The Viking landing missions produced the first photographs from the surface of Mars successfully returned by spacecraft. Although the missions did not prove or disprove conclusively the existence of life there, they did provide a wealth of other information about Mars, including geological observations made from the orbiters that showed a planet that in many ways is as dynamic as Earth.
For centuries, the planet Mars has fired the human imagination to speculate about the wonders that might exist on its surface. Earth-based telescopes revealed numerous features suggestive of seasonal change, running water, growing vegetation, and even canals. The possibility that Mars has some form of intelligent life was not ruled out. With this in mind, it seems only natural that one of the first objectives of the space age would be to go to Mars and see what the planet truly holds.
The first close-up look at Mars came in 1965, when the Mariner 4
It was very fortunate for the exploration of Mars that the 1971 Mariner 9 mission was not canceled. Mariner 9, unlike the three previous missions, was to be an orbiter. It would spend nearly a full year in orbit around Mars, photographing almost the entire Martian surface. The planet Mariner 9 revealed was far different from what the earlier Mariner photographs had depicted. Mariner 9 photographs showed huge volcanoes, dried river channels, glacial deposits at the polar caps, and an enormous rift valley that spanned nearly 4,800 kilometers. Mars was no longer seen as a dead planet but as one that was geologically alive. The question of life being found on Mars was, therefore, once again considered.
The first photo of the Martian surface was taken by Viking 1.
The results of the Mariner 9 mission set the stage for the very sophisticated Viking mission. This mission would utilize a two-component spacecraft that consisted of an orbiter and a lander. The orbiter would provide detailed photographs of the surface of the planet, as well as collect data on its atmospheric composition, wind speeds, and temperature variations. The lander would photograph the surface firsthand, sample and analyze soil specimens, record the Martian weather conditions, and conduct experiments to search for the presence of life. It was hoped that the life-search experiments would prove positive and therefore shed light on the question concerning the origin of life. Viking would prove to be the most ambitious robotic mission flown; its results were eagerly awaited by scientists around the world.
The Viking mission to Mars was first defined in 1968 by the National Aeronautics and Space Administration (NASA). Viking was not, however, the original plan for the exploration of Mars. Its predecessor, Voyager, was discussed from 1965 until 1967, and then dropped. The original Voyager proposal called for a flyby, orbiter, and later lander missions. Successive missions were to have been even more ambitious and costly. The giant Saturn 5 moon rocket was to have been the launch vehicle. Voyager never got beyond the discussion stage as a result of budget cuts, but a less costly mission was sought to replace it.
The Viking spacecraft that eventually flew to Mars was a combination of the original Voyager design and that of the lunar Surveyor spacecraft. The techniques of soft landing on another planetary body had been well developed in the Moon missions and required only a slight modification to accommodate the thin Martian atmosphere. Viking would include two orbiter-lander pairs that were launched separately and placed into slightly different orbits around Mars. The orbiters first would examine proposed landing sites and then certify them according to criteria required for a safe landing. Only then would the landers be released and directed toward their targets. The actual landing would be accomplished by a gradual slowing, resulting first from aerodynamic drag and then by parachute. Retro-rocket firing would complete the soft landing, with no greater impact velocity than a minor jolt.
Viking 1 was launched from Kennedy Space Center at Cape Canaveral on August 20, 1975, with Viking 2 being launched on September 9, 1975. Key personnel from the NASA Langley Research Center, which managed the Viking landing missions, were James S. Martin, Jr., A. Thomas Young, Israel Taback, G. Calvin Broome, and Gerald A. Soffen.
The Viking missions were not the first to attempt a soft landing on Mars. Two Soviet spacecraft (Mars 2 in 1971 and Mars 6 in 1973) apparently crashed into the Martian surface. A third Soviet spacecraft (Mars 3 in 1971) did soft-land but stopped operating after only twenty seconds. These missions taught NASA scientists that landing on Mars would be no easy task. It was hoped that the two-component concept of the Viking spacecraft would avoid the problems encountered by the Soviets.
