figure 21. The Land of the (Martian) Midnight Sun. The north polar region of mysterious white polar caps that were planned with better maps than many Mars is displayed by the camera of the one of the first features of Mars to be terrestrial explorers have had. Viking 2 Orbiter as the spacecraft passed seen 'through Earth-based telescopes. The Vikings also explored other over the Martian Arctic for the first time in The Orbiter found that the amount of worlds near Mars. In February, 1977, October, 1976. Broad regions of white ice water in the atmosphere varies greatly; the Viking 1 Orbiter made two close are broken by darker slopes and valleys it is almost zero near the south (winter) approaches to Phobos, one of the two cut into layered rocks that underlie the polar cap, then increases dramatically moons that circle Mars. From as icecap itself. Individual rock layers appear as one moves northward into the close as 120 kilometers (75 miles) as curved parallel lines that follow the northern (summer) hemisphere of away, the Viking cameras contours of the slopes and valleys. Measurements of 'the surface temperature, Mars. Over the north polar cap itself, photographed the irregular, cratered made by instruments carried on the the atmospheric water content surface of Phobos in such detail that Orbiter, indicate that the ice is frozen decreases and the instruments tiny craters and mounds a few meters water, not frozen carbon dioxide. Top to indicate that the surface temperatures across can be seen in the pictures bottom of the picture is about 360 are about -60" C. (-96" F.). (Figures 23 and 24). Many scientists kilometers (225 miles). The Martian north Cold as these temperatures are, think that Phobos, which is only 20 pole is about 300 kilometers (I 70 miles) they are above the freezing point of kilometers (12 miles) in diameter, is an beyond the top of the picture. (Just like CO, in the Martian atmosphere, and asteroid that was captured by Mars at the Earth's Arctic regions in summer, this scientists are now sure that the part of Mars also has a "midnight sunM--or some time in the past. If they are right, total daylight--because the inclination of permanent polar caps on Mars are the Viking cameras have given us our Mars' axis and the length of the Martian made of water ice instead of frozen f~rstclose look at what we will find day are almost identical to Earth's. CO, ("dry ice"). The polar caps thus when we venture beyond Mars into the contain a large reservoir of the water millions of tiny bodies that occupy the Figure 22. A Valley that Cuts into the that may have cut the channels on Asteroid Belt itself. Past. Walls of a deep valley, eroded in the Mars in an ancient and warmer time. Even as the Viking data continue to Martian north polar cap, display the The cover of ice is not continuous, flood in, there are active discussions layered deposits of rock or windblown and the northern polar cap is cut by dust that underlie the polar ice itself. steep-sided ice free valleys (Figure Individual layers as little as 50 meters (165 feet) thick can be detected, even though 21). High-magnification pictures of the the picture was taken from about 2200 valley walls (Figure 22) revealed to kilometers (1370 miles) away. The different surprised scientists that the "bedrock" layers may record many past changes in the Martian climate, by the same mechanisms that produce the changing ice ages on the Earth. Dark smudges on the ice surface may be recent deposits of windblown dust. This closeup view, taken in Martian mid-summer (October, 1976) by the Viking 2 Orbiter, shows an area of the polar cap about 60 by 30 kilometers (37 by 18 miles). Water ice (white) covers a high, level plateau, and the steep wall of the valley (top) drops about 500 meters (1650 feet) from the ice layer to the bottom. This color picture was made by combining black-and-white pictures taken through three different color filters.

