One of the largest features on Mercury is the Caloris Basin. As the largest crater on the planet's surface, it is about 1300 km in diameter and is similar to the large basins (maria) on the Moon. Hartmann and Kuiper (1962) define a basin as a "large circular depression with distinctive concentric rings and radial lineaments." Most likely, the Caloris Basin was caused by a very large projectile more than 100 kilometers in size early in the formation of Mercury. The impact produced massive concentric mountain rings three kilometers high and hurled ejecta 600 to 800 kilometers across the planet. In ddition to the chaotic terrain produced at ground zero of the impact, the projectile's seismic waves penetrated through the planet's interior and wreaked havoc on the exact opposite side of the planet. Lava flows and other large disturbances reside in that region.
On Jupiter's moon Callisto, the Valhalla region has basins with concentric rings similar to the ones found on the Caloris Basin.
The Caloris Basin 