The Viking 1 spacecraft achieved Martian orbit on June 19, 1976. It was placed into a highly elliptical orbit that brought it as close as 1,513 kilometers and as far as 33,000 kilometers. This orbital configuration provided the combination of close-up and wide-angle photography methods necessary to evaluate properly the Martian surface.
Although the computers on board the Viking spacecraft contained preselected landing sites, the orbiter first had to examine these sites and then had to certify their suitability for a safe landing. This became a very frustrating aspect of the mission. Photographs taken by the Mariner 9 spacecraft showed smooth, flat landing sites, which proved to be rough and unsuitable for landing. When choice after choice of sites failed to meet the landing criteria, the actual landing had to be pushed back from its scheduled date. Safety factors had priority in site selection.
In the early morning hours of July 20, 1976, the computers on Viking 1 initiated the landing sequence to commence. Because Viking 1 was more than 321 million kilometers from Earth at that time, the anxious scientists waited almost twenty minutes for the telemetry to confirm the events taking place on Mars. As each confirmed stage came in to mission control at the Jet Propulsion Laboratory
Shortly after Viking 1 landed, its twin-camera system began taking pictures and transmitting them back to Earth. The cameras on board could operate individually for panoramic views or together for stereoscopic pictures. Also, they had the capability to photograph in black and white or through the use of filters that produced color images. Because their method of photography was line-scan, it required almost five minutes to complete a single image. As the imaging progressed, the spacecraft relayed to Earth each line-scan as it was taken. At mission control, the scientists viewed tantalizing narrow strips of images as they grew into full pictures. It was a historic moment for human exploration.
The first complete image from the surface of Mars showed one of the lander’s footpads resting firmly on a surface consisting of fine soil and scattered rocks. Evidence of volcanic rocks and wind erosion was clearly visible. Red was truly the color of Mars.
While the lander was busy photographing on the surface, the Viking 1 orbiter began a systematic photographic survey of its own that would eventually produce high-resolution photographs of nearly the entire surface. Programmed changes in the spacecraft’s orbit would bring it to within 30 kilometers of the Martian moon, Phobos. The resulting photographs showed a cratered world that may represent one of the most primitive objects in the solar system.
Viking 1 was joined in orbit by Viking 2 on August 7, 1976. Viking 2 began its site selection process as Viking 1 had done. Because of the success of Viking 1, the landing site for Viking 2 could be more ambitious and go to a more exciting location, where the chances of finding life might be greater. Together, this pair of spacecraft would rewrite the knowledge of Mars and present science with a picture of a dynamic planet that was not unlike Earth in many respects.
The primary objectives of the Viking missions to Mars were to provide data in an attempt to determine where Mars fits in when compared to the evolution of Earth and the Moon and to determine if life exists elsewhere in the solar system. For centuries, Mars has been a leading candidate in the search for extraterrestrial life because it shares certain similarities with Earth. Most important of these was the possibility of finding water in liquid form on its surface. It seems apparent that wherever water is present, the potential for some form of life is very good. The ever-changing appearance of the Martian polar caps seemed to confirm the presence of water.
The Viking landers had three kinds of instruments that could detect various forms of life. The first was the camera. Provided that any life-form was at least as large as lichen, it could be photographed directly. The next instrument was the gas chromatograph/mass spectrometer, which could detect organic molecules in the Martian soil. The finding of these molecules would present a serious argument for the presence of life (past or present). Perhaps the most ambitious of the three instruments were the life-detection experiments. These were designed to detect any unusual activity in the Martian soil that might be construed as a life function. Each of the three experiments searched for signs of metabolic processes such as those produced by bacteria, green plants, and animals on Earth. It is important to remember that these experiments were designed to detect life-forms as they occur on Earth. Perhaps some purely Martian organism was not detected because of its unique characteristics, but that is unlikely.
