Comparison diagram of aurora acceleration processes on Earth and Jupiter. Earth’s electron spectrum is from the DMSP F19 spacecraft, and Jupiter’s electron spectrum is from the Juno spacecraft. Both spectra show a similar inverted V-shaped structure, indicating the presence of a stable potential drop above the auroral region. This similarity points to common auroral acceleration mechanisms among the planets and shows how insights from planetary auroras can aid in the interpretation of high-resolution observations near Earth. Image credit: S. Tian and Z. Yao
The dazzling lights of the aurora borealis are produced when high-energy particles from space collide with Earth’s atmosphere. Scientists have long understood this process, but one big mystery remained. So what powers the electric fields that accelerate these particles in the first place?
A new study jointly conducted by 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) provides the answer. The study, published in Nature Communications, revealed that Alfvén waves – plasma waves that travel along the Earth’s magnetic field lines – act like an invisible power source, driving the amazing auroral displays seen in the sky.
By analyzing how charged particles move and gain energy in different regions of the universe, the researchers demonstrated that these waves act as natural accelerators, pushing charged particles into the atmosphere and providing the energy to produce glowing auroral lights.
To confirm their findings, the team analyzed data collected by multiple satellites orbiting Earth, including NASA’s Van Allen spacecraft and the THEMIS mission. This data provided solid evidence that Alfvén waves continuously transfer energy to the auroral acceleration region, maintaining an electric field that would otherwise dissipate.
“This discovery not only provides a definitive answer to the physics of Earth’s auroras, but also provides a universal model that can be applied to other planets in the solar system and beyond,” said Professor Zhonghua YAO from the School of Earth and Planetary Sciences at the University of Hong Kong. Professor Yao leads a dedicated team in space and planetary science at HKU and is recognized for his influential research on planetary auroras.
With deep expertise in the magnetospheric dynamics of planets like Jupiter and Saturn, the HKU team brought an important planetary perspective to this study. “Our team at HKU has long focused on auroral processes on giant planets. By applying this knowledge to the high-resolution data available near Earth, we have bridged the gap between earth science and planetary exploration,” Professor Yao added.
This study represents a model of interdisciplinary collaboration. The UCLA team, led by Dr. Sheng TIAN, provided extensive expertise on Earth’s auroral physics, and the HKU team provided a broader context of planetary astrophysics.
The full research paper can be read below. https://www.nature.com/articles/s41467-025-65819-4
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