Post contributed by Dr. Costanza Rossi, Astronomical Observatory of Padova, Italian National Institute for Astrophysics

During their 1979 flybys of the Jovian system, the Voyager probes revealed to us abundant evidence of global-scale structures on the icy satellite Ganymede (Image 1), showing that tectonic activity played a key role during its geologic history. Ganymede’s puzzling surface covers an internal liquid ocean and is characterized by two main geological units, the dark and light terrains (> 4 billion and 2 billion years old, respectively; Patterson et al., 2010), which are shaped by a complex tangle of linear to curvilinear morpho-tectonic structures (Image 1). There are brittle structures called furrows within the dark terrain, and grooves within the light one, which (apparently) represent disconnected deformation histories. Impact cratering processes affected the dark terrain by forming furrows with graben-like morphologies, which are interpreted as remnants of a multi-ring basin formed by a giant ancient impact (e.g., Prockter et al., 2000). On the other hand, the light terrain formed at the expense of the dark one, as a result of strong tectonics that formed the grooves (e.g., Pappalardo et al., 1998). Although extension is considered as the main process for the groove formation, it is assumed that strike-slip has been also pivotal during their development (Cameron et al., 2018; Rossi et al., 2018). The lack of pure compressional structures still represents one of the open enigmas of the tectonics of Ganymede. Ganymede’s tectonic-related landforms potentially represent pathways connecting the surface with the underlying ocean, and their investigation is pivotal to understand their possible development and interconnection at depth (e.g., Lucchetti et al., 2021), their evolution, and the endogenic processes responsible for their formation.

Image 1: Orthographic projection of the leading hemisphere of Ganymede (Voyager/Galileo global mosaic of Kersten et al., 2021). The dark squares show the location of Image 2 and the white square shows the location of Image 3.