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.

Remark

To the naked eye Mars usually appears of a marked yellow, orange or reddish color and in terms of brightness it is the most variable during its orbit among all the outer planets: its apparent magnitude in fact passes from a minimum of +1.8 to a maximum. of −2.91 to the perihelic opposition (also called the great opposition). Due to the orbital eccentricity its relative distance varies with each opposition causing small and large oppositions, with an apparent diameter from 3.5 to 25.1 arc seconds. On August 27, 2003 at 9:51:13 UT Mars found itself as close to Earth as ever in nearly 60,000 years: 55 758 006 km (0.37271925 au). This was possible because Mars was one day away from the opposition and about three days away from its perihelion, which made it particularly visible from Earth. However, this approach is only slightly inferior to others. For example, on August 22, 1924, the minimum distance was 0.372846 astronomical units (55 777 000 km) and it is expected that on August 24 2208 it will be 0.37279 astronomical units (55 769 000 km). The closest approach of this millennium will instead take place on 8 September 2729, when Mars will be 0.372004 astronomical units (55 651 000 km) from the Earth. astronomers from the sixteenth to the twentieth century