Detecting the surface composition of geological features on Europa and Ganymede using a surface dust analyzer

Europa and Ganymede are both likely to have subsurface oceans (Carr et al., 1998; Khurana et al., 1998; Kivelson et al., 2000). Young surface features may provide an opportunity to sample material from either a subsurface ocean or bodies of liquid water near the surface (McCord et al., 1999, 2001). Detailed compositional information is of large interest for understanding the evolution, oceanic chemistry, and habitability of these moons. To develop an altitude-dependent model for the detectability of ejecta particle composition originating from surface features of a given size, we simulate detections by a dust analyzer with the capability of measuring compositional makeup on board a spacecraft performing close flybys of Europa and Ganymede (Postberg et al., 2011). We determine the origin of simulated detections of ejecta by backtracking their trajectories to the surface using velocity distributions given in the ejecta cloud model by Krivov et al. (2003). Our model is useful for designing flybys with typical closest approach altitudes, such as the ones planned for NASA's Europa Clipper mission, where we wish to accurately identify the composition of surface features using a dust analyzer.