A plume of water vapour escapes from fissures crossing the south polar region of the Saturnian moon Enceladus1,2,3,4,5,6. Tidal deformation of a thin surface crust above an internal ocean could result in tensile and compressive stresses that would affect the width of the fissures7; therefore, the quantity of water vapour released at different locations in Enceladus’ eccentric orbit is a crucial measurement of tidal control of venting. Here we report observations of an occultation of a star by the plume on 24 October 2007 that revealed four high-density gas jets superimposed on the background plume. The gas jet positions coincide with those of dust jets reported elsewhere8 inside the plume. The maximum water column density in the plume is about twice the density reported earlier2. The density ratio does not agree with predictions7—we should have seen less water than was observed in 2005. The ratio of the jets’ bulk vertical velocities to their thermal velocities is 1.5 ± 0.2, which supports the hypothesis that the source of the plume is liquid water, with gas accelerated to supersonic velocity in nozzle-like channels9.
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We acknowledge the Cassini Navigation Team, particularly B. Buffington and Y. Hahn, who were central to the success of this observation. This work was supported by the Cassini Project at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Author Contributions Every co-author contributed a significant piece of analysis to this paper; C.J.H. was lead author of this collection of work.
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Hansen, C., Esposito, L., Stewart, A. et al. Water vapour jets inside the plume of gas leaving Enceladus. Nature 456, 477–479 (2008) doi:10.1038/nature07542
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