Investigation of Carbon Dioxide Distributions on Saturnian and Galilean Satellites through Fusion of Spectrometer Data with Geological Maps

Introduction: Carbon dioxide has been detected on the icy Galilean satellites as well as the icy Sat-urnian satellites. On all of these bodies, spectra indicate that the CO 2 appears to be bound to some other material on the surface rather than existing as ice or as trapped gas. We are working to understand the spatial distribution of CO 2 on these bodies, specifically searching for correlations with geological features. This approach may help to shed light on the origin of the bound CO 2 on the various satellites. Determining CO 2 abundance: The band depth estimates for CO 2 on the Galilean satellites from NIMS data were measured as described in Hibbitts et al. [1], with a new calibration applied to the data. The band depth on the Sautrnian satellites is measured with respect to the continuum using a modification of this same procedure. The continuum is quite low at these wavelengths due to the presence of ubiquitous water ice, resulting in low signal-to-noise and noise-challenged estimates of band depths. Additionally, the CO 2 band is shallow on Dione, generally not exceeding 10% and in many places barely detectable. We take several steps to mitigate these effects. First, we begin with raw data available from the PDS and perform our own despiking routine, and then apply the standard radiometric and wavelength calibrations, with a modification to the wavelength calibration within the CO 2 region [2]. From these improved data sets, we select only those observations that were performed at long integration time, generally 640ms, though occasionally 320ms are used as well. We have found that although there are several large, high resolution observations of Dione at shorter integration times, that the short integration times make the detection and characterization of the CO 2 band significantly less precise than is possible with the longer integration time observations. The shape of the CO 2 band is approximated by a mathematical shape model. A modified gaussian curve is derived that best fits, in a least-squares sense, the average CO 2 absorption band from a total of approximately 100 pixels containing the strongest CO 2 bands extracted from four high-resolution, long-integration time observation from epoch 34 (observations during Cas-sini's 50th orbit of the system). The shape model is then used to determine the depth of bands in individual pixels by again performing a least squares fit at each wavelength within the band and …