In July 1969, a NASA spacecraft Apollo-11 hit the lunar surface and first time a man walked on the Moon surface. In 1960s and 70s, due to various lunar missions, scientists started to understand moon's characteristics. Now scientists had the lunar rock and study of that was going to open the secrets of Earth's alone natural satellite. The study of lunar samples revealed that Moon formed just 50 millions years after the origin of the solar system. It means that Moon came into existence not much later of Earth.
Study also reveals that composition of Moon's rock is very similar of Earth crust composition. Through these study, scientist proposes a theory which explain formation of moon. As per theory, Earth -Moon system is formed due to impact of Mars sized body Theia to proto Earth which causes splashing off a great part of earth into space and orbiting around Earth. Well, in recent, through simulations it is confirmed that a large part of Moon derived from proto Earth. Firstly, it was supposed that the Moon would be formed with greater part of Theia which one supposed to be an outer object but the isotopic similarity with Earth's composition negated this concept.
It is found that Moon's dia is nearly 3500 km which is one fourth of Earth's dia. Moon is being the second densest satellite, only after Io ( satellite of Jupiter), weigh one eightieth of Earth mass. Moon's internal structure too can be classified into core, mantle and crust. Moon has a solid Iron rich core of radius nearly 240 km which is surrounded by liquid iron with radius of 300 km. Moon's core is surrounded by a molten layer of radius nearly 500 km which is rich in iron and magnesium (mafic). Moon has a very weak magnetic field which is nearly one hundred thousandth of Earth. This is due to the crustal magnetization. It is assumed that 4 billion years ago the magnetic strength of Moon was similar to that of earth but as Moon solidified, its dipolar magnetic field diminished and nearly one billion years ago when lunar core had crystallized, its dynamo effect completely expired.
Moon has a very extreme environment as temperature ranging from 140°c to -171°c and atmosphere is so tenuous as nearly vaccum. Although Moon's composition is more or less is similar to Earth, its environment is very different from the Earth. It is predicted that once upon a time the Moon had a thick atmosphere which had been stripped off by solar winds. Scientists' interest in Moon has been increased since detection of water ice on lunar surface by Chandrayaan-1. Further, presence of water ice has been confirmed on north and solid pole by several independent spacecraft. Desire of finding new habitation in universe will lead further exploration of Moon and may be soon more number of humen will walk on lunar surface.
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