Geological Chronicle
Hyginus is a lunar caldera at the east end of Sinus Medii, measuring 8.7 kilometers across. It is one of the few craters on the Moon not created by an impact, and instead is believed to be volcanic in origin. Because of that history, it lacks the raised outer rim typical of impact craters.
The crater rim is split by Rima Hyginus, a 220-kilometer-long rille that branches to the northwest and east-southeast. Hyginus is deeper than the rille and sits directly at the intersection of its branches. Together, the crater and rille form a prominent landmark in an otherwise flat surface, lined with smaller craters that may reflect the collapse of an underlying structure.
Planners considered Hyginus as a possible Apollo landing site because it was thought to harbor potentially active volcanism. The proposed landing point lay northwest of the crater, within a few kilometers of the rim and western rille. A mission there would have sampled the Cayley Formation, dark overlying rocks, the crater rim and floor, and other nearby volcanic features.