On Mercury, there are fewer craters in a given area and they are more widely separated than on the Moon. Material thrown from impact craters is not scattered as far because Mercury's gravity is greater than that of the Moon. Mariner 10 Photomosaic of Caloris Basin. This is the largest feature yet observed on Mercury and was produced by the impact of a large meteoroid. The waves converged at the surface opposite Caloris and shook the region violently.
Similar terrain is found opposite huge impact basins on the Moon.
It appears to be a fault produced by compression of the crust. The shrinking of Mercury during formation of its core explains this surface compression. Before manned exploration of the Moon, these smooth light plains were thought to be volcanic deposits. As a result of returned samples from Apollo 16, it was found that much of the lunar light plains is really ejecta from craters. Thus, it is possible that the smooth plains of Mercury may not be volcanic, but of impact origin.