Journal article
A Durable Electron Density Profile Near the Inner Edge of the Io Torus
Journal of geophysical research. Space physics, Vol.130(1), e2024JA033453
01/2025
DOI: 10.1029/2024JA033453
Appears in UI Libraries Support Open Access
Abstract
The Juno Waves instrument can be used to accurately determine the electron density inside Io's orbit, the inner Io torus. These observations have revealed a local peak in the electron density just inside M = 5 and at centrifugal latitudes above about 10 that is likely the ’cold torus' as identified in Earth‐based observations of emissions. This peak or “finger” is separated from the more dense Io torus by a local minimum or ’trough’ at M 5. The electron densities are inferred by identifying characteristic frequencies of the plasma such as the low‐frequency cutoff of Z ‐mode radiation at and the low‐frequency cutoff of ordinary mode radiation at that depend on the electron density. The “finger” density ranges from about 0.2 to 65 and decreases with increasing centrifugal latitude. The “trough” densities range from 0.05 to 10 . This pattern of a density “trough” followed by the “finger” closer to Jupiter is found on repeated passes through the inner Io torus over a range of centrifugal latitudes. Using a simple model for the electron densities measured above about 10 centrifugal latitude, we've estimated the scale height of the “finger” densities as about 1.17 with respect to the centrifugal equator, which is somewhat surprising given the expected cold temperature of the cold torus. The larger scale height suggests a population of light ions, such as protons, is elevated off the centrifugal equator. This is confirmed by a multi‐species diffusive equilibrium model.
Juno's Waves instrument measures the spectrum of waves in the charged particle plasma in Jupiter's magnetosphere. Some spectral features in the plasma waves are at frequencies determined by the strength of the magnetic field and the number density of electrons that vary along Juno's trajectory. This study uses those spectral features to infer the electron density inward of Jupiter's moon Io, sometimes called the inner Io plasma torus. The Juno observations reveal a persistent density peak about 5 Jovian radii from Jupiter that is separated from the much more dense Io torus by a density minimum. Most earlier observations of this region of Jupiter's plasma environment have been made by remote spectroscopic observations of sulfur ions from Io's volcanoes. The Juno measurements reveal plasma densities much lower than those in the main Io plasma torus and show that these densities decrease with latitude more gradually than would be expected from the remote‐sensing observations of the cold inner torus. The new measurements may imply a population of protons mixed with the plasma from Io's volcanoes.
We determine electron densities derived from Juno Waves data in the inner Io plasma torus A local electron density maximum “finger” is found just inside M = 5 with a value which decreases with centrifugal latitude The local maximum is separated from larger densities closer to Io by a low‐density “trough”
Details
- Title: Subtitle
- A Durable Electron Density Profile Near the Inner Edge of the Io Torus
- Creators
- W. S. Kurth - University of IowaG. B. Hospodarsky - University of IowaJ. B. Faden - University of IowaJ. D. Menietti - University of IowaA. H. Sulaiman - University of MinnesotaS. S. Elliott - University of MinnesotaF. Bagenal - University of Colorado BoulderE. G. Nerney - University of Colorado BoulderJ. E. P. Connerney - Goddard Space Flight CenterF. Allegrini - Southwest Research InstituteS. J. Bolton - Southwest Research Institute
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.130(1), e2024JA033453
- Publisher
- Wiley
- DOI
- 10.1029/2024JA033453
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Grant note
- Southwest Research Institute. Grant Numbers: 699041X, 699050X
- Comment
- This article also appears in: Io and the Galilean Satellites
- Language
- English
- Date published
- 01/2025
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984772250402771
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