Johnson, T.V. (2005). "Imaging Enceladus' Exotic South Polar Regions: Imaging Science Team Results." Eos Trans. AGU 86(52), Fall Meet. Suppl., Abstract P21F-03 I.


The Cassini spacecraft had a close (175 km altitude) encounter with Saturn's moon Enceladus on 14 July 2005, resulting in a major discovery: evidence from multiple experiments show that there is a large `plume' of water vapor and particles emanating from the satellite's south polar region. Infrared data from the CIRS instrument showed that this area is also anomalously warm, providing evidence for internal heat. High resolution images taken by the Imaging Science System during the encounter show that the warm region associated with water vapor venting is a unique area on this icy world. The region has very few if any detectable impact craters, making it the youngest surface seen on Enceladus, or any of the other icy Saturnian satellites, estimates from cratering models place its age at less than 10-100 million years. It is surrounded by tectonic features suggesting a global stress pattern that may be associated with a change in spin rate. Long, parallel fractures, informally dubbed `tiger stripes', cross the region and are correlated with at least some of the thermal anomalies, making them good candidates for the source regions of the water venting. Spectral data and photometric studies also show that the whole area and the tiger stripes in particular have fewer fine grained particles on the surface than most of the moon's surface, in agreement with a young surface and crystalinity and grain size interpretations of data from the Visual and Near Infrared Mapping Spectrometer experiment. Tidal forces and radioactive heating are probably responsible for the activity, although generating such intense internal heating is challenging for current models. Portions of this work were done at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.