Enceladus Hidden Ocean & Thin Ice Shell Fuel Habitability Hopes

Gravity Data Reveals Subsurface Sea

Researchers mapped the gravity field of the 313-mile-wide (504 km) moon by tracking velocity changes in NASA’s Cassini spacecraft during three close flybys between 2010 and 2012, according to study lead author Luciano Iess of Sapienza University in Rome. The team measured radio frequency shifts received at ground stations via NASA’s Deep Space Network, which can detect spacecraft speed variations as small as 1 foot (0.3 meters) per hour, as noted by co-author Sami Asmar of the NASA Jet Propulsion Laboratory.

The tracking data revealed a negative mass anomaly at the south pole, indicating less mass than expected for a spherical body. Because a surface depression roughly 0.6 miles (1 km) deep marks the region, the observed mass deficit was actually smaller than the surface dent warranted. Researchers concluded that denser liquid water beneath the ice shell compensates for the missing surface mass.

Ice Shell and Ocean Dimensions

The subsurface ocean is estimated to be about 6 miles (10 kilometers) deep, trapped beneath an outer shell of ice measuring 19 to 25 miles (30 to 40 km) thick, according to the findings. The sea is likely confined to the southern hemisphere, stretching roughly halfway to the equator from the pole.

This discovery confirms longstanding suspicions sparked in 2005, when the Cassini spacecraft first observed water vapor and ice particles erupting from fractures known as “tiger stripes” near the south polar region. The internal heat required to maintain the liquid ocean is generated by tidal interactions, potentially involving gravitational tugs between Enceladus and another Saturnian moon, Dione. A 2011 study previously found that the south polar region outputs 15.8 gigawatts of thermal power, equivalent to the output of 20 coal-fired power plants.