Understanding Radiation Processing and Alteration of Icy Regoliths

Objectives: The mineral composition of a satellite’s surface informs our understanding of its origin, formation, and geologic evolution. Mineral composition is determined from remote sensing observations; however, exogenic processes (such as radiation from magnetospheric or solar wind particles) alter the chemical and physical properties, thus affecting the remote sensing measurements (namely spectral and color imaging observations). Understanding the alteration process supports research in determining the original mineralogy, and thus provides constraints on the origin, formation, and geologic evolution of the satellite. The purpose of this study is to identify and describe the chemical and physical alteration of the regolith and its components of different Saturnian moons due to radiation from magnetospheric particles. Ion bombardment on silicate surfaces produces nanophase components, namely iron. It is unclear if this same process produces similar components on icy objects, and what is the nature (size, location in rims or agglutinates) and composition of these components. The project will address these questions for satellites within different regions of the magnetosphere.

Methods: Using a variety of photometric analysis techniques, the surface texture and regolith mixing components will be examined for a subset of the Saturnian satellites using ISS images (and VIMS spectra where the spatial resolution is sufficient). Phase ratio maps (ratios of images of the same geographic region obtained at different phase angles) have been demonstrated to identify variations in texture across imaged regions on the Moon [2,3,4,5,6] and Mercury [7]. This study will begin by producing phase ratio images and identifying regions of varying texture. Then using both the techniques of Hapke modeling, and the photometric modeling technique of Kaasalainen et al. (2001) [8] and Shkuratov et al. (2011) [6] as applied to Vesta [9], the areas of varying texture will be examined to determine their photometric textures in more detail. This includes the use of spectral modeling techniques incorporating the possibility of nanometer scale particles as applied to Mercury [10]. The software tools to perform these studies are available from other currently active programs in which the PI is engaged. MIMI data will also be examined to inform radiation precipitation models to the surfaces of these satellites. The precipitation to the surface will be mapped and compared with the regolith textures for correlations and compared between rocky and icy surfaces.