This infrared image gives an unprecedented view of the southern aurora of Jupiter, as captured by NASA’s Juno spacecraft on Aug. 27, 2016. Credit: Photo courtesy of NASA.
When a NASA spacecraft made its first full orbit around Jupiter, a University of Iowa instrument on board recorded haunting sounds befitting the Halloween season. The radio emissions cast by Jupiter’s auroras were recorded by the UI instrument, called Waves, as the Juno spacecraft traveled about 2,600 miles above Jupiter’s swirling clouds. Those emission recordings were then converted into sound files by UI engineers. The emissions from Jupiter were discovered in the 1950s but had never been analyzed from such a close vantage point, according to NASA.
“Jupiter is talking to us in a way only gas-giant worlds can,” says Bill Kurth, research scientist at the UI. “Waves detected the signature emissions of the energetic particles that generate the massive auroras that encircle Jupiter’s north pole. These emissions are the strongest in the solar system. Now we are going to try to figure out where the electrons that are generating them come from.”
Kurth, professor Don Gurnett, associate research scientist George Hospodarsky, and post-doctoral researcher Masafumi Imai — were attending a Juno scientific meeting in late August when data rolled in from Juno’s first close flyby of Jupiter, known as Perijove 1. It was a big moment, the first up-close sampling of the auroras generated by the largest planet in our solar system.
They want to learn how electrons and ions are accelerated along magnetic field lines above Jupiter to eventually collide with the atmosphere, creating the bursts of light that become the auroras. To do that, the Waves instrument will sample plasma waves along different segments in the magnetic field lines with each of its orbits around Jupiter. Kurth said: “If you pluck a string on a violin, the string vibrates,” he says. “The vibrating string is like the plasma itself; in the plasma it is the charged particles that are moving.”
Yet those radio waves can’t be heard. Instead, they need to be “downshifted” to the audio range, Kurth says, and then compressed to turn multiple hours of measurements into an abbreviated soundtrack that captures the greatest hits, so to speak. This translation is performed by UI senior engineering associate Don Kirchner.
The Aug. 27 flyby was the closest the Juno spacecraft will get to Jupiter. 35more close flybys are planned during Juno’s mission, which is scheduled to end in February 2018. The UI scientists can’t wait to learn what’s next from Waves’ next measurement, which will happen on Nov. 2. “It just kind of whets our appetite for what to expect,” Kurth says.
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