The series of events that led to the formation of the moon may not have been as uncertain as we previously thought. Yet, the baffling thought of “How did the moon form?”, marks an end now. However, the puzzle have been resolved in various ways.
The favored theory of lunar formation requires several things, none of them were not possible but cumulatively challenging, as Dr. Alessandra Mastrobuono-Battisti of the Israel Institute of Technology has tackled one of these: the question of why the moon and Earth have such similar chemical compositions.
As astronomers began to reveal the solar system, they inevitably noticed how unusual the moon is. Other satellites in the inner solar system are tiny. Some gas giants have large moons, but these objects are all much, much smaller in comparison to the planets they orbit.
While various theories about the moon’s origins have come and gone, the only one that seems to explain what we can observe is that an object, named Theia, roughly the size of Mars slammed into the Earth early in its development. The impact was so great that huge amounts of rock from both Theia and the proto-Earth’s crust were thrown into orbit. Some eventually returned to the planet, but most were combined to become the moon.
Researchers from the University of Maryland, on the other hand, present evidence that they claim indicates that Theia did not have the same composition as Earth. Instead, they think that the material from Theia and Earth mixed so thoroughly that the Earth’s mantle and the moon each received a similar portion, explaining their resemblance.
According to NASA.Gov, the moon was formed ~4.5 billion years ago, about 30–50 million years after the origin of the Solar System, out of debris thrown into orbit by a massive collision between a smaller proto-Earth and another planetoid, about the size of Mars. Initially the Moon spun much faster, but because it is not perfectly spherical and bulges out slightly at its equator, the orbit slowed down and eventually became tidally locked — keeping the same face toward the Earth. Bulges along the Earth-Moon line caused a torque, slowing the Moon spin, much the same way a figure skater gradually opens to decelerate a spin. When the Moon’s spin slowed enough to match its orbital rate, the bulge was in line with Earth, which is why we always see the same side of the Moon. In our solar system, almost all moons spin at the same rate as they orbit.
The Earth would be a very different place if the moon did not exist. Not only did the Earth slow down the Moon’s rotation, but the Moon is slowing down the rotation rate of the Earth. Since the moon’s formation, the Earth has been slowing its rotation due to the friction of the tides caused by the moon, and in reaction to this exchange of energy, the moon has been moving farther away from the Earth. In fact, at the time of the moon’s formation the Earth rotated much faster than it does today; a day on early Earth was only a few hours long. But the Moon, being small in relation to Earth, will take more than twice the age of the solar system to slow Earth’s spin rate to the Moon’s orbital rate.
NASA scientist Jennifer Heldmann describes the most popular theory of how the solar system and Earth’s moon was formed. Below you can watch a short four minute video of her explanation of the accretion theory.