The largest impact basin on Jupiter’s moon Callisto is Valhalla.
Valhalla is a vast multi-ring impact structure on Callisto’s leading hemisphere. Its bright central region is surrounded by concentric ridges and troughs extending up to roughly 3,800 kilometers across, making it one of the Solar System’s largest known impact features.
The basin was discovered in images from NASA’s Voyager 1 spacecraft in 1979 and is named for Valhalla, the hall of the slain in Norse mythology. Scientists think the impact punched through Callisto’s brittle outer ice shell, allowing softer material beneath to flow and form the rings.
A common mix-up is Asgard, another enormous multi-ring basin on Callisto. Asgard is the second-largest major basin, while Valhalla is the largest. The structures also provide clues about Callisto’s icy interior and the possibility that it once contained a subsurface ocean.