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The minimum distance between Earth and Mars has been declining over the years, and in 2003 the minimum distance was 55.76 million km, nearer than any such encounter in almost 60,000 years (57,617 BC). The record minimum distance between Earth and Mars in 2729 will stand at 55.65 million km.
The size of solid bodies does not include an object's atmosphere. For example, Titan looks bigger than Ganymede, but its solid body is smaller. For the giant planets, the "radius" is defined as the distance from the center at which the atmosphere reaches 1 bar of atmospheric pressure. [11]
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[16] [17] [18] An astronomical unit, or AU, is the distance from Earth to the Sun, which is approximately 150 billion meters (93 million miles). [19] Small Solar System objects are classified by their orbits: [20] [21] Main Asteroid belt (main belt), between Mars and Jupiter, in near circular orbit, 2.2 to 3.2 AU
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Substituting the mass of Mars for M and the Martian sidereal day for T and solving for the semimajor axis yields a synchronous orbit radius of 20,428 km (12,693 mi) above the surface of the Mars equator. [3] [4] [5] Subtracting Mars's radius gives an orbital altitude of 17,032 km (10,583 mi). Two stable longitudes exist - 17.92°W and 167.83°E.
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 order of the planets was conjecture until Kepler determined the distances from the Sun of the five known planets that were not Earth. It had been conjectured that the fixed stars were much farther away than the planets. Moon: Moon of a planet 3rd century BC 20 Earth radii (very inaccurate, true=64 Earth radii) Aristarchus of Samos made a ...