Poor Ganymede. Unlike its other Galilean moons – well, apart from Callisto – it doesn’t get much attention. You’ve got flashy, volcanic, paradoxical Io on one hand, and ocean-hiding, icy, potentially life-containing Europa on the other, all taking up everyone’s attention.
Thanks to a stunning new Nature Communications study, though, it looks like Ganymede is about to take the limelight.
Turns out that a team, led by the GFZ German Research Centre for Geosciences, have been listening in for some time now via the Galileo space probe. They’ve been assessing Ganymede's chorus waves and found out that the moon’s “whistle” is 1 million times more intense than would be expected around other moons and planets.
At this point, you’re understandably asking how moons can, well, whistle, so allow me to explain.
Although predominantly a vacuum, space contains charged particles, and when they interact with the magnetic fields of planets or stars, they move about fairly sharpish. As noted by NASA, they often get violently jostled about by plasma waves – clumps of electrons and ions – and in some instances, their motions can be somewhat rhythmic.
That proves to be rather useful, as these motions occur as very low-frequency radio waves. Using some clever tech here on Earth, we can “hear” them.
Whistler mode waves (WMWs), one type of particularly musical plasma waves, make different “noises” depending on the type of plasma they are passing through. This means that we can ascertain plasma properties based on the music they make.
The more we know about this, the more we know about the planet or star’s properties. At the same time, they aid us in spaceflight: Earth generates its own chorus waves, and the electrons that it launches out into space can potentially damage spacecraft, which is useful to be aware of.