Since last year, NASA researchers have suspected that at the south pole of Saturn moon Encledus was an ocean of liquid water. Now, new analysis of data captured by the Cassini space probe has them thinking the entire moon is covered in water sealed in by the crust.
By looking at seven years of images taken by Cassini, the researchers discovered a distinct wobble that the moon exhibits as it orbits Saturn.
To determine the source of the wobble, also called a "libration," they considered different models, each assuming a different internal structure of the moon. The only one that made sense is the one that has Enceladus surrounded by an icy crust, beneath which lies a liquid ocean that completely covers a rocky core. It's kind of a like a giant chocolate cherry where the cherry's the core, the liquid surrounding it is the ocean and the crust is the chocolate (for those candy-challenged among us).
"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," Matthew Tiscareno said in a statement. Tiscareno is a Cassini participating scientist at California's SETI Institute and a co-author of a paper published this week in the journal Icarus that describes the research. "This proves that there must be a global layer of liquid separating the surface from the core," he said.
According to Space.com, temperatures on the tiny moon, , reach lows of minus 201 degrees Celsius (minus 330 degrees Fahrenheit). At those temperatures it would seem unlikely that anything at all could remain liquid.
Earlier this year, NASA scientists postulated that geothermal activity from the moon's core was heating up the water at its south pole and causing plumes of vapor to shoot off into space. While that could explain how the pocket of water down there stayed liquid, the exact forces that would make the entire moon's ocean from freezing is a mystery. One theory put forth by lead author Peter Thomas and his team is that tidal forces exerted on the moon from Saturn could be generating enough heat to keep things sloshing around.
"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 co-author Carolyn Porco, Cassini imaging team lead at the Space Science Institute. "Cassini has been exemplary in this regard."
Cassini has been exploring Saturn and its environs since arriving there in 2004. It is schedule to make its closest-ever pass through Enceladus' active plumes on October 28, when it will be just 30 miles (49 kilometers) above the moon's surface.