Geology of Mars

Mars is a very different world.

The top half is low and smooth. The bottom half is high and rocky.

There are huge volcanoes on Mars. Some are the biggest in our solar system.

Deep cracks in the ground make giant canyons. These canyons are very long.

Large holes from space rocks sit on the surface. Mars is a very busy place.

Mars is a very different world from Earth.

Scientists study its surface and its inside. This study is called geology. One big secret is the split between its two halves.

The north is low and smooth. It has very few large craters. The south is high and rocky. It is covered in many old craters. This big split is called a dichotomy. Some think huge space rocks made it. Others think the inside of the planet caused it.

Mars also has giant volcanoes. The Tharsis region is a huge, high area. It covers a quarter of the planet. It has the largest volcanoes in our solar system.

There are also massive canyons. Valles Marineris is a huge system of cracks. It is much bigger than the Grand Canyon on Earth. These cracks formed from the crust pulling apart. Mars also has giant basins. These are huge holes made by space rocks. The Hellas basin is the largest one. It is very deep. Some parts are 8 km below the rest of the planet.

Geology is the study of a planet's surface, crust, and interior. On Mars, this science helps us understand how the world was shaped. Scientists look at the makeup and history of the ground. They also study the physical processes that change the planet over time. This work is very similar to the geology we study on Earth.

Some people even use a special name for it called areology. This name comes from the Greek word for Mars. It is a way to explore the solid parts of this distant world.

One of the most amazing things about Mars is its hemispheric dichotomy. This means the two halves of the planet look very different. The northern hemisphere is a huge, smooth lowland. It is much lower than the southern part of the planet. The southern hemisphere is a high, rugged upland. It is covered in many old impact craters.

This split is a major feature of the whole planet. It might have happened because of huge space impacts. Or, it could have come from heat moving inside the planet.

Scientists have used many tools to learn these secrets. They use laser altimeters and radar to see hidden structures. These tools found quasi-circular depressions, which are old craters covered by new dirt.

In 2018, a mission called InSight landed on the surface. It arrived on 26 November 2018. It used a sensitive seismometer to map the deep interior. On 25 October 2023, scientists used this data to find something huge. They found a radioactive magma ocean under the crust. This is a layer of hot, melted rock.

Mars is also home to some of the largest volcanoes in the solar system. The Tharsis region is a massive bulge on the western side. It covers about 25% of the planet's surface. It sits 7 to 10 km above the base level.

This area contains three large volcanoes called the Tharsis Montes. These are Ascraeus Mons, Pavonis Mons, and Arsia Mons. The huge Olympus Mons also sits near this region. There is another volcanic area called Elysium. It is about 2,000 km wide. It has volcanoes like Elysium Mons and Hecates Tholus.

Water and cracks have also shaped the Martian landscape. Valles Marineris is a giant system of canyons. It is over 4,000 km long. If it were on Earth, it would cross North America.

These canyons formed from tectonic activity, which means the crust pulled apart. There are also huge impact basins like the Hellas basin. Hellas is 1,800 km wide. Some parts of its floor are 8 km below the rest of the planet. These features show us how powerful forces once moved on Mars.

The geology of Mars is the scientific study of the planet's surface, crust, and interior. This field explores the composition, structure, and history of the Martian world. It also investigates the physical processes that shape the planet over time. This work is very similar to terrestrial geology on Earth. In the broader field of planetary science, geology refers to studying the solid parts of planets and moons. It combines many different disciplines, such as geophysics, geochemistry, mineralogy, geodesy, and cartography.

One of the most striking features of Mars is its hemispheric dichotomy. This refers to the massive difference between the northern and southern hemispheres. The northern hemisphere consists of a vast topographic depression. This lowland area is mostly located in the north and sits 3 to 6 km lower than the southern two-thirds of the planet. This difference in elevation is a first-order relief feature. It is comparable to the elevation difference between Earth's continents and its ocean basins. The southern hemisphere, often called the southern highlands, is very old and rugged. It is heavily covered in impact craters from the period of heavy bombardment.

This dichotomy is also visible in the thickness of the planet's crust. Data from gravity and topography show the southern crust is much thicker. It reaches a maximum thickness of about 70 km. In contrast, the northern crust peaks at only about 32 km. Scientists debate how this happened. Some suggest exogenic theories, where huge impacts early in Martian history caused the split. Others suggest endogenic theories, where internal processes like mantle convection or plate tectonics thinned the northern crust. A new theory involving the Southern Polar Giant Impact suggests that exogenic theories are stronger. This theory suggests Mars never had plate tectonics to modify the dichotomy.

Mars is also home to massive volcanic provinces, most notably the Tharsis region. This area is a huge volcano-tectonic bulge in the western hemisphere. It is thousands of kilometers wide and covers up to 25% of the planet's surface. The Tharsis region averages 7 to 10 km above the Martian datum. It contains the largest known volcanoes in our solar system. Three massive volcanoes, Ascraeus Mons, Pavonis Mons, and Arsia Mons, sit in a line along the crest. These are collectively known as the Tharsis Montes. The famous shield volcano Olympus Mons also sits near the western edge of this province. The massive weight of Tharsis has even caused the crust to fracture. This created immense extensional fractures that radiate halfway around the planet.

Another volcanic area is the Elysium volcanic complex. This region is about 2,000 kilometers in diameter. It includes volcanoes such as Elysium Mons, Hecates Tholus, and Albor Tholus. Scientists believe the development of these volcanoes involved both lavas and pyroclastics.

Large impact basins also define the Martian landscape. The Hellas basin is the largest visible one. It is located in the southern hemisphere and is 1,800 km in diameter. The floor of this basin is very deep. Some areas lie over 8 km below the datum. Other major basins include Argyre and Isidis. The Argyre basin is 800 km wide and sits in the southern highlands. The Isidis basin is roughly 1,000 km wide and sits on the dichotomy boundary. These basins are extremely old and date back to the late heavy bombardment. They are similar in age to the Imbium and Orientale basins found on the Moon.

Near the equator, the Valles Marineris canyon system stretches across the planet. It is a massive network of interconnected troughs and canyons. The system is over 4,000 km long, which is nearly a quarter of the planet's circumference. If it were on Earth, it would span the width of North America. Some parts are 300 km wide and 10 km deep. Unlike the Grand Canyon on Earth, which was made by water, Valles Marineris is of tectonic origin. This means it was formed by faulting in the crust. The canyons likely formed because of the stress caused by the Tharsis bulge.

Finally, Mars features unique chaotic terrain and outflow channels. At the eastern end of Valles Marineris, the land breaks into jumbles of low, rounded hills. This is called chaotic terrain. It marks the start of huge outflow channels that empty into Chryse Planitia. These channels, such as Ares Vallis, are enormous. For example, Ares Vallis is 28 km wide. Scientists estimate the water flow needed to carve it was 14 million cubic meters per second. This is over ten thousand times the average discharge of the Mississippi River. These channels were likely formed by sudden releases of water from underground or melting ice.