The new findings are an independent line of evidence that hydrothermal activity is taking place in the subsurface ocean of Enceladus. Earlier results, published in March 2015, indicated hot water is interacting with rock beneath the sea of this distant moon. The new discoveries support that conclusion and add that the rock appears to be reacting chemically to produce the hydrogen.
But small moons like Methone are usually geologically inactive and bereft of an atmosphere. Therefore, they are usually unable to smooth away the scars. Dr. Peter Thomas of Cornell University in Ithaca, New York, explained it this way in the May 17, 2013 New Scientist: "When we look at objects less than 200 kilometers in radius, they are all like potatoes. They have lumps, grooves, craters." This makes Methone's smooth surface a mystery. Dr. Thomas is a Cassini team member.
"We developed new operations methods for INMS for Cassini's final flight through Enceladus' plume. We conducted extensive simulations, data analyses, and laboratory tests to identify background sources of hydrogen, allowing us to quantify just how much molecular hydrogen was truly originating from Enceladus itself," explained Dr. Rebecca Perryman in the April 13, 2017 SwRI Press Release. Dr. Perryman is INMS operations technical lead.