Mare Serenitatis, or the Sea of Serenity, is a large, dark plain on the surface of the Moon. It is one of the lunar maria, which are basaltic plains formed by ancient volcanic eruptions. Mare Serenitatis covers an area of about 1,000 kilometers in diameter and is located in the northeastern part of the Moon. This region is notable for its relatively smooth surface, which is marked by a few craters, including the prominent Craters of Theophilus, Cyrillus, and Catharina. Mare Serenitatis is also significant for lunar exploration, as it was the landing site for several missions, including the Apollo 17 mission in 1972.