Our planet’s magnetic field is a prodigy, not a late bloomer, according to a new study.
The protective magnetic field that surrounds Earth is so strong it must have formed early in our history, but there’s a complication in the timing: Earth was probably hit by a Mars-sized protoplanet some time ago. 4.5 billion years old. This crash may be related to the formation of our magnetic field.
“Previous theories had failed to recognize this potentially important link,” co-author David Hughes, an applied mathematician at the University of Leeds, said in a statement. (opens in a new tab) of the peer-reviewed study in PNAS (opens in a new tab)published on Wednesday (November 2).
The interplanetary collision was so colossal that it created masses of material that formed Earth’s moon, according to the “giant impact hypothesis” of the moon’s origin story. Scientists have studied isotopes (types of elements), meteorites, and geology for decades to constrain moon formation, but the magnetic field hypothesis is not explored as thoroughly.
Related: Earth’s moon had an ocean of magma for 200 million years
The Earth generates its magnetic field through a geodynamo process, which requires a planet to spin at a certain speed and have an interior fluid that can conduct electricity, among other properties. The Earth’s outer molten iron core is where the conversion into electrical and magnetic energy takes place.
The field is self-sustaining, because the magnetic field induces electric currents, and the currents generate a magnetic field. But how this process began in the first place is poorly understood. In their paper, the authors state that these are key questions that need to be asked in future research to determine whether the strong field existed before or after the impact:
- What are the conditions under which disk accretion leads to the formation of a highly magnetized protoplanet?
- What types of impact will leave a highly magnetized liquid core? • Conversely, what types of impacts can lead to the strong magnetization of the liquid core?
- Can the removal of the crust and/or the mantle by a giant impact create the conditions for vigorous convection in the core?
- Can the instabilities caused by the rapid loss of angular momentum [loss of rotational speed] lead to a strong magnetization of the nucleus?
- Can the recondensation of accretionary tori [in other words, the coming together of the donut-shaped accretion disk after the impact] lead to dynamo action?
There is too little information at this time to choose between the scenarios, the authors point out, but they add that the big crash cannot be ignored when considering the formation of the Earth’s magnetic field.
The field is related to the relatively rapid rotation of the Earth (24 hours), which is essential to keep magnetism alive. The dynamo only works if maintained, the researchers said, and cannot restart due to physical stresses inside the Earth. It is unknown, however, if the impact caused the dynamo or if the Earth’s rotation created a strong dynamo earlier in history – one strong enough to withstand the impact. Further study will be required to limit the timeline.
“It is this remarkable feature [of dynamo persistence] it allows us to make inferences about early Earth history – including, perhaps, the formation of the Moon,” said lead author Fausto Cattaneo, an astrophysicist at the University of Chicago, in the same press release.
The authors added that keeping this dynamo stress in mind could help future researchers pinpoint when the Earth’s magnetic field occurs, before or after impact. They also call for more studies that delve deep into Earth’s magnetic history.
Elizabeth Howell is co-author of “Why am I taller (opens in a new tab)?” (ECW Press, 2022; with Canadian astronaut Dave Williams), a book on space medicine. Follow her on Twitter @howellspace (opens in a new tab). Follow us on twitter @Spacedotcom (opens in a new tab) Where Facebook (opens in a new tab).
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