Washington: Scientists have come up with two new models to explain the age-old question of how Earth`s moon formed.
The Giant Impact Theory put forth in the 1970s suggested that the moon resulted from a collision with a protoplanet approximately half the size of ancient Earth.
But the physics underlying such a collision implied that the moon should be made up of debris mostly from the protoplanet. Since then we`ve discovered the moon is instead very chemically similar to Earth.
Now, scientists have developed two new models that explain how an impact could have resulted in a moon formed from Earth material.
In one model, Robin Canup, an astrophysicist at the Southwest Research Institute in Boulder, Colo., suggests a much larger impactor than previously considered possible.
However, in another model, astrophysicists Matija Cuk and Sarah Stewart of Harvard University postulate that that a smaller impactor could still create the same effect if Earth was rotating much faster billions of years ago.