After a number of attempts, the Soviet space probes Venera 9 and 10 returned the first pictures from the surface of Venus. Viewing conditions on Venus were considerably better than expected, and images revealed that rock-forming processes at work on the planet’s surface were much more complicated than previously thought.
By the late 1960’s, the United States and the Soviet Union had each developed its own particular approach to space exploration. The United States concentrated its planetary exploration efforts on the outer solar system, especially Mars. Soviet planetary exploration efforts were directed almost exclusively toward the planet Venus. The Soviet geologists and engineers who were involved in studies of space exploration and who played principal roles in the exploration of Venus included Alexander Vinogradov, Kiril Florensky, Alexander Basilevsky, Arnold Selivanov, and Margarita Narayeva.
The first probe to explore Venus was the American probe Mariner 2,
The Soviet series of Venus missions began on April 2, 1964, with the launch of Zond 1, but this probe ceased transmitting before reaching Venus. The next probes in the series, renamed Venera (Venus), were launched on November 12 and 16, 1965. Venera 2 passed 24,000 kilometers from Venus on February 27, 1966, while Venera 3, the first human-made object to land on another planet, crash-landed on Venus on March 1. Contact was lost before the probe could relay any information about the planet.
Venera 4, launched from Tyuratam, Kazakhstan, on June 12, 1967, was the first successful Soviet Venus probe. It reached Venus on October 18 and separated into two parts: a 380-kilogram lander that descended by parachute, and a “bus,” the remainder of the probe, which continued past Venus and served as a communications relay. The lander transmitted data for ninety-eight minutes. Initially, Soviet space authorities claimed a successful landing, but later analysis suggested the probe failed about 25 kilometers above the surface. This misconception led to underestimates of Venus’s atmospheric pressure.
Veneras 5 and 6 were launched on January 5 and January 10, 1969, and arrived on May 16 and 17, respectively. They reported temperatures as high as 400 degrees Celsius, an atmosphere of at least 90 percent carbon dioxide, and atmospheric pressures up to sixty times that of Earth. Such pressures, equal to the pressure beneath 600 meters of water, crushed the probes before they reached the surface. Veneras 7 and 8 were modified on the basis of the earlier Venera findings and successfully landed on the surface and transmitted data. Venera 7 was launched August 17, 1970, and landed on December 15. Venera 8 was launched March 27, 1972, and landed on July 22. These probes found surface temperatures of 480 degrees Celsius and atmospheric pressure about ninety times that of Earth.
The Venera 9 and 10 spacecraft were launched on June 8 and 14, 1975, from the Baykonur Cosmodrome in Kazakhstan. After a four-month voyage, they arrived at Venus on October 22 and 25, respectively. Instead of continuing past Venus, the spacecraft slowed and entered orbit around Venus, the first spacecraft to do so. Each lander then detached from its bus and descended while the bus remained in orbit as a communications link.
Both Venera spacecraft landed on the edges of Beta Regio,
Unlike most landers of American design, the Venera spacecraft lacked legs. Instead, the base of the spacecraft was a circular skirt of crushable material. This design made the Veneras somewhat vulnerable to tipping. Venera 9 landed in very rough terrain, facing uphill on a slope of about 20 degrees. The spacecraft was tilted another 10 degrees by an object beneath it, probably a rock. The total tilt of the spacecraft was 30 degrees from the horizontal. Venera 10 landed in a smoother area. The surrounding terrain was nearly level, and the spacecraft was tilted only about 8 degrees by small rocks beneath it.
The Venera 10 lander touched down on Venus on October 25, 1975, and returned this image of the surface during its brief operation. Objects at the bottom are parts of the spacecraft.
At the temperature of 480 degrees Celsius on the surface of Venus, the survival time of the spacecraft was brief. Because solid-state electronics are very vulnerable to heat, a long-lived probe would require a massive cooling system. All Venus landers have been designed for limited lifetimes, although they have thick insulation and are precooled to prolong their survival time. The insulation surrounding the Veneras was planned to provide about an hour of survival time, enough to transmit basic meteorological and surface chemistry data plus a panoramic photograph. The photographic apparatus consisted of a fixed television camera and a moving mirror that scanned the field of view. Both landers actually survived somewhat longer than expected and were transmitting a second panorama when their electronics finally failed. Viewing conditions on Venus were considerably better than expected. The Veneras had been equipped with artificial light sources in the expectation that the dense clouds of Venus would block most sunlight, but a surprisingly large amount of sunlight penetrated to the surface, which was about as bright as on an overcast day on Earth. The dense atmosphere was clear near the surface, with visibility of at least several hundred meters.
