PLANET MERCURY

Planet Mercury, analysed by telescopic observations over two centuries , and by spacecraft Mariner 10 during three flybys in 1974-75, has a d iameter of 4878 km, a density of 5.44 g/cm3 and a rotation period of 5 8.67 days, which is exactly two thirds of its orbital period. Its inte rior is made of very large iron cores representing 42% of the total vo lume and 75% of the planetary radius, a silicaceous mantle and a crust al surface. This surface is comminuted in a layer of very small silice ous fragments resulting from pulverization by impacts of all size mete oroids. It displays impact craters, randomly superimposed, as for the lunar surface. There are extended, darker and lower plains, compressio n ridges and the cataclysmic huge basin Caloris Planitia, multi-ringed , fractured and partly flooded. A reconstitution of the different phas es of evolution of the planetary body is attempted, since its primordi al accretion up to its present stage.