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SynoPSIs -- The Monster in the Magnetosphere: Missing bites from the Io plasma torus revealed by spectacular spectroscopy

Wednesday, March 9, 2016

Jupiter possesses both the solar system's largest magnetosphere and its most volcanic body.  Material from Io's volcanoes, when ionized, mass loads Jupiter's magnetosphere but curiously sticks at the radius of Io's orbit (more on this later).  Flung out by Jupiter's fast rotation, the collection of ions stretch into an ethereal hula hoop known as the Io plasma torus (IPT).

Using very high-resolution, high signal-to-noise spectra and some wiz-bang spectral analysis software, we have been able to turn Io's exosphere into an in situ plasma probe: the variation in the brightness of Io [OI] 6300A emission is an excellent proxy for the variation in the thermal electron density in the IPT.  Using a sophisticated semi-empirical model of the IPT to predict the nominal variation in the Io [OI] signal as a function of time, we find several dropouts ("bites") in our data.  Two of the events we have investigated in detail so far are coincident with events that occur over large scales in Jupiter's magnetosphere and may be responsible for the majority of the radial transport of mass from the IPT (the monster eating the IPT).  The sequence of events, suggested by Louarn et al. (2014), goes like this: large collections of plasma released from Jupiter's magnetotail (plasmoids) cause magnetic reconnection and inward-propagating disturbances (i.e., a magnetic rubber band
snap).  Energetic particles generated by these disturbances perturb the ring current, which is one of the two competing hypotheses for what confines the IPT.  The evidence for material leaving the IPT is now found in two forms: the bytes of the IPT that we see in our data and bursts of narrow-band kilometric radiation (nKOM), which have been assumed to be caused by blobs of plasma leaving the IPT.

In summary, our detection of missing bites from the IPT when the Louarn et al. (2014) "monster mechanism" is operating will enable quantitative estimation for how efficient this mechanism is at eroding the torus and thus determine if this mechanism is ultimately responsible for the bulk of the material loss from the IPT.

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