Valles Marineris on Mars is the longest and deepest canyon in the Solar System. The deep gash in the side of Mars is a pretty good companion for the tallest mountain in the Solar System, Olympus Mons, which also on Mars. The pair demonstrate the world of extremes that is the Red Planet. Valles Marineris is 4,000 km long, 200 km wide at points, and up to 7 km deep. It runs along the Martian equator and covers nearly a quarter of the planet’s circumference and 59% of its diameter. The Valles Marineris system is a network of interconnected valleys that begin in the west. Noctis Labyrinthus is considered the starting point of the system, then it moves east to include the Tithonium chasmata and Ius chasmata. In the mid region are the Melas, Ophir, Coprates, Ganges, Capri, and Eos chasmata. The canyon moves through an area of chaotic terrain(ridges, cracks, and plains jumbled together)before it ends in the basin region of Chryse Planitia. One of the largest debates surrounding the area is about how it formed. In the 1970s, erosion by water and/or melting permafrost were popular theories. Liquid water can not exist in current Martian conditions, but has in the past, making the feature billions of years old. Another theory from the 1970s was that the feature formed when subsurface magma withdrew from the area. At the end of 1989, a theory emerged that it was formed by tensional fracturing. The theory most widely shared today is that it formed by rift faults and was made bigger by erosion and the collapsing of the rift walls. A rift valley is usually formed between two mountain ranges and is caused by the formation of the mountains. In this case, the formation is tied to the Tharsis Bulge. Valles Marineris is named after NASA’s Mariner 9 spacecraft, which first photographed it up close in 1971-1972. Mariner 9 was the first spacecraft to orbit another planet, just ahead of the Soviet space program’s twin missions Mars 2 and Mars 3. Valles Marineris on Mars is the focus of many astrogeologists because of its tantalizing view into the Martian geologic past. Evidence within the valley also points to a much wetter and warmer climate on Mars millenia ago. You can be sure that scientists will be looking for more clues in every set of data from the area.