Home to both the highest mountain and the deepest, longest valley in the solar system.
Olympus Mons is roughly 17 miles (27 kilometres) high, about three times as tall as Mount Everest, while the Marineris system of valleys — named after the Mariner 9 probe that discovered it in 1971 — reaches as deep as 6 miles (10 km) and runs east-west for roughly 2,500 miles (4,000 km), about one-fifth of the distance around Mars and close to the width of Australia.
Scientists think the Valles Marineris formed mostly by rifting of the crust as it got stretched. Individual canyons within the system are as much as 60 miles (100 km) wide.
The canyons merge in the central part of the Valles Marineris in a region as much as 370 miles (600 km) wide.
Large channels emerging from the ends of some canyons and layered sediments within suggest that the canyons might once have been filled with liquid water.
Olympus Mons being one of them. The massive volcano, which is about 370 miles (600 km) in diameter, is wide enough to cover the state of New Mexico. Olympus Mons is a shield volcano, with slopes that rise gradually like those of Hawaiian volcanoes and was created by eruptions of lava that flowed for long distances before solidifying. Mars also has many other kinds of volcanic landforms, from small, steep-sided cones to enormous plains coated in hardened lava. Some minor eruptions might still occur on the planet today.
Channels, valleys, and gullies are found all over Mars, and suggest that liquid water might have flowed across the planet’s surface in recent times. Some channels can be 60 miles (100 km) wide and 1,200 miles (2,000 km) long. Water may still lie in the cracks and the underground rocks. A study by scientists in 2018 suggested that salty water below the Martian surface could hold a considerable amount of oxygen, which could support microbial life. However, the amount of oxygen depends on temperature and pressure; temperature changes on Mars from time to time as the tilt of its rotation axis shifts.
The lowest of the northern plains are among the flattest, smoothest places in the solar system, potentially created by water that once flowed across the Martian surface. The northern hemisphere mostly lies at a lower elevation than the southern hemisphere, suggesting the crust may be thinner in the north than in the south. This difference between the north and south might be due to a very large impact shortly after the birth of Mars.
