subject: Mars Planet : As The Fourth Planet [print this page] Mars is the fourth planet of the solar system in order of increasing distance from the Sun, and the second by increasing mass and size. Its distance from the Sun is between 1.381 and 1.666 AU with an orbital period of 686.71 days. It is a terrestrial planet, as are Mercury, Venus and Earth, about ten times less massive than Earth, but ten times more massive than the Moon. Its topography has similarities with both the Moon, through its craters and impact basins, with the Earth, with formations of tectonic and climate such as volcanoes, rift valleys, mesas , dune fields and polar ice caps. The highest mountain in the solar system, Olympus Mons (who is also a shield volcano), and the largest canyon, Valles Marineris, located on Mars. The northern basin, if it proves that it is a single basin, would then also the largest impact basin in the solar system.
Mars has now lost most of its internal geological activity, and only minor events still occur sporadically on the surface, such as landslides (which may nevertheless be large), probably CO2 geysers polar regions, perhaps earthquakes, volcanic eruptions and even rare form of small lava flows. The rotation period of Mars is similar to that of Earth's obliquity and gives it a seasonal cycle similar to the one we know, however, these seasons are marked by an orbital eccentricity five and a half times higher than Earth, resulting in a significantly more pronounced seasonal asymmetry between the two hemispheres.
Mars can be seen lil naked with a burst much lower than that of Venus, but which can, in close opposition, exceed the maximum brightness of Jupiter, reaching an apparent magnitude of -2.91 , while its apparent diameter varies from 25.1 to 3.5 seconds of arc by its distance from Earth varies from 55.7 to 401,300,000 kilometers. Mars has always been visually characterized by its red color, due to the abundance of hematite amorphous iron oxide (III) Fe2O3 on the surface. This has been associated with the war since ancient times, hence its name in the West after the war god Mars in Roman mythology, identified with Ares in Greek mythology. In French, Mars is often called "Red Planet" because of that particular color.
Before flying to Mars by Mariner 4 in 1965, it was thought that there was liquid water on the surface and that life forms similar to those existing on Earth could it be developed, subject to very fruitful Science fiction. Seasonal variations of surface albedo of the planet were attributed to vegetation, while rod formations seen in the telescopes and telescopes of the time were interpreted, especially by American amateur astronomer Percival Lowell, as irrigation canals crossing the desert expanses with water after polar ice caps. All these speculations have been scanned by the spacecraft that explored Mars in 1965, Mariner 4, allowed to discover a planet with no global magnetic field, with a cratered surface resembling that of the moon, and a thin atmosphere with a ground pressure about 600 Pa for an average temperature of 210 K .
Since then, despite the somewhat disappointing first contact, Mars is the subject of exploration programs more demanding than for any other object in the solar system: All the stars we know, this is indeed the one with the environment differs the least of our planet. This intensive exploration has brought us a much better understanding of the geological history of Mars, revealing the existence of such an early period where the Noachian surface conditions should be fairly similar to the Earth at the same time, with the presence of large quantities of liquid water, probably loaded with sulfuric acid, known in particular to substantially lower the freezing point, the Phoenix lander, which landed near the northern polar cap, has been discovered in 2008 ice water at a shallow depth in the soil Vastitas Borealis .
Finally, Mars has two tiny moons, Phobos and Deimos, like asteroids and named Accordance Phobos (fear) and Deimos (terror) of Greek mythology, who are children ire.
The exact pressure and composition of the atmosphere of Mars are known for less than half a century back to the first in situ analysis performed in 1976 by "landing" of the Viking 1 and Viking 2 . The first observer to have assumed the existence of an atmosphere around Mars astronomer (and composer) Germano-British William Herschel who in 1783 was attributed to some Martian weather changes observed on the surface of the planet including white spot interpreted as clouds. This hypothesis was challenged at the beginning of the next century with advances in telescope mirror, which provided better images appear to show a rather more static surface until comes at the end of the nineteenth century debate on reality of the canals of Mars observed in Italy and popularized by the astronomer Percival Lowell, American amateur.
Another American astronomer (occupation, this time) and pioneer of spectroscopy, William Wallace Campbell, remained skeptical about the existence of a significant atmosphere around Mars, and announced on the occasion of the opposition of 1909 n have been able to detect any trace of water vapor in the atmosphere possible - his compatriot Vesto Slipher, which supported the theory of channels, told him about the opposite. Based on albedo variations of the Martian disk, Percivall Lowell in 1908 found the ground atmospheric pressure to 87 mbar (8700 Pa), a value that will remain more or less the reference to the measures implemented by the probe Mariner 4 1965.
The difficulty in analyzing the composition of the atmosphere martian spectroscopy was then generally attributed to the presence of nitrogen, difficult to characterize this technique, and thus the French astronomer Gerard de Vaucouleurs, who was working in England , issued in 1950 the idea that the Martian atmosphere was composed of 98.5% nitrogen, 1.2% argon and 0.25% of carbon dioxide. At the McDonald Observatory in Texas, the American astronomer Gerard Kuiper Dutch origin established in 1952 from the infrared spectrum of Mars that carbon dioxide was at least twice as abundant in the Martian atmosphere that occurs in the atmosphere land, most of this atmosphere to be like ours, it incorporated under nitrogen.
