In May 2024, Earth was hit by the strongest geomagnetic storm in more than 20 years.
Known as the Gannon storm or the “Mother’s Day storm,” it was triggered by a series of massive solar eruptions that sent huge clouds of charged particles racing toward our planet.
While the dazzling auroras caught the public’s eye, satellites were quietly capturing something even more dramatic: Earth’s protective plasmasphere was squeezed down to just one-fifth of its normal size.
The plasmasphere is a bubble of charged particles that surrounds Earth and moves with its magnetic field.
It acts as an important shield, helping to protect satellites and other space-based systems from harmful radiation.
Under normal conditions, this layer extends up to about 44,000 kilometers above Earth’s surface. During the height of the May 2024 storm, that boundary was crushed down to only around 9,600 kilometers.
This historic event was captured by the Japanese Arase satellite, which was launched in 2016 to study Earth’s space environment.
By chance, Arase was in exactly the right place at the right time. It recorded the most detailed, continuous measurements ever made of the plasmasphere during a superstorm.
At the same time, scientists on the ground used GPS receivers to monitor changes in the ionosphere, the upper layer of Earth’s atmosphere that feeds charged particles into the plasmasphere.
By tracking both layers at once, the team, led by Dr. Atsuki Shinbori of Nagoya University, could clearly see how the storm unfolded.
Within just nine hours, powerful solar winds compressed the plasmasphere to a fraction of its usual size.
What surprised the researchers even more was how long it took to recover. Instead of returning to normal within a day or two, it took more than four days for the plasmasphere to slowly refill. This was the longest recovery time recorded since Arase began its mission.
One reason for the slow recovery was something scientists call a “negative storm.” At first, the storm caused intense heating near Earth’s poles, driving charged particles into the polar atmosphere. But later on, this heating changed the chemistry of the upper atmosphere, reducing the number of oxygen ions available.
These ions are needed to create the charged particles that restore the plasmasphere. With the supply cut off, the recovery process stalled.
The storm’s effects were also visible from the ground. As Earth’s magnetic field was strongly compressed, solar particles were able to move much farther toward the equator than usual.
This caused brilliant auroras to appear in places that rarely see them, including Japan, parts of southern Europe, and even Mexico. The farther from the poles auroras are seen, the more powerful the geomagnetic storm.
At the same time, several satellites experienced technical problems, GPS signals became less accurate, and radio communications were disrupted. These kinds of issues can affect navigation, aviation, emergency services, and power grids.
By studying this rare event, scientists now have a clearer understanding of how Earth’s protective plasma layer reacts to extreme space weather.
This knowledge is essential for improving future forecasts and protecting the technology that modern life depends on, both on Earth and in space.
