In-situ observations of a neutral gas torus at Europa

A. Lagg; N. Krupp; J. Woch; D. J. Williams

doi:10.1029/2003GL017214

In-situ observations of a neutral gas torus at Europa

A. Lagg^*, N. Krupp, J. Woch, D. J. Williams

^*Corresponding author for this work

Not published at Aalto University

Research output: Contribution to journal › Article › Scientific › peer-review

63 Citations (Scopus)

Abstract

A persistent pattern in the pitch angle distributions of energetic protons near the orbit of Europa has been observed with the Energetic Particles Detector (EPD) on board the Galileo spacecraft during each of the Europa orbit crossings in the last 7 years. The proton fluxes at energies larger than 220 ke V peak at equatorial pitch angles of 90° whereas fluxes of lower energy protons (80-220 ke V) at this pitch angle are depleted. We propose that a Jupiter-surrounding neutral gas torus in the vicinity of the orbit of Europa is responsible for the depletion of energetic particle fluxes by charge exchange collisions. In order to reproduce the observed depletion signature an average neutral number density of 20 to 50 cm^-3 is required.

Original language	English
Pages (from-to)	10-1 - 10-4
Journal	Geophysical Research Letters
Volume	30
Issue number	11
DOIs	https://doi.org/10.1029/2003GL017214
Publication status	Published - 1 Jun 2003
MoE publication type	A1 Journal article-refereed

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10.1029/2003GL017214

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abstract = "A persistent pattern in the pitch angle distributions of energetic protons near the orbit of Europa has been observed with the Energetic Particles Detector (EPD) on board the Galileo spacecraft during each of the Europa orbit crossings in the last 7 years. The proton fluxes at energies larger than 220 ke V peak at equatorial pitch angles of 90° whereas fluxes of lower energy protons (80-220 ke V) at this pitch angle are depleted. We propose that a Jupiter-surrounding neutral gas torus in the vicinity of the orbit of Europa is responsible for the depletion of energetic particle fluxes by charge exchange collisions. In order to reproduce the observed depletion signature an average neutral number density of 20 to 50 cm-3 is required.",

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AU - Woch, J.

AU - Williams, D. J.

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AB - A persistent pattern in the pitch angle distributions of energetic protons near the orbit of Europa has been observed with the Energetic Particles Detector (EPD) on board the Galileo spacecraft during each of the Europa orbit crossings in the last 7 years. The proton fluxes at energies larger than 220 ke V peak at equatorial pitch angles of 90° whereas fluxes of lower energy protons (80-220 ke V) at this pitch angle are depleted. We propose that a Jupiter-surrounding neutral gas torus in the vicinity of the orbit of Europa is responsible for the depletion of energetic particle fluxes by charge exchange collisions. In order to reproduce the observed depletion signature an average neutral number density of 20 to 50 cm-3 is required.

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In-situ observations of a neutral gas torus at Europa

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