Newly Discovered Rectangular Structure Sheds New Light On Moon Mystery

Chuck Bednar for redOrbit.com – Your Universe Online
Analysis of a massive rectangular feature buried just below the lunar surface by NASA’s Gravity Recovery and Interior Laboratory (GRAIL) spacecraft has revealed that the giant basin on the moon’s near side was likely created by ancient lava flows and not a massive asteroid collision, according to a new study.
Writing in the October 1 online edition of the journal Nature, lead author Colorado School of Mines Geophysics Associate Professor Jeff Andrews-Hanna and his colleagues explain that the rectangular structure is roughly 1,600 miles across (nearly as wide across as the US) and could have been formed by magma-flooded rift valleys unlike anything else ever discovered on the moon.
The GRAIL scientists believe that the outline of the moon’s Procellarum region (also known as the Ocean of Storms) may have at one time resembled the rift zones found on the Earth, Mars and Venus. Furthermore, the gravity data being collected by GRAIL is allowing them to look beneath the surface at structures that are not visible by using the subtle gravitational pulls on the orbiting spacecraft, Andrews-Hanna and his colleagues noted.

Image Above: Earth’s moon as observed in visible light (left), topography (center, where red is high and blue is low), and the GRAIL gravity gradients (right). The Procellarum region is a broad region of low topography covered in dark mare basalt. The gravity gradients reveal a giant rectangular pattern of structures surrounding the region. Credit: NASA/GSFC/JPL/Colorado School of Mines/MIT
According to BBC News science correspondent Jonathan Amos, now that the scientists have learned of the feature’s existence, they are able to trace its outline, even in ordinary photographs. Andrews-Hanna told him that it covered approximately 17 percent of the lunar surface, and that in terms of area, it was roughly the same size as North America, Europe and Asia combined.
“It’s really amazing how big this feature is,” the professor told Amos on Wednesday. “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.”
The study authors report that the Ocean of Storms region is comprised of a lot of naturally-occurring radioactive elements, including uranium, thorium and potassium. During the earliest days of the Moon, these elements would have heated the crust, and it would have contracted when it started to cool down.
“The angles seen in the edges of this valley are consistent with rift valleys on Earth,” said Rachel Feltman of the Washington Post, adding that the authors “believe that as the moon was cooling in the early days of its development, a rogue plume of magma shot up in this region.”
“Because the lava made this area so much hotter than the mostly-cooled rock around it, the surface cracked and shrank away from the cool surrounding crust,” Feltman added. Eventually, additional lava seeped out of this rectangular frame and filled the valley, forming Procellarum in the process.
However, the research team is not certain exactly how this magma plume would have reached the surface to begin with. Study co-author and MIT professor of geophysics and vice president for research Maria Zuber told the Washington Post that while some may continue to speculate that the moon’s surface was heated by an asteroid impact, which would have caused the plume to rise, there is no direct evidence to support that notion.
The rectangular shape was revealed by the ultra-precise lunar gravity map created by the GRAIL mission probes, said Space.com contributor Charles Q. Choi. He added that the newly discovered pattern of structures were similar in nature to those found on Enceladus, the icy moon of Saturn, suggesting that both moons had experienced the same type of geological history.
The discovery of these rift zones “reveals a much more dynamic early moon than we had previously envisioned. I think we are only just beginning to understand the earliest history of the moon,” Andrews-Hanna told Choi. He added that since previous research had not predicted the existence of these structures on either the moon or Enceladus, it reveals that there is “much left to learn in order to understand the full spectrum of planetary evolution.”
“Our gravity data is opening up a new chapter of lunar history, during which the Moon was a more dynamic place than suggested by the cratered landscape that is visible to the naked eye,” the professor added in a statement. However, he noted that additional research was needed to better understand the causes of this newly-discovered pattern of gravity anomalies, as well as its implications for the history of the Moon.