The Manannan Impact Crater on Europa: Determination of Surface Compositions of Key Stratigraphic Units

Mannanan is a 22-km-diameter impact crater located at 3 N, 240 W on Europa's orbital trailing side. Detailed high resolution geologic mapping by Moore et al. (2001) revealed the likely presence of extensive deposits of impact melt materials largely filling the crater floor, together with surrounding continuous ejecta deposits that may have been excavated from Europa's interior. Terrains surrounding Mannanàn include some of Europa's visibly darkest surfaces, with extensive areas of chaos, traversed by the prominent structure of Belus Linea. The Mannannàn impact crater and its surrounding areas were imaged during the C3 orbital encounter of the Galileo Mission by the orbiter's Near-Infrared Mapping Spectrometer (NIMS). This NIMS observation (C3ENLINEA01A) has not been subjected to a detailed investigation until now, possibly due to the presence of moderate levels of radiation noise. A "despiked" version of this observation has been produced using methods described in Shirley et al. (2010). In addition, new geologic mapping precisely registered to the NIMS coverage of Manannàn and its surroundings allows the extraction of high-quality near-infrared spectra that are specific to individual geologic units and morphological features. We will present linear mixture modeling solutions for the compositions of several of Manannàn's key stratigraphic units, including the crater floor deposits and the adjacent chaos and linea materials. We will interpret these results in the context of ongoing investigations of the interplay of exogenic and endogenic influences on the surface composition of Europa. This work was performed at the Jet Propulsion Laboratory-California Institute of Technology, Johns Hopkins University-Applied Physics Laboratory, and the SETI Institute under a contract with NASA. Support by NASA's Outer Planets Research program is gratefully acknowledged. Moore, J. M. and 25 others 2001. Impact Features on Europa: Results of the Galileo Europa Mission (GEM), Icarus 151, 93-111. Shirley, J. H., J. B. Dalton III, L. M. Prockter, and L. W. Kamp 2010. Europa's ridged plains and smooth low albedo plains: Distinctive compositions and compositional gradients at the leading side-trailing side boundary, Icarus 210, 358-384, doi:10.1016/j.icarus.2010.06.018.