The greatest known canyon system in the solar system is Valles Marineris, an immense geological feature that cuts across the equatorial region of Mars. Discovered by the Mariner 9 orbiter in the early 1970s, this colossal rift valley is a defining element of the Martian surface. Its vast dimensions and complex structure offer scientists a deep look into the geological history and powerful internal forces that shaped the Red Planet. The size of Valles Marineris helps in understanding the differences between Earth’s dynamic crust and the massive tectonic events that occurred on Mars.
Valles Marineris: Location and Scale
Valles Marineris is positioned just south of the Martian equator and stretches eastward from the edge of the Tharsis volcanic bulge, a massive, elevated region that hosts the planet’s largest volcanoes. This placement suggests a direct link between the forces that built the Tharsis rise and the formation of the canyon system. The sheer size of this planetary-scale scar is difficult to comprehend, extending for over 4,000 kilometers, nearly a quarter of the circumference of Mars.
The width of the canyon varies significantly, averaging about 200 kilometers, but expanding to more than 600 kilometers in some areas. Valles Marineris plunges to staggering levels, reaching up to 7 kilometers below the surrounding plains in its deepest sections. Some measurements suggest depths approaching 10 kilometers in localized areas, making the walls of the rift far higher than Mount Everest is tall above sea level.
The westernmost extension begins in a chaotic, fractured region known as Noctis Labyrinthus, or the “Labyrinth of the Night.” From there, the system extends into a series of interconnected trenches, or chasmata, before terminating in the eastern plains near the Chryse Planitia basin. These dimensions establish Valles Marineris as the largest known canyon system in the solar system.
Internal Geological Features
The canyon system is not a single, continuous valley but rather an intricate network of distinct, named depressions. Major trenches, such as Ius Chasma, Tithonium Chasma, Melas Chasma, and Candor Chasma, combine to form the overall Valles Marineris structure. The walls of these individual chasmata exhibit evidence of massive structural failure and gravitational collapse.
The floors of the canyon are often covered in enormous landslide deposits, some traveling over 100 kilometers from the canyon rim. The steep cliff faces reveal numerous distinct geological layers, often referred to as interior layered deposits. These layers are thought to be ancient sedimentary materials, possibly deposited when the canyons held standing bodies of water or ice, or they may be volcanic ash and dust.
Structural evidence, such as the presence of grabens and fault scarps, indicates that the system is fundamentally a large tectonic rift. The parallel nature of several major trenches, like Ius and Tithonium, points to the underlying crust being pulled apart by tensional stresses. In the eastern sections, chaotic terrain suggests areas where the ground collapsed after subsurface water or ice drained away.
Theories of Origin
The prevailing scientific explanation for the formation of Valles Marineris centers on the geological forces exerted by the Tharsis volcanic province. Tharsis is an enormous bulge on the Martian surface, and as it formed, its mass and uplift placed tremendous stress on the surrounding lithosphere. This stress caused the planet’s crust to stretch and fracture, leading to the formation of gigantic rift faults.
This theory posits that Valles Marineris began as a great “crack” in the Martian crust, a vast network of fractures formed by strain radiating outward from the Tharsis bulge. This initial tectonic rifting created the foundational structure, which was then modified and enlarged. The concept is similar to the formation of rift valleys on Earth, though Mars lacks a global system of plate tectonics.
Other hypotheses suggest additional processes played a role in shaping the canyon. Some scientists proposed that the withdrawal of subsurface magma led to the collapse of the overlying crust. While initial rifting is widely accepted, the canyon’s features also show modification from erosion, possibly involving liquid water or carbon dioxide. These erosional processes, combined with massive landslides, worked to widen the initial fractures over time.
Comparing Valles Marineris to Earth’s Canyons
To appreciate the scale of Valles Marineris, a comparison to Earth’s most famous canyon system, the Grand Canyon, is useful. The Grand Canyon is approximately 446 kilometers long, making the Martian system nearly ten times longer. If Valles Marineris were placed on Earth, it would stretch across the entire continental United States, reaching from the Atlantic to the Pacific coasts.
The depth difference is striking; the Grand Canyon descends about 1.6 kilometers at its deepest point, while Valles Marineris reaches up to 7 kilometers or more. The Martian feature is over four times deeper than its terrestrial counterpart. The Grand Canyon was carved primarily by the erosive action of the Colorado River, a process fundamentally different from the tectonic rifting that formed Valles Marineris.
The width comparison is also stark, with Valles Marineris being up to 20 times wider than the Grand Canyon’s average width. The scale means that if a person were standing on the floor in the center of Valles Marineris, the canyon walls would be below the horizon and completely invisible. This feature is a testament to the powerful geological forces that once dominated the Red Planet.