Importance of Earth’s magnetic field

 Earth’s magnetic field shields us from space weather and radiation

The Earth’s magnetic field plays a big role in protecting people from hazardous radiation and geomagnetic activity which could affect satellite communication and the operation of power grids. Our planet’s magnetosphere has seen dramatic shifts across its history, even total reversals. Scientists have studied and tracked the motion of the magnetic poles for centuries. The historical movement of these poles indicates a change in the global geometry of the Earth’s magnetic field. It may even indicate the beginning of a field reversal, a “flip” between the north and south magnetic poles. About 780,000 years ago, something strange happened to Earth’s magnetic field. The giant, protective shield which surrounds the planet weakened immensely over thousands of years, which may have exposed the surface to increased doses of particles and radiation from space. Perhaps most dramatic of all, the magnetic north and south poles flipped positions. While the north magnetic pole moving a little bit isn’t a big deal, a reversal could have a big impact on Earth’s climate and our modern technology. But these reversals don’t happen instantaneously. Instead, they occur over thousands of years.

The event, known as the Matuyama-Brunhes reversal, wasn’t totally out of the ordinary, such a flip has happened an estimated 183 times in the last 83 million years, but nothing quite like it has been recorded since. Exactly what caused this polar reversal remains a mystery, but it is just one example of the odd side effects of the dynamic nature of the Earth’s core. Magnetic north wanders and shifts, the field sometimes falters, and the whole system has nearly collapsed. Now, a recent analysis of satellite data suggests that once again, “something special” is happening in the magnetic field, says Chris Finlay, a researcher of geomagnetism at the Technical University of Denmark. This time, the strange behaviour is located over the southern Atlantic Ocean, and it’s not a reversal. Rather, it’s a growing weak spot, but this doesn’t pose a threat to life. Magnetic fields are generated by moving electric charges. A material that enables charges to easily move in it is called a conductor. Metal is one example of a conductor, people use it to transfer electric currents from one place to the other. The electric current itself is simply negative charges called electrons moving through the metal. This current generates a magnetic field. Layers of conducting material can be found in the Earth’s liquid iron core. Currents of charges move throughout the core, and the liquid iron is also moving and circulating in the core. These movements generate the magnetic field. The Earth's magnetic field deflects particles emitted by the Sun. Earth isn’t the only planet with a magnetic field, gas giant planets like Jupiter have a conducting metallic hydrogen layer that generates their magnetic fields.

The movement of these conducting layers inside planets results in two types of fields. Larger motions, such as large-scale rotations with the planet, lead to a symmetric magnetic field with a north and a south pole, similar to a toy magnet. These conducting layers may have some local irregular motions due to local turbulence or smaller flows which do not follow the large-scale pattern. These irregularities will manifest in some small anomalies in the planet’s magnetic field or places where the field deviates from being a perfect dipole field. These small-scale deviations in the magnetic field can actually lead to changes in the large-scale field over time and potentially even a complete reversal of the polarity of the dipole field, where the north becomes south and vice versa. The designations of “north” and “south” on the magnetic field refer to their opposite polarities, they’re not related to geographic north and south. While the North Pole is a fixed point at the northern end of Earth’s rotational axis, magnetic north is an ever-changing spot where the planet’s magnetic field lines meet. Magnetic north has long been wandering around the Arctic, but within the last century, it has accelerated toward Siberia. Since the 19th century, scientists have been tracking the weak spot in Earth’s magnetic field, also known as the South Atlantic Anomaly. The first satellite measurements of this magnetic “dent” came in 1958, and researchers spent the following decades seeking to understand it. The recent analysis revealed the weak spot is growing, and since 2014, it expanded by an area nearly half the size of continental Europe.

The Earth’s magnetic field creates a magnetic “bubble” called the magnetosphere above the uppermost part of the atmosphere, the ionosphere layer. The magnetosphere plays a major role in protecting people. It shields and deflects damaging, high-energy, cosmic-ray radiation, which is created in star explosions and moves constantly through the universe. The magnetosphere also interacts with solar wind, which is a flow of magnetized gas sent out from the Sun. The magnetosphere and ionosphere’s interaction with magnetized solar wind creates what scientists call space weather. Usually, the solar wind is mild and there’s little to no space weather. The shift is “not completely unexpected and the growth ultimately confirms what researchers have been expecting for decades. According to the new findings, it turns out the weak spot actually contains two parts, one that has moved closer to South America and a second to the southwest of Africa. The spot near Africa is weakening the fastest, especially in the last few years. However, there are times when the Sun sheds large magnetized clouds of gas called coronal mass ejections into space. If these coronal mass ejections make it to Earth, their interaction with the magnetosphere can generate geomagnetic storms. Geomagnetic storms can create auroras, which happen when a stream of energized particles hits the atmosphere and lights up. During space weather events, there’s more hazardous radiation near the Earth. This radiation can potentially harm satellites and astronauts. Space weather can also damage large conducting systems, such as major pipelines and power grids, by overloading currents in these systems. Space weather events can also disrupt satellite communication and GPS operation, which many people rely on.

The weak spot in the magnetic field grew by an area nearly half the size of continental Europe between 2014 and 2025. While a weak spot in the protective magnetic bubble that surrounds Earth might sound like the start of a science fiction movie about the end of the world, scientists say it’s not a problem, and it almost certainly won’t become one in your lifetime. Though the geomagnetic field plays a crucial role in protecting Earth from space radiation, the atmosphere also protects us from harmful rays. Instead, satellites that orbit beyond the densest parts of the atmosphere can be affected by a weak spot, since increases in radiation can cause malfunctions or outages. Earth’s magnetic field is generated deep within the planet by the flow of liquid iron in the outer core. As the fluid metal churns, its motion generates electrical currents which create the magnetic field that envelops the planet. This is known as a dynamo, and the entire region affected by Earth’s magnetic field is called the magnetosphere. Scientists map and track the overall shape and orientation of the Earth’s magnetic field using local measurements of the field’s orientation and magnitude and, more recently, models. The location of the north magnetic pole has moved by about 600 miles (965 km's) since the first measurement was taken in 1831. The migration speed has increased from 10 miles per year to 34 miles per year (16 km to 54 km) in more recent years. This acceleration could indicate the beginning of a field reversal, but scientists really can’t tell with less than 200 years of data.

