The Northern and Southern Lights have dazzled and inspired all who have witnessed them since time immemorial. Much like the Moon, stars, constellations, and planets, they are considered an intrinsic part of our shared cultural heritage. These spectacular light displays result from the interaction between charged particles emanating from our Sun and Earth’s magnetic field. Nevertheless, some mysteries regarding the mechanisms driving the auroras persist, which scientists have aimed to solve for several decades. Chief among these is the question of what fuels the electric fields that accelerate these particles.
In a recent study, researchers from the Department of Earth and Planetary Sciences at the University of Hong Kong (HKU) and the Department of Atmospheric and Oceanic Sciences at the University of California, Los Angeles (UCLA) have provided an answer. Their analysis suggests that plasma waves propagating along Earth’s magnetic field lines—known as Alfvén waves—function as a natural accelerator. By examining how charged particles gain energy and move across different regions of space, the team established that these waves supply the requisite energy to propel the charged particles down into the atmosphere, thereby generating the auroras.
The research group scrutinized data gathered from multiple near-Earth satellites, including NASA’s Van Allen Probes and the THEMIS mission (Time History of Events and Macroscale Interactions during Substorms). As detailed in their paper published in Nature Communications, the collected data illustrated how Alfvén waves sustain the electric fields, preventing them from dissipating and continuously channeling energy into the acceleration region. Professor Zhonghua Yao of the University of Hong Kong leads a specialized group focused on space and planetary science.
“This breakthrough not only resolves a long-standing question in the physics of Earth’s aurora but also proposes a universal framework applicable to other planets within our Solar System and beyond. Our team at the University of Hong Kong has been extensively studying auroral processes on the giant planets for a long time. By adapting this expertise to the high-resolution, near-Earth data available, we have effectively bridged the gap between Earth sciences and planetary exploration,” he stated.
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