about foilow-up missions to Mars that shock of a hard landing. In this way a can now be planned on the basis of network of instruments could be what we have already learned. For all placed on Mars to give us global that Viking has done, it is only a coverage of the planet's chemistry, beginning; what we have learned from Marsquakes, and weather. the robots on Mars is still not much More ambitious, but entirely within more than we had learned from the our abilities, is a more complex robot robots (Surveyor spacecraft) that we that would land on Mars, collect sent to the Moon before the first samples of rocks and soil, and return astronauts landed there. We know that them to Earth, where they could be the surface of Mars will support the studied directly with the resources of weight of machines and humans. We all of Earth's laboratories. Only in this have the first rough chemical analyses way can we make the thousand of the soil. We have taken pictures of necessary analyses that are too the surface and dug trenches in it. complex to be made by machines on And we can now make excellent maps the surface of Mars. Only with such of the planet and pick the sites for returned samples can we determine future landings. with confidence the ages of the rocks, To send astronauts to Mars would the minerals that compose them, their be a major undertaking. Not only complete chemical composition, and would a manned mission require the weathering they have undergone. Figure 23. A Battered Moon of Mars. extensive technological developments, With instruments that are now Even tiny craters in the surface of Mars' but there are serious medical available, we could finally establish innermost moon, Phobos, are captured ln problems involved in keeping the crew beyond doubt whether such returned this photograph taken by the Viking 1 physically fit during a two-year trip in samples contain any Martian life. With Orbiter cameras on February 18, 1977. To zero gravity. the experience of a decade in space, take this plcture, the spacecraft came as For the near future at least, and w~ththe knowledge gained from close as 480 kilometers (300 miles) to the tiny moon, photographing features as machines must do our exploring for sampling the Moon, we can collect, small as 20 meters (65 feet) across. us. One possibility would be a robot preserve, and analyze such samples Phobos 1s elliptical ~nshape; the top-to- "rover" that would land on Mars and from the surface of Mars whenever we bottom diameter is 19 kilometers (12 then drive across its surface, making choose. miles), but diameters ~nother direct~ons chemical and biological analyses as it The Vikings have become a bridge are 21 kilometers (13 miles) and 27 went. Another possible mission would into the future. When the Landers have kilometers (1 7 miles). Because of its involve a new kind of Orbiter around sent their last data back to Earth, they irregular shape and anc~ent,cratered Mars, one that would carry instruments will remain like monuments on the surface, scientists think that Phobos may to measure the chemical composition be an asteroid that was captured by Mars, surface of Mars, waiting silently until possibly billions of years ago. A large of Mars' surface, just as instruments new machines, and finally human crater at the lower right is named Hall after carried on the Apollo spacecraft beings, come to stand beside them. the American astronomer who discovered mapped the chemistry of nearly one- (Figure 25.) the two moons of Mars in 1877. The quarter of the Moon. From this Orbiter, ragged appearance at the right slde is probes could be dropped to the produced by shadows on the unlit parts of surface, carrying instruments Phobos' ~rregularsurface. especially designed to survive the Figure 24. A Moon About to Break? Parallel 11nes of fractures and craters extend across the whole surface of Mars ~nnermoon Phobos Some sclentlsts thlnk that the whole moon IS gradually breaklng up from the Impacts of large meteror~tesand from the tldal forces produced during ~tsrotations around Mars In the future, Phobos may dlslntegrate completely into small fragments, formlng a nng around Mars 11ke the fam111arr~ngs of Saturn or the s~mllarr~ngs d~scovered recently around the distant planet Uranus Thls plcture was taken by the Vlk~ng1 Orblter as lt passed wlthln 300 kilometers (200 mlles) of Phobos on May 27, 1977 The picture on the right 1s the onglnal data, the left-hand picture w the computer- processed vers~on

