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AGU: Geophysical Research Letters

 

Keywords

  • Saturn
  • Enceladus

Index Terms

  • Planetary Sciences: Solar System Objects: Saturn
  • Planetary Sciences: Solar System Objects: Saturnian satellites
  • Magnetospheric Physics: Planetary magnetospheres

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L14202, 5 PP., 2008
doi:10.1029/2008GL034749

Cassini detection of water-group pick-up ions in the Enceladus torus

R. L. Tokar

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

R. J. Wilson

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

R. E. Johnson

University of Virginia, Charlottesville, Virginia, USA

M. G. Henderson

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

M. F. Thomsen

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

M. M. Cowee

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

E. C. Sittler Jr.

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

D. T. Young

Southwest Research Institute, San Antonio, Texas, USA

F. J. Crary

Southwest Research Institute, San Antonio, Texas, USA

H. J. McAndrews

Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

H. T. Smith

Applied Physics Laboratory, Laurel, Maryland, USA

This study reports direct detection by the Cassini plasma spectrometer of freshly-produced water-group pick-up ions within the proposed Enceladus torus, a radially narrow toroidal region surrounding Saturn that contains a high density of water-group neutrals. This torus is produced by the icy plumes observed near the south pole of Enceladus. The ions are created by charge exchange collisions between water-group neutrals in the Enceladus torus and thermal ions corotating with Saturn. They are identified in the Cassini data via their characteristic ring-like signatures in ion velocity distributions. In the radial distance range of 4.0 to 4.5 RS, the density of these non-thermalized ions is estimated to be at least 5.2 cm−3, about 8% of the total ion density. The estimated density together with ionization, charge exchange, and loss times, yield an ion thermalization time of at least 3150 s, in reasonable agreement with hybrid particle simulations.

Received 21 May 2008; accepted 20 June 2008; published 24 July 2008.

Citation: Tokar, R. L., et al. (2008), Cassini detection of water-group pick-up ions in the Enceladus torus, Geophys. Res. Lett., 35, L14202, doi:10.1029/2008GL034749.

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