New research suggests that understanding the factors common to celestial light shows over Earth, Saturn and Jupiter could help predict risky space weather.
The stunning Northern Lights and Southern Lights are examples of auroras above Earth that are very familiar to sky watchers. Earlier in May, Earth experienced the most powerful aurora event in 21 years, reminding us of the stunning beauty of these phenomena.
Auroras are generated over our planet’s poles when charged particles that make up the Sun’s solar wind hit Earth’s protective magnetic field, known as the magnetosphere. These particles travel down magnetic field lines, interact with atoms in our atmosphere, and cause them to emit light. The bombardment of charged particles from the sun doesn’t just generate beautiful light shows above Earth, though. It can also lead to “space weather,” such as geomagnetic storms, which sometimes threaten satellites, communications systems, and even Earth’s energy infrastructure.
Our planet is not the only world in the solar system that experiences auroras at its poles. These incredible light shows also occur above the gas giants Jupiter and Saturn, as well as the cold ice giant Uranus. In fact, auroras should be possible around any planet with an atmosphere and magnetic field — and, as astronomers discovered in 2018, auroras can also be seen over extrasolar planets, or “exoplanets.”
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The magnetic fields of Earth, Saturn, and Jupiter are similar in that they all have a funnel-shaped geometry. This causes energetic particles such as electrons in the solar wind to settle in the polar regions, localizing all but the strongest auroras to the poles of these planets.
There are many ways in which the auroras are generated over each of these planets, making them unique to each other. Differences in the strength of magnetic fields, the speed at which these planets rotate, the conditions of the solar winds when they hit the planets, and even the activity of the moons around these worlds can lead to different auroral structures.
Yet despite these differences, a team of scientists from the Department of Earth Sciences at the University of Hong Kong (HKU) believes that a unified understanding of how the solar wind drives auroral displays over different planets could lead to important practical applications. This unity can help us observe, predict and study the magnetic environment of our solar system, including around Earth.
“Our study revealed the complex interplay between the solar wind and the planet’s rotation, providing a deeper understanding of auroras on different planets,” Binzheng Zhang, team leader and HKU scientist, said in a statement. “These findings will not only improve our knowledge of auroras in our solar system, but also potentially extend to the study of auroras in exoplanetary systems.”
To study the dynamics of the planetary magnetic field, the team looked at how electromagnetic fields like those of Earth’s magnetosphere interact with electrically conductive fluids that act as charged particles in the solar wind. Modeling this in three dimensions helped them better understand how auroras over different planets take on different shapes, or “morphologies.” This can then be used to understand how these different aurora morphologies affect different planetary conditions.
As it turns out, combining the conditions of the solar wind and planetary rotation leads to a new parameter that controls the basic structure of the auroras. This may explain exactly why different auroral structures are observed on Earth, Saturn and Jupiter. The fact that the different auroras on Earth and Jupiter could be explained using a unified framework was a big surprise, the team said.
The interaction of stellar winds with planetary magnetic fields is a fundamental process in space.
Thus, these discoveries can not only help us better understand the magnetic environment of Earth and the wider solar system, but can also help us better understand the conditions of distant planetary systems.
The team’s research is published in the journal Nature Astronomy.
