The Plumes of Enceladus: Measuring slow Particles by combining Numerical Simulations and Infrared Spectra

The south pole region of Saturn’s icy moon Enceladus is known for its volcanic activity, emitting a stream of ice particles and water vapor into the Saturnian system. After the discovery by the Cassini spacecraft [2, 3, 8, 10], the ice particles’ dynamics and density distribution in the vicinity of the moon have been described using numerical models [8, 7, 1]. Here we make use of numerical simulations to predict the light scattering properties of the jets and compare them to spatially resolved near-infrared spectra taken by the VIMS camera. We identify a component of systematically larger, slower particles in the spectra that does not show up in the simulations. We argue that this constitutes the diffuse particle population as seen in optical close-up images and as proposed to explain the chemical segregation of the plume particles [6].