Mariner 8 & 9
Launch (Mariner 9): May 30, 1971
Arrival (Mariner 9): November 13, 1971
Mariner 8 and 9 were the third and final pair of Mars missions in NASA's Mariner series of the 1960s and early 1970s. Both were designed to be the first Mars orbiters, marking a transition in our exploration of the red planet from flying by the planet to spending time in orbit around it.
Unfortunately, Mariner 8 failed during launch on May 8, 1971. Mariner 9 was launched successfully on May 30, 1971, and became the first artificial satellite of Mars when it arrived and went into orbit, where it functioned in Martian orbit for nearly a year. Mariner 9 complete its final transmission October 27, 1972.
Upon arrival, Mariner 9 observed that a great dust storm was obscuring the whole globe of the planet. Ground controllers sent commands to the spacecraft to wait until the storm had abated, the dust had settled, and the surface was clearly visible before compiling its global mosaic of high-quality images of the Martian surface. The storm persisted for a month, but after the dust cleared, Mariner 9 proceeded to reveal a very different planet than expected -- one that boasted gigantic volcanoes and a grand canyon stretching 4,800 kilometers (3,000 miles) across its surface. More surprisingly, the relics of ancient riverbeds were carved in the landscape of this seemingly dry and dusty planet. Mariner 9 exceeded all primary photographic requirements by photo-mapping 100 percent of the planet's surface. The spacecraft also provided the first closeup pictures of the two small, irregular Martian moons: Phobos and Deimos.