You’d think the moons would be quieter compared to their host planets, but that’s not entirely true – if you know how to listen. NASA’s chief researcher Juno, Scott Bolton, made an audio recording of magnetic field activity around Jupiter’s moon Ganymede as the Juno spacecraft flew on June 7, 2021. A 50-second video reveals a sharp change in probe activity entered another part of Ganymede’s magnetosphere, probably as he left the night side to enter the daylight.
The sound came from the movement of electrical and magnetic frequencies in the audible range. Jupiter’s magnetosphere dominates the magnetosphere of its moons and is present in the image, but Ganymede is the only moon in the solar system that has a magnetic field (probably because of its liquid iron core). This is not a feat you could repeat elsewhere in the near future.
The soundtrack was part of a larger Juno briefing where the mission team uncovered the most detailed map of Jupiter’s magnetic field to date. The data showed how long it takes for the Great Red Spot and the equatorial Great Blue Spot to move around the planet (approximately 4.5 years and 350 years, respectively). The findings also showed that east-west jet streams are tearing up the Great Blue Spot and that polar cyclones behave similarly to ocean vortices on Earth.
You wouldn’t hear these sounds if you could visit Ganymede on your own. However, they are a reminder that even seemingly dead worlds are often full of activities that you can discover using the right instruments. It’s just a question of how easy it is to notice that activity.
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