Researchers have uncovered evidence of Saturn's moon Enceladus harboring a large underground ocean of liquid water, which suggests that it could support life.
The new data provide the first geophysical measurements of the internal structure of Enceladus, consistent with the existence of a hidden ocean inside the moon.
Co-author Sami Asmar of NASA's Jet Propulsion Laboratory in Pasadena, California, said that the way they deduce gravity variations is a concept in physics called the Doppler effect, the same principle used with a speed-measuring radar gun.
He said that 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 their ground stations here all the way across the solar system."
The gravity measurements suggest a large, possibly regional, ocean about 6 miles (10 kilometers) deep, beneath an ice shell about 19 to 25 miles (30 to 40 kilometers) thick. The subsurface ocean evidence supports the inclusion of Enceladus among the most likely places in our solar system to host microbial life. Before Cassini reached Saturn in July 2004, no version of that short list included this icy moon, barely 300 miles (500 kilometers) in diameter.
Lead author Luciano Iess of Sapienza University of Rome said that 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.
He said this is why they concluded 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.
The study has been published in the journal Science.