Longitudinal Distribution of Io’s Dayside Atmospheric Density
4 affiliations
- 1Southwest Research Institute
- 2Khan Enterprises LLC
- 3LEISA
- 4Instituto de Astrofisica de Andalucia
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 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 200 ∘ W and the lowest densities near 305 ∘ W. 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.
Related
- Kelvin–Helmholtz Spectral Redistribution by Flow and Density Structure at the Dusk Dayside Magnetopause
- Global Distribution of Atmospheric Formaldehyde Deposition Correlated with Water Vapor on a Warm Early Mars
- Size, shape, density, and atmospheric limit of (50000) Quaoar revealed from 14 years of stellar occultation
- The σ_s^2- relation in the multi-phase interstellar medium. Exploring the density distribution with the Cloud Factory simulations
- Exploring the ultrahot Neptune LTT 9779 b with CRIRES+. Non-detection of helium transmission spectra and detection of H2O on the dayside
BibTeX
@article{giles2026longitudinal,
title = {{Longitudinal Distribution of Io’s Dayside Atmospheric Density}},
author = {Rohini S. Giles and John R. Spencer and Thomas K. Greathouse and Constantine C. C. Tsang and Emmanuel Lellouch and Miguel A. López-Valverde},
journal = {The Planetary Science Journal},
year = {2026},
month = oct,
doi = {10.3847/psj/aeb269},
url = {https://iopscience.iop.org/article/10.3847/PSJ/aeb269},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Longitudinal Distribution of Io’s Dayside Atmospheric Density
AU - Rohini S. Giles
AU - John R. Spencer
AU - Thomas K. Greathouse
AU - Constantine C. C. Tsang
AU - Emmanuel Lellouch
AU - Miguel A. López-Valverde
PY - 2026
DA - 2026/10/30
JO - The Planetary Science Journal
DO - 10.3847/psj/aeb269
UR - https://iopscience.iop.org/article/10.3847/PSJ/aeb269
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 200 ∘ W and the lowest densities near 305 ∘ W. 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.
SN - 2632-3338
ER -