Crater on Ganymede emplaced at the border of the dark and bright terrain – view into the subsurface properties

Kurzfassung

Two major terrain units dominate Ganymede’s surface: 1) the ancient heavily cratered dark terrain and 2) the tectonically resurfaced bright or light terrain (Collins et al., 2013). Previous studies suggest that the dark material is a relatively thing lag deposition overlying a brighter ice-rich subsurface formed by processes such as impact gardening, thermal segregation, and mass wasting (Prockter et al., 1998). The younger bright or light terrain cross cutting the older dark terrain formation is believed to have formed predominantly through the modification of dark terrain by tectonic and possibly also cryovolcanic resurfacing processes (Collins et al., 1998). Particularity, the better understanding of the formation of the bright terrain and its possible interaction with a subsurface ocean makes its investigation one of the top goals of the upcoming JUICE mission (Grasset et al., 2013). In order to prepare for the JUICE mission and maximizing its science return, we started the re-investigated the available Galileo SSI and NIMS data set. In this work, we focus on Ganymede’s numerous impact craters that have been directly emplaced at the border of both terrains. Often fresh impact craters and their ejected material offer a glimpse into the subsurface properties. Therefore, the study of the selected impact craters could enable to reveal any changes in the bright terrain properties during its formation compared to the subsurface of the dark terrain. Variations in the subsurface properties could be indirectly mirrored in the morphology and surface texture of the crater material, the superimposed crater density but also the composition of the crater material excavated for the subsurface.