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    Rights statement: Accepted for publication in Journal of Geophysical Research: Space Physics. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted.

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Energetic particle signatures above Saturn’s aurorae

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Article numbere2019JA027403
<mark>Journal publication date</mark>1/01/2020
<mark>Journal</mark>Journal of Geophysical Research: Space Physics
Issue number1
Volume125
Number of pages17
Publication statusPublished
Original languageEnglish

Abstract

Near the end of its mission, NASA's Cassini spacecraft performed several low‐altitude passes across Saturn's auroral region. We present auroral imagery and various coincident particle and field measurements of two such passes, providing important information about the structure and dynamics of Saturn's auroral acceleration region. In upward field‐aligned current regions, upward proton beams are observed to reach energies of several tens of keV; the associated precipitating electron populations are found to have mean energies of about 10 keV. With no significant wave activity being apparent, these findings indicate strong parallel potentials responsible for auroral acceleration; about 100 times stronger than at Earth. This is further supported by observations of proton conics in downward field‐aligned current regions above the acceleration region, which feature a lower energy cutoff above ~50 keV ‐ indicating energetic proton populations trapped by strong parallel potentials while being transversely energized until they can overcome the trapping potential, likely through wave‐particle interactions. A spacecraft pass through a downward current region at an altitude near the acceleration region reveals plasma wave features which may be driving the transverse proton acceleration generating the conics. Overall, the signatures observed resemble those related to the terrestrial and Jovian aurorae, the particle energies and potentials at Saturn appearing to be significantly higher than at Earth and comparable to those at Jupiter.

Bibliographic note

Accepted for publication in Journal of Geophysical Research: Space Physics. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted.