Large Volcanic Event on Io Inferred from Jovian Sodium Nebula Brightening

Abstract

Using narrow-band images recorded on over 150 nights by the 35 cm coronagraph which comprises PSI's Io Input/Output Facility (IoIO), we detected a 6-month long enhancement in the Jovian sodium nebula. The onset of the enhancement occurred in the mid December 2017 -- early January 2018 timeframe. Sodium emission over the IoIO 0.4 degree field-of-view of was seen to increase through January 2018 and peak in early March 2018. By early June 2018, the surface brightness of the emission returned to the value seen 2017 April -- June, making this the longest such event observed by this technique (Brown & Bouchez 1997, Yoneda et al. 2015) and comparable in length to that observed by the Galileo Dust Detector in 2000 (Krueger et al. 2003). A new IR hot-spot was found on Io near Susanoo/Mulungu paterae between January 2 and 12, however this hot-spot was neither bright nor long-lasting enough to have been independently identified as the source of a major sodium nebula enhancement. Furthermore, no other report of this event has been made despite a significant number of observations of the Jovian system by and in support of NASA's Juno mission. This detection therefore places those observations in valuable context and highlights the importance of synoptic observations by facilities such as IoIO, which provide a global view of neutral material in the Jovian magnetosphere.