Earth's Radiation Barrier Breached As 'Killer' Electrons Surge 5,000 Times

Scientists have discovered that one of Earth's supposedly strongest natural radiation barriers can be breached during extreme solar storms. The finding challenges an earlier understanding of how the planet's magnetic field protects the space around it from highly energetic particles. The discovery centres on the Van Allen radiation belts, two doughnut-shaped regions surrounding Earth that contain electrically charged particles trapped by the planet's magnetic field.

The inner belt contains large numbers of energetic protons, while the outer belt is largely populated by electrons influenced by solar activity. These regions play an important role in protecting Earth from some forms of radiation, although they can pose risks to satellites and astronauts.

For more than a decade, scientists believed that the inner radiation belt acted as an almost impenetrable barrier, preventing extremely energetic electrons, often called 'killer electrons', from moving closer to Earth.

However, a powerful solar storm in May 2024 provided evidence that this barrier is not as secure as previously thought.

According to a study published in the journal Geophysical Research Letters, researchers detected unusually energetic electrons inside the supposedly protected region during the storm.

The observations were recorded by Japan's Arase satellite, which has been monitoring Earth's radiation belts since 2017.

The May 2024 solar storm was classified as a G5 geomagnetic storm, the highest category on the scale. It followed a series of powerful solar flares and coronal mass ejections that sent enormous amounts of charged particles towards Earth.

The storm significantly reduced the amount of cold plasma in a region surrounding Earth called the plasmasphere. This created conditions that allowed electromagnetic waves, known as chorus waves, to accelerate electrons to extremely high energies.

At around three megaelectronvolts, the number of energetic electrons increased more than 5,000 times compared with levels recorded before the storm.

The researchers believe the particles were accelerated within the inner radiation belt rather than simply being pushed inwards from elsewhere.

Such electrons can travel at speeds close to that of light. Their high energy allows them to penetrate satellite shielding, potentially damaging sensitive electronic equipment and shortening spacecraft lifespans. They can also increase radiation exposure risks for astronauts.

The study found that the increase in energetic electrons was gradual. Lower-energy particles appeared first, followed by more energetic ones over the next 24 hours. This suggested that the electrons were gaining energy within the inner radiation belt itself.

The effects of the storm were not short-lived. Arase continued to record declining levels of these highly energetic electrons until October 2024, when another solar storm affected the region.

The researchers, led by space physicist Yoshizumi Miyoshi of Nagoya University in Japan, said the findings highlight the need to understand how energetic particles behave during extreme space weather events.

The discovery could help scientists improve space weather forecasts and assess radiation risks to satellites, spacecraft and astronauts.

The research was published in Geophysical Research Letters on October 26, 2026.