Mare Orientale: The Moon's Hidden Bullseye
Journey to the enigmatic Mare Orientale, a colossal multi-ring impact basin revealing the Moon's violent past and complex geological history.
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Overview
Lunar Mare
Mare Orientale, Latin for "Eastern Sea," is a prominent lunar mare located on the western limb of the Moon's near side, extending slightly onto the far side. Its unique position makes it challenging to observe fully from Earth.
Striking Appearance
Spacecraft imagery reveals Mare Orientale as one of the Moon's most visually striking large-scale features. It presents a distinct bullseye or target-ring appearance, a testament to its formation process.
Dimensions
The mare itself spans approximately 294 kilometers (183 miles) in diameter. The entire impact structure, including its concentric rings, is significantly larger, measuring about 900 kilometers (560 miles) across.
Location & Coordinates
Situated on the Moon's western edge, Mare Orientale's coordinates are approximately 19.4° S latitude and 92.8° W longitude. Its antipode (opposite point) on the Moon is Mare Marginis.
Geology and Formation
Impact Origin
Mare Orientale is not a volcanic mare in the traditional sense but rather the result of a massive impact event. An asteroid-sized object, estimated to be around 64 km (40 miles) in diameter, struck the lunar surface approximately 3.7 to 3.8 billion years ago.
Multi-Ring Structure
The immense energy of the impact created concentric ripples in the lunar crust, forming a spectacular multi-ring structure. The innermost rings are the Montes Rook, followed by the Montes Cordillera as the outermost ring, defining the basin's boundary approximately 930 km (580 miles) in diameter.
Limited Basalt Flooding
Unlike many other lunar basins, Mare Orientale exhibits less extensive flooding by mare basalts. The basaltic layer in the central basin is relatively thin (less than 1 km), allowing much of the original impact structure to remain visible and well-preserved.
Age and Epoch
Mare Orientale is considered one of the Moon's most recent large impact basins. The surrounding basin material dates to the Lower Imbrian epoch, while the mare basalts themselves belong to the Upper Imbrian epoch, indicating a relatively ancient origin.
Global Seismic Effects
The colossal impact is theorized to have caused significant global seismic shaking. This event is credited with leveling almost all slopes steeper than 35 degrees on lunar surfaces dating from the Imbrian epoch or earlier.
Discovery and Naming
Earthbound Observation
Due to its location on the Moon's western limb, Mare Orientale is difficult to observe clearly from Earth. Only the outer mountain ranges, Montes Rook and Montes Cordillera, are typically visible, with occasional glimpses of the mare material itself during periods of lunar libration.
Early Descriptions
Hints of the mare were noted by various astronomers, but it was German astronomer Julius Franz who first comprehensively described it in his 1906 work, Der Mond. Franz named it "Eastern Sea" based on the prevailing astronomical convention of the time.
Shifting Conventions
The naming convention shifted significantly. While Franz named it "Eastern Sea" based on its appearance from Earth, the International Astronomical Union (IAU) later adopted the astronautic convention, where East and West are defined relative to an observer on the lunar surface. This reclassified the limb as the western edge.
Naming History
Hugh Percy Wilkins conducted early detailed studies, referring to it as "Lunar Mare X." While Franz's initial naming was later recognized, there were periods where others, like Patrick Moore, were credited with its discovery and naming, highlighting the complex history of lunar nomenclature.
Visual Archive
While direct image display is limited, these descriptions represent key visual data captured by various missions, offering insights into Mare Orientale's structure and characteristics.
Topographic Map
A detailed map illustrating the elevation changes and topographical features of the Mare Orientale basin, highlighting its concentric rings and central plains.
Gravity Map (GRAIL)
Data from the GRAIL mission reveals gravitational anomalies within the basin, indicating subsurface mass concentrations (mascons) likely caused by the dense material beneath the impact structure.
Albedo Mosaic (Clementine)
A mosaic created from Clementine spacecraft data showing the surface reflectivity (albedo) across the basin, differentiating between the darker mare material and lighter highland regions.
LRO Photomosaic
A high-resolution photomosaic captured by the Lunar Reconnaissance Orbiter (LRO) in 2010, providing an unprecedentedly clear view of the basin's intricate details.
Earth View
An image taken from Earth during a full moon, with Mare Orientale marked on the limb, illustrating its position relative to our planet and the challenges of observation.
Lava Flow Hills
Observations reveal dome-shaped hills near the southern edge of the basin, potentially formed by ancient lava flows, adding another layer to its geological complexity.
Apollo 17 View
Photographs taken during the Apollo 17 mission captured the eastern extent of Mare Orientale under the faint light of Earthshine, offering a unique perspective.
References
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Disclaimer
Important Notice
This page has been generated by an Artificial Intelligence and is intended for informational and educational purposes only. The content is derived from publicly available data, primarily the Wikipedia article on Mare Orientale, and may not be exhaustive or reflect the absolute latest scientific findings.
This is not professional astronomical advice. The information provided is not a substitute for consulting peer-reviewed scientific literature, official astronomical databases, or expert analysis. While efforts have been made to ensure accuracy based on the source material, users should independently verify critical information.
The creators of this page are not responsible for any errors or omissions, or for any actions taken based on the information provided herein. Always consult primary sources and expert opinions for definitive research.