Figure 25. A Viking Sees a Sunset on a New World. The Sun has set on Mars, but a bngenng twil~ghtbnngs a reddrsh glow to the Martian surface (left) and to the top of the Vlklng I Lander (lower nght) The 11ghtof the Sun 1s scattered by red dust ~n the atmosphere, colonng the surface and producing a reddlsh color ln the sky where the Sun has set Near the Sun, the plcture 1s overexposed, and that part of the sky appears whlte (upper nght) The colored nngs around the whlte spot are not real, they are produced dunng the computer processing of the camera's pictures A human eye. looklng at the same scene, would see a black nlght sky, grad~ng un~formlyInto a reddlsh glow where the Sun has set

Figure 26. "Mars, this is Viking .. . Viking, this is Mars." An apparent welcoming committee of lava-11ke Martlan rocks 1s framed by the radlo antenna (top) and other ~nstrumentson the Vlklng 2 Lander The pink color of the sky 1s produced by hne red dust carried by the Maroan wlnds The Amencan flag (left) and several color cal~braboncharts helped scient~stsdetermine the actual color of the Marhan sky and landscape from the plctures returned by V~kingScameras Appendix Suggestions for Further Reading

The Planet Mars

Avener, M.M., and R.D. MacElroy our knowledge about Mars in the pre- Mutch, T.A., R.E. Arvidson, J.W. .(1976), On the Habitability of Mars, Mariner and pre-Viking years. Still a Head Ill, K.L. Jones, and R.S. NASA Special Publication SP-414, useful source of information about the Saunders (1976), The Geology of U.S. Government Printing Office, 105 general characteristics of Mars and Mars, Princeton, N.J., Princeton p., price $5.25. A long-range the history of study of the planet. University Press, 400 p., price $35.00. consideration of whether life can A graduate-level textbook on the survive on Mars and of how we m~ght Hartmann, W.H., and 0. Raper surface features, geological bring life . . . Including ourselves . . . to (1974), The New Mars: the Discoveries processes, and rock formations of the planet to change its present of Mariner 9, NASA Special Publication Mars as determined from spacecraft environment into something more SP-337, U.S. Government Printing observations. (There is a brief Earthlike. Office, 179 p., price $8.75. A appendix containing early Viking beautifully illustrated textbook that results.) The book provides a detailed Bradbury, R., A.C. Clarke, B. combines the early discoveries about scientific summary of our current Murray, C. Sagan, and W. Sullivari Mars with the findings of Mariner 9's knowledge about Mars. It also (1973), Mars and the Mind of Man, close-up pictures. Carefully selected provides good comparisons of how New York, Harper and Row, 143 p., photographs highlight separate the same geological forces . . . price $7.95. A collection of essays chapters that describe different volcanoes, wind, and water . . . about Mars, in which five scientists features of Mars. Photographs operate in different ways on the Earth, and writers discuss their feelings compare similar views of Mars and Moon, and Mars. about Mars and what might be found Earth. Veverka, J. (1977), "Phobos and there as Mariner 9 went into orbit Deimos," Scientific American, Vol. 236, around the planet in 1971. The book Mars as Viewed by Mariner 9 No. 2, February, 1977, pp. 3037. A also presents some later reactions of (1974), NASA Special Publication SP- description of the two tiny moons of the same people to the discoveries 329, U.S. Government Printing Office, Mars, revealed in close-up made by the spacecraft. 225 p., price $8.15. A detailed "picture photographs taken by the Mariner and book" of Mars as seen through the Viking spacecraft. The moons may be Carr, M. (1976), "The Volcanoes of cameras of Mariner 9, this document captured asteroids. They give us an Mars." Scientific American, Vol. 234, contains several hundred captioned indication of what millions of other No. 1, January, 1976, pp. 3243. A illustrations of the craters, volcanoes, small bodies in the solar system may detailed discussion of the huge canyons, dunes, clouds, and ice caps be like. volcanoes discovered on Mars in 1971 that make Mars a complex and by the Mariner 9 spacecraft: their size fascinating planet, partly like Earth and and appearance, their differences from partly lhke the Moon. Viking Results terrestrial volcanoes, their ages, and what they tell about the history and Hoyt, W.G. (1976), Lowell and Mars, "Mars: Our First Close Look," internal structure of Mars. Tucson, University of Arizona Press, Nat~onalGeographic, Vol. 151, No. 1, 376 p., price $13.95 hardbound, $8.50 January, 1977, pp. 2-31. Handsomely Glasstone, S. (1968), 7he Book of paperback. A detailed and scholarly illustrated presentation of Viking results Mars, NASA Special Publication SP- biography of the astronomer Percival for the general reader. Scientific 179. U.S. Government Printing Office. Lowell and his involvement in the results are combined with beautiful 31 5 p., price $5.25. A thorough controversy over the existence of color panoramas of the surface of compilation, now somewhat dated, of intell~gentlife on Mars. For people Mars. interested in the history of astronomy and the study of Mars in the early 20th Century. Experiments and Activities Young, R. S. (1976) "Viking on 1. Geography and Mission letting the inflated balloon expel air in Mars-the First Months," NASA Report Planning. the direction that the block is moving to Educators, Vol. 4, No. 4, December, (i.e., "downhill"). Show that this The following are the Martian arrangement slows the block down, 1976, pp. 1-5. To obtain write latitudes and longitudes of locations Educational Programs DivisionIFE, just as retrorocket motors slowed that were considered as possible down the Viking Landers. Turn the National Aeronautics and Space landing sites for the Viking spacecraft: Administration, Washington, D.C. block around so that the balloon 20546. Latitude Longitude expels air in the "uphill" direction as 22" N. 48" W. (Viking 1 landed the block slides down the plane. Two technical summaries of the near here.) Calculate the amount of velocity V~kingscientific results are: 20" N. 108" E. added to (or subtracted from) the 44"N. 10" W. block by the action of the balloon in Young, R.S. (1976), "Viking on Mars: 46"N. llOOW. each use. A Preliminary Survey ," American 46" N. 150" E. (Viking 2 landed Scientist, Vol. 64, No. 6, November- near here.) 3. Life Detection December, 1976, pp. 620-627. 7" S. 43" W. Carry out simple versions of the 5"s. 5"W. Viking life detection experiments by Viking 1: Early Results, (1976), If MASA (the Martian Aeronautics making chemical tests for the NASA Special Publication SP-408, and Space Administration) sent presence of life in terrestrial soils. An U.S. Government Printing Office, 67 p., spacecraft to land at the same apparatus to detect carbon dioxide orice $2.00. latitudes and longitudes on Earth, (CO,) or water (H,O) given off by where would each one land? What organisms in the soils can be made by Technical articles on all aspects of hazards would be encountered? What connecting two bottles with a U-tube. Viking science, written by the scientists would happen to the spacecraft? What Place a sample of organic-rich soil in themselves, have appeared in the would the spacecraft see? Would it one bottle. (Use commercial peat if no following issues of the magazine detect water? life? intelligence? suitable soil is available.) Science, published by the American If you were working for MASA, what To detect CO,, place a limewater Association for the Advancement of sites would you pick for a landing on solution in the other bottle. The end of Science: Earth? Why? For each site, identify the the U-tube should be placed about 10 27 August 1976, Vol. 193, No. 4255, hazards that your spacecraft lander mm ('12 inch) above the surface of the pp. 759-815. would have to survive. What would you limewater. Any CO, given off will react 1 October 1976, Vol. 194, No. 4260, expect to find? Find some pictures of with the limewater to produce a cloudy pp. 57-105. the Earth from space to examine for or milky appearance. (Try using a 17 December 1976, Vol. 194, No. interesting locations. photographic light-meter to measure 4271, pp. 1274-1 353. 2. Retrorockets Demonstrate the retrorocket principle by attaching a balloon to a wooden block and sliding the block down an inclined plane. Determine the velocity from the length of the plane and the time it takes the block to slide down it. Repeat the same experiment, how rapidly the limewater turns 5. Stereo Photography the soil, e.g., scraping the magnet cloudy.) Demonstrate how three-dimensional through the soil, pouring the soil over Although water in the soil may not stereo pictures, like those produced the magnet, or spreading out the soil be produced by organisms, its by the Viking cameras, are made and in a thin layer and passing the magnet presence indicates the possibility of used. Take one picture of a scene over it. First wrap the magnet in paper life. Water given off by the soil can be (e.g., a classroom), move the camera or plasiir: film so that you can easily observed by usirig a commercial 2-3 feet sideways, and take another remove the magnetic material that drying agent, like "Indicating Drierite" picture of the same scene. Examine adheres to it. or cobalt chloride paper, instead of the two pictures with a stereoscope, Examine the collected material with limewater. The drying material can be moving them until the picture is seen a hand lens or a low-power placed either in the U-tube or in the in three dimensions. Make sketches microscope. How much white second bottle. Water can be detected and maps of the scene, indicating nonmagnetic sand was collected with by weighing the drying material or by objects that are high and low, near the dark magnetic material? noting the change in color. and far. A print-making color camera Prepare a soil sample that contains In experimenting with heating the is convenient, but any camera can be a known weight of magnetic material. soil, low heat should increase organic used. Try various collection methods and activity and should cause a faster If you use a color camera, you can weigh the amount of magnetic material evolution of CO, or H,O. Too much demonstrate how the Viking cameras collected in each way. Calculate the

heat will kill the organisms and stop produce color pictures by combining : efficiency of each method, i.e., the gas production. In addition, test a photographs taken through different weight collected divided by the weight "control sample" that has been color filters. Experiment by placing originally present. Discuss why some sterilized by heating the soil bottle in colored filters (of glass or plastic) in collection methods do not approach boiling water, and observe the front of the camera lens before you 100 percent efficiency. difference in behavior. take the picture. Wratten gelatin filters Make up several soil samples with are best: number 47B (blue), 29 (red), varying amounts of magnetic materia!, 4. Wind Erosion 61 (green). Colored acetate can also e.g., 1, 5, 10, and 25 percent. Process Experiment with making wind- be used; it is cheaper, but it w~lldistort each sample with the most efficient produced landforms by blowing an the image somewhat. Take each collection method, and weigh the electric fan (or hair dryer) over a large picture in a stereo-pair through amount of magnetic material collected. shallow box filled with loose sand. different colored filters, then "combine" Calculate the total amount of magnetic Vary the force of the wind, the the colors by viewing the stereo-pair material present, knowing that: distance of the fan from the sand, and with the stereoscope. Which pair of (amount present) = (amount collected) the angle at which the wind strikes the color filters produces the best match / (efficiency). Repeat the experiment a surface. Try to dupl~catethe sand with the colors in the original scene? few times. How reproducible are your dunes and ripples seen in Viking Are two colors adequate to make a results? How accurate are they? pictures of the Martian surface. good match? Substitute a different magnetic Place rocks on the sand surface, material (iron metal filings for and try to duplicate other features 6. Magnetic Material in the magnetite or vice versa) and repeat seen on Mars: wind-scour under rocks, Soil the experiments. Does the efficiency of trails of sand on the downwind side of Make a synthetic "Martian soil" by the collecting methods change? Why? rocks, and sand deposits on top of mixing about 5 percent of magnetic rocks. How can these features be material (crushed magnetite, FeQ, or 7. Mechanical Properties of used to determine the wind direction? iron metal filings) with clean white the Soil Reverse the direction of the wind, and sand. Using a large bar or horseshoe Study how the mechanical see how much wind force is needed to magnet, try various methods of properties of different soils affect the change these wind features so that collecting this magnetic material from appearance of trenches dug in them. they indicate the new wind direction. Make a series of soil samples by Do wind features on Mars necessarily mixing loose sand with varying indicate the present wind amounts of fine clay or chalk powder. direction? Try making and studying 3-dimensional stereo photographs of your artificial wind features. (See Experiment #5.) Experiment on mixtures that contain Maunder to demonstrate the eye's zero percent clay (pure sand), 25 tendency to produce imaginary lines to percent, 50 percent, and 100 percent connect objects that are entirely clay (pure clay). separate but poorly seen.) Make trenches by sticking a ruler into the soil and pulling it through the soil sample. Note the appearance of 9. Mars in Fact and Fiction. each trench, and describe what People have often commented that happens to the walls after the trench is science-fiction literature often predicts formed. What percentage of clay is future facts and developments. (Jules needed to form a steep-walled trench Verne's From the Earth to the Moon, like those in the Viking pictures? and 20,000 Leagues Under the Sea Pour a sample of each soil onto a flat are often cited as examples.) surface from a height of a few