In a unique cosmic event last April, Earth unexpectedly ejected charged particles toward the sun, leading to a rare aurora display. Typically, solar storms from the sun impact Earth’s magnetosphere, creating auroras on our planet. However, on April 24, 2023, a surge of charged particles from the sun disrupted this norm.
During this event, particles from the sun lit up skies as far south as Arizona, Arkansas, and parts of Australia and New Zealand. Unusually, these particles temporarily deactivated Earth’s bow shock, creating a “two-way highway” that allowed particles to travel from Earth to the sun, where they triggered a solar light display. Although this solar aurora was likely too faint to be seen against the sun’s brightness, the phenomenon itself was significant.
NASA’s Magnetospheric Multiscale spacecraft observed that a coronal mass ejection (CME) from the sun, which usually moves faster than magnetic waves known as Alfvén waves, played a key role in this event. The CME’s speed caused the bow shock to temporarily vanish, creating a direct magnetic link between Earth and the sun. This temporary “highway” allowed particles from Earth’s magnetosphere to escape towards the sun, providing new insights into solar and space weather dynamics.
The phenomenon, while rare on Earth, is more common in other parts of the universe. For instance, magnetic highways similarly transport charged particles from Jupiter’s moons to the planet, resulting in spectacular auroras.
This research, detailed in the July 24 issue of *Geophysical Research Letters*, provides valuable new information about the interactions between Earth and the sun.