The southern pole of Enceladus has active jets of water and vapor (as you can see in the photo). This means that there had to be at least a liquid reservoir of some sort under the surface–or there would be no water and vapor to expel. However, previous research had posited a regional body of water under the southern pole, as there was no evidence that corroborated anything more.
Here’s where the new research comes in.
Researchers Peter Thomas, et. al., used data on Enceladus from the past 7 years to map surface features and track the moon’s rotation. They discovered that the moon has a small but distinct wobble, called a libration. Their research allowed them to precisely measure the libration amplitude–and then apply different models on the planet’s interior composition, attempting to figure out which one best fit the measurements. For example, they applied a few rigid models (such as if the moon is completely frozen from the crust all the way to the core), as well as a model where the icy exterior crust is not solidly connected to the core–in essence, a model where the moon has a global subsurface ocean. And guess which one fits the data? The latter!
We now know, with a high degree of certainty, that there is indeed a global ocean lying under Enceladus’s icy crust! If you have access to science direct through a university, you can check out the original research article here. Or you can read NASA’s briefing here.
As you probably know, Jupiter’s moon Europa is also likely to have a subsurface ocean. Both of these places might have the potential for extraterrestrial life. Think of what we might find in the future! This is incredibly exciting science.
Don’t forget that Cassini will be engaging in two more flybys of Enceladus in October, the second of which will be within 30 miles of the south pole, resulting in the most accurate measurements ever regarding the composition of the water and vapor plumes mentioned above.