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Mars is the 4th planet from the Sun with an average distance of 1.524 AU or 2.279 x 108 km. It takes 686.98 Earth days to orbit the Sun, and rotates at a rate of 1 rotation every 24 hours 37 minutes and 22 seconds. Its mass is 6.418 x 1023 kg or 0.107 Earth masses. It has two moons, and a thin atmosphere composed of 95% carbon dioxide, 2.7% nitrogen, 0.03% water vapor and 2% other gases. The surface temperature ranges from 133 to 293 K (−140 °C to 20 °C, −220 °F to 70 °F) with an average temperature of 250 K (-23 °C or -10 °F)
Mars is visible to the naked eye and is one of the brightest objects in the night sky. It is a bright red color because its surface contains large amounts of iron oxide. Mars' two moons, Phobos and Deimos are small and irregularly shaped, and are probably captured asteroids. The largest volcano in the solar system is located on Mars: Olympus Mons, and the deepest canyon in the solar system the is Valles Marineris.
Many spacecraft have been sent to Mars, including most recently the two Mars Exploration Rovers, Spirit and Opportunity.