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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 length of time for Mars to complete one orbit around the Sun in respect to the stars, its sidereal year, is about 686.98 Earth solar days (≈ 1.88 Earth years), or 668.5991 sols. Because of the eccentricity of Mars' orbit, the seasons are not of equal length.
The basic time periods from which the calendar is constructed are the Martian solar day (sometimes called a sol) and the Martian vernal equinox year.The sol is 39 minutes 35.244 seconds longer than the Terrestrial solar day, and the Martian vernal equinox year is 668.5907 sols in length (which corresponds to 686.9711 days on Earth).
A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. [2] The gravitational potential difference and thus the delta-v needed to transfer between Mars and Earth is the second lowest for Earth. [186] [187] The axial tilt of Mars is 25.19° relative to its orbital plane, which is similar to the axial tilt of Earth. [2]
On both Earth and Mars, these two precessions are in opposite directions, and therefore add, to make the precession cycle between the tropical and anomalistic years 21,000 years on Earth and 29,700 Martian years (55,900 Earth years) on Mars. As on Earth, the period of rotation of Mars (the length of its day) is slowing down.
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.
In an aquifer, water occupies open space (pore space) that lies between rock particles. This layer would spread out, eventually coming to be under most of the Martian surface. The top of this layer is called the water table. Calculations show that the water table on Mars was for a time 600 meters below the surface. [14] [15]
This system consists of uniform time units. However, Mars Year sols may be confused with rover mission times that are also expressed in sols. Unlike in the day vs. sol distinction, "Mars Year" has no unique Latin term. Start and End dates of Mars Years were determined for 1607–2141 by Piqueux et al. [2] Earth and Mars dates can be converted ...