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Global Ocean Discovered Under Ice Shell on Saturn’s Moon

Under the surface of Enceladus there could be hydrothermal activity. (Image: photojournal.jpl.nasa.gov)
Under the surface of Enceladus there could be hydrothermal activity. (Image: photojournal.jpl.nasa.gov)

The third largest moon of Saturn called Enceladus is now believed to be one of several icy “water worlds” in our solar system, according to NASA researchers.

Enceladus has more than 100 individual cryovolcanoes (active geysers), which eject organic materials, and water beyond the frozen surface of the moon. Most of the cryovolcanoes are in the southern polar region.

Now with the careful analysis of more than seven years’ worth of data from the NASA’s Cassini mission, researchers believe that the moon’s slight wobble, is because outer ice shell is not frozen solid to its interior. This suggests there must be a global ocean beneath its icy shell.

The third largest moon of Saturn called Enceladus

An illustration of the interior of Saturn’s moon Enceladus shows a liquid water ocean between its rocky core, and icy crust. (Image: saturn.jpl.nasa.gov)

Researchers from Cornell University, and SETI say the findings imply the fine spray of water vapor Cassini has been observing is coming from fractures near the moon’s south pole. This vapor comes from a vast liquid water reservoir. The research has been presented in a paper published in the journal Icarus.

In previous analysis of Cassini data, it had suggested the presence of a lens shaped body of water at the moon’s South Polar Region. However, gravity data collected during the spacecraft’s close pass over the South Polar Region supports the idea that the sea might be global. Now this has been confirmed by using an independent line of evidence based on Cassini’s images.

Lead author of the paper, Peter Thomas, a Cassini imaging team member at Cornell University, New York, said: “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.”

Watch footage showing Saturn’s moon Enceladus and its warm global ocean:

As a result, they found Enceladus has a tiny, but measurable wobble as it orbits Saturn. Because the icy moon is not perfectly spherical — and because it goes slightly faster, and slower during different portions of its orbit around Saturn — the giant planet subtly rocks Enceladus back, and forth as it rotates, NASA said.

The team combined their measurement of the wobble, called a libration, with different models for how Enceladus might be arranged on the inside, including ones in which the moon was frozen from surface to core, NASA added.

Matthew Tiscareno, co-author of the paper said: “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. This proves that there must be a global layer of liquid separating the surface from the core.”

Watch a NASA video of the global ocean on Saturn’s Moon Enceladus:

Co-author Carolyn Porco said: “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.”

The story of Enceladus has been a great triumph of Cassini’s long mission at Saturn.

The moon’s icy plume was first detected in early 2005, which were then followed up with more discoveries about the material that was coming from warm fractures near its South Pole.

In 2014, news spread of strong evidence suggesting a regional sea but in 2015 the results suggested there was hydrothermal activity taking place on the ocean floor.

It was not until October 28 when Cassini is scheduled to make a close flyby of Enceladus. This mission will be the closest yet, diving through the moon’s active plume of icy material. Cassini will pass just 30 miles (49 kilometers) above the moon’s surface.

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