NASA researchers uncovered evidence that indicates Saturn's moon Enceladus has a large underground ocean made up of liquid water.
Researchers were first suspicious of an underground reservoir on Enceladus when they observed water and ice spewing from the moon's vents back in 2005, a NASA news release reported. The finding could mean there are microbes hiding below Enceladus' surface as well.
The new study provides the first "geophysical measurements of the internal structure of Enceladus," the news release reported. These measurements matched up with the theory of an underground ocean.
"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," Sami Asmar of NASA's Jet Propulsion Laboratory (JPL), a coauthor of the paper, said in the news release. "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."
According to the gravity measurements, there is most likely a "regional" underground ocean on Enceladus that spans is about six miles deep; it is estimated to lie beneath the moon's 19 to 25-mile thick ice shell. The moon is believed to being one of the top candidates for hosting microbial life in our solar system.
"This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole," David Stevenson of the California Institute of Technology, a co-author of the paper, said in the news release.
NASA's Cassini spacecraft has flown by the moon about 19 times; researchers were able to measure the tug of gravity on the craft by looking at variations in its velocity. This method can detect velocity changes as small as one foot per hour.
Using these velocity measurements the researchers were able to determine that there was a region of higher density at the Southern end of Enceladus.
"The Cassini gravity measurements show a negative gravity anomaly at the south pole that however is not as large as expected from the deep depression detected by the onboard camera," said the paper's lead author, Luciano Iess of Sapienza University of Rome. "Hence the conclusion that there must be a denser material at depth that compensates the missing mass: very likely liquid water, which is seven percent denser than ice. The magnitude of the anomaly gave us the size of the water reservoir."
In the future researchers hope to gain more insight into this possibly life-hosting moon.
"Material from Enceladus' south polar jets contains salty water and organic molecules, the basic chemical ingredients for life," Linda Spilker, Cassini's project scientist at JPL, said in the news release. "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."
