Earth was just hit by the strongest solar radiation storm in over 20 years — here’s what it means

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gif animation showing white flecks speed across the screen, it looks like it's snowing in space — A portion of the solar radiation storm captured on Jan. 19. The incoming protons look like a ‘snowstorm’ on the SOHO spacecraft’s LASCO instrument. The bright specks of light in the frame are Venus, Mercury and Mars. (Image credit: ESA/SOHO)

While a severe G4 geomagnetic storm impressed skywatchers with vivid auroras around the world this week, a far less visible, but historically significant, space weather event was also underway.

Solar radiation storms occur when a powerful magnetic eruption on the sun, often involving a coronal mass ejection (CME), accelerates charged particles, mainly protons, to extreme speeds. These particles can reach a significant fraction of the speed of light, allowing them to traverse the roughly 93 million miles (150 million kilometers) between the sun and Earth in tens of minutes or less, according to NOAA. When they arrive, the most energetic protons can penetrate Earth’s magnetic defenses and travel along our planet’s magnetic field lines toward the polar regions, where they plunge into the upper atmosphere.

NOAA classifies solar radiation storms on a scale from S1 (minor) to S5 (extreme) based on GOES satellite measurements of incoming high-energy protons. The Jan. 19 event reached S4 (severe) levels.

While it may sound dramatic, this type of storm poses no threat to people on the ground, thanks to Earth’s thick atmosphere and magnetic field, which absorb the radiation before it reaches the surface.

Notably, this was not a “ground-level event,” in which particles are energetic enough to be detected at Earth’s surface. As space weather physicist Tamitha Skov explained, this storm had a relatively “soft” particle spectrum — historic in strength, but lacking the extreme energies needed to reach the ground.

graphic detailing the impact the of the severe solar radiation event on Jan. 19 and the effects it has on space technology. — A NOAA graphic explaining the severe S4 solar radiation storm event on Jan. 19. (Image credit: NOAA Space Weather Prediction Center)

High above the surface, it’s a slightly different story.

Severe radiation storms increase exposure risks for astronauts and for airline crews and passengers flying along polar routes, where Earth’s magnetic shielding is weaker. Satellites are also vulnerable: energetic particles can interfere with onboard electronics, disrupt sensors, and overwhelm instruments. During this storm, some space weather forecasters reported temporary data dropouts, likely caused by intense proton fluxes degrading spacecraft measurements.

Is a solar radiation storm the same as a geomagnetic storm?

No, they are distinct space weather phenomena with different effects. Solar radiation storms are driven by fast-moving particles from the sun, while geomagnetic storms occur when disturbances in the solar wind interact with Earth’s magnetic field.

Geomagnetic storms occur most often when a CME’s magnetic field slams into Earth’s own, but sometimes also when fast streams of solar wind flow outward from coronal holes. These interactions can trigger auroras and cause disturbances in navigation, radio communications and power systems.

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