Cassini discovers global ocean beneath surface of Saturn’s moon Enceladus
NASA announced on Tuesday (Sept. 15) that researchers using data from the space agency’s Cassini mission have discovered a global ocean beneath the icy crust of Saturn’s moon Enceladus. The researchers found that the magnitude of the moon’s slight wobble can only be explained by the presence of liquid beneath its outer ice shell.
The team’s findings indicate that the fine spray of water vapor, icy particles, and simple organic molecules that Cassini has observed coming from fractures near the moon’s south pole are being fed by this enormous liquid reservoir. The research was presented in a paper published this week in the online version of the journal Icarus.
This illustration is a speculative representation of the interior of Saturn’s moon Enceladus with a global liquid water ocean between its rocky core and icy crust. The thickness of layers shown here is not to scale. (Click to view larger annotated version.) Image Credit: NASA/JPL-Caltech
Previous research using Cassini data indicated the presence of a lens-shaped body of water beneath the moon’s south polar region. Gravity data collected by Cassini during several close passes of Enceladus supported the alternate theory of a global ocean beneath the ice. These findings were confirmed by the most recent study, which used seven years’ worth of images taken by Cassini to measure changes in the moon’s rotation with extreme precision.
“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 at Cornell University, Ithaca, New York, and lead author of the paper.
The team found that Enceladus has a tiny but detectable wobble as it orbits Saturn. The researchers plugged their measurement of the wobble, also called a libration, into different models of Enceladus’ internal makeup, including ones in which the moon was frozen from the surface to the core.
“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 Matthew Tiscareno, a Cassini participating scientist at the SETI Institute, Mountain View, California, and a co-author of the paper. “This proves that there must be a global layer of liquid separating the surface from the core.”
One question that remains to be answered is what mechanisms prevent Enceladus’ ocean from freezing. One possibility proposed by Thomas’ team is that tidal forces created by Saturn’s gravity could be generating more heat within Enceladus than had been previously thought.
“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 Space Science Institute, Boulder, Colorado, and visiting scholar at the University of California, Berkeley. “Cassini has been exemplary in this regard.”
Several important discoveries about Enceladus have been made during Cassini’s long mission at Saturn. Researchers detected signs of the moon’s icy plume in early 2005 and followed up with a series of discoveries about the material gushing from warm fractures near its south pole. Strong evidence for a regional sea was announced in 2014, and earlier this year, scientists shared results that suggest hydrothermal activity is taking place on the ocean’s floor.
Jim Sharkey
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.
