On June 7, 2021, NASA's Juno spacecraft made its closest flyby of Jupiter's moon Ganymede, the largest moon in the solar system. The frozen Jovian moon is larger than planet Mercury, and it's the only natural satellite in the solar system with a magnetic field. While zooming past, Juno recorded Ganymede's electromagnetic waves and revealed what the moon's soundtrack is like, reports Michelle Starr for Science Alert.
A 50-second audio track—featuring a wide range of eerie, whistle-like noises—was released during the 2021 American Geophysical Union Fall meeting, after researchers first converted it to a frequency humans can actually hear, reports Jody Serrano for Gizmodo.
Flying at 41,600 miles per hour, Juno swooped 645 miles above Ganymede's surface to capture the audio, per Science Alert. Juno's Waves instrument captured the track by measuring radio and plasma waves in Jupiter's magnetosphere. The Waves instrument was designed to help scientists understand how the planet's magnetic field, atmosphere, and magnetosphere interact.
An audio visualization charts where a sharp change in frequencies is heard around the mid-point of the recording. Researchers suspect the change may have occurred when the Juno probe entered a different part of Ganymede's magnetosphere. Based on timing, the tonal shift may have specifically happened when Juno whipped past the moon's night side to enter the side closest to the sun, explains William Kurth, a co-lead investigator for the Waves instrument based at the University of Iowa in Iowa City, in a statement.
"This soundtrack is just wild enough to make you feel as if you were riding along as Juno sails past Ganymede for the first time in more than two decades," says Scott Bolton, an experimental space physicist and Juno's principal investigator, in a statement. "If you listen closely, you can hear the abrupt change to higher frequencies around the midpoint of the recording, which represents entry into a different region in Ganymede's magnetosphere."
Jupiter's gigantic magnetosphere—the most powerful of any planet—interacts with Ganymede's internal magnetic field, which is produced by its liquid iron core, Engadget reports. The Galileo spacecraft, which observed the Jovian planet in the 1990s and early 2000s, found that plasma waves around Ganymede are a million times stronger than the activity around Jupiter, Science Alert reports. Ganymede's magnetic field punches a cavity inside Jupiter's magnetosphere, which in turn creates a mini magnetosphere within Jupiter's own, according to a study from 2004 published in the Cambridge University Press on magnetospheric interactions with satellites.
Further analysis of the audio waves collected by the probe is still ongoing. At the meeting, researchers also revealed the most detailed map of the gas giant's magnetic field from data collected by Juno and more details on Jupiter's elusive Great Blue Spot, per Science Alert.