Although the biological experiments performed as designed, they did not confirm the presence of any life-form. They discovered that Martian soil mimics life when it is exposed to water vapor. These chemical reactions, which were attributed at first to a life process, were the result of oxidants present in the soil and atmosphere of Mars. This was a particularly disturbing discovery, because oxidants such as peroxides and superoxides tend to break down organic matter and living tissue. This suggests that if life did exist on Mars, it would be destroyed quickly by these compounds.
The Viking missions to Mars did not prove or disprove conclusively the existence of life there, but the missions did provide a wealth of other information about Mars. Geological observations made from the orbiters portray a planet that in many ways is as dynamic as Earth. Huge volcanoes tower over the flat plains of the Martian northern hemisphere, while the southern half is seen as a cratered, frozen world. Dried-up river valleys with their associated features were clearly in evidence in the north, and glacial features were obvious in the polar regions. Valles Marineris (Valley of the Mariners), a huge rift valley that has no comparison on Earth, spans more than 4,800 kilometers. Prior to the Viking missions, no one had guessed how complex the Martian geology would be.
The Viking missions not only returned valuable information about Mars but also demonstrated what a robot spacecraft can do far from Earth. The two Viking landers proved that spacecraft could work independently and successfully for extended periods of time. The landers pushed around rocks, recorded “Marsquakes,” observed windstorms and snowfalls, and even repaired a troublesome mechanical arm. Viking rates as one of the most successful missions ever flown.
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Bane, Don. Viking: The Exploration of Mars. NASA EP-208. Washington, D.C.: U.S. Government Printing Office, 1984. This booklet presents a wealth of descriptive information on the Viking missions from the point of lift-off to the very last data sent back from Mars. It is beautifully illustrated with the best of the Viking photographs. -
Boyce, Joseph M. Smithsonian Book of Mars. Washington, D.C.: Smithsonian Institution Press, 2002. Firsthand account detailing Mars’s atmosphere, climate, surface, and interior. Draws on Mars missions from 1965 to 2001. Useful for school projects. -
Carr, Michael H., and Nancy Evans. Images of Mars: The Viking Extended Mission. NASA SP-444. Washington, D.C.: U.S. Government Printing Office, 1980. This booklet serves as a good continuation of the work by Bevan M. French cited below. Although it presents good background information on the Viking missions, its best feature can be found in the explanations of the photographs presented. -
French, Bevan M. Mars: The Viking Discoveries. NASA EP-146. Washington, D.C.: U.S. Government Printing Office, 1977. This booklet describes the initial results obtained from the Viking 1 and 2 missions. It presents a clear and concise report that is readable at most levels. An excellently reviewed bibliography complements the text and illustrations. -
Greeley, Ronald. Planetary Landscapes. 2d ed. New York: Chapman & Hall, 1994. This book offers the reader both the fundamentals of planetary geology and an in-depth look at specific topics. The chapter that discusses Mars is comprehensive and utilizes many of the Viking images. It is an extremely well-illustrated and readable book. A handy reference for those interested in the planets. -
Mutch, Thomas A., et al, comps. The Geology of Mars. Princeton, N.J.: Princeton University Press, 1976. It is unfortunate that this work was published just after the Viking 1 landing; therefore, it contains only minimal reference to that mission. This text, nevertheless, represents perhaps the most comprehensive discussion of Martian geology available up to the Viking mission. -
National Aeronautics and Space Administration, Viking Lander Imaging Team. The Martian Landscape. NASA SP-425. Washington, D.C.: U.S. Government Printing Office, 1978. This book complements the work by Spitzer (cited below) by presenting a detailed view of Mars as seen from the planet’s surface. Details of the missions are explained in chapter 1, with spectacular photographs following in subsequent chapters. Explanations of the features illustrated are extensive. -
Spitzer, Cary R., ed. Viking Orbiter Views of Mars. NASA SP-441. Washington, D.C.: U.S. Government Printing Office, 1980. This book represents a detailed look at the Martian surface as seen from orbit. Very good descriptions of the features are represented, along with numerous photographs. Accompanying the text is a thorough glossary and suggestions for further reading.
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