A study led by the University of Hong Kong, with contributions from researchers at the Atmospheric and Planetary Physics Laboratory (LPAP) at the University of Liège, proposes a new approach to the interactions between planetary magnetic fields and the solar wind and explores the fundamental laws governing the production of auroras on planets as different as the Earth, Jupiter and Saturn.
T
he aurora borealis and aurora australis on Earth have been a source of fascination for centuries. At the beginning of May, an exceptional geomagnetic storm triggered the most intense auroral event in 21 years, allowing magnificent multicolored auroras to be observed as far south as the Liège region.
The Earth, Saturn and Jupiter all generate a quasi-dipolar magnetic field whose field lines form a funnel at the poles that funnels energetic electrons into the polar regions, where their interaction with the planets' atmospheres produces polar auroral emissions. However, the three planets are very different in many respects, notably in terms of magnetic field strength, rotation speed, solar wind intensity and the activity of the moons orbiting them. It's not clear how these characteristics relate to the different auroral structures that have been observed on these planets for decades. For example, observations from various satellites and space observatories show that the aurorae of Saturn and Earth form a ring around the magnetic pole, while those of Jupiter can cover the entire polar cap. The Earth, Saturn and Jupiter all generate a quasi-dipolar magnetic field whose field lines form a funnel at the poles that funnels energetic electrons into the polar regions, where their interaction with the planets' atmospheres produces polar auroral emissions. However, the three planets are very different in many respects, notably in terms of magnetic field strength, rotation speed, solar wind intensity and the activity of the moons orbiting them. It's not clear how these characteristics relate to the different auroral structures that have been observed on these planets for decades. For example, observations from various satellites and space observatories show that the aurorae of Saturn and Earth form a ring around the magnetic pole, while those of Jupiter can cover the entire polar cap.
“The interaction of stellar winds with planetary magnetic fields is a fundamental process in the universe,” explains Bertrand Bonfond, FNRS-Research Associate at LPAP and co-author of the study. The results of this research may help us to understand the space environments of Uranus, Neptune and even exoplanets. “By understanding the fundamental physics of the magnetosphere behind auroras, scientists can unlock the mysteries of the celestial light shows that captivate us and enrich our understanding of planetary space environments” suggests Zhonghua YAO, Professor at the University of Hong Kong and former LPAP post-doctoral researcher. “Our study has revealed the complex interaction between the solar wind and planetary rotation, providing a better understanding of aurorae on different planets,” says Professor Binzheng Zhang of the University of Hong Kong, project leader and first author of the paper. “Thanks to multiple observations of planetary auroral emissions, in particular with the Hubble Space Telescope and the various planetary probes that have visited Jupiter and Saturn, such as Juno and Cassini, we know that aurorae vary very strongly from planet to planet. It is therefore very surprising that they can be explained within a unified theoretical framework", adds Professor Denis Grodent, director of the STAR Institute and of LPAP and co-author of the study.
This study represents an important milestone in our understanding of auroral phenomena on planets, paving the way for future research into these mesmerizing celestial light shows that continue to captivate our imagination.
Zhang, B., Yao, Z., Brambles, O.J. et al. A unified framework for global auroral morphologies of different planets. Nature Astronomy (2024). https://doi.org/10.1038/s41550-024-02270-3
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