The most accepted scenario for the formation of the Earth-Moon system involves a dramatic impact between the proto-Earth and some other cosmic body. Many features of the current Earth-Moon system constrain the nature of this impact. These constraints vary from a model in which the impactor hits the newly formed Earth with a glancing blow and then escapes to a model where the collision is so energetic that both the impactor and the Earth vaporizes.
Scientists from the Universities of Leeds and Chicago have now examined fluid dynamics and electrically conductive fluids. They conclude that the Earth must have been magnetized before or as a result of the collision.
They say this could help narrow down theories of Earth-Moon formation and inform future research into what happened.
This updated assessment is based on the resilience of Earth’s magnetic field, which is preserved by a geodynamo, a rotating fluid that conducts electricity to the outer core.
Professor David Hughes, an applied mathematician from the School of Mathematics at the University of Leeds, said: “Our new idea is to point out that our theoretical understanding of the Earth’s magnetic field today can tell us something about the formation Earth itself Lunar system.
“At first glance, this seems somewhat surprising, and previous theories had not recognized this potentially important connection.”
Professor Fausto Cattaneo, an astrophysicist at the University of Chicago, said: “A peculiar property of the Earth’s dynamo is that it can maintain a strong magnetic field but not amplify a weak one.”
Therefore, scientists concluded that the Earth’s field could not be turned back on if it was turned off or decreased to a very low level.
Professor Cattaneo said: “It is this remarkable feature that allows us to make inferences about the history of the early Earth, including possibly how the Moon formed.”
Professor Hughes added: “And if that’s true, then you have to think, where did the Earth’s magnetic field come from in the first place?”
“We hypothesize that it got to this peculiar state early on, either before the impact or as an immediate result of the impact.”
“However, any realistic model of the formation of the Earth-Moon system must include the evolution of the magnetic field.”
Journal reference:
- Fausto Cattaneo, David W. Hughes. How did the Earth-Moon system form? New knowledge of the geodynamo. Proceedings of the National Academy of Sciences, 2022; 119 (44) DOI: 10.1073/pnas.2120682119