Click to view attachmentGRAIL's gravity map has revealed a "hidden valley system", acording to the
BBC article and the
paper published in Nature.
QUOTE
Scientists have identified a huge rectangular feature on the Moon that is buried just below the surface.
The 2,500km-wide structure is believed to be the remains of old rift valleys that later became filled with lava.
Centred on the Moon's Procellarum region, the feature is really only evident in gravity maps acquired by Nasa's Grail mission in 2012.
But knowing now of its existence, it is possible to trace the giant rectangle's subtle outline even in ordinary photos.
Mare Frigoris, for example, a long-recognised dark stripe on the lunar surface, is evidently an edge to the ancient rift system.
"It's really amazing how big this feature is," says Prof Jeffery Andrews-Hanna.
"It covers about 17% of the surface of the Moon. And if you think about that in terms relative to the size of the Earth, it covers an area equivalent to North America, Europe and Asia combined," the Colorado School of Mines scientist told BBC News.
"When we first saw it in the Grail data, we were struck by how big it was, how clear it was, but also by how unexpected it was.
"No-one ever thought you'd see a square or a rectangle on this scale on any planet."
What are your thoughts on the possible causes of its formation? The article mentions heating from radioactive decay, and subsequent cooling, but could this have been possibly caused by the giant impacts that created the maria on the near side?
[Edit]
NASA article.