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Energetic particle phase space densities at Saturn: Cassini observations and interpretations

Energetic particle phase space densities at Saturn: Cassini observations and interpretations
Energetic particle phase space densities at Saturn: Cassini observations and interpretations

Saturn's magnetosphere has been studied extensively by the Cassini spacecraft during the last 6 years. We present mission-averaged energetic proton and electron measurements obtained by the MIMI/LEMMS instrument onboard Cassini in an energy range from several 10 keV to several 10 MeV separated by equatorial pitch angle. We discuss the resulting radial profiles and energy spectra. The measured intensities are converted to phase space densities. The distribution of energetic particles is governed by a large variety of processes. For instance, moons absorb energetic particles, creating macrosignatures or microsignatures. We have found that the moon Rhea is partly responsible for a change in gradient of electron phase space densities. We show that, in contrast to larger distances, the particle distribution for L < 8 is not driven by radial diffusion alone. There, the particle profiles are significantly modified due to Saturn's Neutral Torus, plasma environment, E ring, injection events, and cosmic ray albedo neutron decay. Large parts of our analysis are focused near L = 7. There, protons are lost within the Neutral Torus and not the E ring. For electrons, we find that these two losses are of comparable rate but have discovered that neither process is the dominant driver of loss. We point out that intensity measured by a energy channel, such as in a particle instrument, can actually increase in the region of ring and torus instead of decrease. The importance of injection events is shown to be at least of similar importance as radial diffusion.

2169-9380
Kollmann, P.
e8028cc0-a696-4475-8836-c67ae718bb14
Roussos, E.
6b85b964-976c-4bd0-b1aa-b2ba918482da
Paranicas, C.
afafdeb4-2f93-4322-848f-f35eb7054fb0
Krupp, N.
81e8ae1f-7fab-4ea8-b8d3-44c5a489c283
Jackman, C.M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Kirsch, E.
3fc872b0-2652-45b5-8866-86a43196f857
Glassmeier, K.H.
0061e9bf-fd95-4535-81cd-479d7f3b8b4d
Kollmann, P.
e8028cc0-a696-4475-8836-c67ae718bb14
Roussos, E.
6b85b964-976c-4bd0-b1aa-b2ba918482da
Paranicas, C.
afafdeb4-2f93-4322-848f-f35eb7054fb0
Krupp, N.
81e8ae1f-7fab-4ea8-b8d3-44c5a489c283
Jackman, C.M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Kirsch, E.
3fc872b0-2652-45b5-8866-86a43196f857
Glassmeier, K.H.
0061e9bf-fd95-4535-81cd-479d7f3b8b4d

Kollmann, P., Roussos, E., Paranicas, C., Krupp, N., Jackman, C.M., Kirsch, E. and Glassmeier, K.H. (2011) Energetic particle phase space densities at Saturn: Cassini observations and interpretations. Journal of Geophysical Research: Space Physics, 116 (5), [A05222]. (doi:10.1029/2010JA016221).

Record type: Article

Abstract

Saturn's magnetosphere has been studied extensively by the Cassini spacecraft during the last 6 years. We present mission-averaged energetic proton and electron measurements obtained by the MIMI/LEMMS instrument onboard Cassini in an energy range from several 10 keV to several 10 MeV separated by equatorial pitch angle. We discuss the resulting radial profiles and energy spectra. The measured intensities are converted to phase space densities. The distribution of energetic particles is governed by a large variety of processes. For instance, moons absorb energetic particles, creating macrosignatures or microsignatures. We have found that the moon Rhea is partly responsible for a change in gradient of electron phase space densities. We show that, in contrast to larger distances, the particle distribution for L < 8 is not driven by radial diffusion alone. There, the particle profiles are significantly modified due to Saturn's Neutral Torus, plasma environment, E ring, injection events, and cosmic ray albedo neutron decay. Large parts of our analysis are focused near L = 7. There, protons are lost within the Neutral Torus and not the E ring. For electrons, we find that these two losses are of comparable rate but have discovered that neither process is the dominant driver of loss. We point out that intensity measured by a energy channel, such as in a particle instrument, can actually increase in the region of ring and torus instead of decrease. The importance of injection events is shown to be at least of similar importance as radial diffusion.

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More information

Published date: May 2011

Identifiers

Local EPrints ID: 437326
URI: http://eprints.soton.ac.uk/id/eprint/437326
ISSN: 2169-9380
PURE UUID: 4a09b3ad-9432-413b-90f1-8fe76e8bbcf3
ORCID for C.M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

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Date deposited: 24 Jan 2020 17:31
Last modified: 10 Nov 2021 03:35

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Contributors

Author: P. Kollmann
Author: E. Roussos
Author: C. Paranicas
Author: N. Krupp
Author: C.M. Jackman ORCID iD
Author: E. Kirsch
Author: K.H. Glassmeier

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