Mars has the most dramatic surface features of any rocky planet in the solar system, including the tallest volcano, the deepest canyon, and one of the largest impact craters ever discovered. Its landscape divides into two strikingly different halves: ancient, cratered highlands in the south and smooth, low-lying plains in the north, separated by an elevation difference of roughly 5 kilometers. That split, called the crustal dichotomy, is one of the oldest visible features on the planet and shapes nearly everything else about Martian geography.
The Hemispheric Divide
If you could stand on Mars and walk from south to north, you’d cross a dramatic boundary. The southern highlands are heavily cratered, ancient, and sit kilometers higher than the northern lowlands. The northern half is smoother, younger, and lower in elevation. The crust beneath the southern highlands is roughly 26 kilometers thicker than under the northern plains. Scientists still debate what caused this global asymmetry. Leading theories include a massive ancient impact that reshaped the entire northern hemisphere or deep internal convection early in the planet’s history. Either way, this two-faced structure is the foundation on which every other Martian surface feature sits.
Olympus Mons and the Tharsis Volcanoes
Mars is home to the largest known volcano in the solar system. Olympus Mons rises 23 kilometers above the surrounding terrain, more than twice the height of Earth’s Mauna Loa measured from the ocean floor. Its base stretches roughly 600 kilometers across, wide enough to cover most of Arizona. The volcano is a shield type, meaning it built up gradually from fluid lava flows rather than explosive eruptions, giving it a broad, gently sloping profile.
Olympus Mons sits near the western edge of the Tharsis bulge, a continent-sized volcanic plateau that dominates the planet’s western hemisphere. Three additional massive shield volcanoes line up along the bulge’s spine: Arsia Mons, Pavonis Mons, and Ascraeus Mons. Each one is 350 to 400 kilometers in diameter and towers about 17 kilometers above the surrounding plain. They sit roughly 700 kilometers apart, aligned along what appears to be a buried fracture zone. North of these peaks, the broader, lower-profile Alba Mons rounds out the Tharsis region. This entire area represents the most intensely volcanic region Mars has ever produced.
Mars lacks tectonic plates, which is a key reason its volcanoes grew so enormous. On Earth, a moving plate carries a volcano away from its magma source, creating chains of smaller peaks like the Hawaiian Islands. On Mars, magma kept feeding the same spot for hundreds of millions of years, piling lava higher and wider.
Valles Marineris
Stretching more than 3,000 kilometers across the Martian equator, Valles Marineris is the largest canyon system in the solar system. It spans as much as 600 kilometers across in places and plunges up to 8 kilometers deep. For comparison, the Grand Canyon is about 450 kilometers long, 30 kilometers wide, and less than 2 kilometers deep. Valles Marineris would stretch from New York to Los Angeles.
Unlike the Grand Canyon, which was carved primarily by flowing water, Valles Marineris likely formed as the Tharsis bulge swelled upward billions of years ago, cracking the crust apart. Tectonic stretching opened the rift, and subsequent landslides, possible water erosion, and collapse widened and deepened it over time. Some sections show layered sedimentary deposits that hint at ancient lakes pooling inside the canyon.
Impact Craters
Mars is covered in impact craters, particularly across the southern highlands where ancient surfaces have been preserved for billions of years. The most impressive is Hellas Planitia, a basin roughly 2,250 kilometers (about 1,400 miles) in diameter that reaches the lowest elevations on the planet. It is one of the largest impact craters in the entire solar system, formed by an enormous asteroid collision early in Martian history. The floor of Hellas sits so deep that atmospheric pressure there is noticeably higher than on the surrounding plains, occasionally allowing conditions where liquid water could briefly exist at the surface.
Other notable craters include Jezero Crater, where NASA’s Perseverance rover is currently working. Jezero is far smaller than Hellas but scientifically rich because it preserves a fan-shaped river delta where water once flowed into an ancient lake, depositing layers of sediment. Craters like these act as natural time capsules, preserving rock layers and mineral deposits that reveal what conditions were like billions of years ago.
Evidence of Ancient Water
Dry river channels, lake beds, and sedimentary deltas scattered across the surface tell a clear story: Mars once had significant amounts of liquid water. The delta inside Jezero Crater is one of the best-preserved examples. Billions of years ago, a river flowed into this crater lake, depositing rocks and sediments in the classic fan shape seen from orbit. Perseverance has been studying these sedimentary layers up close.
In early 2025, Perseverance climbed to the rim of Jezero Crater and began finding rocks with striking compositions. One sample, cored from a rock called “Shallow Bay,” likely formed at least 3.9 billion years ago during Mars’ earliest geologic period. Another rock, dubbed “Tablelands,” turned out to be made almost entirely of serpentine minerals, which only form when large amounts of water react with iron- and magnesium-bearing minerals in igneous rock. A third sample, from a rock called “Main River,” displayed alternating bright and dark bands unlike anything the science team had seen before. These finds paint a picture of a planet where water was once abundant enough to chemically transform the rock itself.
The Red Surface
Mars gets its iconic red color from iron oxide minerals in its soil and dust. The surface material has a basaltic composition, similar to volcanic rock on Earth, but is enriched with nanophase iron oxides, extremely fine-grained particles of rust-like minerals including forms of hematite and goethite. These particles are tiny, just 1 to 3 micrometers across, and coat virtually everything on the surface. Wind has distributed this fine dust globally, giving the entire planet its uniform reddish hue even in areas with different underlying rock types.
Beneath the dust, the soil contains minerals you’d expect from volcanic origins: olivine, pyroxene, and magnetite. Roughly 15 to 25 percent of Martian soil is made up of clay-sized particles, and the grains tend to have irregular shapes with rounded edges worn smooth by billions of years of wind erosion. The soil is also unusually rich in sulfur and chlorine compared to Mars’ crustal rocks, a signature of chemical weathering in an environment very different from Earth’s.
Polar Ice Caps
Both poles of Mars have bright white ice caps that change dramatically with the seasons. The northern polar cap, called Planum Boreum, consists of thick layered deposits of nearly pure water ice with less than 5 percent dust mixed in. Beneath these clean ice layers sits a sand-rich base that may contain around 55 percent water ice blended with fine rock particles. The total structure is a layered record of climate cycles, somewhat like ice cores on Earth.
The southern cap is smaller and behaves differently. It retains a thin layer of frozen carbon dioxide (dry ice) year-round, while the northern cap’s dry ice covering sublimates completely each summer, exposing the water ice underneath. During winter at either pole, temperatures drop low enough to freeze carbon dioxide directly out of the atmosphere, dramatically expanding the cap’s visible area. This seasonal freezing and thawing of carbon dioxide means Mars’ atmospheric pressure fluctuates by as much as 25 percent over the course of a year.
Wind-Shaped Landscapes
With no liquid water at the surface today, wind is the dominant force reshaping Mars. Vast dune fields cover portions of the northern lowlands and fill the floors of many craters. These dunes shift over time, driven by the same thin atmosphere that generates planet-wide dust storms capable of obscuring the entire surface for weeks.
Dust devils are common and far larger than their Earth counterparts. While terrestrial dust devils might reach tens of meters high, Martian dust devils can grow several kilometers tall and span kilometers across. Orbital measurements put the median height at about 450 meters, with the largest examples towering far beyond that. They leave dark tracks across the surface that are visible from orbit, tracing paths many kilometers long. These vortices play an important role in lofting fine dust into the atmosphere, contributing to the hazy, salmon-colored Martian sky.