15 Jul 2026

For decades, scientists have thought that there is a ceiling to how intensely Earth responds to solar storms. However, a NASA-led paper published Wednesday in Nature suggests this upper limit is an illusion. If so, it means solar storms could have far worse effects on our technology than previously thought.

Observations have suggested that electric currents in Earth’s upper atmosphere — which can affect satellites, communications, and navigation signals — increase as the solar wind strengthens, but only to a point.

However, a team led by space physicist Nithin Sivadas of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, says this apparent limit is merely an effect of uncertainties in solar wind measurements.

The issue is that most solar wind measurements are taken by spacecraft located a million miles closer to the Sun than Earth is. However, statistically, the solar wind that ultimately reaches Earth’s magnetic shield is most likely weaker, said Sivadas. This makes it look like strong solar winds do not produce equally strong currents, because it is actually driven by weaker solar winds.

The team analyzed evidence from more than a million solar wind measurements taken by NASA spacecraft much closer to Earth, such as MMS and THEMIS. Unlike the measurements captured farther away, these showed a direct relationship between the strength of the solar wind and the currents, suggesting there is no upper limit.

The findings challenge decades of understanding, and more observations of strong solar wind will help determine whether Earth’s response truly has an upper limit.

[Image]

As solar wind strikes Earth during a solar storm, electric currents intensify in the upper atmosphere. In the chart on the left, a blue line shows how the average strength of electrical currents in Earth’s upper atmosphere increases with solar wind strength but then gradually levels off or “saturates” when measured about a million miles from Earth. (Both values are represented in millivolts per meter.) In the chart on the right, a new analysis based on solar wind measurements taken closer to Earth suggests that the average strength of the electrical currents (pink line) continues to increase as the solar wind strength increases, with no upper limit.