It is named after the Mare Tranquillitatis (Sea of Tranquility), the place on the Moon from which the rock samples in which it was found were brought during the Apollo 11 mission in 1969.
"Mare Tranquillitatis"), места на Луне, в котором были найдены образцы горных пород, и были доставлены на Землю во время миссии Аполлон-11 в 1969 году.