MARE ORIENTALE

(Latin: Eastern Sea), circular, dark plain of basaltic material that fills the interior part of the multiringed Orientale basin on the western limb of the Moon; it covers an area of about 50,000 square kilometres (19,300 square miles). The Orientale basin is defined by a most conspicuous outer ring, the Montes Cordillera, 900 km (560 mi) in diameter. Other vast circular structures associated with the basin are the outer Montes Rook, 620 km (385 mi) in diameter; the inner Montes Rook, 480 km in diameter; and the inner ring that encloses Mare Orientale, 320 km in diameter. For years very little was known about Mare Orientale because it lies at the edge of the lunar surface that can be seen from the Earth. Extensive explorations of the Moon by both manned and unmanned spacecraft during the 1960s and 1970s enabled scientists to make detailed observations of the feature and its surroundings.