What Are Mars's Principal Features?

Mars is the fourth planet from the Sun and the second-smallest planet in the solar system, with a radius of approximately 3,390 kilometers, roughly half of Earth's. Its surface is dominated by reddish iron-oxide dust and rock, giving it a distinctive appearance that has made it a subject of observation since antiquity. Mars has a thin atmosphere composed primarily of carbon dioxide, with smaller proportions of nitrogen and argon, insufficient to retain heat or support liquid water on its surface under present conditions. Surface temperatures range from about 20 degrees Celsius at the equator during summer to as low as minus 153 degrees Celsius at the poles in winter, a range driven largely by the thinness of the atmosphere.

The planet hosts some of the most extreme geological features in the solar system. Olympus Mons, a shield volcano on the Tharsis plateau, rises more than 40 kilometers above the surrounding plain, making it the tallest known volcano in the solar system. Valles Marineris, an interconnected canyon system, extends approximately 4,000 kilometers in length and reaches depths of more than 10 kilometers. These features, along with abundant evidence of ancient river channels, lake beds, and sedimentary layering, indicate a geologically complex and once hydrologically active planet. As documented on NASA's Mars facts page, Mars has two small, irregularly shaped moons, Phobos and Deimos, which are thought to be captured asteroids.

Geology and Surface Features

Mars is divided into two geologically distinct hemispheres: a heavily cratered southern highlands, which preserve some of the oldest surfaces in the solar system, and a smoother, lower-elevation northern plains region. The crustal dichotomy between these hemispheres has been debated for decades, with hypotheses ranging from a giant impact to differential internal evolution. Volcanic activity was concentrated in the Tharsis and Elysium regions and appears to have continued into geologically recent times, though no currently active volcanism has been confirmed. Extensive polar ice caps contain both water ice and seasonal deposits of frozen carbon dioxide. NASA's Mars exploration science goals overview prioritizes understanding how these geological processes shaped habitability conditions over time.

Atmosphere and Climate

Mars's atmosphere is approximately one hundred times thinner than Earth's at the surface, with a mean surface pressure of about 600 pascals. This thin envelope produces a weak greenhouse effect, wide diurnal and seasonal temperature swings, and vulnerability to solar ultraviolet radiation at the surface. Global dust storms, which can enshroud the entire planet for weeks to months, are a distinctive feature of Martian climate and pose challenges for solar-powered surface missions. The MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft, in orbit since 2014, has provided direct measurements of how the solar wind strips atmospheric gases into space, a process thought responsible for the transition from an early warmer, wetter Mars to the cold desert it is today. NASA's MAVEN mission page describes how the spacecraft measures ion escape rates and the interaction of the upper atmosphere with solar energetic particles.

Exploration Missions

Robotic exploration of Mars began with NASA's Mariner 4 flyby in 1965 and has expanded to include orbiters, landers, and rovers from the United States, European Space Agency, China, and United Arab Emirates. The Curiosity rover, operating since 2012, confirmed that Gale Crater once contained liquid water and had chemistry compatible with microbial life. The Perseverance rover, which landed in 2021, is collecting rock and sediment core samples for potential return to Earth, representing the first stage of a planned Mars Sample Return campaign. ESA's Mars Express has produced detailed radar subsurface mapping and high-resolution stereo imaging of the surface.

Applications

Mars has applications in a wide range of disciplines, including:

• Planetary science, studying geological and climate processes to understand terrestrial planet evolution
• Astrobiology, assessing ancient habitability and searching for biosignatures in sedimentary records
• Aerospace engineering, developing entry, descent, landing, and surface mobility systems for extreme environments
• Human spaceflight planning, designing life support, radiation shielding, and habitat systems for long-duration missions
• Technology demonstration, testing in-situ resource utilization and autonomous operations for future crewed landings