Evidence for Liquid Water Beneath the Enceladus Plumes
Abstract
We present our analysis of the Enceladus plumes using data from the Imaging Science Subsystem (ISS) on the Cassini spacecraft. The ISS is sensitive to the particles but not to the gas. From the fall-off of brightness with respect to height, we infer the velocity distribution of the particles as they leave the vent. From the variation of brightness with scattering angle and wavelength, we infer the particle size distribution. From integrated brightness, we infer the total mass of particles in the plume and the rate at which particle mass is leaving the vents. Both the mass and the mass rate are comparable to those for the gas inferred from Cassini ultraviolet imaging spectrometer (UVIS) data [1]. Thus the solid/gas ratio is of order unity, which rules out models in which the particles form from the vapor. These data imply that the particles were initially liquid droplets from a liquid water reservoir. The droplets froze when exposed to the vacuum of space. This result is consistent with results from the Cosmic Dust Analyzer (CDA), which detects salt in the icy particles [5]. The result is also consistent with the low speed of plume particles, which is much leas than the thermal speed of the gas and the escape speed of Enceladus. A comprehensive model of liquid water, either evaporating, bubbling, or boiling, with dissolved salt and gases, is needed to explain these observations, but such a model does not yet exist.
- Publication:
-
EPSC-DPS Joint Meeting 2011
- Pub Date:
- October 2011
- Bibcode:
- 2011epsc.conf.1664I