Key points: New analysis of NASA MMS data and computer simulations shows that Earth's magnetosphere carries an unexpected charge pattern: the dawn side is negative and the dusk side positive. The reversal arises from plasma motion interacting with magnetic field lines rather than from static charge buildup. This finding refines models of how solar energy enters near-Earth space and could improve space-weather forecasting and protections for satellites and power infrastructure.
Scientists Reveal an Unexpected Reversal in Earth’s Magnetic 'Heartbeat'
Key points: New analysis of NASA MMS data and computer simulations shows that Earth's magnetosphere carries an unexpected charge pattern: the dawn side is negative and the dusk side positive. The reversal arises from plasma motion interacting with magnetic field lines rather than from static charge buildup. This finding refines models of how solar energy enters near-Earth space and could improve space-weather forecasting and protections for satellites and power infrastructure.
12:33 AM, 11/14/2025Science
Scientists Reveal an Unexpected Reversal in Earth’s Magnetic 'Heartbeat'
Researchers have discovered that the large-scale electric pattern in Earth’s magnetosphere is partially reversed from long-standing expectations: the dawn side carries a negative charge while the dusk side is positive. This surprising result comes from a combination of satellite observations and high-resolution computer simulations and changes how we think about how solar energy enters near-Earth space.
What the magnetosphere does
The magnetosphere is a vast magnetic shield that surrounds Earth and protects the planet from the solar wind, a continuous stream of charged particles emitted by the sun. When the solar wind interacts with Earth's magnetic field it drives electric currents and magnetic forces that power space weather — from brilliant auroras to storms that can disrupt satellites, communications and power grids.
New observations and models
A team led by Yusuke Ebihara of Kyoto University's Research Institute for Sustainable Humanosphere analyzed measurements from NASA’s Magnetospheric Multiscale (MMS) mission and ran detailed numerical simulations reproducing steady solar-wind conditions. Their results, published earlier this year in the Journal of Geophysical Research: Space Physics, show that while the polar regions behave as expected, broad equatorial regions display an opposite charge pattern.
'In conventional theory, the charge polarity in the equatorial plane and above the polar regions should be the same,' Ebihara said. 'Why, then, do we see opposite polarities between these regions?'
Why the reversal occurs
The study explains the reversal as a dynamic effect of plasma motion rather than a static buildup of charge. When solar energy and magnetic reconnection set plasma in motion, that plasma circulates around the planet. On the dusk side the flow tends to circulate clockwise and move toward the poles. Meanwhile, Earth's magnetic field lines generally run from the Southern Hemisphere to the Northern Hemisphere, pointing upward near the equator and downward near the poles. Because the plasma flow and field-line orientation are opposite in these regions, their interaction alters how charge accumulates and produces the observed reversed pattern.
'The electric force and charge distribution are both results, not causes, of plasma motion,' Ebihara added.
Implications
By showing that different parts of the magnetosphere can behave oppositely, the work refines models of how solar energy enters Earth's upper atmosphere and drives space weather. Improved understanding of these charge patterns can enhance space-weather forecasting and the protection of satellites, power grids and other technologies. The findings may also inform studies of the magnetospheres of other planets such as Jupiter and Saturn, where similar processes operate on a larger scale.
Reference: Journal of Geophysical Research: Space Physics (study by Y. Ebihara et al., published earlier this year).