Scientists offer insight into moon mystery
Scientists studying NASA’s Gravity Recovery and Interior Laboratory (GRAIL) data believe they have found evidence the craggy outline of this rectangular region -- roughly 1,600 miles across -- is the result of the formation of ancient rift valleys, according to the space agency.
The rifts are buried beneath dark volcanic plains on the nearside of the moon and have been detected only in the gravity data provided by GRAIL. The lava-flooded rift valleys are unlike anything found anywhere else on the moon and may have once resembled rift zones on Earth, Mars and Venus. The findings are published online in the journal Nature.
Another theory arising from recent data analysis suggests this region formed as a result of churning deep in the interior of the moon that led to a high concentration of heat-producing radioactive elements in the crust and mantle of this region. Scientists studied the gradients in gravity data from GRAIL, which revealed a rectangular shape in resulting gravitational anomalies.
The rectangular pattern, with its angular corners and straight sides, contradicts the theory that the region is an ancient impact basin, since such an impact would create a circular basin. Instead, the new research suggests processes beneath the moon’s surface dominated the evolution of this region.
Over time, the region would cool and contract, pulling away from its surroundings and creating fractures similar to the cracks that form in mud as it dries out, but on a much larger scale.
The study also noted a surprising similarity between the rectangular pattern of structures on the moon and those surrounding the south polar region of Saturn’s icy moon Enceladus. Both patterns appear to be related to volcanic and tectonic processes operating on their respective worlds.
Launched as GRAIL A and GRAIL B in September 2011, the probes, renamed Ebb and Flow, operated in a nearly circular orbit near the poles of the moon at an altitude of about 34 miles (55 kilometers) until their mission ended in December 2012. The distance between the twin probes changed slightly as they flew over areas of greater and lesser gravity caused by visible features, such as mountains and craters, and by masses hidden beneath the lunar surface.
The twin spacecraft flew in a nearly circular orbit until the end of the mission on Dec. 17, 2012, when the probes intentionally were sent into the moon’s surface. NASA later named the impact site in honor of late astronaut Sally K. Ride, who was America's first woman in space and a member of the GRAIL mission team.
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