Devotees of this blog surely know how much we love Earth’s magnetic field. Indeed, it’s a pretty important component for sustaining life on our planet, shielding us from the harmful radiation hurled out by the sun. Other planets have them, too. Jupiter’s magnetic field is the largest entity in our entire solar system!

Conversely, our moon does not have a magnetic field, but this wasn’t always the case. Based on magnetic rock samples brought back from Apollo missions, research suggests our humble little moon once possessed a very powerful magnetic field, one that could rival Earth’s.

Where Does the Moon Come From?

Before we dive into where the moon’s magnetic field went, let’s remember where the moon came from. In fact, the moon was once part of Earth! That’s the most widely-accepted theory at least. Billions of years ago, when our sun was still in its infancy, tons of space dust and gases started gathering to form our planets—including Earth. Some of these newly formed celestial bodies weren’t as lucky and never made it to orbit. As a result, they were sent rocketing through space.

One of these masses smacked right into Earth, breaking it back apart. Thus, the moon was born—a hunk of rock split from Earth but couldn’t bear to leave.

The Dynamo Effect

If this separation theory holds true, it’s easy to see why the moon would’ve had a magnetic field in that it had the same geological make-up as Earth. So, what’s the next piece of the puzzle?

Again, we must look at Earth for a little insight. Scientists theorize that Earth’s magnetic field is propelled by the dynamo effect. Essentially, the outer core—made of molten iron ore—rotates in the opposite direction of the surface, creating our magnetic field. So, it stands to reason the moon could’ve produced a similar phenomenon.

Where’d The Moon’s Magnetic Field Go?

In short, the moon’s magnetic field ran out of fuel. The dynamo we have on Earth relies on immense pressure and heat to keep the outer core in a liquid state. The moon’s core, conversely, could not maintain these essential elements. So, as the core cooled and the dynamo slowed down, the moon’s magnetic field steadily weakened until it disappeared for good.

Knowing the moon once had its own magnetic field and the rate at which it died out helps scientists confirm some long-held theories while challenging others. Namely, we can more accurately assess its geochemical make-up and even estimate when it split from Earth. Magnetism once again provides us with answers.

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