Valhalla impact basin on Callisto
Valhalla impact basin on Callisto
Voyager 2 imaged a ring-shaped structure on Jupiter's moon Callisto on 6 March 1979, when the mission flew past at a distance of 214,000 kilometres. It is due to the impact of a large asteroid. The Valhalla impact basin is probably the largest impact structure in the Solar System; the concentric rings that formed in the ice crust during the impact have a maximum diameter of 3000 kilometres. Since the impact traces earlier markings through the melted and quickly refrozen ice, like ancient parchment writing, these structures on the icy moons are called palimpsests.
