Vertical and temporal H3+ structure at the auroral footprint of Io

A. Mura; A. Moirano; V. Hue; C. Castagnoli; A. Migliorini; A. Altieri; A. Adriani; A. Cicchetti; C. Plainaki; G. Piccioni; R. Noschese; G. Sindoni; R. Sordini

arXiv · 2410.20589

Vertical and temporal H3+ structure at the auroral footprint of Io

A. Mura·A. Moirano·V. Hue·C. Castagnoli·A. Migliorini·A. Altieri·A. Adriani·A. Cicchetti·C. Plainaki·G. Piccioni·R. Noschese·G. Sindoni·R. Sordini

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Abstract

We report the first observation of the vertical and temporal structure of the H3+ emission at the auroral footprint of Io, as observed by Juno/JIRAM. The brightness vertical profile shows a maximum at 600 km above 1 bar, with no apparent difference between the Main Alfv\'en Wing spot emission and the tail of the footprint. This observation is more compatible with a broadband energy distribution of the precipitating electrons, than a monoenergetic one. The temporal profile of H3+ column density has been observed after the passage of the MAW and shows a hyperbolic decrease. A model of H3+ decay is proposed, which takes into account the second-order kinetic of dissociative recombination of H3+ ions with electrons. The model is found to be in very good agreement with Juno observation. The conversion factor from radiance to column density has been derived, as well as the half-life for H3+, which is not constant but inversely proportional to the H3+ column density. This explains the wide range of H3+ lifetimes proposed before.

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A. Mura, A. Moirano, V. Hue, C. Castagnoli, A. Migliorini, A. Altieri, A. Adriani, A. Cicchetti, C. Plainaki, G. Piccioni, R. Noschese, G. Sindoni, R. Sordini. 2024-10-27. Vertical and temporal H3+ structure at the auroral footprint of Io. https://arxiv.org/abs/2410.20589

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