NCCS-Enabled Gravity Models Reveal Density of Moon’s Crust

NASA's GRAIL mission

NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission flew twin spacecraft in tandem orbits around the Moon to measure its gravity field in unprecedented detail. GRAIL’s primary mission lasted from early March to late May 2012. An extended mission lasted from late August to mid-December 2012. Artist concept by NASA/JPL.

Employing NASA Center for Climate Simulation (NCCS) computing resources, NASA Goddard Space Flight Center (GSFC) and university scientists built high-resolution models of the Moon’s gravity field that reveal the structure of the lunar crust in never-before-seen detail.

The 4.5- by 4.5-kilometer model uses the full dataset from NASA’s Gravity Recovery and Interior Laboratory (GRAIL), twin spacecraft that observed the Moon during primary and extended missions in 2012.

A newly developed constraint incorporating topography information from NASA’s Lunar Reconnaissance Orbiter/Lunar Orbiter Laser Altimeter allows for direct estimation of the Moon’s crustal density from the GRAIL tracking data.

Impact: Using data from NASA’s GRAIL mission to make a high-resolution model of the Moon’s gravity field in turn enables mapping the high-resolution structure of the Moon’s crust. These results can inform future studies on the properties of the Moon’s upper crust, especially in local areas, as well as the geophysical setting of potential lunar mission landing sites.

This project’s daunting data analysis and processing challenges led the researchers to split the work across two NCCS computing platforms and five stages of computation.

First, pre-analysis used up to 58 cores on the NCCS ADAPT Science Cloud.

Next, the NCCS Discover supercomputer solved multiple levels of mathematical matrices (using up to 840 cores) and performed primary gravity model processing (using 4,032 cores for 11 runs of ~20 hours each). Discover’s disk stored the ~50 terabytes of data generated.

Finally, ADAPT virtual nodes hosted post-analysis and development of linear and exponential crust density models.

Mollweide projection map of the Moon's crust

This Mollweide projection map reflects density differences in the Moon’s crust as indicated by Bouguer anomalies — calculated as the entire lunar gravity field minus the contribution of the top crust layer. Black lines trace mare areas, so-called “seas” of the Moon that are generally filled with higher-density basalt materials. Measurement units are 1 mGal = 10^-5 m/s^2 (roughly 1 millionth of average Earth gravity). Visualization by Sander Goossens, NASA/GSFC.

The new models represent significant advances over previous efforts. For the first time, the research team can determine a global trend of how the lunar crust’s density increases with depth as well as reliably estimate crustal density closer to the Moon’s surface. “We could not do this with our earlier models, mainly because we now have our novel constraint,” said Sander Goossens, associate research scientist in NASA/GSFC’s Planetary Geology, Geophysics, and Geochemistry Laboratory.

In addition, the scientists can better characterize crustal density variations across topographically distinct areas: mare, farside highlands, South Pole-Aitken, etc.

“This research would not have been possible without NCCS resources,” Goossens stressed. “Our own cluster just does not have enough memory to do such a problem, nor the other infrastructure needed, including a file system to relatively quickly read a 7.6-terabyte data file! And, with a limited set of cores, it would also take forever.”

“The continuing support of NCCS and its administrators has been invaluable to our work, and it has been a great joy for me to work with them,” Goossens noted.

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Jarrett Cohen, NASA/Goddard Space Flight Center