A new analysis of the navigational data from NASA’s Cassini space probe allowed to obtain new information about the ocean of liquid water beneath the surface of Enceladus, one of Saturn’s moons. This research, coordinated by Luciano Iess of the department of mechanical and aerospace engineering at Rome’s University La Sapienza, was carried out by a team of Italian and American researchers exploiting the influences of the very small gravitational changes on Cassini’s movements.

Between 2010 and 2012, the Cassini spacecraft made ​​flybys at Enceladus, reaching even to less than 100 km (60 miles) from this moon. In two cases, the spacecraft passed over the southern hemisphere and once over its northern hemisphere. Enceladus’s gravity caused Cassini to move a bit, changing its speed. We’re talking about really tiny movements that still cause a Doppler effect on the probe’s radio broadcasts.

When those radio waves are received on Earth, their extremely precise analysis provided a gravitational map of at least a part of Enceladus. With this result, it was possible to infer the mass distribution within this moon. In particular, researchers have found an anomaly with a slightly lower gravity on the surface of the south pole and a slightly higher gravity about 30-40 km (19-25 miles) deep.

This analysis of gravity, combined with the topography of Enceladus available thanks to the pictures taken by the Cassini spacecraft, have allowed to infer the internal structure of this moon. The simplest explanation to certain perturbations of the spacecraft’s motion is that Enceladus has an asymmetrical internal structure. Its crust of ice most likely hides an ocean of liquid water at a depth of 30-40 km (19-25 miles) about 10 km (6 miles) deep.

There were already a number of elements that indicated the presence of liquid water beneath the icy surface of Enceladus. This moon is similar in many ways to Europa, one of Jupiter’s moons, which is much larger and has been under observation for years. Studies on the presence of liquid water beneath the icy surface of Europa had already suggested that Enceladus might have an underground ocean. Saturn’s moon has also an icy surface with cracks that show signs of gravitational tension that can warm up the moon’s inside enough to bring water to its liquid state.

The detection of geysers emitted from Enceladus was already a proof of the existence of underground liquid water. The discovery of organic molecules in those jets made ​​everything much more interesting. This new research gives an idea of the minimum size of Enceladus ocean but it would take a specific mission for further analysis, of the organic materials too.

Both NASA and ESA are planning missions to Europa but they’re only in the initial stages. It’s possible that the two agencies will join forces but even if a mission is approved it will take a long time and, unless other extraordinary discoveries on Enceladus are made, a Jupiter’s moon will be the first target of the search for extraterrestrial life. As a result, it’s likely that Enceladus will have to wait a long time for a specific research.

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