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Communication Dans Un Congrès Année : 2018

High-resolution spectra of Io's Neutral Clouds: insights on Io-plasma interaction and new escape processes

Résumé

We present high resolution ground-based spectroscopic observations of Io's exospheric sodium environment taken at the TNG (Telescopio Nazionale Galileo) telescope in 2007 and 2009. Long-slit spectra of Na D-line emissions were obtained to determine sodium density profiles near Io within 10 RIo distance. Several nights of observations spanned the entire orbital longitude range of Io, and included pre- and post-eclipse periods to study the behavior of Io's atmosphere as the solar illumination changes [Grava et al. 2014]. A leading/trailing (or downstream/upstream) hemisphere asymmetry in the abundance of sodium atoms, first reported in Mendillo et al. [2007], is more clearly established, with the leading (downstream) region being more abundant in sodium. This asymmetry is likely consistent with Io's wake of denser and stagnated plasma flow being populated with faster Na atoms originating from dissociative recombination of sodium-bearing molecular ions (e.g. NaCl+). A spectral asymmetry in the emission line profile is also observed, with a tail in the redshift direction for orbital dusk-side (Western sky) observations, and likewise a blueshift in the dawnside (Eastern sky). This deviation from a Gaussian was observed by Trafton & Macy [1977] and attributed to fast streaming of the sodium neutrals along the line of sight. We also observe a previously undetected emission feature, blueshifted of tens of km/s compared to the main Neutral Clouds, as well as a deep absorption on top of Io's disk. We present preliminary results from models developed to explain these phenomena. Our models aim to reproduce the two-dimensional features of our data (in both spectral and spatial direction) by changing parameters such as the origin of the sodium atoms and their velocity distribution. Together with the modeling, these observations will allow to understand the plasma environment parameters in the wake of Io's interaction region, source rates for the more distant Neutral Clouds, and new escape processes.
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insu-04421962 , version 1 (28-01-2024)

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Cesare Grava, Timothy A. Cassidy, Nicholas M. Schneider, François Leblanc, Jeffrey P. Morgenthaler, et al.. High-resolution spectra of Io's Neutral Clouds: insights on Io-plasma interaction and new escape processes. DPS 50, Annual Meeting for Division for Planetary Sciences, Oct 2018, Knoxville, United States. pp.id.416.09. ⟨insu-04421962⟩
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