Moon: Mare Orientale 20S 095W

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Scale: 1 pixel = approximately 4.7 km. 10-degree grid;             Lambert Azimuthal Equal Area Projection, Center 20S 095W

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Copernican: Beginning with the formation of the bright crater Copernicus, about 1.1 Ga. Formation of bright ray craters.
Eratosthenian: Begins with the formation of the crater Eratosthenes. Fresh but non-rayed craters and late mare eruptions. 1.1 to 3.1 Ga.
Imbrian: Begins with the formation of the Imbrium Basin. Includes most mare eruptions. 3.1 to 3.8 Ga.
Nectarian: Begins with the formation of the Nectaris Basin, and includes most of the major impact basin events. 3.8 to 3.9 Ga.
pre-Nectarian: Before 3.9 Ga


The Orientale Basin nicely displays the direction problem on the Moon. The name means "Eastern Sea," and the basin is on the eastern limb of the Moon as seen from Eart, but on the western side to a lunar traveler using standard directions.

The Orientale Basin is the youngest multiple-ring impact basin on the Moon, and its structure and ejecta deposits are still fresh and well displayed. The rings are believed to have been created by giant seismic waves in the wake of the impact. Several hundred million years after the impact, lava welled up along fractures and filled most of the central basin as well as ponding against fault scarps.

Unlike the near side maria, the Orientale Basin is only partially filled. It seems to be a pattern that maria more than about 90 degrees from the center of the near side are smaller and more patchy than the near side maria.

Notes and References

Lunar Geology Index
Global and Planetary Geology Index
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Created 11 April 2014, Last Update 19 January 2020