Survey of Cold Plasma Blobs in Jupiter's Magnetosphere: Evidence for Centrifugal Instabilities

In Jupiter's magnetosphere, plasma originating from Io's escaping atmosphere is radially transported outward via two modes of centrifugally driven dynamics. In flux tube interchange events from the Rayleigh–Taylor instability, the cold and dense flux tube moves outward, while hot and depleted flux tubes are injected inwards. In the ballooning mode of the firehose instability, the flux tube breaks off with bursts of plasma blobs. Both modes suggest outward transport of cold, dense plasma blobs. In this study, we survey the cold blobs, analyzing 147 events based on thermal plasma measurements from the Juno/JADE-I instrument. The cold blobs are identified by searching time-of-flight spectra for very narrow signatures in the energy distributions. Plasma parameters determined by forward modeling reveal two types of cold blob events. The first type of event, occurring outside 25 R_J, exhibits high density and fast radial velocity accompanied by magnetic nulls and mainly occurs on the dawnside, suggesting an origin from the ballooning mode. The second type of event, occurring within 35 R_J, shows simultaneous outward moving cold, dense plasma with inward moving hot, tenuous plasma with no dependence on local time, indicating flux tube interchange. Based on statistics between 15 R_J and 30 R_J, the mass transport rate of the cold blobs is estimated to be about 100 kg/s, which is insufficient to account for the plasma production rate at Io.