The idea of water beneath Enceladus isn’t new. In previous years, data from the Cassini spacecraft hinted at the existence of a lens-shaped body of water, or sea, beneath the moon’s south polar region. But gravity data from Cassini’s most recent flybys support the idea of a global sea.
How do scientists even tackle this question without being able to see the ocean? The answer lies in the gravity data collected by Cassini. Scientists noticed a very slight wobble in the moon as it orbits Saturn. This wobble doesn’t make sense if the entire moon is solid. The only way scientists can explain it is if there’s an ocean underneath Enceladus’ icy shell.
“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, a Cassini imaging team member, and lead author of the paper.
NASA’s Cassini spacecraft has been orbiting Saturn and its moons since 2004. Cassini’s team poured over more than seven years’ worth of images to reach yesterday’s conclusion. Surface features, mostly craters, were meticulously mapped in order to measure changes in the moon’s rotation.
Matthew Tiscareno, a Cassini participating scientist and co-author of the paper, explains why a global layer of liquid is the only thing that makes sense.
“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,” said Tiscareno. “This proves that there must be a global layer of liquid separating the surface from the core,” he said.
The existence of this global ocean raises its own questions. The biggest is why isn’t the liquid ocean frozen? One possible reason is the tidal forces created by Saturn’s gravity could be generating a lot more heat than expected.
Co-author Carolyn Porco cheered the Cassini mission for making these findings possible.
“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,” said Porco. “Cassini has been exemplary in this regard.”
The Active Jets of Enceladus
Enceladus is probably best known for its dramatic plumes spraying water ice above its surface. Back in 2013, the Cassini team found that the intensity of these jets was based on the moon’s proximity to Saturn.
“The jets of Enceladus apparently work like adjustable garden hose nozzles,” said Matt Hedman, a Cassini team scientist. “The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity.”
Soon, Cassini will get its best look yet at Enceladus’ active plume region. On October 28th, Cassini is scheduled to fly by the moon at just 30 miles above its surface. I wonder what other secrets will Cassini uncover about the mysterious Enceladus.