The Geysers of Enceladus: An Overview of Cassini Results

Cassini has found in the small Saturnian moon Enceladus a surprising degree of present-day geologic activity. The closest Enceladus flyby so far occurred in July 2005. During this event, Cassini instruments confirmed the presence of a plume of vapor over the South Pole detected by the Cassini Magnetometer (MAG) in an earlier close flyby. The Ultraviolet Spectrometer (UVIS) observed a stellar occultation by the plume and measured the abundance of water vapor near the surface. In situ plume measurements in July indicated a composition of water vapor and trace amounts of simple organic molecules but lacking ammonia (Ion and Neutral Mass Spectrometer (INMS)). Micron-sized particles of water ice were also detected in situ (Cosmic Dust Analyzer (CDA)). The Cassini Imaging Science (ISS) experiment obtained detailed images of the south polar region, finding a prominent set of fractures stradding the South-Polar region. The Visual and Infra-Red Mapping Spectrometer (VIMS) found carbon-dioxide and simple organic materials coincident with these fractures; it, too, failed to detect ammonia. The Composite Infra-Red Spectrometer (CIRS) found the entire South-Polar region to be excessively warm. Combination of ISS and CIRS high resolution observations revealed the fractures straddling the South Pole to be the warmest places of all. Images of Enceladus acquired by the Cassini ISS experiment later in 2005 and 2006 clearly showed many tall geysers and an enormous plume extending for several Enceladus diameters above the South Pole and most likely venting through the prominent South-Polar fractures. These latter results, together with the measurements of water-vapor abundances from other Cassini instruments, suggest near-surface subterranean chambers of organic- containing liquid water beneath the South Pole. This presentation will offer an overview of these results and their implications.