According to new research using data from NASA’s Cassini mission, a global ocean lies beneath the icy crust of Satrun’s geologically active moon, Enceladus.
Previous data from NASA’s Cassini space mission revealed there was steam, liquid, and ice located at the southern pole of the moon. But now scientists believe the vast water reservoir is coming from an ocean between the moon’s rocky core and icy crust. The research is presented in a paper published online this week in the journal Icarus.
Previous analysis of Cassini data suggested the presence of a lens-shaped body of water, or sea, underlying the moon’s south polar region. However, gravity data collected during the spacecraft’s several close passes over the south polar region lent support to the possibility the sea might be global. The new results–derived using an independent line of evidence based on Cassini’s images–confirm this to be the case.
“This was a hard problem that required years of observations and calculations involving a diverse collection of disciplines, but we are confident we finally got it right,” said Peter Thomas, lead author of the study and a Cassini imaging team member at Cornell University in New York.
Cassini scientists analyzed more than seven years’ worth of images of Enceladus taken by the spacecraft, which has been orbiting Saturn since mid-2004. They carefully mapped the positions of features on Enceladus–mostly craters–across hundreds of images, in order to measure changes in the moon’s rotation with extreme precision.
As a result, they found Enceladus has a tiny, but measurable wobble as it orbits Saturn. Because the icy moon is not perfectly spherical — and because it goes slightly faster and slower during different portions of its orbit around Saturn — the giant planet subtly rocks Enceladus back and forth as it rotates.
“If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,” Cassini scientist Matthew Tiscareno said.
“This proves that there must be a global layer of liquid separating the surface from the core.”