We’ve long known that Enceladus, one of Saturn’s many moons, contains a subsurface pocket of water, but it turns out there’s much more than we thought. Previous studies and observations had shown a large lake in the moons South Pole region but recent research has proven that there is actually a global ocean.
Evidence of the subsurface ocean comes from careful observations of Enceladus using seven years of images taken by the Cassini spacecraft orbiting Saturn. By tracking features such as craters on the surface in the images, the team was able to observe the slight wobble (also called libration) in the moon as it orbited Saturn. They then created models of Enceladus to determine how much wobble there would be in two scenarios: if there was a global ocean or if the icy exterior is in contact with the rocky core.
The libration value they calculated was much too high to be explained by the core contacting the icy exterior. In this case the moon would be heavier resulting in much less wobble. Instead it matched up closely with the value they would expect to find if there was a global ocean. The ocean is estimated to be between 26 and 31 kilometres deep while the ice crust is about 13 kilometres thick.
“This is a major step beyond what we understood about this moon before, and it demonstrates the kind of deep-dive discoveries we can make with long-lived orbiter missions to other planets. Cassini has been exemplary in this regard,” Said Carolyn Porco, one of the scientists in the study.
While it is currently not known what is keeping the ocean in liquid state, one possibility may be the tidal forces of Saturn. The large mass of Saturn could be pulling on parts of Enceladus’ exterior creating a slight bulge. The movement of matter being pulled creates a significant amount of friction and heat, which could be maintaining a liquid ocean. This has been observed on Jupiter’s moon Europa, which also has a subsurface ocean.
This discovery is exciting for astrobiologists as it gives a lot more ocean area where life could have originated on Enceladus. The likely fuel source would be deep-sea vents like those on Earth, which harbor small but diverse ecosystems of extremophile life.
The Cassini spacecraft is set to make a close flyby of Enceladus in late October through one of the water ice plumes in its South Pole.