Antum Crater: A Window Into Ganymede's Icy Evolution

Located within the extensive dark terrain of Marius Regio, in the anti-Jovian trailing quadrant of Ganymede, Antum crater is marked by dark-rayed ejecta that obscure older features and reshape the surrounding landscape. This study investigates Antum and its geological context using optical and infrared data from the Voyager and Galileo missions, complemented by numerical simulations. The terrain around Antum can be divided into three facies based on albedo and texture, reflecting a complex history shaped by impact and resurfacing. Galileo/NIMS spectra reveal sharp contrasts between the crater interior and its ejecta: the interior shows deeper water ice absorption bands, while the ejecta appear darker and more contaminated. Spectral features also indicate salts, complexed CO2, and hydrated sulfuric acid, pointing to subsurface alteration and cumulative space weathering. Numerical simulations of the cratering process with the iSALE-2D code highlight the influence of impact velocity, thermal gradients, and surface cohesion on crater formation. Under plausible impact conditions, the modeled crater dimension and morphology closely match observations, offering insight into the processes controlling cratering on icy surfaces. By integrating geological mapping, Galileo/NIMS spectral analysis, and impact modeling, this study refines our understanding of Ganymede's geological evolution. The results suggest past or present subsurface liquid activity and highlight the mechanisms that shape icy moons. Antum thus represents a key case study with broader implications for planetary science and the evolution of outer Solar System bodies, and its investigation is also relevant for upcoming missions such as JUICE and Europa Clipper.