subject: Mars : Geologically Very Active Planet [print this page] The geology of Mars, sometimes called areologie , covers the scientific study of Mars and its physical properties, its landforms, its composition, its history, and all phenomena that have affected or even affect planete.
This is a relatively new discipline, which opened July 14, 1965 at the first flyby of Mars by spacecraft, Mariner 4 in this case, which led to the discovery of a planet with no magnetic field overall, with a cratered surface resembling that of the Moon, and a thin atmosphere with a surface pressure of about 600 Pa and an average temperature of 210 K (-63 C). But it was really with the probe Mariner 9 that the systematic and thorough study of the planet Mars began, November 13, 1971; first craft to orbit around a planet other than Earth, Mariner 9 mapped the entire Martian surface with a resolution between 100 m and 1 km per pixel, revealing all the major geological structures of the planet, its crustal dichotomy, its volcanic mountains and huge canyon system called Valles Marineris with reference to the Mariner program in general, and Mariner 9 in particular.
Since then, the Viking program in the late 1970s, the Phobos program in the late 1980s, and the missions Mars Global Surveyor and Mars Pathfinder in 1990, helped refine our understanding of Mars.
More recently, "Orbiters" 2001 Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express and the rovers Spirit and Opportunity on the ground, supplemented by the "lander" Phoenix has pioneered in the 2000s, a veritable Martian geological study, which should normally be continued in 2012 with the U.S. mission and the Mars Science Laboratory mission Russian Phobos-Grunt, which will carry the small Chinese satellite Yinghuo one to study the interaction of the solar wind and the atmosphere of Mars, even at more distant future, with the European ExoMars rover, the Aurora program, designed to analyze the soil of Mars with a view to search for traces of past or present exobiology, and with the Mars Sample Return, joint ESA and NASA, designed to bring a few hundred grams of samples of Martian soil to Earth.
The systematic study of the red planet has radically transformed the vision we have. Mars is now seen as a planet with its rich and geologically very active, once surrounded by a global magnetic field, which had then almost certainly a thick atmosphere and vast quantities of liquid water more acidic. Moreover, its nucleus would still primarily or entirely liquid, and it is not totally excluded that some volcanoes can still enjoy an occasional activity .
The topography of the Martian surface reveals a clear dichotomy between crustal one hand, a region of the southern hemisphere corresponding to a thick bark and irregular even under the Tharsis bulge, and, secondly, a region of northern hemisphere corresponding to a finer bark fairly uniform . As a first approximation, we can consider that the Martian crust has a uniform density of 2900 kg/m3, which leads to an average thickness of about 50 km, or 4.4 of the volume of the planet, with the 92 km in extreme values of the Syria Planum region and just 3 km beneath the impact basin Isidis Planitia, while the bark would be less than 10 km beneath the region of Utopia Planitia. From a macroscopic point of view, consistency of physical parameters of Mars means that the bark should never have more than 125 km thick .
One of the revelations made by the gravity measurements made thin by Mars Global Surveyor was the discovery of structures reminiscent of channels buried beneath the surface of the northern hemisphere and detected by their mass deficit even though they remain invisible surface .
These structures, which corresponded to reliefs from 1.5 to 4.5 km if they are filled with dry sediment but 1 to 3 km in the case of sediments mixed with ice , are perfectly consistent with model, generally accepted to describe the history of Mars, that would have housed the Northern Hemisphere, the Noachian, large areas of liquid water, an ocean or semi-permanent may be covered with ice, the center of a global hydrosphere before being filled with volcanic material to Hesperian and eolian deposits in the Amazon to give birth to low plains uniform characteristics of this hemisphere.
Mars does not have a magnetosphere. However, the magnetometer and electron reflectometer MAG / ER of the Mars Global Surveyor revealed a residual magnetism in 1997 , up to 30 times that of Earth's crust , above geologically older parts of the southern hemisphere , especially in the Terra Cimmeria and Terra Sirenum . The measurements show a magnetic field up to 1.5 FT at 100 km altitude, which requires a significant amount of magnetization of Martian crust, at least 106 km 3.
For nine years, AMS has the magnetic parameters measured above the Martian surface, the instrument MGS MAG (Magnetometer AMS) collecting vector data from a typical altitude of 400 miles, sometimes approaching 90 km from the surface, ER and MGS (MGS Electron Reflectometer) measuring the total magnetism from an altitude of 185 km on average. There is not currently magnetic stripe of the Martian surface itself, as well as the exact nature of magnetized minerals can only be assumed in the present state of our knowledge.
