What Is A Geomagnetic Field, And What Sets It Apart From Other Electromagnetic Fields?

But wait – isn’t that a geomagnetic field? Well, yes – but if someone’s told you that makes it a different kind of thing from the electromagnetic field coming out of your cellphone, then we’ve got bad news.

What are electromagnetic fields?

Partly because of their fancy-pants name, and partly because they’re most familiar to us through the myriad modern appliances that create and use them, we tend to think of electromagnetic fields as a quintessentially high-tech phenomenon. 

But in fact, they’ve been all around us for… well, forever: “Natural electromagnetic fields occur mainly as thermal radiation (infrared), visible light or ultraviolet radiation from the sun,” pointed out Akram Alomainy, Deputy Dean for Postgraduate Research in the Faculty of Science and Engineering and Professor of Antennas and Applied Electromagnetics at Queen Mary University, London. “Fire and lightning are also sources of electromagnetic fields.”

So, what is an electromagnetic field – this mysterious thing that powers our Wifi, is produced by the sun, and freaks out your Facebook-pilled aunt?

“An electromagnetic field (EM field) is a physical existing field,” Alomainy told IFLScience. “[It] can be described as mathematical functions of position and time linked mainly to electric charge and how those fields can alter the charge.”

It sounds insanely complicated, right? But it rests on a fact that physicists have long known and the rest of us aren’t usually aware of: that electricity and magnetism are kind of the same thing.

Let’s go as basic as we can: “Every substance is made up of tiny units called atoms. Each atom has electrons, particles that carry electric charges,” explains National Geographic. “Spinning like tops, the electrons circle the nucleus, or core, of an atom. Their movement generates an electric current and causes each electron to act like a microscopic magnet.”

So, why isn’t absolutely everything in the world magnetic? Well, in a way, it is – but usually, all those electrons spinning in different directions end up canceling each other out. It’s when that balance is skewed that something becomes magnetic.

Now, the movement of an electrical charge induces a magnetic field – and when considered together, the two aspects combine to make an electromagnetic field. It’s basically a way to describe how strong the electric and magnetic force is at some point in time and space – just, considered all at once.

What types of electromagnetic fields exist?

Since they’re generated by the movement of electrical currents, there are an awful lot of sources for EM fields. “Electromagnetic fields are part of the electromagnetic spectrum,” explains the German Federal Office for Radiation Protection. “Over its entire range, the spectrum extends from static electric and magnetic fields over optical radiation to very energetic gamma radiation.” 

But “for the part of the spectrum in between static electric and magnetic fields and infrared radiation, the generic term ‘electromagnetic fields’ is common,” it explains.

That’s quite a big gap, as it turns out. It covers fields from gigantic bodies like the Sun and Earth, as well as those emanating from the movement of neural currents in your brain. It includes your WiFi and cellphone signals, and the result of charged particles moving in plasma.

“EM waves and fields are everywhere around us, since all wireless communications and networks are based on their principle of operation,” Alomainy told IFLScience. “This means the WiFi we use, the mobile phone we are glued to continuously, the signals from satellite, TVs, Radios, remote controlled automated devices and so on.”

“We also see EM fields in medical diagnosis devices and imaging,” he added, “and the tags and monitors sportsperson[s] wear for performance analytics and training. They are literally everywhere.”

What are geomagnetic fields?

So, that’s electromagnetic fields – now, what are geomagnetic fields? Well, in a way, that’s like defining “fruit” and then asking what a banana is: “’geo’ – that can be translated to ‘Earth’,” explained Neesha Schnepf, a Research Geophysicist at the USGS Geomagnetism Program, “so it’s the electromagnetic field surrounding the Earth.”

Despite the name, though, Earth is far from unique in possessing this kind of geomagnetic forcefield. “Mercury also has one,” Schnepf told IFLScience, as do all four gas giants. Mars used to have a geomagnetic field, but it waned into nothingness about four billion years ago; Venus, meanwhile, may have never had one at all – the scientific jury is still out.

It’s a core property that separates out those planets that do and do not have an internally made magnetic field – literally: the existence of the field is due to the “churning” of the planetary core, creating a self-sustaining dynamo, Schnepf explains. At least, that’s the textbook explanation – the truth is more nuanced, akin to “when you hear someone playing the piano,” Schnepf told IFLScience. “You can hear the overall tune, but it’s made of all these individual notes – and if you know what you’re doing, you can pick those out.”

The Earth’s magnetic field, then, is mainly produced by its core dynamics – but there’s more than a few other ingredients adding some top notes too. The oceans, electrically conductive as they are, induce their own currents and magnetic fields; volcanoes are basically a collection of various ways to induce electromagnetic effects. Meanwhile, Mars has “quite strong crustal magnetic fields,” Schnepf points out, and plasma in the atmosphere can also create smaller magnetic fields – though “mostly on the daytime side of a planet,” they explained.

With such a diverse range of origin points, it’s no wonder that scientists have found myriad ways to exploit these fields. They can tell us about our own world and others: countless animals use the Earth’s magnetic field for navigation – humans included if you allow for compasses or phone map apps – and on a more grand scale, they provide evidence of the potential for life hundreds of millions of kilometers away from home. 

“NASA and the European Space Agency are both sending crafts to [Jupiter’s moon] Europa,” Schnepf told IFLScience. “The magnetic fields Galileo measured from those icy moons – the only way they made sense was if there were saltwater oceans under the ice.”

But the other famous application of the Earth’s magnetosphere – protecting us from the solar winds and devastating coronal mass ejections that are shot out from the Sun and would otherwise strip away our atmosphere – well, that’s slightly more complex than we’ve traditionally thought, they explain. It’s not that the magnetosphere doesn’t deflect the danger at all – but only outside of the Earth’s poles. Otherwise, the most recent research suggests, our magnetosphere might actually act more like a funnel, increasing the amount of solar energy that hits the area.

It’s perhaps reassuring, then, that a magnetosphere may not be vital for life. “There’s no correlation in the fossil record between the poles flipping and mass extinctions,” Schnepf told IFLScience. “We’re starting to think that a planet’s gravity matters more for protecting its atmosphere.”

Still, though – it’s definitely vital for navigating your way around a new city. So, for that reason, if no other, we should probably be grateful for our planet’s geomagnetic field.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.