The U.S. unmanned space probe Mariner 9 is launched on a mission to gather scientific information on Mars, the fourth planet from the sun. The 1,116-pound spacecraft entered the planet’s orbit on November 13, 1971, and circled Mars twice each day for almost a year, photographing the surface and analyzing the atmosphere with infrared and ultraviolet instruments. It gathered data on the atmospheric composition, density, pressure, and temperature of Mars, and also information about the surface composition, temperature, and topography of the planet.

When Mariner 9 first arrived, Mars was almost totally obscured by dust storms, which persisted for a month. However, after the dust cleared, Mariner 9 proceeded to reveal a very different planet–one that boasted enormous volcanoes and a gigantic canyon stretching 3,000 miles across its surface. The spacecraft’s cameras also recorded what appeared to be dried riverbeds, suggesting the ancient presence of water and perhaps life on the planet. The first spacecraft to orbit a planet other than earth, Mariner 9 sent back more than 7,000 pictures of the “Red Planet” and succeeded in photographing the entire planet. Mariner 9 also sent back the first close-up images of the Martian moon. Its transmission ended on October 27, 1972.