The most widely accepted scenario for forming the Earth-Moon system involves a dramatic impact between the proto-Earth and some other cosmic body. Many features of the present-day Earth-Moon system constrain this impact’s nature. These constraints vary from a model where the impacting object strikes the newly formed Earth with a glancing blow and then escapes through to one where the collision is so energetic that both the impactor and the Earth are vaporized.

Scientists from the Universities of Leeds and Chicago have now examined the dynamics of fluids and electrically conducting fluids. They conclude that the Earth must have been magnetized either before or as a result of the collision.

They claim this could help to narrow down the theories of the Earth-Moon formation and inform future research into what happened.

This updated assessment is based on the Earth’s magnetic field‘s resilience, which is preserved by a geodynamo, a revolving fluid that conducts electricity in the outer core.

Professor David Hughes, an applied mathematician in 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 very formation of the Earth-Moon 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.”

Hence, scientists concluded that the Earth’s field wouldn’t be able to turn on again if it turned off or decreased to a very low level.

Professor Cattaneo said, “It is this remarkable feature that allows us to make deductions about the history of the early Earth, including, possibly, how the Moon was formed.”

Professor Hughes added: “And if that is true, then you have to think, where did the Earth’s magnetic field come from first?”

“We hypothesize that it got to this peculiar state way back at the beginning, either pre-impact or as an immediate result of the impact.”

“Either way, any realistic model of the formation of the Earth-Moon system must include magnetic field evolution.”

Journal Reference:

  1. Fausto Cattaneo, David W. Hughes. How was the Earth–Moon system formed? New insights from the geodynamo. Proceedings of the National Academy of Sciences, 2022; 119 (44) DOI: 10.1073/pnas.2120682119