Portal:Solar System/Selected article/7
Mars is the fourth planet and the furthest terrestrial planet from the Sun. 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". There is a sharp contrast between the two Martian hemispheres: the northern hemisphere is on average flatter and smoother than the southern hemisphere. The planet's two poles are covered by water and carbon dioxide ice caps. Surrounding the Martian surface is a dynamic thin atmosphere (1% of Earth's surface pressure), made primarily of carbon dioxide. Mars has two irregularly shaped natural satellites, Phobos and Deimos.
Mars has a mean radius of 3,389.5 km (2,106 mi), the second smallest among planets in the Solar System. The gravity on its surface is about 3.72 m/s2 (12.2 ft/s2), which is 38% of Earth's. The temperature on the Martian surface usually ranges from −110 °C (−166 °F) to 35 °C (95 °F). Geologically, Mars is fairly active, with dust devils sweeping the landscape and marsquakes trembling in the ground, a Martian analog to earthquakes. The surface of Mars also hosts the highest mountain (Olympus Mons) and one of the largest canyons in the Solar System (Valles Marineris). Days and seasons on Mars are comparable to those of Earth, with a day length of 24.5 hours, a year length of 1.88 Earth years, and an axial tilt only slightly greater than Earth's. (Full article...)