Earth’s 'peculiar' magnetic field is proof of how strange our solar system came to be

Furthermore, pinpointing the moment the magnetic field emerged could also aid scientists in determining what produced it.

Still, what if the existence of Earth's magnetic field could hint to even more than this? This is where a recent study by scientists from the University of Leeds and the University of Chicago comes in.

The researchers not only theorized on when the Earth's magnetic field emerged but are also the first to recognize that its existence is essential to how the Earth and Moon formed.

Interesting Engineering (IE) spoke with the lead author, Professor David W. Hughes, to gain a deeper insight into the team's work.

Earth's geodynamo process is "somewhat peculiar"  

"The Earth is composed of a solid inner core, a liquid metal outer core, and an outer, electrically insulating mantle," Hughes explained. Scientists know that the vast majority of the magnetic field originates in the fluid outer core of Earth. 

Convective forces, which transfer heat from one point to another (typically through air or water), continuously stir the molten metals that exist there as spinning whirlpools. 

As the Earth rotates, this swirling or roiling mass of metal induces electrical currents, which in turn create another magnetic field that reinforces the original magnetic field. This, the magnetic field sustains itself. It is this mechanism, known as the geodynamo, that is responsible for maintaining Earth's magnetic field.

This magnetic field extends for thousands of miles out in all directions and is in constant flux.

"This geodynamo process is somewhat peculiar in that the fluid motions necessary for maintaining the field are determined by magnetic forces – a sort of "bootstrapping" effect, reliant on a strong magnetic," Hughes told IE. 

Remarkably, if switched off, it would not "kick in again"

He argued that as a result, if the Earth's magnetic field were, somehow, to be reduced to a minimal strength, then the fluid motions would change drastically. They would then be of such a form as to be unable to amplify the magnetic field. Or in other words, the Earth's magnetic field would not be able to "kick in again."

"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," clarified Professor Cattaneo, an astrophysicist at the University of Chicago, in a press release. 

"This prompts the question: How and when did this strong field come into existence?" Hughes expressed to IE. 

"The key point of our work is to argue that the Earth's strong magnetic field (which can be maintained once in place but cannot be generated from a weak field) must therefore have been in place since the Earth's formation," he explained. 

Hughes noted that this new theory underscores that, what we currently know theoretically about the Earth's magnetic field, can really teach us something about how the Earth-Moon system came into being.

What is the "moon-forming impact"?

Various hypotheses have been proposed regarding how the Earth and Moon were created, most of which involve a massive impact. One widely recognized theory relates to how the Earth, like all the other planets in the solar system, began as a disc of dust and gas swirling around the newborn Sun.

Drag forces pulled the dust particles together to create rock clumps. These evolved into "planetesimals" (tens to hundreds of miles across) before merging to form "protoplanets" around the size of a moon. Through one final significant impact with another object the size of Mars, Earth reached its final size.

This final collision - often referred to as the "moon-forming impact"- was so powerful that it did not just add more material to Earth. It had sufficient energy to vaporize some of the proto-Earth as well as rock and metal in the impacting object. Around the Earth, this vapor condensed into a disc, which later cooled and solidified into the Moon.

This theory on the history of the Moon and its relationship to Earth is supported by rigorous chemical studies of lunar meteorites and rock samples brought to Earth by the Apollo moon landings in the 20th century.

An important connection

In 1977 NASA's robotic Voyager 1 spacecraft captured the first full view of Earth & the Moon together in a single frame. Today @NASA_Orion, designed to carry astronauts to the Moon, sent its own view of the Earth-Moon system. Follow along with #Artemis I: https://t.co/w2DE9JLHPq pic.twitter.com/ktWe0SuV4R

— NASA Solar System (@NASASolarSystem) November 28, 2022

By looking at the dynamics of fluids and electrical conduction, Hughes' team found that Earth must have been magnetized either before or as a result of this impact.

"Our argument places a new powerful constraint on theories of the Earth-Moon system and will help distinguish between the various candidates," said Hughes. Simply put, the new theory helps inform future research into what really happened. 

"Not only must such theories account for quantities such as the masses and angular momentum of the Earth and Moon, but must also account for a strongly magnetized Earth," he explained. Previous theories had yet to recognize this potentially important connection.

Going forward, the researchers argue that any realistic model of the formation of the Earth-Moon system must include magnetic field evolution.

In a broader sense, understanding the formation of the Earth and Moon is crucial for reconstructing the evolution of the solar system. It also addresses questions such as how long planets take to develop, what materials accrete to assemble planets, and what characteristics make a planet favorable for life.

Ultimately, all of this directs planetary scientists in their search for more habitable worlds inside and beyond our solar system.