GAT: Mars
Mars is the fourth planet in distance from the Sun. Its orbit lies between Earth and the asteroid belt. It takes 667 Earth days for Mars to complete an orbit.
The martian day, or sol, is 24 hours 39 minutes 35 seconds long, and its axial tilt of 25.2 degrees is nearly the same as the Earth's 23.5 degrees.
Mars has two natural moons, Phobos and Deimos.
Mars is a rocky planet, with a thin atmosphere. Its surface gravity is approximately one-third of Earth's, but its atmosphere is much thinner: instead of the standard Earth sea-level air pressure of 1013 hectopascals, Mars's is 4 to 6 hPa. The martian atmosphere is mostly carbon dioxide and argon gas. Pictures from Mars show the sky is a pinkish color, except near the Sun, where refraction makes the sky a light blue.
History of Martian Observation and Exploration
Mars has been known since antiquity. Its reddish color as seen from Earth led for the planet to be associated with warfare; the Roman god of war is Mars.
The Danish astronomer Tycho Brahe made precise observations of Mars, which he gave to his assistant, Johannes Kepler, to use in calculating Mars' orbit. Kepler tried for years to fit the data into a circular orbit, until he realized the orbit was an ellipse, and thus became the basis of Kepler's Second Law.
In 1877, when Mars approached opposition with Earth, Italian Giovanni Schippareli observed features on the surface of Mars that he named canali, or "channels." Percival Lowell, an American astronomer, observed the canals extensively and popularized the notion that Mars was inhabited by creatures capable of building great engineering works.
Also in 1877, Asaph Hall, an American astronomer working at the U.S. Naval Observatory in Washington, D.C., discovered Mars' two moons, Phobos and Deimos.
The first successful flyby of Mars took place in 1964 with the U.S. probe Mariner 4, which discovered Mars was heavily cratered, and had evidence of once having free water.
The first successful probe landings on Mars were in 1976, with the U.S. probes Viking 1 and 2, which returned geological and weather data for several months.
Geography of Mars
Mars does not have a molten core; therefore, geographical features that formed over martian history tend to remain there, including many craters formed in the early history of the Solar System. Another feature is several tall extinct volcanoes, including Mons Olympus, the largest volcano in the Solar System.
Mars also exhibits geographical features that indicate liquid water once existed on the planet. The Mariner 4 probe which flew by in 1964 revealed a giant valley, Valles Marineris, which is 4000 kilometers long. In this valley, geologists have detected water outflow channels.
Weather of Mars
Periodically Mars is covered with planet-wide sandstorms, which obscure views from space.
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