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Mars hosts many enormous extinct volcanoes (the tallest is Olympus Mons, 21.9 km or 13.6 mi tall) and one of the largest canyons in the Solar System (Valles Marineris, 4,000 km or 2,500 mi long). Geologically , the planet is fairly active with marsquakes trembling underneath the ground, dust devils sweeping across the landscape, and cirrus clouds .
Mars has an orbit with a semimajor axis of 1.524 astronomical units (228 million km) (12.673 light minutes), and an eccentricity of 0.0934. [ 1 ] [ 2 ] The planet orbits the Sun in 687 days [ 3 ] and travels 9.55 AU in doing so, [ 4 ] making the average orbital speed 24 km/s.
It takes 250 days (0.68 years) in the transit to Mars, and in the case of a free-return style abort without the use of propulsion at Mars, 1.5 years to get back to Earth, at a total delta-v requirement of 3.34 km/s. Zubrin advocates a slightly faster transfer, that takes only 180 days to Mars, but 2 years back to Earth in case of an abort.
Deimos (/ ˈ d aɪ m ə s /; systematic designation: Mars II) [11] is the smaller and outer of the two natural satellites of Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. [5] Deimos is 23,460 km (14,580 mi) from Mars, much farther than Mars's other moon, Phobos. [12]
This system is also much more precise: while the Mars Exploration Rovers could have landed anywhere within their respective 93-mile by 12-mile (150 by 20 kilometer) landing ellipses, Mars Science Laboratory landed within a 12-mile (20-kilometer) ellipse. [7] Mars 2020 has even more precise system, and landing ellipse of 7.7 by 6.6 km. [8]
The Viking 1 Orbiter was inserted into Mars orbit on June 19, 1976, [8] and trimmed to a 1,513 x 33,000 km, 24.66 h site certification orbit on June 21. Landing on Mars was planned for July 4, 1976, the United States Bicentennial , but imaging of the primary landing site showed it was too rough for a safe landing. [ 9 ]
Hellas Planitia is thought to have been formed during the Late Heavy Bombardment period of the Solar System, approximately 4.1 to 3.8 billion years ago, when a protoplanet or large asteroid, suggested to be around 370 kilometres (230 mi) in diameter, hit the surface. [9] [10]
About 30 minutes prior to entry, the cruise stage and entry capsule separated. [4] When the capsule hit the atmosphere it decelerated from about 7.3 km/s to 0.4 km/s (16,330 mph to 900 mph) over three minutes. [4] As it descended the parachute opened to slow it down further, and soon after the heat shield was released. [4]