Historical Information One of five planets known to ancient civilizations. Mars is the Roman god of war, agriculture and the state. The larger of Mars' 2 moons, Phobos ("fear"), and the smaller moon Deimos ("panic"), are named for attributes personified in Greek mythology as sons of Ares, the god of war. Mars has a reddish color, and at times is the third brightest object in the night sky (the Moon and Venus are first and second, respectively).		Environment The atmosphere is composed chiefly of carbon dioxide (95.3% by volume), nitrogen (2.7%) and argon (1.6%). The average, surface atmospheric pressure is 560 Pa, or about 1/180 times that of Earth. Surface winds can be up to 40 m/s (80 miles/hour) There are local dust storms, or dust devils, and global dust storms. The surface temperature averages -53 °C (-64 °F) and varies between -128 and 27 °C (-199 and 80 °F).
Physical Characteristics Average Diameter = 6,780 km (4,212 mi), about half the diameter of Earth, and twice the diameter of the Moon. Equatorial Radius = 3,397 km (2,110 mi) Mars has the same land area as Earth; that is, the surface area of Mars is approximately equal to the land area of Earth. Mass = 6.4 x 10 23 kg (1.4 x 10 24 lbs) Average Density = 3933 kg/m3 A planet-wide magnetic field has not been detected; however, ancient remnant fields have been located in certain regions.		Surface Features The highest point on the planet is Olympus Mons, a huge shield volcano about 26 km (16 miles) high and 600 km (370 mi) across, about the same area as Arizona. The canyon system of Valles Marineris is the largest and deepest known in the solar system. It extends more then 4,000 km (2,500 miles) and reaches depths of 5 to 10 km (3 to 6 miles) below the surface. Mars has polar caps, composed primarily of frozen carbon dioxide and water ice, that grow and shrink with the changing Martian seasons.
Orbit Mars is the fourth planet from the Sun, the next beyond Earth. Mars is about 1.5 times as far from the Sun as the Earth. Its orbit is quite elliptical: its distance from the Sun varies from 206.7 million km to 249.2 million km. Its average distance from the Sun is 227.7 million km. A Mars year is equal to 687 Earth days, or 1.88 Earth years. A Mars day is 24 hours, 37 min, 23 sec, or 1.026 Earth days.		Moons Mars has two irregularly shaped moons, Phobos and Deimos. It is commonly believed that Phobos and Deimos are "captured" asteroids; they did not form in their present location. Measurements of Phobos' orbit suggest that it has been orbiting Mars no more than 100 million years. Phobos revolves around Mars almost 3 times every Martian day! Deimos appears smoother than Phobos because many of its craters are covered in dust up to 50 m thick.