Water vapour jets inside the plume of gas leaving Enceladus (original) (raw)

Nature volume 456, pages 477–479 (2008)Cite this article

Abstract

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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Acknowledgements

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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Authors and Affiliations

  1. Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California 91109, USA ,
    C. J. Hansen, B. Wallis & A. R. Hendrix
  2. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA ,
    L. W. Esposito, A. I. F. Stewart, B. Meinke & K. Larsen
  3. Planetary Sciences Group, University of Central Florida, Orlando, Florida 32816, USA ,
    J. E. Colwell
  4. Science Department, Central Arizona College, Coolidge, Arizona 85228, USA,
    W. Pryor
  5. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA,
    F. Tian

Authors

  1. C. J. Hansen
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  2. L. W. Esposito
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  3. A. I. F. Stewart
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  4. B. Meinke
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  5. B. Wallis
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  6. J. E. Colwell
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  7. A. R. Hendrix
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  8. K. Larsen
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  9. W. Pryor
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  10. F. Tian
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Corresponding author

Correspondence toC. J. Hansen.

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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). https://doi.org/10.1038/nature07542

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Editorial Summary

Saturn's moons: Enceladus by starlight

When the Cassini probe flew by Enceladus, Saturn's sixth-largest moon, it detected a plume of water vapour escaping from fissures near the moon's south pole. That was in 2005: the source and nature of the plume are still unclear, but new Cassini data are beginning to narrow down the possibilities. In October 2007 Cassini's ultraviolet imaging spectrograph observed an occultation of a distant star by the plume. Four high-density water vapour jets were detected against the background of the plume, in positions that coincide with those of dust jets seen previously. The jets' density and temperature profiles are consistent with a model in which the source of the plume is liquid water, accelerated to supersonic velocities in nozzle-like channels.