Alfven vortices in Saturn's magnetosheath: Cassini observations

First signatures of Alfven vortices in the Kronian magnetosheath are presented. An Alfven vortex is a non-linear bi-dimensional magnetic structure associated with sheared magnetic field and velocity perturbations, propagating obliquely to the external magnetic field direction. Such structures have been recently discovered by Cluster in Earth's magnetosheath downstream of a quasi-perpendicular bow-shock at scales close to 10c/w(pi) (where c is the speed of light and w(pi) the ion plasma frequency). The presence of Alfven vortices downstream of a quasi-perpendicular bow-shock of Saturn with comparable scales to the ones at Earth indicates the universality of this phenomenon. It suggests that such non-linear structures are an inherent property of plasma flow downstream of collisionless shock waves, which can have broad astrophysical applications.