Mars
Mars, in astronomy, 4th planet from the sun, with an orbit next in order beyond that of the earth. Physical Characteristics Mars has a striking red appearance, and in its most favorable position for viewing, when it is opposite the sun, it is twice as bright as Sirius, the brightest star. Mars has a diameter of 4,200 mi (6,800 km), just over half the diameter of the earth, and its mass is only 11% of the earth's mass. The planet has a very thin atmosphere consisting mainly of carbon dioxide, with some nitrogen and argon. Mars has an extreme day-to-night temperature range, resulting from its thin atmosphere, from about 80°F; (27°C;) at noon to about −100°F; (−73°C;) at midnight; however, the high daytime temperatures are confined to less than 3 ft (1 m) above the surface. Surface Features A network of linelike markings first studied in detail (1877) by G. V. Schiaparelli was referred to by him as canali, the Italian word meaning "channels" or "grooves." Perci