As a child, I enjoyed Wallace and Gromit: A Grand Day Out, most especially because the moon was constructed as a ball of cheese. My understanding of lunar matters has thankfully grown, but the moon still holds many mysteries, including the asymmetrical pattern of its terrain.
The surface of the moon has two distinct planar shapes: lowlands and high mountains. Unlike Earth, the moon does not have moving tectonic plates—which create volcanoes and earthquakes—to explain this difference in geography.
But scientists are coming closer to understanding the far side of the moon, according to recently published work in the scientific journal Nature by Erik Asphaug and Martin Jutzi.
Asphaug’s theory places the blame on a second moon that collided with our moon. This second moon would have formed around the same time as our moon, as a result of debris from the still-forming Earth. At this time, no life existed on Earth, as its molten crust was still too hot for anything to survive.
The second moon would have been very similar to our moon, rising and setting at the same time for millions of years. Perhaps the close proximity of their orbits would have led to the collision over time.
The moon is full of craters from interplanetary debris that crashed into it. So why would a second moon have created such a different physical structure? Simply put, a rare set of circumstances would have made it possible for this “sister” moon to hit our moon and not create a hole. Instead, part of the sister moon’s debris formed into a mountainous shape.
Asphaug and Jutzi have successfully created computer simulations to find those rare circumstances, but there is not yet evidence for their theory. In order to prove the theory, rock samples would need to be collected from the moon’s mountains and compared to samples from the other parts of the moon.
As of yet, no missions are planned to test the theory, but scientists are excited about Asphaug’s innovative ideas. However, next month, a mission called the Gravity Recovery and Interior Laboratory might reveal some answers. By mapping the lunar gravitational field, scientists may find out how likely the sister moon theory may be.