Photos made with 24 hours interval to show how the illumination angle changes the lunar landscape.

They have been proposed several mechanisms to explain the formation of the Moon, which occurred 4,527 ± 0.010 billion years ago and between 30 and 50 million years after the origin of the solar system. Recent research suggests a slightly younger age, between 4.4 and 4.45 billion years. Among the proposed mechanisms are the fission of the Moon from the Earth's crust through centrifugal force (which would require an immense force of Earth's rotation), the gravitational capture of a pre-formed moon (which would require an unlikely Earth extended atmosphere able to dissipate the energy of the passage of the Moon) and the simultaneous formation of the Earth and the Moon in the primordial accretion disk (which does not explain the depletion of metallic iron in the Moon). These hypotheses also can not account for the high angular momentum of the Earth-Moon system.

The hypothesis that prevails today is that the Earth-Moon system formed as a result of a giant impact, during which a Mars-sized body called Theia collided with the newly formed proto-Earth, casting material . its orbit that coalesced to form the moon Eighteen months before a conference on the possible origin of the Moon in October 1984, Bill Hartmann, Roger Phillips and Jeff Taylor challenged fellow scientists to say. "you have 18 months Return for the data of Apollo, turn to computers, do what you have to do, but decide to. do not come to the conference unless they have something to say about the birth of the moon. " In 1984 conference in Kona, Hawaii, the giant impact hypothesis has emerged as the most popular. Before the conference there were supporters of the three "traditional" theories, and some people who were beginning to consider the giant impact as a serious possibility and there was a huge apathetic group thought that the debate was never resolved. Later, there were essentially only two groups: the defenders of great impact and agnostics.

It is thought that the giant impacts have been common in the early days of the solar system. The simulations of the large impact computer model are consistent with measurements of the angular momentum of the Earth-Moon system and the small size of the lunar core. These simulations also show that most of the moon originates in the body that collided, and not the proto-Earth. However, more recent trials suggest that most of the Moon formed from the Earth, and not the impact. The meteorites show that other bodies in the inner solar system, like Mars and Vesta have very different oxygen and tungsten isotopic compositions of found on Earth as the Earth and Moon have isotopic compositions virtually identical. The mixture vaporized material between Earth and the moon in formation after the impact could have balanced their isotopic compositions, although this is still debated.

The large amount of energy released in the large impact event and the subsequent bonding material in Earth orbit would have melted the Earth's outer layer, forming a magma ocean. The newly formed Moon would also have had its own lunar magma ocean; whose depth is estimated to be between 500 km and the total distance of the Moon. Despite the giant impact hypothesis be precise in explaining many lines of evidence, there are still some open questions, most of them on the composition of the moon.

In 2001, a team at the Carnegie Institution of Washington released the most accurate measurement of isotopic signatures of lunar rocks to the present day. To their surprise, they found that the rocks of the Apollo program had an isotopic signature identical to that of the Earth stones and different from almost every other solar system bodies. This was an unexpected observation, since it is believed that most of the material into orbit to form the Moon was from Theia. In 2007, a group of researchers at the California Institute of Technology announced that the probability of Earth and Theia had identical isotopic signatures was less than 1%. An analysis of titanium isotopes in lunar samples returned by Apollo, published in 2012, demonstrated that the Moon has the same composition as the Earth.

Source: Wiki Books - Astronomy / Moon