Water Vapor & Particles Over Enceladus

This plot shows results from Cassini's Ion Neutral Mass Spectrometer (INMS) and Cosmic Dust Analyzer (CDA), obtained during the spacecraft's close approach to Enceladus on July 14, 2005. Within a minute of that closest approach, the 2 instruments detected material coming from the surface of the Moon. The INMS measured a large peak in the abundance of water vapor at approx. 35" before closest approach to Enceladus, as it flew over the South Polar Region at an altitude of 270 Km. The high rate detector of the CDA observed a peak in the number of fine, powder-sized icy particles coming from the surface approx. 1' before reaching closest approach, at an altitude of 460 Km. The character of these detections is very similar to the venting of vapor and fine, icy particles from the surfaces of comets when they are warmed as they near the Sun. On Enceladus, it is believed that internal heat, possibly from tidal forces, is responsible for the activity. The close but different occurrences of the two detections are yielding important clues to the location of the vents and even the venting process.