Io's Plasma Torus and Neutral Clouds
Time: Tue 2017-04-04 13.15 - 14.00
Lecturer: Carl Schmidt
Location: Seminar room, Teknikringen 29
The volcanically active moon Io supplies nearly 1 ton/s of escaping material that is rapidly ionized and shaped by Jupiter's magnetic field to form a toroidal plasma nebula. This talk offers an introduction to the torus and its interaction with Io from an observational perspective, by means of a visible wavelength campaign coordinated with JAXA's Hisaki spacecraft. Radial and azimuthal structure of the torus is characterized from collisionally excited S+ emissions. The mean plasma density, derived from line ratios along the line of sight, peaks at 3500 cm-3, with the dusk-side being denser and more spatially confined than the dawn-side. This asymmetry is caused by a dawn-ward displacement of 0.125 Jovian radii, and set up by electric fields from plasma convection through the magnetosphere. Recurrent traits in brightness and location are observed as a function Jovian magnetic longitude (λIII). Torus positions yield a good match to the λIII behavior in earlier data sets, but a poor match to theory, which prescribes that the torus should track the location of the centrifugal equator at a given magnetic radius. This geometry guides the plasma interaction with Io, which supplies neutral clouds and energetic atoms through charge exchange and dissociative recombination. The fast neutral stream from Io has been observed periodically impacting the adjacent moon, Europa, under certain geometry, and has sufficient energy to escape the Jovian system entirely.