Low energy electron microsignatures at the orbit of Tethys: Cassini MIMI/LEMMS observations

We report on low energy electron microsignature observations by the Low Energy Magnetospheric Measurement System (LEMMS) in the vicinity of Tethys's L-shell, during the first seven orbits of the Cassini mission. Tethys, due to its large size, is the source of strong microsignatures. Shallower absorption features seen are the result of aged Tethys microsignatures rather than the effect of its small Lagrangian moons. Several remarkable observations are also discussed: the displacement of the microsignatures indicates that the drift shell deviation from axisymmetry is greater than previously expected. Midnight to dawn wakes have drifted toward the planet whereas noon to dusk ones have drifted outward, revealing possible magnetospheric convection effects. Double microsignatures seen for the first time, suggest low radial diffusion coefficients and point to dynamic events in the magnetosphere.