Mariner 9 Is the First Spacecraft to Orbit Another Planet

Mariner 9 was launched on May 30, 1971; between September, 1971, and October, 1972, Mariner 9 sent back to Earth a wealth of close-up photographs of Mars and many other data essential to interplanetary exploration.

Summary of Event

On September 22, 1971, an unmanned American spacecraft designated Mariner 9 successfully achieved orbit around the planet Mars at an altitude of 1,398 kilometers. Over the next thirteen months, television relays aboard the satellite sent back almost three thousand high-quality, close-up photographs of Mars’s surface that, along with other data recorded by sophisticated scientific equipment on board the Mariner, revolutionized scientific knowledge about Mars, about planetary development and the evolution of the solar system, and about Earth. The information gathered by the Mariner 9 mission represented an indispensable step in humankind’s exploration of outer space. It also produced a completely unexpected dividend in the form of increased cooperation between space scientists in the United States and their counterparts in the Soviet Union, one of the small steps toward easing international tensions and reducing the threat of nuclear war. Mariner program
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[kw]Mariner 9 Is the First Spacecraft to Orbit Another Planet (May 30, 1971-Oct. 27, 1972)
[kw]First Spacecraft to Orbit Another Planet, Mariner 9 Is the (May 30, 1971-Oct. 27, 1972)
[kw]Spacecraft to Orbit Another Planet, Mariner 9 Is the First (May 30, 1971-Oct. 27, 1972)
[kw]Orbit Another Planet, Mariner 9 Is the First Spacecraft to (May 30, 1971-Oct. 27, 1972)
[kw]Planet, Mariner 9 Is the First Spacecraft to Orbit Another (May 30, 1971-Oct. 27, 1972)
Mariner program
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[g]North America;May 30, 1971-Oct. 27, 1972: Mariner 9 Is the First Spacecraft to Orbit Another Planet[00310]
[g]United States;May 30, 1971-Oct. 27, 1972: Mariner 9 Is the First Spacecraft to Orbit Another Planet[00310]
[c]Spaceflight and aviation;May 30, 1971-Oct. 27, 1972: Mariner 9 Is the First Spacecraft to Orbit Another Planet[00310]
[c]Science and technology;May 30, 1971-Oct. 27, 1972: Mariner 9 Is the First Spacecraft to Orbit Another Planet[00310]
Briggs, Geoffrey Arthur
Levinthal, Elliot Charles
Leovy, Conway B.
McCauley, John Francis
Pollack, James B.
Sagan, Carl
Smith, Bradford A.
Vaucouleurs, Gérard Henri de

It is not surprising that Mars has received more attention from space scientists than any other planetary body. Since the inception of modern astronomy in the sixteenth century, both scientists and the writers of speculative fiction have identified Mars as the most likely of the planets to bear Earth-like life. Beginning with H. G. Wells and Edgar Rice Burroughs, modern science-fiction writers have made the Red Planet the abode of a host of fantastic sentient creatures. Their imaginary Martians were hardly more startling than the assertions by prominent astronomers such as Percival Lowell in the earlier part of the twentieth century that an ancient race of Martians were engaged in a massive irrigation project on their dying world, their canals clearly visible through the most powerful Earth telescopes on particularly clear nights.

The Mariner 9 mission was the fifth and most ambitious of the Mariner missions designed to gather information concerning Mars. Three earlier missions, Mariner 4 in 1965 and Mariners 6 and 7 in 1969, had achieved close flybys of Mars. All three spacecraft sent back photographs of parts of Mars’s surface and limited data concerning Martian surface conditions. The information gained by the three missions was enormously interesting, but incomplete. Consequently, American space scientists began planning a space mission that they hoped would answer many of the perplexing questions concerning Mars.

National Aeronautics and Space Administration (NASA) officials authorized the Mariner 8 and 9 projects in 1968. NASA scientists planned the missions to take place during the next “window” period (a “window” is what astronomers call a period of time during which two heavenly bodies are in the most favorable relative positions to facilitate travel between them) in 1971. NASA scientists planned six objectives to be performed by the Mariners over a period of three months after they achieved orbit. These objectives included the relay of photographs of almost the entire Martian surface to Earth, along with data concerning Martian atmospheric content and surface temperatures. To design experiments to achieve the objectives, NASA officials selected scientists to form several different teams and task forces and appointed a principal investigator to head each one. The principal investigators included Conway B. Leovy, John Francis McCauley, James B. Pollack, Carl Sagan, and Gérard Henri de Vaucouleurs. The task group leaders were Geoffrey Arthur Briggs, Elliott Charles Levinthal, and Bradford A. Smith. These team and task force leaders coordinated their efforts with those of the scientists and engineers responsible for designing the spacecraft and launching them into Martian orbit.

