Happy Anniversary, Voyager 2 !

Thirty-five years ago today, a NASA spacecraft got an up-close look at beautiful, enigmatic Saturn.

On Aug. 25, 1981, the Voyager 2 probe zoomed within 26,000 miles (41,000 kilometers) of the ringed planet’s cloud tops. The discoveries made by Voyager 2 — and by its twin, Voyager 1, which had flown past Saturn nine months earlier — reshaped scientists’ understanding of the Saturn system and planted the seed for NASA’s Cassini mission, which began orbiting the ringed planet in 2004, NASA officials said.

“Saturn, like all of the planets the Voyagers visited, was full of exciting discoveries and surprises,” Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, said in a statement. “By giving us unprecedented views of the Saturn system, Voyager gave us plenty of reasons to go back for a closer look.”

The PWS plasma wave instrument on Voyager 2 recorded these signals as the spacecraft was approaching Jupiter on July 2, 1979, between 1556 and 1645 spacecraft event time (essentially UTC). These are the authentic sounds of Jupiter in contrast to the multitude of artistic interpretations and “therapeutic” mixes found on YouTube that may be based on PWS data, but have been highly manipulated and sound very little like the original signals. The audio presented here is not shifted in frequency and not filtered or mixed with music.

The PWS wideband waveform instruments on the two Voyager spacecraft sample the electric field on the dipole wire antenna at a rate of 28800 4-bit samples per second, using an automatic gain control. Consequently, the audio is just slightly better than telephone quality. Packets of 1600 samples are acquired, separated by the equivalent of 128 missing samples. Running these packets together results in the playback taking less than real-time (by a factor of 1600 / 1728), and also introduces a slight audible flutter. The amplitudes at the edges of these packets have been smoothed to reduce this flutter, but this is the only modification to the signal.

These are by no means the only “sounds” that Jupiter makes, but there is nice variety during this hour interval. All of the available measurements during this interval are present but since there are time gaps, the total run time is approximately 27 minutes (plenty long to become tedious to listen all the way through). Let me assure you, however, that there are less-interesting intervals.

Although I’m not qualified to interpret the science, I should at least point out some of the interference present. The constant tone at 2.4kHz is caused by the spacecraft power supply. The occasional sounds like someone pounding a drum or thumping on an oil barrel are due to either a stepper motor on another instrument or to spacecraft attitude thruster firings. The tones with harmonics that build slowly and end abruptly and appear as multiple horizontal lines in the spectrogram are due to interference from other science instruments onboard. Unless I’ve missed something, everything else is the genuine “sound” of Jupiter.