"Ganymede's ocean might be organized like a Dagwood sandwich," commented Dr. Steve Vance in a May 1, 2014 statement. Dr. Vance, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, went on to explain the weird moon's resemblance to the Blondie cartoon character's famous multi-layered sandwiches. The study, headed by Dr. Vance, provides new theoretical indications for the team's "club sandwich" model, originally proposed in 2013. The research appears in the journal Planetary and Space Science.
"The rectangular pattern of gravity anomalies was completely unexpected. Using the gradients in the gravity data to reveal the rectangular pattern of anomalies, we can now clearly and completely see structures that were only hinted at by surface observations," Dr. Jeffrey Andrews-Hanna explained in the October 1, 2014 NASA Press Release. Dr. Andrews-Hanna, a GRAIL co-investigator at the Colorado School of Mines in Golden, Colorado, is lead author of the paper.
The astronomers found that larger craters, which excavated pits much deeper into the Moon's surface, only increased porosity in the underlying crust. This indicates that these deeper layers have not reached a steady state in porosity, and are not as fractured as the megaregolith.