The specifics of the plan that eventually evolved called for two virtually identical spacecraft to be inserted into Martian orbit, one with a periapsis (closest approach to the planet) of 1,250 kilometers with an inclination of 80 degrees to Mars’s equator, the second with a periapsis of 850 kilometers and a 50 degree inclination. NASA scientists expected three thousand photographs from the two spacecraft, which would permit virtually the entire surface of the planet to be mapped. The other scientific equipment aboard the Mariners would permit much more sensitive analyses of the surface and high-altitude atmospheric conditions on Mars than were possible with the earlier flyby missions.

The design of the two spacecraft was very similar to that of Mariners 6 and 7. The major difference was the large rocket engines necessary to insert Mariners 8 and 9 into Martian orbit. At the same time, other NASA scientists and engineers built new facilities to track the mission and record and interpret the data sent back by the spacecraft. Mission controllers also evolved plans for emergency changes in the mission plans if something should go wrong, or in the event of unexpected discoveries. Subsequent events proved the wisdom of those contingency plans. NASA personnel moved Mariners 8 and 9 from the Jet Propulsion Laboratory Jet Propulsion Laboratory in California, where they were built, to the Kennedy Space Center in Florida early in 1971. Technicians at the Kennedy Space Center launched Mariner 8 aboard a Centaur rocket on May 9, 1971, only to witness its crash into the Atlantic Ocean 563 kilometers northwest of Puerto Rico, caused by a malfunction in the rocket’s guidance system. Project scientists immediately began implementing contingency plans that resulted eventually in Mariner 9 accomplishing almost all of the goals originally set for the two spacecraft. Scientists chose a new orbit with an 11.98-hour orbital period, a periapsis of 1,250 kilometers, and a 65 degree inclination. This orbit permitted Mariner 9 to observe and photograph almost as much of the Martian surface as would have been possible had both Mariners achieved Martian orbit.

The Kennedy Space Center personnel successfully launched Mariner 9 on May 30, 1971. Six days later, launch mission control scientists made a correction in the spacecraft’s trajectory that delivered it into orbit around Mars 167 days later. The hoped-for results of the mission, however, were not immediately forthcoming. More than three months after Mariner’s launch and almost two months before it achieved Martian orbit, astronomers detected a problem on the surface of Mars that might prevent Mariner 9 from achieving most of its objectives. The problem was a gigantic dust storm that eventually grew to the point that the entire planet was shrouded by a huge cloud of dust. The storm was not unprecedented. Astronomers had observed similar but smaller storms on Mars during other close approaches in preceding years, but it was sheer bad luck that such an enormous storm should occur just as Mariner 9 approached orbit around the Red Planet.

The Mariner 9 spacecraft did the work for both the Mariner 8 and 9 missions. As the first artificial satellite of another planet, Mars, it experienced a Martian dust storm, measured the two Martian moons, and mapped the entire planet in less than a year.


When the spacecraft sent back its first photographs of Mars as it approached orbit on November 8, 12, and 13, no details of the planet’s surface could be discerned through the dust except several dark spots that were identified eventually as high mountain peaks. After Mariner 9 achieved orbit, the photographs it relayed to Earth showed virtually nothing of Mars’s surface, only the dust storm itself. The other equipment aboard the spacecraft was able to perform measurements of the Martian atmosphere, but not to the degree originally planned.

Fortunately for the Mariner 9 mission, NASA ground control was able to control equipment aboard the spacecraft. They delayed the photography of the planet’s surface and other tests until the dust storm abated. Space scientists in the Soviet Union were not so fortunate. On November 13, 1971, officials in the Soviet Union announced that their space program five months earlier had launched two spacecraft toward Mars with even more ambitious objectives than those of Mariner 9. The Soviet spacecraft—designated Mars 2 and Mars 3—both contained soft-landing components that were to separate from the orbital craft and parachute to the Martian surface. The landing craft would then relay photographs of the Martian surface and data concerning surface conditions to Earth via the orbiters.

Mars 2 achieved Martian orbit on November 27 and separated into its two components. The landing component of Mars 2 became the first known human-made object to land on Mars, but it apparently crash-landed and never transmitted the hoped-for data. Mars 3 arrived in Martian orbit three days later and successfully separated its landing component. The lander soft-landed on Mars but ceased transmitting signals less than two minutes later for unknown reasons. The Mars 2 and Mars 3 orbiters were designed to take all their pictures immediately after arriving in orbit and thus transmitted nothing to their designers but pictures of the raging dust storm with no surface features of the planet visible. The Soviet Mars missions of 1971 thus failed to accomplish most of their objectives.

The more flexible Mariner 9, however, exceeded the most optimistic expectations of its designers. Mariner 9 continued to send information to Earth until October 27, 1972, 516 days after leaving Earth. On that date, its supply of attitude control gas depleted, it tumbled out of control. Significantly, U.S. space scientists shared the information with their Soviet counterparts under an agreement reached by the governments of the two nations on October 20, 1971, while Mariner 9, Mars 2, and Mars 3 were still en route to Mars.


