Does anyone listen to FM radio anymore? NASA does and it’s a good thing they do – otherwise, we might have missed an FM signal coming from Ganymede, one of the larger moons of Jupiter. What do the residents of Ganymede listen to? Rock? Rap? Techno-pop? Space-age bachelor pad music? Ganymedean folk music?
“Since its first orbit in 2016, Juno has delivered one revelation after another about the inner workings of this massive gas giant. With the extended mission, we will answer fundamental questions that arose during Juno's prime mission while reaching beyond the planet to explore Jupiter's ring system and largest satellites."
Before we do the big reveal, it’s important to note that this is the second time NASA’s the Juno mission has been in the mainstream media this week. First, the space agency announced a mission extension for Juno to September 2025, the projected “best used by” date of the spacecraft. This gives Juno more time to gather close-up data on Jupiter, its rings and three of its largest moons -- Ganymede, Europa, and Io. Ganymede is not only its largest moon (bigger that Mercury in size but not mass) but the only one known to have a magnetic field.
What does this have to do with its FM radio signal – you haven’t forgotten about that, have you?
No, not forgotten – just hoping to delay the disappointing news.
“It’s not E.T. It’s more of a natural function.”
Not only was the signal natural, the event was so insignificant that the response to the media was delivered by Patrick Wiggins, one of NASA’s Solar System Ambassadors in Utah. These are over 1,000 volunteer ambassadors (you can look yours up here) – many with backgrounds in science, space, teaching, etc. – who engage with the public to communicate information on NASA's missions. Patrick Wiggins is retired from Utah's Hansen Planetarium and works part time with the University of Utah Department of Physics and Astronomy. For a more disappointing but interesting observation on the signal, here’s one from Curiosmos.com”
“If you need the scientific name, the signal was a “decametric radio emission” but we actually know it by its much more widespread name – Wi-Fi. The range of the frequency corresponds to that used by our Earthly signals.”
Jupiter’s decametric radio emission was first discovered in 1955 by B.F. Burke and K.L. Franklin at the frequency of 22.2 MHz. The current one was detected by Juno while orbiting near Jupiter’s polar regions close to the magnetic field that connects with Ganymede. It’s believed to have been caused by electrons oscillating slower than their normal rate – a process known as cyclotron maser instability. (Possible prog-rock band or album name?)
Before you sulk away dejectedly, this “decametric radio emission” was the first ever detected from Ganymede. While not broadcast from an FM tower by an intelligent life form, a connection could be found in the future – perhaps even from Juno – because Ganymede has an internal ocean that may contain more water than there is on Earth.
In mythology, Ganymede was a Trojan prince desired by Zeus (the Greek Jupiter), who carried him off to be the cupbearer of the gods. Will Ganymede the moon bear the cup of news of extraterrestrial life beyond Earth? It’s up to you, Juno.