The astronomers then conducted an analysis called a Bouger correction in order to subtract the gravitational effect of topological features, such as valleys and mountains, from the total gravity field. What is then left is the gravity field hidden beneath the lunar surface, existing within its crust.
The team of scientists used data gathered by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, composed of a duo of twin spacecraft that circled Earth's Moon throughout 2012, each measuring the push and pull of the other as an indicator of lunar gravity.
The scientists also considered other possible sources of hydrogen from the little moon itself, such as a preexisting reservoir in the icy crustal shell or a global ocean. Subsequent analysis indicated that it was unlikely that the observed hydrogen was obtained during the formation of Enceladus or from other processes on the moon-world's surface or in the interior.