Valles Marineris is a massive canyon system stretching across the surface of Mars, spanning over 3,000 kilometers long, up to 600 kilometers wide, and plunging as deep as 8 kilometers. It is the largest known canyon in the solar system, dwarfing Earth’s Grand Canyon by every measure. If placed on Earth, it would stretch from New York to Los Angeles.
How It Compares to Earth’s Grand Canyon
The Grand Canyon is roughly 2 kilometers deep. Valles Marineris reaches depths of 10 to 15 kilometers in some estimates, making it five to seven times deeper. In length, the Martian canyon is about ten times longer. It’s wide enough in places to swallow entire mountain ranges: the broadest section, Melas Chasma, stretches 290 kilometers across, while the Capri-Eos area reaches 390 kilometers. The narrowest parts still measure around 10 kilometers wide.
How the Canyon Formed
Valles Marineris didn’t form the way the Grand Canyon did. The Grand Canyon was carved by a river over millions of years. Valles Marineris was ripped open by tectonic forces. The leading explanation centers on the Tharsis Rise, an enormous volcanic bulge on the Martian surface that includes some of the largest volcanoes in the solar system. As the Tharsis region swelled upward, it stretched and fractured the crust along its crest. The canyon system sits directly along that crest.
The initial fractures developed as parallel faults. Over time, blocks of crust between those faults sank downward, forming elongated trench-like features called grabens. Rifting, wall collapse, and subsidence widened and deepened the chasms further. The faulting extends deep into the planet’s outer rocky shell, which helps explain the extraordinary depth. Water erosion likely played a secondary role, reshaping the canyon walls and floors after the initial fractures opened.
The 12 Canyons Within the System
Valles Marineris isn’t a single canyon. It’s a network of 12 distinct troughs, each with its own name and character. Seven of them (Ius, Ophir, Candor, Melas, Coprates, Capri, and Eos Chasmata) are interconnected through the central corridor. Two more connect from the ends: Tithonium Chasma links in from the west, and Ganges Chasma joins from the east through chaotic terrain. One canyon, Hebes Chasma, is entirely enclosed with no connection to the others. Two more, Echus and Juventae Chasmata, open directly northward into the Martian plains through outflow channels.
The deepest sections are Candor and Coprates Chasmata, reaching approximately 10 kilometers. The shallowest are Echus and Tithonium Chasmata, dropping only a few kilometers.
From the Labyrinth to the Chaos
The western end of Valles Marineris begins at a region called Noctis Labyrinthus, or “Labyrinth of the Night.” It’s a dense maze of intersecting fractures and canyons, some 5,000 meters deep, formed by the same tectonic stress that created the main canyon system. The upper crust here is heavily fractured, with debris piled at the bottom of trenches and younger rock formations visible along the upper edges. It’s a visual preview of the forces that shaped the entire system.
The eastern end tells a different story. Here, the canyon system transitions into what geologists call chaotic terrain: jumbled, broken landscapes where the ground appears to have collapsed. From this chaotic terrain, several massive outflow channels (Shalbatana, Simud, Tiu, and Ares Valles) drain northward into the Chryse basin. These channels are strong evidence that enormous volumes of water once flowed out of the canyon system and across the Martian surface. Tiu and Simud Valles form a complex network of connected channel floors and collapsed ground that extends south into eastern Valles Marineris itself.
Signs of Ancient Water
Mineral deposits found in and around Valles Marineris point to a wetter past. Orbital instruments have detected hydrated sulfates and hydrated silica in thin, layered deposits surrounding the canyon. These minerals form in the presence of liquid water. Thicker layered deposits containing sulfates mixed with iron-bearing minerals line portions of the canyon interior. Some highland craters nearby hold deposits of sulfates alongside clay minerals, further suggesting prolonged contact with water. Based on the chemistry and age of these deposits, some environments within and near the canyon may have had conditions suitable for microbial life during Mars’s earliest era, over 3.5 billion years ago.
Hidden Water Beneath the Surface
In 2021, the European Space Agency’s Trace Gas Orbiter made a striking discovery. Using a neutron detector that can sense hydrogen in the top meter of Martian soil, the orbiter found a region in the central part of Valles Marineris where up to 40% of the near-surface material appears to be water. The water-rich zone is roughly the size of the Netherlands and overlaps with an area called Candor Chaos.
This water most likely exists as ice, similar to permafrost on Earth, where frozen water persists permanently beneath dry soil due to constant low temperatures. Previous instruments couldn’t detect it because it sits beneath a layer of dust. The find is notable not just scientifically but practically: a shallow, accessible reservoir of water ice in an equatorial region of Mars could be significant for future exploration, since most known Martian ice deposits are locked near the poles.
Why the Canyon Is So Large
One question that comes up naturally is why Mars has a canyon so much larger than anything on Earth. Part of the answer is that Mars lacks plate tectonics. On Earth, tectonic stress gets distributed across many plate boundaries, producing numerous smaller features around the globe. On Mars, the stress from the Tharsis bulge concentrated along a single zone and had nowhere else to go. The dome shape of the Tharsis Rise also enhanced the crust’s ability to crack along its highest point, much like the top of a loaf of bread splitting as it rises. Lower gravity on Mars (about 38% of Earth’s) allowed canyon walls to grow taller before collapsing, contributing to the extreme depth. The result is a single feature of almost incomprehensible scale, visible from orbit as a scar stretching nearly a quarter of the way around the planet.