New gravity data from ESA’s Cassini spacecraft reveal that Enceladus – the sixth-largest of the moons of Saturn – harbors a regional subsurface sea at depths of 30 to 40 km.
This color view of Enceladus was taken by Cassini spacecraft on 31 January 2011, from a distance of 50,330 miles (NASA / JPL-Caltech / SSI / G. Ugarković)
Planetary scientists led by Dr Luciano Iess of Sapienza Università di Roma in Italy investigated the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three Cassini flybys.
“Using geophysical measurements, we have been able to confirm that there is a large ocean beneath the surface of Enceladus’ south-polar region. This provides a possible source for the water that Cassini has seen spewing from the geysers in this region,” said Prof David Stevenson, a co-author of the paper published in the journal Science.
Dr Iess, Dr Stevenson and their colleagues analyzed Doppler data and found that the southern polar region of the moon doesn’t have enough mass at its surface to account for the hemisphere’s gravity field. So, they suggest that something dense below the surface of Enceladus – probably liquid water – must be compensating.
This water sea “may extend halfway or more towards the equator in every direction,” Dr Stevenson
The findings imply that Enceladus is a differentiated body with a low-density core and a separate mantle and crust. They also help to explain the mineral-rich jets of water vapor that were first observed flowing from long, distinctive fractures in the moon’s southern polar region – called tiger stripes – in 2005.
In addition, the team posits that the subsurface ocean on Enceladus sits atop silicate rock instead of ice, which means that the environment there is ripe for complex chemical reactions, including some that – with the help of an energy source – might create conditions like those on the early Earth.
“Enceladus shows some similarity to Europa – a much larger moon of Jupiter – which, like Enceladus, has an ocean that is in contact with underlying rock,” Dr Stevenson said.
“In this respect these two bodies are of particular interest for understanding the presence and nature of habitable environments in our Solar System.”
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L. Iess et al. 2014. The Gravity Field and Interior Structure of Enceladus. Science, vol. 344, no. 6179, pp. 78-80; doi: 10.1126/science.1250551
