Mare Orientale

"Oriental Sea" redirects here. For other uses, see East Sea (disambiguation).

Mare Orientale
Close-up view of Mare Orientale
Coordinates	19.4°S 92.8°W / -19.4; -92.8
Diameter	327 km (203 mi)
Eponym	Eastern Sea

1967 photograph of Mare Orientale made by NASA's Lunar Orbiter 4

Photo by Lunar Reconnaissance Orbiter

Mare Orientale ("eastern sea" in Latin) is a Lunar mare. It is located on the western border of the Moon's nearside and farside and is thus difficult to see from an Earthbound perspective. Images from spacecraft have revealed it to be one of the most striking large scale lunar features, resembling a target ring bullseye.

Geology

During the 1960s, rectified images of Mare Orientale by Gerard Kuiper at the Lunar and Planetary Laboratory gave rise to the notion of it being an impact crater. The mare is about 900 kilometres (560 mi) across and was formed by the impact of an asteroid-sized object. Unlike most other basins on the Moon, Orientale is relatively unflooded by mare basalts, exposing much of the basin structure to view; the central portion of Mare Orientale is covered by a thin layer of mare basalt probably less than 1 kilometer deep, much less than in other nearside mare basins. The collision caused ripples in the lunar crust, resulting in the three concentric circular features. The innermost rings of this vast, multi-ringed crater are the inner and outer Montes Rook, and the outermost ring are the Montes Cordillera, 930 km in diameter. Basin ejecta begins just outside the Montes Cordillera and extends up to 500 kilometers beyond the base of the mountains. This ejecta has a rough, hummocky texture and contains linear patterns that point back toward the center of Mare Orientale.

Material from Mare Orientale was not sampled by the Apollo program so the basin's precise age is not known. However, it may be the freshest impact basin on the Moon and is believed to be slightly younger than the Imbrium Basin, which formed about 3.85 billion years ago. The surrounding basin material is of the Lower Imbrian epoch with the mare material being of the Upper Imbrian epoch.

Located at the antipode of Mare Orientale is Mare Marginis.

Discovery and name

Mare Orientale is difficult to observe from Earth, as it lies at the extreme western edge of the near side. All that can be seen are the rough mountain ranges - the Montes Rook and the Montes Cordillera - and some glimpses of the dark mare material beyond them. However, the Moon's libration means that on rare occasions Mare Orientale is turned slightly more toward the Earth, and becomes a little more discernible.

Although various astronomers had observed hints of the mare, it was first fully described by the German astronomer Julius Franz in his 1906 book Der Mond ("The Moon"). Franz also gave the mare its name. At the time, it was located on what by convention was considered the eastern side of the Moon, hence Franz named it the "Eastern Sea". In 1961, however, the International Astronomical Union adopted the astronautic convention for East and West on the Moon and this limb became the western edge.

The first detailed study of the Mare Orientale was by H.P. Wilkins, who called it "Lunar Mare X". Franz's discoveries were not well known, and in the 1976 edition of his book Guide to the Moon, Patrick Moore claims that he and Wilkins discovered and named Mare Orientale in 1946. However, Moore credits Franz as discoverer in his 2009 Yearbook of Astronomy (p.133-135).

Images

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  Field of massive artifacts at the edge of the Mare Orientale Basin centered at -28 Latitude -96 Longitude.

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  Enhanced version of image showing field of massive artifacts on the edge of the Mare Orientale Basin centered at -28 latitude -96 longitude.

External links

• Wood, Chuck (January 11, 2007). "How high the Moon (and low too)?". Lunar Photo of the Day. Retrieved 2008-01-11. 
• Mare Orientale: the Eastern sea in the West - Discovery and nomenclature
• LROC WMS Image Map
• LROC Lunar Image Interface Tutorial