Uranus's mysteriously asymmetrical and skewed magnetic field has long confounded astronomers—until now.
When the Voyager 2 spacecraft zipped past Uranus in 1986, it noticed that the huge gas giant's magnetic field was tilted 60 degrees away from the axis of its spin, resulting in the field being asymmetrical in strength.
The spacecraft also found that the radiation belt around Uranus, which is a belt of charged particles from space that have been captured by a planet's magnetic field, was about 100 times weaker than they would have predicted.
Now, a paper in the journal Geophysical Research Letters has revealed that the field's asymmetry might explain this conundrum.
Uranus is the seventh planet from the sun in our solar system. Its extreme axial tilt is about 98 degrees, meaning it rotates on its side. Uranus's tilt results in unique seasonal variations, with each pole getting around 42 years of continuous sunlight followed by 42 years of darkness.
Radiation belts are zones of energetic charged particles, primarily electrons and protons, which are trapped by a planet's magnetic field. These particles move in spiral trajectories along magnetic field lines, bouncing between the poles of the planet. The most well-known example of radiation belts in our solar system is the Van Allen radiation belts surrounding Earth.
"The radiation belts of Uranus are of particular interest to us as the Voyager 2 flyby indicated that they were much weaker than expected despite the strong magnetic field presence. We suggest that this could be explained by the unique magnetic field structure causing variations in the speed at which particles drift around the planet," the researchers wrote in the paper.
Using the Boris algorithm, which is often used to simulate how particles move in a magnetic field, the researchers modeled how Uranus's asymmetrical field would affect its radiation belt. They discovered that due to Uranus's asymmetrical field, the particles in its radiation belt change speed as they pass through areas where the field is stronger or weaker.
This means that the particles' density varies across the belt, decreasing by up to 20 percent in some areas.
"This would create regions where particles are packed closer together and other regions where they are more spread-out; we show Voyager 2 flew past a region where particles were more spread-out." the researchers wrote.
While this explanation doesn't account for all the radiation belt weaknesses seen by Voyager 2, it certainly makes the case for another mission to the further reaches of our solar system.
"This lack of conclusiveness of results surrounding the icy giants highlights the need for a future flagship mission to one of these planets—to understand these mechanisms fully, more data would be needed within the inner magnetosphere where the quadrupole (and higher order terms) become significant so that we can fully interpret the intertwined nature of the particle distributions with the magnetic field structure," the researchers wrote.
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