Mars - the fourth in distance from the Sun and the seventh largest planet of the Solar System; The mass of the planet is 10.7% of the Earth's mass. Named after Mars, the ancient Roman god of war, corresponding to the ancient Greek Ares. Sometimes Mars is called a "red planet" because of the reddish shade of the surface imparted to it by iron oxide.
Mars - the planet of the terrestrial group with a rarefied atmosphere (the pressure at the surface is 160 times smaller than the terrestrial one). Features of the surface relief of Mars can be considered shock craters like the lunar, as well as volcanoes, valleys, deserts and polar glacial caps like earth.
Mars has two natural moons - Phobos and Deimos (translated from Greek as "fear" and "horror", the names of the two sons of Ares accompanying him in battle), which are relatively small (Phobos - 26.8 × 22.4 × 18 , 4 km, Deimos - 15 × 12.2 × 10.4 km) and have an irregular shape.
Since the 1960s, the USSR (Mars and Phobos programs), the USA (Mariner, Viking, Mars Global Surveyor and others), the European Space Agency (the program "Mars Express") and India (the Mangalian program). To date, after the Earth, Mars is the most thoroughly studied planet in the solar system.
The atmosphere of Mars, consisting mainly of carbon dioxide, is very rarefied. The pressure at the surface of Mars is 160 times smaller than the earth's surface pressure - 6.1 mbar at the average surface level. Due to the large difference in altitude on Mars, the pressure at the surface varies greatly. Approximate thickness of the atmosphere is 110 km.
According to NASA (2004), the atmosphere of Mars is 95.32% of carbon dioxide; It also contains 2.7% nitrogen, 1.6% argon, 0.13% oxygen, 210 ppm steam, 0.08% carbon monoxide, nitrogen oxide (NO) - 100 ppm, neon (Ne) - 2, 5 ppm, heavy hydrogen-deuterium-oxygen heavy water (HDO) 0.85 ppm, krypton (Kr) 0.3 ppm, xenon (Xe) 0.08 ppm  (the composition is shown in volume fractions).
According to the Viking descent vehicle (1976), about 1-2% of argon, 2-3% of nitrogen, and 95% of carbon dioxide were determined in the Martian atmosphere. According to AMC "Mars-2" and "Mars-3" data, the lower boundary of the ionosphere is at an altitude of 80 km, the maximum electron concentration 1.7 × 105 electrons / cm3 is located at an altitude of 138 km, the other two maxima are at altitudes of 85 and 107 Km.
The radio transmission of the atmosphere on radio waves 8 and 32 cm, carried out by AMS Mars-4 on February 10, 1974, revealed the existence of a night ionosphere of Mars with a maximum ionization maximum at 110 km and an electron concentration of 4.6 × 103 electrons / cm³, as well as secondary maxima At an altitude of 65 and 185 km.
The sparseness of the Martian atmosphere and the absence of the magnetosphere are the reason that the level of ionizing radiation on the surface of Mars is substantially higher than on the surface of the Earth. The equivalent dose rate on the surface of Mars averages 0.7 mSv / day (varying depending on solar activity and atmospheric pressure in the range from 0.35 to 1.15 mSv / day) and is due mainly to cosmic radiation; For comparison, on Earth, the world average equivalent dose of irradiation from natural sources, accumulated over a year, is 2.4 mSv, including 0.4 mSv from cosmic rays. Thus, in one or two days, the astronaut on the surface of Mars will receive the same equivalent dose of radiation as would be received on the surface of the Earth for a year.
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