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AGU: Journal of Geophysical Research, Space Physics

 

Keywords

  • photoelectrons

Index Terms

  • Planetary Sciences: Fluid Planets: Magnetospheres
  • Ionosphere: Solar radiation and cosmic ray effects
  • Planetary Sciences: Fluid Planets: Tori and exospheres
  • Planetary Sciences: Fluid Planets: Composition
Abstract
Cited By (3)
 

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, A12212, 8 PP., 2009
doi:10.1029/2009JA014368

Identification of photoelectron energy peaks in Saturn's inner neutral torus

P. Schippers

Université de Toulouse, UPS, CESR, Toulouse, France

UMR 5187, CNRS, Toulouse, France

N. André

Université de Toulouse, UPS, CESR, Toulouse, France

UMR 5187, CNRS, Toulouse, France

Research and Scientific Support Department, SRE-SM, ESTEC, European Space Agency, Noordwijk, Netherlands

R. E. Johnson

Engineering Physics, University of Virginia, Charlottesville, Virginia, USA

M. Blanc

Université de Toulouse, UPS, CESR, Toulouse, France

UMR 5187, CNRS, Toulouse, France

I. Dandouras

Université de Toulouse, UPS, CESR, Toulouse, France

UMR 5187, CNRS, Toulouse, France

A. J. Coates

Mullard Space Science Laboratory, University College London, Surrey, UK

S. M. Krimigis

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA

D. T. Young

Southwest Research Institute, San Antonio, Texas, USA

We present observations from the Cassini Plasma Electron Spectrometer (CAPS/ELS) of characteristic peaks in the electron energy spectrum that are identified in the innermost regions of the Saturnian magnetosphere during low-latitude orbits of the Cassini spacecraft around Saturn. We show how a narrow electron energy peak at about 20 eV and a possible peak at about 42 eV can be extracted from the background in CAPS observations after the contamination from high-energy particles has been removed from the measurements. We estimate the density of the newly discovered electron population to be a small fraction (10%) of the electron density measured in the CAPS/ELS energy range, and a much smaller fraction (about 1%) of the total electron density measured by Radio and Plasma Wave Science since our measurements are affected by spacecraft negative potential. We suggest that this population corresponds to photoelectrons generated by the solar EUV photoionization of the extended cloud of neutral gas observed in these regions. We use pitch angle information to assess the near-equatorial source of these photoelectrons and a simple model of chemistry in order to further support our interpretation. Therefore, photoionization seems to be an additional process for plasma production in the innermost Saturnian magnetosphere. Finally, we mention that the comparison of the modeled and the observed photoelectron peak energies could be used to estimate the spacecraft potential in this region which is measured independently by the Langmuir Probe.

Received 17 April 2009; accepted 9 September 2009; published 18 December 2009.

Citation: Schippers, P., N. André, R. E. Johnson, M. Blanc, I. Dandouras, A. J. Coates, S. M. Krimigis, and D. T. Young (2009), Identification of photoelectron energy peaks in Saturn's inner neutral torus, J. Geophys. Res., 114, A12212, doi:10.1029/2009JA014368.

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