First Detection of [SI] in Near‐IR JWST Observations of Io in Eclipse, and Comparison With SO Emissions, Evolving Volcanic Eruptions, and Prior UV HST‐STIS [SI] Emissions

Abstract We observed Io with the James Webb Space Telescope (JWST) NIRSpec/Integral Field Unit (1.0–5.3 μm, ) in August 2023 while the satellite was in eclipse. Thermal emission from Kanehekili Fluctus is consistent with the cooling of lava flows after a vigorous eruption in November 2022. At Loki Patera, after a new brightening event was detected in November 2022, the lava lake was in a quiescent state, as expected from previous analyses. We mapped the SO emission band at 1.707 μm, and detected, for the first time, [SI] emission lines at 1.082 and 1.131 μm. The SO emissions are concentrated above Kanehekili Fluctus, and in two regions in the northern hemisphere. The disk‐averaged brightness is 14.5 kR. The emissions are sourced from SO molecules ejected from 1,500 to 1,700 K vents in an excited state, with a typical SO column density above the northern hemisphere of . Sulfur emissions are distributed homogeneously across a band in the northern hemisphere. The disk‐averaged total brightness is 5.6 kR, versus 9.65 kR in the north. The emissions are produced through direct electron impact excitation by 4 eV electrons in the torus (density 2,500 ) penetrating the atmosphere, and require the atmosphere to be hot (1,700 K) to populate the upper levels before excitation. The sulfur column density over the northern hemisphere is . These same parameters can explain recent 0.7725‐m observations, as well as the 147.9‐nm multiplet emissions observed with HST‐STIS 20 years earlier. This suggests a quite stable system over decades‐long timescales.

Authors

Institutions

Publication Details

Journal
Journal of Geophysical Research Planets
Published
2025-10-31
DOI
https://doi.org/10.1029/2024je008850
Citations
3
Primary Topic
Astrophysics and Star Formation Studies
Type
article
Field-Weighted Citation Impact
3.46
Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

First Detection of [SI] in Near‐IR JWST Observations of Io in Eclipse, and Comparison With SO Emissions, Evolving Volcanic Eruptions, and Prior UV HST‐STIS [SI] Emissions

Zachariah Milby, Carolyn E. Jordan, D. A. Williams, Joachim Saur et al.
3 citations
Journal of Geophysical Research Planets
Astrophysics and Star Formation Studies
3.46
article

First Detection of [SI] in Near‐IR JWST Observations of Io in Eclipse, and Comparison With SO Emissions, Evolving Volcanic Eruptions, and Prior UV HST‐STIS [SI] Emissions

Zachariah Milby, Carolyn E. Jordan, D. A. Williams, Joachim Saur, Carl Schmidt, Jason Perry, Stephan Schlegel, Lorenz Roth, Thierry Fouchet, Katherine de Kleer, David M. Nelson, Leigh N. Fletcher, D. F. Strobel, A. G. Davies, Jake Harkett, Imke de Pater, Michael H. Wong, Richard Cartwright, E. Lellouch, Michael T. Roman, Julie Renaud‐Kim
article en
3 citations

Abstract

Abstract We observed Io with the James Webb Space Telescope (JWST) NIRSpec/Integral Field Unit (1.0–5.3 μm, ) in August 2023 while the satellite was in eclipse. Thermal emission from Kanehekili Fluctus is consistent with the cooling of lava flows after a vigorous eruption in November 2022. At Loki Patera, after a new brightening event was detected in November 2022, the lava lake was in a quiescent state, as expected from previous analyses. We mapped the SO emission band at 1.707 μm, and detected, for the first time, [SI] emission lines at 1.082 and 1.131 μm. The SO emissions are concentrated above Kanehekili Fluctus, and in two regions in the northern hemisphere. The disk‐averaged brightness is 14.5 kR. The emissions are sourced from SO molecules ejected from 1,500 to 1,700 K vents in an excited state, with a typical SO column density above the northern hemisphere of . Sulfur emissions are distributed homogeneously across a band in the northern hemisphere. The disk‐averaged total brightness is 5.6 kR, versus 9.65 kR in the north. The emissions are produced through direct electron impact excitation by 4 eV electrons in the torus (density 2,500 ) penetrating the atmosphere, and require the atmosphere to be hot (1,700 K) to populate the upper levels before excitation. The sulfur column density over the northern hemisphere is . These same parameters can explain recent 0.7725‐m observations, as well as the 147.9‐nm multiplet emissions observed with HST‐STIS 20 years earlier. This suggests a quite stable system over decades‐long timescales.

Journal of Geophysical Research PlanetsVol. 130(11)
Boston University (US), California Institute of Technology (US), Centre National de la Recherche Scientifique (FR), Planetary Science Institute (US), Jet Propulsion Laboratory (US), University of Arizona (US), Johns Hopkins University (US), University of Leicester (GB), University of Cologne (DE), Université Paris Cité (FR), Adolfo Ibáñez University (CL), Observatoire de Paris (FR), W.M. Keck Observatory (US), Johns Hopkins University Applied Physics Laboratory (US), Sorbonne Université (FR), Sorbonne Paris Cité (FR), Arizona State University (US), University of Baltimore (US), KTH Royal Institute of Technology (SE), University of California, Berkeley (US)
Openalex Percentile: Top 7%
Astrophysics and Star Formation Studies
3.46
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.