Ingersoll, A.P. (2007). "Models of the Enceladus Plumes: Is Liquid Water Required?" Eos Trans. AGU 88(52) Fall Meet. Suppl., Abstract P11F-02 INVITED.

What do the observations of the plumes and surface environment tell us about the interior of Enceladus? We have information about the gas composition, particle composition, particle size, the collimation and speed of the jets, the composition and size of crystals on the surface, and the surface temperatures, from which we can infer the surface heat flow. All of this is preliminary; new data are expected and the old data are still being analyzed. We also know a lot about the geologic setting around the south pole where the plumes originate. The basic questions are: What is Enceladus made of, especially in the icy upper crust? What is the internal temperature distribution? Is liquid water present, and how deep is it? How does the heat get to the surface? Two important end members in the spectrum of possibilities are the boiling liquid model and the cold condensing vapor model. They both produce jets of water vapor and ice, as observed, but they differ in many important respects. Accounting for the other gases observed in the plumes, many of which are more volatile than water, is a challenge for any theory. The gas-to-solid ratio is an important observable, but its value may depend more on the geometry of the vents than on the temperature of the sub-surface sources. A liquid transports heat more effectively than a low-density gas, but even the gas seems able to supply the observed heat. If this is true, any liquid water may be far below the surface. At most we can hope to rule out some hypotheses, but the range of possibilities remains large. The talk will review models that have been published at the time of the meeting. One can expect further progress in the months ahead.