What critical component does our planet have that just-down-the street solar neighbor Mars is missing? Water’s not a bad guess, and life always tops the list when tantalizing new hints about Martian creatures come to light. But today, we’re talking about a more protective property: Earth’s strong magnetic field.
How does Earth’s magnetic field work? Where did it come from, and how is it changing over time? How is the concept used (and misused) in popular media, and what are actual STEM experts doing with magnetic field functions?
What Are Magnetic Fields, and How Do They Work?
Despite the ubiquity and familiarity of magnets, their exact operation remains a mystery. The basics are easy: It’s all about electron spin. In most objects, electron spin is fairly even — approximately half spin one way and half spin in the opposite direction. However, in materials such as iron, nickel, and cobalt, more electrons spin one direction than the other. When exposed to an external magnetic force, these objects become permanently magnetized. In practice, this means the creation of north and south poles and a corresponding magnetic field that flows from north to south. This type of magnetism is known as ferromagnetism.
There’s also another type of magnetism that matters: electromagnetism. In this case, an electric current applied to an object causes the electrons to align, in turn creating a magnetic field. This field only exists so long as the current is on — when the source shuts off, the magnetic field fails.
The challenge? While we understand how magnetism works in context, scientists still aren’t exactly sure why the conditions for magnetism exist in the first place.
What Causes Earth’s Magnetic Field?
Earth’s magnetic field is likely tied to the movement of molten metal in the Earth’s core that causes electric currents and effectively makes the planet into a massive magnet with two poles, north and south. But these don’t always line up with the geographical north and south poles. In fact, Earth’s magnetic poles switch places approximately once every 300,000 years, and there’s evidence that we’re due for another switch soon. Right now, the poles are moving at 35 miles per year.
The result of this molten movement is a magnetic field that extends out and around our planet in a “teardrop” shape thanks to pressure and compression from solar wind. It’s this wind we’d need to be worried about if our magnetic field ever disappeared — the strength of Earth’s field means that most high-energy particles tossed our way by the sun never reach the surface; instead, they’re trapped by constantly moving field lines. Worth noting? The intensity of these particle pushes isn’t consistent. Solar “storms” can cause an uptick in particle volume, which in turn creates brighter and more easily visible northern and southern lights.
But this isn’t the whole story. New research suggests that Earth may have had a magnetic field more than 4 billion years ago, long before the core started solidifying and molten rock movement began the process of massive magnet creation. The result? Other forces must have been at work — but there’s no consensus around exactly what causes Earth’s magnetic field.
Magnetic Movie Magic
Given the ubiquity and familiarity of our magnetic field, it’s no surprise that the concept shows up in a host of sci-fi movies. The caveat? Some do it better than others.
In the swing-and-a-miss magnetism department, we’ve got films like Terminator 3: Rise of the Machines. In the film — spoiler alert! — the heroes turn on a massive electromagnetic coil to pull in the evil T-X for an untimely demise. The problem? Other magnetic items in the scene are totally unaffected. This is an oversight we see in sci-fi quite a bit: the science conveniently stops working when the fiction demands it.
On the other side of the coin are movies like The Core, which do a decent job of explaining the protective impact of Earth’s magnetic field and why it’s such a massive problem that the planet’s core has stopped spinning. It’s not all good news, however. The movie claims that Earth’s magnetic field protects us from solar microwaves, which simply isn’t true. Not only does the sun produce a minimal amount of microwaves compared with other types of radiation, but these waves are absorbed by the air when they arrive. Even more problematic? Magnetic fields don’t affect microwaves. At all.
Making Magnetic Fields Work for Us
While movies may not make the most of magnetism, scientists are hard at work looking for new ways to leverage this field-producing framework.
Consider work from MIT on ferrimagnetic substances. While similar to ferromagnetic materials, there’s a significant difference between the two. Ferromagnets see the north-south axes of their atoms lined up in the same direction, in turn producing a strong magnetic field. Meanwhile, ferrimagnets have sets of atoms with axes in the opposite direction. If the number of atoms pointing in each direction is equal, the result is no magnetic field. However, changing the orientation of even a few atoms produces a weak magnetic field. While they can’t compete with ferromagnets for strength, their ability to flip directions with only minor adjustments makes ferrimagnets a great choice for data storage — new research leverages small changes to rapidly flip the magnetic polarity, effectively allowing these magnets to act as a “1” or “0” in binary storage devices.
Efforts from the University of Konstanz managed to isolate a new type of magnetism that exists in strontium ruthenate (Sr2RuO4), which is a well-known superconductor. Using a beam of muons, the team found surface magnetism that exists independently of superconductivity and can coexist alongside it — something long thought impossible. The muon beam revealed that, unlike most magnetic materials that rely on electron spin, circulating electron currents at nanometer scale are responsible for Sr2RuO4‘s magnetism. Other work includes the development of ultra-sensitive magnetometers capable of pinpointing positions even if GPS systems are damaged or unavailable.
Simply put, our planet’s magnetic field offers a massive benefit for life on Earth. Without it, solar radiation would slowly strip away our atmosphere, in turn giving rise to a second red planet in our solar system.
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