The discovery was made using data from the NASA Cassini spacecraft

Apr 4, 2014 07:10 GMT  ·  By
Artist's impression of the ocean buried under miles of icy crust, on Saturn's moon Enceladus
   Artist's impression of the ocean buried under miles of icy crust, on Saturn's moon Enceladus

Using data collected by the NASA Cassini orbiter over several years, scientists with the Jet Propulsion Laboratory (JPL) in Pasadena, California, were recently able to confirm the existence of a large ocean of liquid water underneath the icy crust of Saturn's moon Enceladus. This ocean was first hypothesized to exist long ago, but evidence for it has remained circumstantial until recently. 

Discovering a liquid ocean on a body other than Earth is a monumental finding, since this suggests Enceladus may have the right conditions to support the development of extraterrestrial life forms, such as basic microbes and bacteria. Additionally, this study implies that similar moons, such as Jupiter's Europa, may also contain liquid oceans at their cores, buried deep under thick ice sheets.

In the new experiments, scientists compiled the first geophysical measurements of Enceladus' interior. The most important data used in this research were collected during flybys Cassini carried out around the Saturnine moon, when it conducted a series of very sensitive gravity measurements. This allowed the spacecraft to determine the internal structure of the celestial body.

The fact that an interior reservoir of water may exist on Enceladus was first proposed some 9 years ago, but it was not until the new study that researchers could get confirmation of their ideas. The new work is published in the April 4 issue of the top journal Science. JPL expert Sami Asmar was one of the coauthors on the paper.

“The way we deduce gravity variations is a concept in physics called the Doppler Effect, the same principle used with a speed-measuring radar gun,” Asmar explains. The researcher holds an appointment with the Radio Science Systems Group at JPL.

“As the spacecraft flies by Enceladus, its velocity is perturbed by an amount that depends on variations in the gravity field that we're trying to measure. We see the change in velocity as a change in radio frequency, received at our ground stations here all the way across the solar system,” he adds.

According to the newly published paper, the ocean inside Enceladus lies at a depth of 30 to 40 kilometers (19 to 25 miles) under the thick surface ice sheets. The body of water itself is around 10 kilometers (6 miles) thick, Cassini data suggest. Enceladus is a relatively small moon, boasting a diameter of just 500 kilometers (300 miles).

Cassini flew by this moon a total of 19 times since achieving orbital insertion around Saturn, on July 1, 2004. Shortly after arrival, the spacecraft observed plumes of material being released from so-called tiger stripe features at the south pole. In-depth analyses conducted later on revealed the presence of water-ice and organic molecules in these plumes.

A buried ocean “then provides one possible story to explain why water is gushing out of these fractures we see at the south pole,” explains California Institute of Technology investigator and study coauthor, David Stevenson.