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Mare Cognitum 10.0°S, 23.0°W
Mare Cognitum (the ‘Known Sea’) has a diameter of approximately 370 km and grades without any transition into Oceanus Procellarum in the west. The basin probably arose in the early Imbrium period of the lunar timescale, and it was flooded by lava in the late Imbrium period. In the northwest it is bordered by Montes Riphaeus (probably the remnants of a large flooded crater) and in the south and southeast by Mare Humorum and Mare Nubium. Until 1964 it was considered to be part of Mare Nubium.
On 31 July 1964, the American lunar probe Ranger 7 crashed southwest of the crater Bonpland and transmitted images until 0.2 seconds before the impact (a total of 4308 images). They were the first close-up images of the Moon's surface, with an image resolution of just about 0.5 m. The mission ushered in a new stage in lunar research. It showed a lava plain saturated with craterlets and crater pits, whereas observations from Earth did not show any craters in this area. As a reminder of this occasion, the name Mare Cognitum was introduced officially into lunar nomenclature by the IAU in 1964.
Montes Riphaeus 7.7°S, 28.1°W
The Riphaean Mountains lie between Oceanus Procellarum (to the west) and Mare Cognitum (in the east). They were named after a chain of mountains in the Urals.
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