Вадим Дудченко
Администратор портала

The magnetosphere of Ganymede, the Jupiter’s largest moon, is a source of electric and magnetic radio emissions, which have been monitored by the Waves instrument onboard NASA’s Juno spacecraft.

This image of Ganymede was obtained by the JunoCam imager aboard NASA’s Juno spacecraft during its June 7, 2021, flyby of the icy moon. This image is a preliminary product — Ganymede as seen through JunoCam’s green filter. Juno is a spin-stabilized spacecraft (with a rotation rate of 2 rpm), and the JunoCam imager has a fixed field of view. To obtain Ganymede images as Juno rotated, the camera acquired a strip at a time as the target passed through its field of view. These image strips were captured separately through the red, green, and blue filters. To generate the final image product, the strips must be stitched together and colors aligned. At the time this preliminary image was generated, the spice kernels (navigation and other ancillary information providing precision observation geometry) necessary to properly map-project the imagery were not available. The red, and blue filtered image strips were also not available. When the final spice kernel data and images from the two filters are incorporated, the images seams (most prevalent on lower right of sphere) will disappear and a complete color image will be generated. Image credit: NASA / JPL-Caltech / SwRI / MSSS.

The 50-second audio track was generated from data collected during Juno’s close flyby of Ganymede on June 7, 2021.

At the time of Juno’s closest approach to the moon — during the mission’s 34th trip around Jupiter — the spacecraft was within 1,038 km (645 miles) of the moon’s surface and traveling at a relative velocity of 67,000 kph (41,600 mph).

Juno’s Waves instrument, which tunes in to electric and magnetic radio waves, collected the data on those emissions. Their frequency — which range from 10 to 50 kHz — was then shifted into the lower audio range.

“The Juno trajectory approached Ganymede on its corotational wake hemisphere (orbital leading hemisphere),” said lead author Dr. William Kurth, a researcher at the University of Iowa, and colleagues.

“The Waves instrument observed plasma waves associated with Ganymede’s magnetosphere, including whistler-mode hiss, electrostatic emissions between harmonics of the electron cyclotron frequency, a band at the upper hybrid frequency, and broadband bursty emissions associated with Ganymede’s magnetopause and wake.”

“Waves found broadband bursts of plasma waves demarcating the magnetopause and entry into an extended wake-like region.”

“Continuing bursty emissions were observed until the entry into a magnetospheric region hosting multiple electron cyclotron harmonic emissions.”

“These emissions evolved into just one or two bands near the upper hybrid frequency separated by the electron cyclotron frequency.”

The detailed analysis and modeling of the new data from Juno’s Waves instrument are ongoing.

“The 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,” said Juno principal investigator Dr. Scott Bolton, a planetary researcher at the Southwest Research Institute.

“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.”

“It is possible the change in the frequency shortly after closest approach is due to passing from the nightside to the dayside of Ganymede,” Dr. Kurth added.

The scientists presented the new results December 14, 2021 at the American Geophysical Union Fall Meeting 2021 (AGU21).

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William S. Kurth. Juno Plasma Wave Observations at Ganymede. AGU21, abstract # P24D-05

 



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