Longitudinal distribution of Io's dayside atmospheric density
Abstract
Since 2001, we have used the TEXES high resolution mid-infrared spectrograph at NASA's Infrared Telescope Facility to study the density of Io's SO2-dominated atmosphere. The spectra cover several SO2 absorption lines near 530 cm−1 and are used to retrieve the equatorial SO2 column density. In addition to covering a long time period, our 191 independent observations also cover the full range of Io central longitudes, allowing us to study the longitudinal variability of Io's dayside atmosphere in more depth than has previously been possible. By improving our modeling of longitudinal variability and using a seasonal model to apply a temporal normalization to the retrieved SO2 densities, we produce two complete longitudinal distributions of Io's equatorial SO2 column abundances, one representing perihelion and one representing aphelion. Both show the same hemispheric asymmetry that has been observed in previous studies, with the highest densities near 200W and the lowest densities near 305W. We find that the contrast between the maximum and minimum densities is a factor of ~27 at aphelion and a factor of ~16 at perihelion. Both longitudinal distributions are asymmetric, with a sharper drop-off on Io's trailing hemisphere than on the leading. We compare these longitudinal distributions to the distributions expected if the spatial variability were primarily driven by volcanic activity, SO2-ice inhomogeneity or the effects of eclipses. We conclude that the effect of eclipses is important, but insufficient to explain the shape of the observed longitudinal variability, and frost distribution is likely to also be important.
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BibTeX
@misc{giles2026longitudinal,
title = {{Longitudinal distribution of Io's dayside atmospheric density}},
author = {R. S. Giles and J. R. Spencer and T. K. Greathouse and C. C. C. Tsang and E. Lellouch and M. A. López-Valverde},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12275},
eprint = {2610.12275},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12275},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Longitudinal distribution of Io's dayside atmospheric density
AU - R. S. Giles
AU - J. R. Spencer
AU - T. K. Greathouse
AU - C. C. C. Tsang
AU - E. Lellouch
AU - M. A. López-Valverde
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12275
UR - https://arxiv.org/abs/2610.12275
AB - Since 2001, we have used the TEXES high resolution mid-infrared spectrograph at NASA's Infrared Telescope Facility to study the density of Io's SO_2-dominated atmosphere. The spectra cover several SO_2 absorption lines near 530 cm^−1 and are used to retrieve the equatorial SO_2 column density. In addition to covering a long time period, our 191 independent observations also cover the full range of Io central longitudes, allowing us to study the longitudinal variability of Io's dayside atmosphere in more depth than has previously been possible. By improving our modeling of longitudinal variability and using a seasonal model to apply a temporal normalization to the retrieved SO_2 densities, we produce two complete longitudinal distributions of Io's equatorial SO_2 column abundances, one representing perihelion and one representing aphelion. Both show the same hemispheric asymmetry that has been observed in previous studies, with the highest densities near 200W and the lowest densities near 305W. We find that the contrast between the maximum and minimum densities is a factor of ~27 at aphelion and a factor of ~16 at perihelion. Both longitudinal distributions are asymmetric, with a sharper drop-off on Io's trailing hemisphere than on the leading. We compare these longitudinal distributions to the distributions expected if the spatial variability were primarily driven by volcanic activity, SO_2-ice inhomogeneity or the effects of eclipses. We conclude that the effect of eclipses is important, but insufficient to explain the shape of the observed longitudinal variability, and frost distribution is likely to also be important.
ER -