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. (ANI)