10 Mar. 2011

 

More heat than predicted from Enceladus

 

A study published recently in the Journal of Geophysical Research reveals that the thermal energy produced by Enceladus, a satellite of Saturn, is an order of magnitude greater than predicted by theoretical models.
That Enceladus has a particularly warm south pole, and is also geologically active, has been known since 2005, the year in which the Cassini probe started to observe a long series of eruptions of water ice particles mixed with other elements coming mainly from 4 fractures. These almost parallel fractures, about 130 km long and 2 km wide (sometimes called "tiger stripes"), appear to open at various points, erupt, and then close again. This is thought to be caused by the heating from tidal forces caused by the orbital resonance between Enceladus and Dione.
The tidally induced internal friction generates heat, and this may be sufficient to maintain a liquid water ocean between the frozen surface and the rocky core, that may be limited to the south polar region or extended over the entire satellite.
A study of this heating mechanism, conducted in 2007, predicted that the thermal energy released on Enceladus by the tidal forces and the decay of radioactive isotopes would be approximately 1.4 gigawatts. However, this latest study with Cassini's Composite Infrared Spectrometer (by Carly Howett and John Spencer of the Southwest Research Institute in Boulder, Colorado, and John Pearl and Marcia Segura, of NASA's Goddard Space Flight Center in Greenbelt) show that the energy produced by Enceladus is over ten times greater: 15.8 gigawatts, about the output of 20 coal-fired power stations!
Why this should be the case is presently a mystery, but it is suspected that the combination of tidal forces from Dione and Saturn can cause relatively brief periods of high energy release, and one of these was in progress during the Cassini observations. Such high levels of heat release make it likely that there is a liquid ocean beneath the icy surface, and given previous results that the water ice in the eruptions is actually salty and mixed with carbon-rich compounds, Enceladus will undoubtedly start to attract the attention of astrobiologists.

 

by Michele Ferrara & Marcel Clemens

credit: NASA/JPL/SWRI/SSI