The Mariner 9 mission represents a significant step in humankind’s painfully slow attempt to reach the stars. The mission achieved a number of firsts in space exploration, revolutionized scientific understanding of Mars and of planetary evolution, and furnished information essential to the success of subsequent American and Soviet missions to Mars. Mariner 9 also occasioned an important bridging of the ideological chasm between the United States and the Soviet Union.

Mariner 9 was the first Earth-built spacecraft to orbit another planet. The photographs it relayed to Earth allowed the first accurate mapping of the surface of another planet. While waiting for the dust storm to clear, it relayed the first close-up photographs of Mars’s two satellites, Phobos and Deimos. After the dust storm cleared, the cameras aboard the spacecraft photographed almost the entire surface of Mars. When the nearly three thousand photographs arrived on Earth, they forced a complete reevaluation of Mars by NASA scientists. In addition to evidence of recent volcanism and photographs of a huge canyon that dwarfs the Grand Canyon in Arizona, the pictures relayed to Earth by Mariner 9 provided positive indications that some form of liquid (presumably water) once flowed freely on the Martian surface. The flowing liquid carved typical river valley channels in many areas of Mars.

Other equipment aboard Mariner 9 detected water vapor and oxygen in the Martian atmosphere in much greater quantities than predicted by NASA experts. Other instruments determined that the Martian atmosphere had at some time in the past been denser than is currently the case. These data, together with the evidence for free-flowing liquid on the Martian surface, led NASA scientists to conclude that Mars at some time in the past had a much more Earth-like atmosphere, very possibly conducive to the evolution of life. This conclusion raises a chilling question: What happened on Mars to transform it into the barren and apparently lifeless planet revealed by Mariner 9’s cameras and by subsequent Viking space probes? Scientists wondered if something similar could happen to Earth.

Mariner 9’s success, coupled with the failure of the Soviet spacecraft, revealed the necessity of flexibility in the programming of subsequent space probes. Equally important, the pictures Mariner 9 transmitted to Earth permitted NASA scientists to choose the most favorable locations for the Viking missions Viking (spacecraft)
National Aeronautics and Space Administration;Viking missions that soft-landed scientific equipment on Mars several years later. Mariner 9 thus became an indispensable step in the continuing human efforts to explore the planets of the solar system. The data transmitted by Mariner 9 were also of great importance to the Soviet space program and of great importance to world peace. The information-sharing agreement reached during Mariner’s voyage has since been expanded and extended to areas other than space exploration.

Finally, the success of the Mariner 9 mission greatly stimulated public interest in the space program in the United States. That interest, and the congressional support it generated in the United States, accelerated the NASA program of unmanned planetary exploration. Mariner program
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Further Reading

  • 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.
  • Ezell, Edward Clinton, and Linda Neuman Ezell. On Mars: Explorations of the Red Planet, 1958-1978. NASA SP-4212. Washington, D.C.: Scientific and Technical Information Office, NASA, 1984. A summary of everything learned about Mars through 1978 from the various space missions of the United States and the Soviet Union. Contains numerous photographs and technical drawings of Mars and the space vehicles sent there from Earth. Concentrates on U.S. accomplishments, but evaluates Soviet contributions to Martian exploration. Suitable for all audiences.
  • Firsoff, Valdemar Axel. The New Face of Mars. Hornchurch, England: Ian Henry, 1980. Contains a short history of astronomical observations of Mars and conjectures based on these observations. Shows how those conjectures have evolved with the ever-increasing knowledge about Mars. Contains some photographs. Suitable for readers from high school level through adult.
  • Greeley, Ronald. Planetary Landscapes. 2d ed. New York: Chapman & Hall, 1994. Discusses the origin, surface features, and evolution of all the inner planets in the light of discoveries made through space exploration. Especially valuable in putting planetary features of Mars into the context of the other planets of the solar system. Contains many maps and photographs. Suitable for high school and college readers.
  • Hartmann, William K., and Odell Raper. The New Mars: The Discoveries of Mariner 9. NASA SP-337. Washington, D.C.: Scientific and Technical Information Office, NASA, 1974. Contains an account of speculations concerning Mars before Mariner 9, and a brief account of earlier Mars space missions. Valuable for a sophisticated analysis of the data sent to Earth by Mariner 9 in nontechnical language. Includes many Mariner 9 photographs.
  • National Aeronautics and Space Administration. Mars As Viewed by Mariner 9: A Pictorial Presentation by the Mariner 9 Television Team and the Planetology Program Principal Investigators. NASA SP-329. Washington, D.C.: Scientific and Technical Information Office, NASA, 1974. Contains a brief account of the Mariner 9 mission and most of the photographs sent back to Earth during the mission. Photographs are accompanied by expert analysis. Recommended for all audiences.
  • Sheldon, Charles S. United States and Soviet Progress in Space: Summary Data Through 1972 and a Forward Look. Washington, D.C.: U.S. Government Printing Office, 1973. Overview of the space exploration efforts of the United States and the Soviet Union, with particular reference to the Mariner 9 and Mars 2 and 3 missions. Offers speculation about the nature and scope of future missions and the possibility of U.S.-Soviet cooperation in space exploration.

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