Often, people explain the magnetic field as a bar magnet. Imagine, at the centre of Earth, an amazingly strong bar magnet with lines emerging from the north pole and curving back down at the south. The field is the strongest at the poles, where the lines are closest together. But the reality is a bit more complicated, experts say. The motion happening at the core has a lot more variation than a bar magnet would. The natural variation in turn causes changes in the magnetic field. Researchers say it is important to understand these changes, and study the past, present and future of the magnetosphere, because of what it can reveal about our planet. The Earth’s magnetic field reverses on time scales that vary between 100,000 to 1,000,000 years. Scientists can tell how often the magnetic field reverses by looking at volcanic rocks in the ocean. These rocks capture the orientation and strength of the Earth’s magnetic field when they are created, so dating these rocks provides a good picture of how the Earth’s field has evolved over time. Field reversals happen fast from a geologic standpoint, though slow from a human perspective. A reversal usually takes a few thousand years, but during this time the magnetosphere’s orientation may shift and expose more of the Earth to cosmic radiation. These events may change the concentration of ozone in the atmosphere.

Scientists can’t tell with confidence when the next field reversal will happen, but we can keep mapping and tracking the movement of Earth’s magnetic north. The magnetosphere “contains a lot of information about the structure, dynamics and the story of the Earth. It all adds up to be “quite important, for deciphering the planet’s geological history. The magnetosphere protects Earth from dangerous solar radiation and high-energy space particles called cosmic rays. The magnetic field prevents the atmosphere from eroding off into space. It is also critical in shielding from radiation some of the technology intrinsic to modern life, including the satellites constantly feeding information back down to Earth. As satellites circle the planet, they are exposed to charged particles from the solar system. Flying through the South Atlantic Anomaly raises the risk of exposure, because the field is weaker there. Imagine the magnetic field lines as farther apart in that area, letting a higher dose of radiation pass through. Satellite operators are aware of the South Atlantic Anomaly and can plan ahead. For example, the Hubble Space Telescope routinely shuts down some of its electronics while it passes through the weak spot, so as to avoid interference.

Sometimes, when the sun expels an unusually high amount of charged particles as solar wind, the incoming energy disturbs the magnetosphere in what is known as a geomagnetic storm, and our technology can be interrupted, despite the protective magnetic field. This gives us a hint of why the field is so important to modern life as we know it. You can have power line disruption or grid disruption. You can have telecommunication disruption, and you can also have disruption in satellite operations. To approximate what might happen to Earth in the absence of a magnetic field, we can look to other planets. Mars, for example, lost its global magnetic field long ago, and over time, its atmosphere has been stripped away by solar wind. Mercury has a weak magnetic field, and Venus doesn’t generate one at all. Many people use the magnetic field on a daily basis, even if they don’t realize it. Smartphones use it to figure out which direction they are pointing, just as many animals use it for navigation.

The processes which dictate the magnetic field’s behaviour happen in the Earth’s core, and with its outer edge at roughly 1,800 miles beneath the surface, this region is very difficult to study. It’s probably one of the least known places on the planet. While scientists understand the basic physics principles at play to power the planet’s magnetic dynamo, they still don’t entirely know what causes extreme events or anomalies. Studying past magnetic changes can help reveal underlying trends in the core. When gathering real-time data about the magnetic field, satellites are key. The recent paper showing the changes in the South Atlantic weak spot is based on 11 years’ worth of observations from Swarm, a group of satellites from the European Space Agency meant to measure the magnetic field. Each of the original three satellites (a fourth was added in 2018) is armed with an Absolute Scalar Magnetometer and a Vector Field Magnetometer. The former instrument is used to calibrate the latter, and together, along with other tools, they record the strength and direction of the magnetic field. Satellite information about the field only goes back to the 1950s, but first-hand measurements of the field go back about 500 years.

Going back even further, researchers can’t rely on human accounts and measurements anymore. Instead, they turn to rocks. As a rock forms, electrons within the molten magma move around based on the orientation of Earth’s magnetic field. When it solidifies and cools to its Curie temperature, the temperature at which electrons’ orientations are set, it records a vestige of the surrounding magnetic field at that time. Researchers venture outside, often to very remote areas like Western Australia, the Arctic and Greenland, to gather rock samples from specific times. Once collected, the researcher puts the samples into a rock magnetometer, which can sense the remnant magnetism in the rock. In theory, the magnetic properties a rock displays are like a time capsule for the Earth’s magnetic field when the rock was formed. Complementing the satellite and rock magnetometer measurements are complex computer models aimed at approximating past magnetic field changes and predicting future situations. Throughout Earth’s history, there have been several such extremes, including complete polarity reversals like the Matuyama-Brunhes event, in which the north and south magnetic poles traded places. Researchers don’t know when, or if, that will happen again. Based on models and knowledge about past weak spots in the magnetic field, experts expect the South Atlantic Anomaly to keep getting bigger over the next decade. If the weak spot does continue to grow, there could be more technological implications. The magnetic field plays a vital role in protecting against interference from solar wind and geomagnetic storms, and a weak spot makes technology like satellites and power grids more vulnerable to interruptions or damage.