Durham University scientists have revealed that Earth's Moon likely formed instantly, and not gradually, after a massive cosmic impact.
A Mars-sized astronomical object called Theia collided with the Earth about 4.5 billion years ago, forming the Moon. This is what most scientists have maintained to date, and we really haven’t got a better explanation that would explain why the Moon is where it is right now, orbiting our blue marble. But there’s a story to the Moon’s formation. Previous theories suggested that the Moon was formed as a result of the gradual accumulation of debris from this impact. Lunar rock measurements, however, challenge these views, showing that they are similar to the Earth’s mantle, while debris from the impact would have originated predominantly from the impactor, Theia.
Durham University scientists have developed a new explanation for the Moon’s origin, predicting an impact that created a Moon-like body that orbits Earth almost immediately, and not gradually, as many scientists had maintained until now. So, how did experts come to this conclusion, and is it really possible for a body the size of our Moon to form almost immediately post impact? To find out, they based their research on a simulation of hundreds of different impacts, using various angles and speeds of the collision, in addition to factoring in the masses and spins of the two colliding bodies. Durham University’s High-Performance Computing facility used the DiRAC Memory Intensive service (“COSMA”) to perform these calculations using the SWIFT open-source simulation code.
What they found was interesting; using the extra computational power, researchers were able to discover features that were previously hidden in lower-resolution simulations about large-scale collisions. As a result of the high-resolution simulations, a Moon-like satellite was created, with the additional detail showing the richer outer layers with material from the primordial Earth. It is also possible that less of the Moon became molten during formation if much of the Moon formed immediately after the giant impact rather than within the debris disk surrounding Earth. Different internal structures for the Moon may be predicted based on details of the subsequent solidification.
Vincent Eke, the co-author of the study, said, “This formation route could help explain the similarity in isotopic composition between lunar rocks and Earth’s mantle.” Additionally, the thickness of the lunar crust may also bear observable consequences, which could help us determine what type of collision took place.” Further, they discovered that even when a satellite passes so close to Earth that it might be expected to be destroyed by “tidal forces” from Earth’s gravity, the satellite actually survives, being pushed into a wider orbit, reducing its chance of being destroyed later.
According to Jacob Kegerreis, lead researcher of the study, “This opens up a whole new range of possible starting points for the evolution of the Moon. At the outset of this project, we were unsure what the outcome would be from such high-resolution simulations.” It was exciting to know that the new results could include a tantalizing Moon-like satellite in orbit, as well as the big eye-opener that standard resolutions can yield wrong answers. Whether this is true or not can be more clearly determined by future manned missions to the Moon. These missions will also reveal what kind of giant impact led to the Moon, which will hopefully reveal new insight into the formation and history of our planet.