A Cosmic Surprise
In the vast, silent expanse of space surrounding our planet, invisible rivers of charged particles flow and swirl, trapped by Earth’s magnetic field. These regions, known as the Van Allen radiation belts, have been a known feature of our cosmic neighborhood for decades. They typically exist as two distinct, donut-shaped zones: an inner belt dominated by high-energy protons and a dynamic outer belt filled with energetic electrons. Between them lies a calmer “slot region,” usually swept clean of the most energetic particles. This familiar map of near-Earth space was dramatically redrawn in 2024.
Following a historic geomagnetic storm on May 10, 2024 – the most powerful in over two decades – scientists discovered something entirely unexpected. Two new, persistent radiation belts had formed, occupying regions of space previously thought to be inhospitable to such long-lived particle populations. One belt is composed of extremely high-energy electrons lodged deep within the slot region, while the other is a robust ring of protons situated closer to Earth than its counterpart.
The findings, detailed in the paper “A New Electron and Proton Radiation Belt Identified by CIRBE/REPTile-2 Measurements After the Magnetic Super Storm of 10 May 2024” by Xinlin Li and colleagues, published in the Journal of Geophysical Research: Space Physics, challenge existing models of radiation belt physics and have significant implications for the safety of the satellites we depend on for modern life. It’s a story of cosmic violence, technological resilience, and the patient collection of data that reveals the hidden dynamics of our planet’s magnetic environment. It underscores how much we still have to learn about the intricate interplay between the Sun and Earth, a relationship that can reshape our corner of the solar system in a matter of hours.
The Storm of a Generation
The story of the new belts begins with our Sun. On May 10, 2024, a series of powerful solar flares and coronal mass ejections (CMEs) slammed into Earth’s magnetosphere, the magnetic bubble that protects us from the worst of the solar wind. This event triggered a severe geomagnetic storm, a disturbance that energized particles throughout the magnetosphere and sent them spiraling down into our atmosphere, creating spectacular auroras seen at unusually low latitudes around the globe.
For space physicists, such a powerful storm is a rare natural experiment. It provides an opportunity to see how the radiation belts respond to an extreme injection of energy. In the past, major storms have been known to deplete the belts, rearrange them, or even add a temporary third belt that dissipates within weeks. The aftermath of the May 2024 storm would prove to be different. It didn’t just create a temporary structure; it forged new, surprisingly stable features in the architecture of near-Earth space. The full picture of this transformation would have remained hidden if not for a stroke of good fortune involving a tiny satellite that had fallen silent just weeks before the storm hit.
A Fortunate Return
The key observations came from a NASA mission called CIRBE, short for the Colorado Inner Radiation Belt Experiment. Managed by the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics, CIRBE isn’t a massive, billion-dollar observatory. It’s a CubeSat, a satellite no larger than a loaf of bread, designed to provide high-quality measurements from a low-Earth orbit. After a successful year of operation, CIRBE unexpectedly malfunctioned on April 15, 2024, going silent just 25 days before the historic storm.
The science team feared the mission was lost. Yet, through a combination of persistence and luck, engineers managed to re-establish contact and restore the satellite to full functionality. On June 16, 2024, more than a month after the storm had subsided, CIRBE’s science instrument, REPTile-2, began sending data back to Earth again.
When the scientists analyzed this new data, they were stunned. The readings were unlike anything seen before. The familiar structure of the radiation belts was there, but with additions. Clear, undeniable signatures of two new, distinct populations of trapped particles had appeared in the storm’s wake. The satellite’s accidental hiatus and fortunate recovery provided a perfect before-and-after comparison, revealing a lasting change to our planet’s radiation environment.