Venera 9 photographed a scene of cobbles and small boulders averaging a few tens of centimeters in size. One conspicuous set of boulders appeared to have once been a single slab, broken into three pieces, all of which showed an apparent layered structure. The Venera 10 scene showed broad expanses of slablike or layered rock outcrops with patches of pebbly material. Similar slabby rock surfaces have been photographed elsewhere on Venus by later landers in the Venera series, indicating that processes that form layered rocks are widespread on the planet. The Venera 9 and 10 chemistry probes could detect only a limited number of chemical elements. The low potassium contents of rocks at the landing sites suggested that the rocks probably were equivalent to terrestrial basalt, a dark, silica-poor volcanic rock. This finding has been supported by data from later probes.
As similar as Venus is to Earth in size and location in the solar system, the two planets are radically different in many ways. The dense clouds that cover Venus once led to free speculation about the possibility of abundant water and life on Venus. Even though Mariner 2 had sent data in 1962 indicating that the surface of Venus was very hot, there was a widespread reluctance, on the part of many scientists and the public alike, to believe that Venus, seemingly so Earth-like, was actually as hostile as it is.
Because of its global cloud cover, physical conditions on Venus were poorly known when the Soviet Union began its Venus explorations. The clouds hid the true surface conditions from view, conditions so hostile that a number of early spacecraft did not survive to reach the surface. It was only by learning from early failures that spacecraft robust enough to survive briefly on Venus were eventually built.
Landing on another planet is a great technical accomplishment; landing on a planet with the surface conditions of Venus and successfully returning data and photographs is an achievement of the highest order. On a planet where spacecraft survive only an hour after landing, every second of telemetered data is a significant increase in knowledge. As important as the meteorological data returned by Venera 9 and 10 were, the most significant achievements of these landers were the first pictures of the surface of Venus.
It had been supposed that the surface of Venus might be very dark; it turned out to be much lighter than expected. With no water, only wind was likely to cause erosion on Venus. Many scientists expected a bland surface of wind-blown dust and smoothly worn rocks. The pictures returned by the Venera spacecraft superficially look rather mundane, but actually show that there is an unexpected level and variety of rock-forming processes at work on the surface of Venus. The photographs show that some processes break down and transport rock fragments. Most rock-forming processes on the surface of Earth are related in various ways to water. What might break down rocks and form layers on a waterless world like Venus is still a subject of debate. The layered rocks could be lava flows, layers of volcanic ash, or possibly layers of wind-blown sediment. In place of the water-deposited cementing minerals that bind such rocks on Earth, rocks on Venus might be cemented by chemical reactions with Venus’s dense atmosphere. Also, it may be hot enough on Venus for partial melting of some rocks to occur.
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Burgess, Eric. Venus: An Errant Twin. New York: Columbia University Press, 1985. One of the most comprehensive books on Venus available for general audiences. The book surveys the history of Venus exploration by telescope and spacecraft, as well as the findings from Soviet and American missions. -
Carr, Michael H., et al. The Geology of the Terrestrial Planets. NASA SP-469. Washington, D.C.: U.S. Government Printing Office, 1984. A comparison of the planets from Mercury to Mars, with many photographs from planetary spacecraft. The chapter on Venus contains a detailed history of missions to that planet. -
Grinspoon, David Harry. Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet. New York: Perseus Books, 1998. Provides both romantic and scientific explanations of the planet closest to Earth and incorporates the latest data from the Magellan spacecraft. -
Morrison, David, and Tobias Owen. The Planetary System. 3d ed. San Francisco: Addison Wesley, 2003. Provides contemporary data on all planetary bodies visited by spacecraft since the early days of the space age. Suitable for high school and college students and the general reader. -
Oberg, James E. Red Star in Orbit. New York: Random House, 1981. An account of Soviet space exploration that attempts to penetrate the secrecy that has surrounded the Soviet space program. The primary emphasis is on manned space exploration. -
Von Braun, Wernher, Frederick I. Ordway III, and David Dooling. Space Travel: A History. Rev. ed. New York: Harper & Row, 1985. A comprehensive history of space exploration, with lengthy coverage of the early history of rocketry. The emphasis is on manned spaceflight, but there is a good summary of planetary missions.
Mariner 10 Uses the Gravitational Pull of One Planet to Reach Another
Voyagers 1 and 2 Explore the Outer Planets
Magellan Probe Maps Venus