P14A-01
Enceladus Plume Composition
The composition of the gas plume emanating from Enceladus' southern pole has been measured twice by the Cassini Ion Neutral Mass Spectrometer. The plume contains 90% water vapor, with small percentages (1 to 4%) of methane, carbon dioxide, and an unresolved contribution from both molecular nitrogen and carbon monoxide. Trace amounts of more complex organics are also identified, including both C2 and C3 compounds. Structure in the variation of the water vapor profile during the flyby appears to be correlated with the structure of the dust jets.
P14A-02
Cassini CAPS-ELS observations of Enceladus's plume
The Electron Spectrometer, ELS, of the Cassini Plasma Spectrometer, CAPS, was oriented for the direct sampling of material inside Enceladus's plume during two of the three close encounters with this moon in 2008, on March 12, and October 9. We present ELS observations obtained during these two encounters, approaching to within 52 and 25 km of the moon's surface, respectively. Several unanticipated features were observed within the plume; we present our interpretations of these features, comparing them with other instruments' observations of the plume and its surface sources.
P14A-03
Sodium Salts in Ice Grains from Enceladus' Plumes: Evidence for an Ocean below the Moon's Surface
One key requirement for the formation of life on Enceladus, is liquid water below its icy surface. Although measurements and model calculations for Enceladus plume source suggest temperatures close to the melting point, direct evidence for liquid water has not been produced so far. We present compositional measurements by Cassini's dust detector of ice particles emitted from Saturn's cryo-volcanic moon Enceladus into the E ring. Since sodium is considered as crucial tracer for an Enceladus ocean, our detection of sodium salts within the grains provide the first evidence for mineral enriched liquid water below the moon's icy surface. In nearly all particles detected in situ by the Cosmic Dust Analyser (CDA) aboard the Cassini spacecraft, we found sodium (Na) in varying concentrations. Most spectra also show potassium (K) in lower abundance. In mass spectra that are particularly sodium rich, sodium salts (like NaCl and NaHCO3) are identified as Na bearing components. This is only possible if the plume source is liquid water that is or has been in contact with the rocky material of Enceladus' core. The abundance of minerals as well as the inferred basic pH value of those grains exhibit a compelling similarity with the predicted composition of an Enceladus ocean. As for terrestrial oceans, sodium (Na+) and chloride (Cl-) are expected to be the most abundant components, followed by hydrogen carbonate (HCO3-). From the compositional analysis, models for grain production and ejection can be derived which give new insights into dynamic, subsurface processes.
P14A-04
Habitability of Enceladus: Planetary Conditions for Life
The prolific activity and presence of a plume on Saturn's tiny moon Enceladus offers us a unique opportunity to sample the interior composition of an icy satellite, and to look for interesting chemistry and possible signs of life. Based on studies of the potential habitability of Jupiter's moon Europa, icy satellite oceans can be habitable if they are chemically mixed with the overlying ice shell on Myr time scales. We hypothesize that Enceladus' plume, tectonic processes, and possible liquid water ocean may create a complete and sustainable geochemical cycle that may allow it to support life. We discuss evidence for surface/ocean material exchange on Enceladus based on the amounts of silicate dust material present in the Enceladus' plume particles. Microphysical cloud modeling of Enceladus' plume shows that the particles originate from a region of Enceladus' near surface where the temperature exceeds 190 K. This could be consistent with a shear-heating origin of Enceladus' tiger stripes, which would indicate extremely high temperatures (~250-273 K) in the subsurface shear fault zone, leading to the generation of subsurface liquid water, chemical equilibration between surface and subsurface ices, and crustal recycling on a time scale of 1 to 5 Myr. Alternatively, if the tiger stripes form in a mid-ocean-ridge-type mechanism, a half-spreading rate of 1 m/yr is consistent with the observed regional heat flux of 250 mW m-2 and recycling of south polar terrain crust on a 1 to 5 Myr time scale as well.