Science-fiction has been written centimeters. Note how the piles differ about Mars for more than three- in smoothness, in slope, and in the quarters of a century. A partial list of number and size of clumps formed by books, all available in paperback, is: the soil. H.G. Wells, The War of the Worlds Is there any difference in behavior (1898). between the soil that has 25 percent Edgar Rice Burroughs. A Princess of clay and the soil that is pure clay? Mars (1912). Examine the Viking pictures of the C.S. Lewis, Out of the Silent Planet trenches dug in Martian soil. Does the (1944). Martian soil behave like loose sand? Robert A. Heinlein, Red Planet Which soil sample best duplicates the (1949). behavior of the Martian soil? Ray Bradbury, The Martian Study the effect of water by Chronicles (1950). sprinkling a little water on the surface Arthur C. Clarke, Sands of Mars of the soil sample before digging the (1 952). trench. Through which soil does the What conditions of temperature, water move fastest? How does the atmosphere, and climate did the water affect the shape of the trench in various authors attribute to Mars? What each soil? kinds of Martians lived in these conditions? How did Earth people 8. The "Canal" Illusion adjust to Mars, and Martians to Earth? On a white sheet of paper about 2 Did the authors' view of Martian feet by 3 feet in size, draw a random conditions change as we learned more arrangement of dots, circles, ovals, about Mars? How accurately did the straight lines, wavy lines and irregular authors predict the real nature of Mars smudges. Make sure that the diagram as we have determined it from Viking is a completely random pattern. Hang and other spacecraft? the paper at the front of the classroom How would you write an "accurate" so that it is well-lit, and have the science-fiction novel based on the students draw what they see. view of Mars revealed by Viking? What Compare the drawings by students kinds of "Martians" could exist? What who are closest to the diagram with protection would humans need on the those by students who are further surface of Mars? What hazards would away. Which ones reproduce the humans on Mars face from natural pattern best? How many in which processes or from "Martians"? group draw straight lines where none are present in the picture? (This experiment was first performed many years ago by the astronomer Suggested Viewing A series of four films produced by A Question of Life NASA discuss the planet Mars and the HQ 270-COLOR-28% MINS. Viking life detection experiments. The The film is a composite version of three films, produced before the Viking 15-minute films: Life? (HQ 261), Mars: landings on Mars, may be borrowed Is There Life? (HQ 263) and Mars and from NASA Regional Film Libraries Beyond(HQ 264). A definition of life without rental charge. and general conditions necessary to sustain life are discussed. Viewers are Life? introduced to the possible past history HQ 261 -COLOR-1 4% MINS. of Mars as well as its present surface General characteristics of life are first topography and its capacity to support described with non-life similarities life as we know it. Major emphasis is noted. A number of adaptations are placed on the Viking life detection included to show how life has adapted experiments including the three to Earth c~ndition~,and how certain biology experiments and the organic individuals 'ban withstand analysis instrument. Consideration is environmental insults. In conclusion, given to the potential significance of the habitat of Mars is described with discovering life elsewhere in the the question raised as to the possibility universe. of life existing there.

Mars-Is There Life? HQ 263-COLOR-1 4% MINS. Students are introduced to the possible past history of Mars, as well as its present surface topography-from volcanoes, ice caps, stream beds, impact craters, canyons and wind- eroded surfaces. The Viking lander and its biology experiments are discussed in relationship to the search for life on Mars. In conclusion, students are asked to consider life forms that might be able to survive on Mars, and the potential significance of their discovery.

Mars and Beyond. HQ 264-COLOR-1 4% MINS. This film traces the Viking mission to Mars to specifically explore the biochemical evidence of life. Elementary chemical components of life (as we know it) are introduced; these are related to the organic analysis instrument on board the Viking lander. The instrument is described by design and operations. The program concludes with the potential significance of biochemical findings- how they may relate to past, present and future Martian life.

$7 U.S. GOVERNMENT PRINTING OFFICE: 1977 0-247-91 5