Enceladus is a key source of plasma and neutrals in Saturn’s magnetosphere through its active south polar plume, which drives complex dust–plasma interactions and modifies the local environment. In this paper, we investigate electron density perturbations near Saturn’s moon Enceladus using Cassini observations from 12 targeted flybys that sampled the upstream and downstream regions. Electron densities are derived from the upper hybrid resonance frequencies detected by the Radio and Plasma Wave Science (RPWS) instrument, and energetic electron intensities are obtained from the Low Energy Magnetospheric Measurement System (LEMMS) of the Magnetospheric Imaging Instrument. Flybys are classified as upstream or downstream encounters, enabling a direct comparison of spatial variations. The results reveal a pronounced upstream–downstream asymmetry in RPWS electron density. Downstream flybys exhibit strong depletions near Enceladus, with anomalies reaching up to ∼60 cm−3 below background levels, whereas upstream flybys display only modest variations of a few cm−3. The magnitude of dropouts in the downstream region also depends on flyby geometry. These observations are consistent with the presence of plume-generated dust and Alfvén wings downstream and offer insight into the spatial scale of the interaction region. In contrast, LEMMS energetic electron observations show no clear upstream–downstream asymmetry, with intensity dropouts occurring in both geometries. This may indicate that cold and energetic electron populations exhibit different behaviors influenced by physical processes operating on different spatial scales in the vicinity of Enceladus.
Fiona Wai Chung Law, Dingnuo Wang, Yin Ching Law, Zhonghua Yao, Shangchun Teng, and Binzheng Zhang. Asymmetric Distribution of Electron Density near Enceladus: A Comparative Survey of Upstream and Downstream Cassini Flybys
Title: Asymmetric Distribution of Electron Density near Enceladus: A Comparative Survey of Upstream and Downstream Cassini Flybys.
Abstract
Published 2026 August 31 • © 2026. The Author(s). Published by the American Astronomical Society.
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Citation Fiona Wai Chung Law et al 2026 ApJ 1008 127
DOI 10.3847/1538-4357/ae9150
The Astrophysical Journal, 1008(1), 127.
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