The Moon may have formed intact just hours after a giant collision

Scientists have discovered that the Moon-forming collision may have depended heavily on how hot and physically strong early Earth and Theia were. New simulations found that some impacts create the familiar disk of debris that later becomes the Moon, while others can produce an intact Moon in only about five hours. The results challenge the long-standing assumption that the enormous collision could be modeled as if both worlds behaved mostly like fluids.

The Moon may have formed intact just hours after a giant collision. Simulations using older models that don’t factor in structural strength produce a debris disk (top), while the new models can produce an intact moon from the outset (bottom). Pyle Earth has an unusually large moon compared with other rocky planets in the solar system, but scientists still do not fully understand how it formed.

A new study from researchers at the Southwest Research Institute and the University of Arizona suggests that one long-overlooked factor may have played a major role in the Moon’s birth: the physical strength of the worlds that collided. Using advanced computer simulations, the researchers examined the enormous impact thought to have occurred about 4.5 billion years ago between the young Earth and a Mars-sized object. Their results reveal strikingly different outcomes depending on the temperature and structural properties of the two bodies.