You may have heard of the music of the spheres, but NASA has discovered the songs of the moons. Using data returned by the unmanned Cassini spacecraft as it made its Grand Finale, space scientists have captured the dynamic interaction of plasma waves moving between Saturn and its moon Enceladus and turned them into a haunting cosmic soundtrack.
Saturn isn't just a beautiful planet with its distinct set of rings, it's also a giant electric generator. First discovered by the Pioneer 11 deep-space probe in 1979, the planetary magnetic field around Saturn is second in size and intensity only to Jupiter's. It stretches for 20 to hundreds of times the radius of Saturn and is filled with ionized plasma that circulates between the planet and its moons.
The chief source of this plasma is the moon Enceladus, which ejects a tonne of water per second from the geysers located near its south pole. What's more, as Enceladus orbits Saturn, it acts like the armature of a dynamo, cutting across the magnetic lines of force and generating electricity. This creates a plasma circuit between the moon and the planet that gives off radio waves.
One bonus of the last days of the Cassini mission was that the orbiter's Radio Plasma Wave Science (RPWS) instrument picked up these radio signals on September 27, 2017, which were relayed back to Earth for analysis before the probe burned up in Saturn's atmosphere. Scientists found was that not only was the plasma interaction remarkably powerful, but that the signals could be sped up from a duration of 16 minutes to 28.5 seconds and converted into an audio file.
"Enceladus is this little generator going around Saturn, and we know it is a continuous source of energy," said Ali Sulaiman, planetary scientist at the University of Iowa, Iowa City, and a member of the RPWS team. "Now we find that Saturn responds by launching signals in the form of plasma waves, through the circuit of magnetic field lines connecting it to Enceladus hundreds of thousands of miles away."
Such planet/moon interactions are not unique to Saturn. A similar plasma circuit exists between Jupiter and its inner moon Io, but NASA says that no such circuit exists between the Earth and the Moon because the latter is outside Earth's magnetic field.
Listen to the Saturn/Enceladus radio transmissions converted into an audio format in the video below.
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