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The fourth-largest asteroid, Hygiea (radius 216.5 ± 4 km), is icy. The question remains open if it is currently in hydrostatic equilibrium: while Hygiea is round today, it was probably previously catastrophically disrupted and today might be just a gravitational aggregate of the pieces. [ 75 ]
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.
where G is the universal constant of gravitation (commonly taken as G = 6.674 × 10 −11 m 3 kg −1 s −2), [10] M is the mass of Mars (most updated value: 6.41693 × 10 23 kg), [11] m is the mass of the satellite, r is the distance between Mars and the satellite, and is the angular velocity of the satellite, which is also equivalent to (T ...
For example, if a TNO is incorrectly assumed to have a mass of 3.59 × 10 20 kg based on a radius of 350 km with a density of 2 g/cm 3 but is later discovered to have a radius of only 175 km with a density of 0.5 g/cm 3, its true mass would be only 1.12 × 10 19 kg.
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.
In the 1950s, Wernher von Braun and Willy Ley, writing in Colliers Magazine, updated the idea, in part as a way to stage spacecraft headed for Mars. They envisioned a rotating wheel with a diameter of 76 meters (250 feet). The 3-deck wheel would revolve at 3 RPM to provide artificial one-third gravity. It was envisaged as having a crew of 80. [2]
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]
During a year, there are large surface temperature swings on the surface between −78.5 °C (−109.3 °F) to 5.7 °C (42.3 °F) [c] similar to Earth's seasons, as both planets have significant axial tilt, Earth at 23.5 degrees and Mars at 25 degrees. Mars was formed approximately 4.5 billion years ago.