Mars (astronomy)
Article
July 6, 2022
Mars is the fourth planet in the solar system in order of distance from the Sun; it is visible to the naked eye and is the last of the terrestrial-type planets after Mercury, Venus and the Earth. Called the red planet because of its characteristic color caused by the large amount of iron oxide that covers it, Mars takes its name from the homonymous deity of Roman mythology and its astronomical symbol is the stylized representation of the shield and the spear of the god (; Unicode: ♂). Despite having rather low average surface temperatures (between −120 and −14 ° C) and a very rarefied atmosphere, it is the closest planet to the Earth among those in the solar system. Its dimensions are intermediate between those of our planet and those of the Moon, and it has the inclination of the axis of rotation and the duration of the day similar to those of Earth. Its surface features volcanic formations, valleys, polar ice caps and sandy deserts, and geological formations that suggest the presence of a hydrosphere in the distant past. The planet's surface appears heavily cratered, due to the almost total absence of erosive agents (mainly geological, atmospheric and hydrosphere activity) and the total absence of plate tectonic activity capable of forming and then modeling tectonic structures. The very low density of the atmosphere is not able to consume most of the meteors, which therefore reach the ground more frequently than on Earth. Among the most notable geological formations of Mars we highlight: Olympus Mons, or Mount Olympus, the largest volcano in the solar system (27 km high); the Valles Marineris, a long canyon considerably larger than the terrestrial ones; and a huge crater on the northern hemisphere, about 40% wide of the entire Martian surface. Upon direct observation, Mars presents color variations, historically attributed to the presence of seasonal vegetation, which change as the periods of the year change; but subsequent spectroscopic observations of the atmosphere have long ago abandoned the hypothesis that there might be seas, canals and rivers or a sufficiently dense atmosphere. The final denial came from the Mariner 4 mission, which in 1965 showed a desert and arid planet, animated by periodic and particularly violent sandstorms. The most recent missions have highlighted the presence of frozen water. Two natural satellites orbit around the planet, Fobos and Deimos, of small size and irregular shape.