Exploration of zodiacal dust environment at Saturn by CASSINI-CDA

We present a progress report on the analysis of the CASSINI-CDA data set to constrain the zodiacal dust environment at Saturn orbit distance. CDA dust measurements rely on impact-ionization detection of sub-micrometer and micrometer size dust grains. The primary objective of CDA is the study of Saturn faint E ring and the characterization of the dust environment surrounding the icy moons. The majority of the CDA data set has been obtained during inclined crossings of the E ring and targeted Moon flybys. However, CDA remains in measurement mode over large portions of Cassini orbits, potentially enabling the detection of exogenous dust material. Dust particles not gravitationally bound to Saturn belomg in two categories: particles of interplanetary (IDPs) or interstellar (ISDs) origin. The later can in principle be well characterized by their impact direction. IDPs detection is extremely valuable because the zodiacal dust complex is very poorly known at Saturn orbit distance. Theoretical works predict the presence of IDPs originating from comets and from the Kuiper belt. Their abundance is however poorly constrained due to the uncertainty on the efficiency of dust production processes by the source on one hand, and by the gravitational shielding due to mean motion resonance by the outermost gas giant planets on the other hand. As CDA is equipped with a time of flight mass spectrometer, detection of both cometary and Kuiper belt material may lead to important compositional information of the parent bodies. Also, knowing the dust abundance at Saturn will allow an estimate on the in-fall rate of material on the rings, which is an important unknown factor to describe ring evolution.