Geological Chronicle
Near the Moon’s western limb, Grimaldi is a large basin classified as a peak-ring basin. This type of formation has a single interior topographic ring, or a discontinuous ring of peaks, with no central peak. Subsequent impacts heavily wore and eroded its inner wall, leaving a low, irregular ring of hills, ridges and peaks. Some remaining peaks reach over 2 kilometers in height.
Grimaldi’s mare lava floor is flat, relatively smooth and featureless, with a particularly low albedo. Its dark shade contrasts with the brighter surroundings, making the crater easy to locate. The approximate diameter of the inner rim is 174 kilometers. Scattered remnants of an outer wall extend to 220 kilometers in diameter, and its rim is more intact to the north and west.
A mass concentration, or gravitational high, has been identified at Grimaldi’s center, corresponding with the mare. GRAIL mapped the mascon at high resolution. The area has a history of transient lunar phenomena, including occasional flashes of light, color patches and hazy visibility. Gaseous emissions have also been detected there using spectroscopy.