The Influence of Io's 2015 Volcanic Activity on Jupiter's Magnetospheric Dynamics

Embedded deep inside the huge magnetosphere of Jupiter, the moon Io has active volcanos. Jovian magnetospheric dynamics are driven by the expulsion of Iogenic plasma in the strongly magnetized, fast-rotating system and should vary in response to Io's volcanic activity. In early 2015 when various observations indicated an increase in volcanic activity, the EXCEED instrument onboard the Hisaki spacecraft continuously observed the Jovian magnetosphere via the aurora emission and the emission from the Io plasma torus. The plasma diagnosis of the enhanced Io plasma torus spectrum along with a physical chemistry model for deducing plasma parameters revealed a higher plasma density and a 2-4 times faster radial flow as compared with a volcanically quiet period. Aurora emissions reflecting midmagnetospheric activities showed multiple highly elevated brightness peaks about a month later. Long-term and continuous monitoring by Hisaki enabled the first comprehensive observations of the Jovian magnetosphere in response to Io's enhanced volcanic activity. Plain Language Summary This article, based on the high-resolution and continuous extreme ultraviolet spectroscopic data taken by the Japanese Hisaki satellite, shows that the plasma dynamics in the Jovian magnetosphere is highly influenced by Io's volcanic activity. The observations were made continuously from the beginning to end of a volcanic event. Through the detailed analysis of the spectra around Io's orbit and the Jovian aurora, and by fitting the data to a physical chemistry model, this first comprehensive study concludes that the plasma transport within the magnetosphere is enhanced by a factor of 2-4 by Io's volcanic activity.