Mariner 9 in the context of Fretted terrain

Valles Marineris (/ˈvælɪs mærɪˈnɛərɪs/; Latin for Mariner Valleys, named after the Mariner 9 Mars orbiter of 1971–72 which discovered it) is a system of canyons that runs along the Martian surface east of the Tharsis region. At more than 4,000 km (2,500 mi) long, 200 km (120 mi) wide and up to 7 km (23,000 ft) deep, Valles Marineris is the largest canyon in the Solar System.

Valles Marineris is located along the equator of Mars, on the east side of the Tharsis Bulge, and stretches for nearly a quarter of the planet's circumference. The canyon system starts in the west with Noctis Labyrinthus; proceeding to the east are Tithonium and Ius chasmata, then Melas, Candor and Ophir chasmata, then Coprates Chasma, then Ganges, Capri and Eos chasmata; finally it empties into an outflow channel region containing chaotic terrain that ends in the basin of Chryse Planitia.

Mariner 10 was an American robotic space probe launched by NASA on 3 November 1973, to fly by the planets Mercury and Venus. It was the first spacecraft to visit Mercury and the first to perform a flyby of multiple planets.

Mariner 10 was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program. (Mariner 11 and Mariner 12 were allocated to the Voyager program and redesignated Voyager 1 and Voyager 2.)

Volcanic activity, or volcanism, has played a significant role in the geologic evolution of Mars. Scientists have known since the Mariner 9 mission in 1972 that volcanic features cover large portions of the Martian surface. These features include extensive lava flows, vast lava plains, and, such as Olympus Mons, the largest known volcanoes in the Solar System. Martian volcanic features range in age from Noachian (>3.7 billion years) to late Amazonian (< 500 million years), indicating that the planet has been volcanically active throughout its history, and some speculate it probably still is so today. Both Mars and Earth are large, differentiated planets built from similar chondritic materials. Many of the same magmatic processes that occur on Earth also occurred on Mars, and both planets are similar enough compositionally that the same names can be applied to their igneous rocks.

The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA's Jet Propulsion Laboratory (JPL) designed and built 10 robotic interplanetary probes named Mariner to explore the inner Solar System – visiting the planets Venus, Mars and Mercury for the first time, and returning to Venus and Mars for additional close observations.

The program included a number of interplanetary firsts, including the first successful planetary flyby, the planetary orbiter, and the first gravity assist maneuver. Of the 10 vehicles in the Mariner series, seven were successful, forming the starting point for many subsequent NASA/JPL space probe programs. The planned Mariner Jupiter-Saturn vehicles were adapted into the Voyager program, while the Viking program orbiters were enlarged versions of the Mariner 9 spacecraft. Later Mariner-based spacecraft include Galileo and Magellan, while the second-generation Mariner Mark II series evolved into the Cassini–Huygens probe.

Noctis Labyrinthus (Latin for 'Labyrinth of the Night') is a region of Mars located in the Phoenicis Lacus quadrangle, between Valles Marineris and the Tharsis upland. The region is notable for its maze-like system of deep, steep-walled valleys. The valleys and canyons of this region formed by faulting and many show classic features of grabens, with the upland plain surface preserved on the valley floor. In some places the valley floors are rougher, disturbed by landslides, and there are places where the land appears to have sunk down into pit-like formations. It is thought that this faulting was triggered by volcanic activity in the Tharsis region. Research described in December 2009 found a variety of minerals, including clays, sulfates, and hydrated silicas, in some of the layers.

Don Edward Wilhelms (born July 5, 1930) is a former United States Geological Survey geologist who contributed to geologic mapping of the Earth's moon and to the geologic training of the Apollo astronauts. He is the author of To a Rocky Moon: A Geologist's History of Lunar Exploration (1993), The geologic history of the Moon (1987), and he co-authored the Geologic Map of the Near Side of the Moon (1971) with John F. McCauley. Wilhelms also contributed to Apollo Over the Moon: A View from Orbit (NASA SP-362). He has also contributed to the study of Mars (including Mariner 9), Mercury, and Ganymede.