NASA’s GRAIL mission data provides clues about Moon’s geology
The Mare Orientale impact basin, one of the lunar features observed by the twin GRAIL spacecraft, is about 580 miles (930 kilometers) wide and has three distinct concentric rings, which form a bullseye-like pattern. This view is a mosaic of images from NASA’s Lunar Reconnaissance Orbiter. (Click to enlarge) Image Credit: NASA / GSFC / Arizona State University
What does a 3.8 billion-year-old crater have in common with data from a pair of spacecraft that crashed into the Moon nearly four years ago? Both are helping to provide clues about the geology of Earth’s natural satellite.
Though the Moon may be Earth’s nearest neighbor in space, that doesn’t mean it has long since given up its secrets. NASA’s Gravity Recovery and Interior Laboratory (GRAIL) twin spacecraft orbited the Moon for nearly a year, collecting a wealth of gravitational field data, before impacting the Moon’s surface on December 17, 2012.
Researchers have been poring over the data collected from 1.2 miles (2 kilometers) above the enormous Mare Orientale impact basin, and have published two papers in the journal Science this week – one focusing on understanding the structures of large impacts, and the other detailing how Orientale formed and applying that information to create simulations accurately portraying the formation of the basin.
GRAIL measured the gravity around the Orientale basin. Colors represent the measurement of gravitational acceleration in units of “gals“. (Click to enlarge) Image Credit: NASA/JPL-Caltech
Of particular interest was the structure of the crater itself. With smaller impacts, “classic” bowl-shaped craters are formed. However, larger collisions create a markedly different formation – wide, flat basins, often with multiple walls or rings. It had been theorized that the rings in Orientale were remnants of the initial impact.
Data from GRAIL, however, showed that to not be the case.
“We’ve been able to show that none of the rings in Orientale basin represent the initial, transient crater,” noted GRAIL Principal Investigator Maria Zuber of the Massachusetts Institute of Technology, lead author of the first paper, in a Thursday, October 27, 2016, release from JPL. “Instead, it appears that, in large impacts like the one that formed Orientale, the surface violently rebounds, obliterating signs of the initial impact.”
The Orientale basin, as well as other multi-ring basins, have long interested scientists because they represent cataclysmic events, disrupting the surface far from the impact area and thought to eject material from deep within the crust or mantle and deposit it on the surface. However, Orientale’s composition matched that from the rest of the lunar crust, and scientists were keen to discover why.
Brown University’s Brandon Johnson, lead author of the second paper, was pleased with the data from GRAIL and is positive that researchers now have a firm grasp on what happened following the large impact.
“Because our models show how the subsurface structure is formed, matching what GRAIL has observed, we’re confident we’ve gained [an] understanding of the formation of the basin close to 4 billion years ago,” Johnson stated in Thursday’s release.
But what about that missing mantle material? Simulations, bolstered by data from GRAIL, show that when a catastrophic impact occurs, the gash in the mantle quickly collapses and material from the crust rushes in to fill the crater.
Though GRAIL may have ended nearly four years ago, its findings will be keeping researchers busy for quite some time.
“The data set we obtained with GRAIL is incredibly rich,” noted Zuber. “There are many hidden wonders on the Moon that we’ll be uncovering for years to come.”
The GRAIL mission began in September of 2011 when it was launched atop a United Launch Alliance Delta II rocket from Cape Canaveral Air Force Station’s Space Launch Complex 17, located in Florida. Photo Credit: Jason Rhian / SpaceFlight Insider
Curt Godwin
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.
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