Several space probes have flown past or landed on Mars, providing information on its atmosphere and features, such as the volcano Olympus Mons. This stands 27 km high –more than three times the height of Mount Everest. The latest craft to visit the red planet is Mars Reconnaissance Orbiter, which began a four-year orbit in 2006. NASA’s Phoenix Mars landed in May 2008. Diameter: 6,794 km Mass: 6,421,900,000,000 tonnes Average distance from Sun: 227,940,000 km Rotation: 1.025957 days Orbit: 686.98 days Average temperature: -63 ◦ C Moons: 2