Ocean inside Saturn’s moon, Enceladus, may be the next place to look for extraterrestial life

Using the Cassini spacecraft and their Deep Space Network communication system, NASA has found evidence that Saturn's tiny moon, Enceladus, may have an ocean of liquid water under its icy crust.

NASA's Cassini spacecraft has been investigating science targets in the Saturn system for close to 10 years now, and NASA has kept in contact with the spacecraft using its Deep Space Network, a system of radio telecommunication antennas scattered around the Earth. For one particular target, the icy moon Enceladus, NASA scientists used the combination of the spacecraft and the telecommunications system to investigate the plumes of water vapour that they've been seeing shooting out of Enceladus' south pole. The way they did this was to have Cassini fly by the moon one more time, and take careful measurements of the gravity being experienced by the spacecraft as it made its pass.

"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," said study co-author Sami Asmar, of NASA's Jet Propulsion Laboratory, in a statement. "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."

Camera views of Enceladus' south pole show a deep depression in the ice there, and Cassini experienced a corresponding dip in the strength of gravity as it flew over the area. However, something unusual was discovered in Cassini's data. The dip in gravity the spacecraft experienced wasn't as big as it should be, if the area with the depression was just ice all the way down to the rocky core. There had to be something else — some denser material — between the ice and the rocky core, to account for this 'anomaly' and liquid water (which is seven per cent denser than ice) fits the bill.

According to the researchers, the measurements taken suggest that it's likely an ocean about 10 kilometres deep, under a 30-40 kilometre-thick layer of ice. However, unlike the ocean that's thought to be under the icy surfaces of moons like Europa and Ganymede, the scientists figure the one under Enceladus' ice is probably just a regional one, only around the south pole. It may be difficult to imagine an ocean of liquid water on an object that far out in the solar system, but Enceladus' close orbit around Saturn (it only takes about 33 hours to go around) means that it likely experiences tidal heating, which can generate enough heat to melt the ice nearest to it's rocky core.

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Combined with some of Cassini's previous discoveries about Enceladus, this is generating some excitement, as it apparently gives us another location in our solar system to look for life!

"Material from Enceladus' south polar jets contains salty water and organic molecules, the basic chemical ingredients for life," said Linda Spilker, Cassini's project scientist at the Jet Propulsion Laboratory, according to the statement. "Their discovery expanded our view of the 'habitable zone' within our solar system and in planetary systems of other stars. This new validation that an ocean of water underlies the jets furthers understanding about this intriguing environment."

(Image courtesy: NASA/JPL-Caltech)

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