Mars is among the brightest objects in Earth's sky, and thus has been known from ancient times.

It is unknown whether life has ever existed on Mars. The Amazonian period, which continues to the present, was marked by the wind's influence on geological processes. The Hesperian period from 3.7 to 3.2–2 billion years ago was dominated by widespread volcanic activity and flooding that carved immense outflow channels. During the Noachian period from about 4.1 to 3.7 billion years ago, Mars's surface was marked by meteor impacts, valley formation, erosion, and the possible presence of water oceans.

Like the other planets in the Solar System, Mars was formed approximately 4.5 billion years ago. A Martian solar day ( sol) is equal to 24.5 hours and a Martian solar year is equal to 1.88 Earth years. Mars's significant orbital eccentricity and axial tilt cause large seasonal changes to the polar ice caps' coverage and temperature swings between −110 ☌ (−166 ☏) to 35 ☌ (95 ☏) on the surface. The surface of Mars hosts a large shield volcano ( Olympus Mons) and one of the largest canyons in the Solar System ( Valles Marineris). Geologically, Mars is fairly active, with dust devils sweeping across the landscape and marsquakes (Martian analog to earthquakes) trembling underneath the ground.

Mars has a thin atmosphere made primarily of carbon dioxide, and two irregularly shaped natural satellites, Phobos and Deimos. The Martian dichotomy is visible on the surface: on average, the terrain on Mars's northern hemisphere is flatter and lower than its southern hemisphere. Mars's radius is second smallest among the planets in the Solar System at 3,389.5 km (2,106 mi). The reddish color of its surface is due to finely grained iron(III) oxide dust in the soil, giving it the nickname ' the Red Planet'. Mars is the fourth planet and the furthest terrestrial planet from the Sun.

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