The New Electron Belt: A High-Energy Remnant
One of the most striking discoveries was a new belt of electrons located between L-shells 2.5 and 3.5. This region, known as the slot, is typically an empty buffer zone between the inner and outer Van Allen belts. While storms can sometimes push electrons into this area, they are usually cleared out relatively quickly. This new belt was different. It was composed exclusively of very high-energy electrons, specifically those in the 1.3 to 5 megaelectronvolt (MeV) range. Even more strangely, there was a complete absence of measurable electrons with energies below 1.3 MeV in that specific region.
The Mystery of the Missing Particles
This peculiar energy signature was the key to understanding the belt’s formation. The REPTile-2 instrument on CIRBE has exceptionally high energy resolution, meaning it can distinguish between particles of very similar energy levels with great precision. Older instruments might have seen this new belt as a general increase in electron flux, but REPTile-2’s detailed measurements revealed the sharp energy cutoff.
Scientists believe that during the May 10th super storm, a massive flood of electrons with a wide of energies was injected deep into the magnetosphere, filling the slot region. In the weeks that followed, the space environment began its slow return to normal. A phenomenon known as plasmaspheric hiss – a persistent, low-frequency plasma wave that permeates this region of space – started to do its work.
Hiss waves are very effective at scattering lower-energy electrons. One can imagine these waves as a constant cosmic “wind” blowing through the slot region. This wind is strong enough to knock electrons with energies below about 1.3 MeV out of their stable orbits, causing them to rain down into Earth’s atmosphere where they are lost. The highest-energy electrons are like heavy boulders in this wind. The hiss waves aren’t strong enough to dislodge them effectively.
So, over the course of a month, the hiss waves “cleaned house,” removing the lower-energy population and leaving behind a “remnant” belt of only the most energetic electrons. This process explains why CIRBE observed a new belt with a distinct lower-energy boundary. The long-lasting nature of this belt – it was still clearly visible when CIRBE resumed measurements a month later – provided a perfect real-world laboratory for studying these wave-particle interactions. The data showed that the lifetime of these trapped electrons is strongly dependent on their energy; the higher the energy, the longer they can resist the scattering effects of the hiss waves and remain trapped.
An Eventual Disruption
The new electron belt, while persistent, wasn’t permanent. Its fate was sealed by another, much weaker, geomagnetic storm that occurred on June 28, 2024. While minor compared to the May super storm, this event was enough to stir up the magnetic environment around the new belt. The disturbance likely introduced other types of plasma waves, such as EMIC and chorus waves, or enhanced the existing hiss waves, which scattered the remaining high-energy electrons. When CIRBE passed through the region on July 3, the belt had decayed significantly, though it was still detectable. This subsequent decay reinforced the understanding that the belt’s existence was a delicate balance, maintained during a period of relative quiet and erased by the next significant solar disturbance.
The New Proton Belt: A More Stable Fixture
The second discovery made by CIRBE was, in some ways, even more surprising. The satellite’s data revealed the formation of a new, intense belt of protons with energies between 6.8 and 20 MeV, concentrated around L-shell 2. This is deep inside the inner radiation zone, a region typically known for its long-term stability. Following the May 2024 storm, the intensity of protons in this specific energy range and location increased by more than tenfold, creating a distinct and dense new ring of radiation.
Built to Last
Unlike the new electron belt, which was subject to rapid decay from wave interactions, the new proton belt appears to be far more stable. Protons are much heavier than electrons (nearly 2,000 times more massive), and they interact with the space environment in different ways. Their primary loss mechanism in this region isn’t from plasma waves, but from direct collisions with the tenuous atoms of Earth’s upper atmosphere and interactions with free electrons. This is a much slower and more gradual process.
Scientists analyzed the orbital characteristics of these newly trapped protons and found that their trajectories were highly stable. The magnetic field in that region is strong and uniform enough to hold them securely. The forces that might otherwise cause their orbits to drift and decay, such as field line curvature scattering, are very weak at this location for protons of this energy.
