Imaging Icy Moon Atmospheres and Energetic Ion Impact Patterns From JIMO Using Energetic Neutral Atoms

With column densities in excess of 1.E14 /cm2 (Hall et al., 1998; Carlson 1999), the atmospheres of Europa, Ganymede and Callisto provide substantial targets for the conversion of energetic ions from Jupiter's magnetosphere into energetic neutral atoms (ENA). Here we document the value of using the technique of ENA imaging to determine the dynamics and structure of the icy moon bound and extended atmospheres, and to further elucidate the electromagnetic environments of the moons that control the pattern of ion impacts onto the icy moon surfaces. ENA imaging has become a standard technique for characterizing the structure of planetary magnetospheres, and its value in determining the presence of neutral gas from icy moons has recently been demonstrated (Mauk et al. 2003). The Cassini mission will use such imaging to diagnose the upper atmosphere and the electromagnetic environment of Titan (Amsif et al., 1997). In the work presented here, Galileo inputs are used to simulate the ENA emission patterns from Jupiter's icy moons, as they would appear to the Jupiter Icy Moon Orbiter (JIMO) platform. We show that such imaging will provide important spatial and temporal information on the processes that control the structure of icy moon atmospheres. In combination with in situ charged particle measurements, it will also provide critical information needed to separate temporal from spatial variations as we try to understand the dynamic electromagnetic environments of the icy moons. Understanding these changing electromagnetic environments is vital to using electromagnetic fields to probe the interiors of these moons. Amsif, A., J. Dandouras, E. C. Roelof, J. Geophys. Res., 102, 22181, 1997 Carlson, R. W., Science, 283, 820, 1999. Hall, D. T., P. D. Feldman, M. A. McGrath, and D. F. Strobel, ApJ, 499, 1998. Mauk, B. H., D. G. Mitchell, S. M. Krimigis, E. C. Roelof, and C. P. Paranicas, Nature, 421, 920, 2003.