The implication is that this new proton belt is here to stay, at least for a while. Models suggest it will persist for many months, and possibly for more than a year. It stands as a long-lasting monument to the power of the May 2024 storm. Its stability and slow decay will give scientists an unprecedented opportunity to study the gradual loss processes that affect inner-belt protons over long timescales, providing valuable data to refine models of this complex and hazardous region of space.
Implications for Space Technology
The discovery of these new radiation belts is more than an academic curiosity. It has direct and important consequences for space weather forecasting and the operation of satellites. The space surrounding Earth is an increasingly crowded frontier, and our global infrastructure – from communications and finance to navigation and national security – depends on the health of thousands of operational spacecraft.
High-energy particles, like those found in these new belts, are a primary threat to satellites. They can penetrate spacecraft shielding and cause a variety of problems, from minor electronic glitches known as single-event upsets to catastrophic failures. Over time, the cumulative effect of radiation exposure, known as total ionizing dose, degrades sensitive components like solar panels and onboard computers, shortening a satellite’s operational lifespan.
A New Hazard for Modern Satellites
The location of these new belts is particularly concerning for a specific class of modern satellites. Many new spacecraft, especially those destined for geostationary orbit (GEO) some 36,000 kilometers above the Earth, get there via a long, spiraling path called a geostationary transfer orbit (GTO). Instead of using powerful chemical rockets for a quick trip, many modern satellites use highly efficient electric propulsion systems. These “solar electric” engines produce very gentle thrust and must operate for long periods – often many months – to slowly raise the satellite’s orbit to its final destination.
During this extended orbit-raising phase, the satellite makes repeated passes directly through the inner radiation belt and slot region. The unexpected appearance of a long-lasting, high-energy electron belt and a dense, stable proton belt creates a significantly harsher radiation environment than what these satellites were designed and tested for. A spacecraft that was expected to accumulate a certain amount of radiation dose over its months-long journey might now accumulate much more, potentially leading to premature degradation of its solar panels or other critical systems.
The new proton belt is a particular concern for solar arrays, as energetic protons are known to be especially damaging to photovoltaic cells. The new electron belt poses a threat to internal electronics. Engineers and satellite operators now have to account for these new features in their mission planning. The discovery serves as a stark reminder that the space environment is not static; it can and does change in response to extreme events, creating new hazards that can persist long after the initial storm has passed.
A New Era of Discovery
The identification of these two new radiation belts is a testament to the value of continuous, high-quality monitoring of near-Earth space. The CIRBE mission, with its advanced REPTile-2 instrument, demonstrated that even a small, low-cost CubeSat can deliver groundbreaking science. Its high-resolution measurements were essential to unraveling the specific physics behind the new electron belt’s formation – a discovery that would have been obscured by less capable instruments.
The event highlights the dynamic and often unpredictable nature of space weather. The May 2024 super storm didn’t just temporarily disturb the Van Allen belts; it fundamentally altered their structure in a way that will last for months or even years. This provides a rich dataset for scientists looking to improve their models of how the radiation belts are created, sustained, and lost. Understanding these processes is vital for protecting our technological assets in space and ensuring the reliability of the services they provide.
Summary
The great geomagnetic storm of May 2024 left a lasting mark on our planet’s space environment. In its wake, scientists aboard the fortunately-revived CIRBE CubeSat mission discovered two entirely new radiation belts. One, a persistent ring of high-energy electrons with energies from 1.3 to 5 MeV, was carved out by natural plasma waves in the weeks following the storm, offering a unique view into the complex physics of wave-particle interactions. The other, an even more stable belt of energetic protons (6.8-20 MeV), was injected deep into the inner magnetosphere and is expected to remain for more than a year.
These discoveries have reshaped our understanding of Earth’s radiation belts, showing them to be more dynamic and susceptible to long-term change than previously thought. They also introduce new, practical challenges for satellite operations, creating a more hazardous environment for spacecraft journeying through these regions. As we continue to explore and utilize the space around our planet, these new belts serve as a powerful reminder of the Sun’s ability to reshape our cosmic backyard in an instant.
