Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus
We observed Io’s optical aurora in eclipse on six nights between 2022 and 2024 using Keck I/HIRES. Spectra revealed 13 new auroral emissions not identified previously, tripling the total number of optical emissions lines detected at Io. These included the O i lines at 777.4 and 844.6 nm, the Na i li...
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IOP Publishing
2025-01-01
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| Series: | The Planetary Science Journal |
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| Online Access: | https://doi.org/10.3847/PSJ/ade0b1 |
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| author | Zachariah Milby Katherine de Kleer Carl Schmidt |
| author_facet | Zachariah Milby Katherine de Kleer Carl Schmidt |
| author_sort | Zachariah Milby |
| collection | DOAJ |
| description | We observed Io’s optical aurora in eclipse on six nights between 2022 and 2024 using Keck I/HIRES. Spectra revealed 13 new auroral emissions not identified previously, tripling the total number of optical emissions lines detected at Io. These included the O i lines at 777.4 and 844.6 nm, the Na i lines at 818.3 and 819.5 nm, the [S i ] lines at 458.9 and 772.5 nm, the S i triplet at 922.3 nm, the [O ii ] lines at 732.0 and 733.0 nm, and the [S ii ] lines at 406.9, 407.6, 671.6, and 673.1 nm. We leveraged these new detections by comparing with imaging data from the 2001 Cassini flyby to better understand the distribution of atmospheric species and their contribution to the observed auroral brightnesses. Our auroral emission model showed that the observed 557.7, 777.4, and 844.6 nm oxygen emission-line brightnesses could be explained by excitation by electron impact of canonical 5 eV torus electrons on an atmosphere composed of O, SO _2 , and an isoelectronic proxy for SO. The SO _2 emission did not decrease immediately after eclipse ingress, suggesting that the emitting column may be restricted to higher altitudes. The derived O/SO _2 mixing ratio was typically about 10%, but it also exhibited order-of-magnitude variance during some observations. Io’s 630.0 nm [O i ] brightness did not strongly vary with plasma sheet distance, suggesting that electron flux at Io varies substantially beyond model predictions. |
| format | Article |
| id | doaj-art-60a0bdf835b346319ba4e3a67b7916dd |
| institution | Kabale University |
| issn | 2632-3338 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Planetary Science Journal |
| spelling | doaj-art-60a0bdf835b346319ba4e3a67b7916dd2025-08-20T03:45:10ZengIOP PublishingThe Planetary Science Journal2632-33382025-01-016818110.3847/PSJ/ade0b1Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma TorusZachariah Milby0https://orcid.org/0000-0001-5683-0095Katherine de Kleer1https://orcid.org/0000-0002-9068-3428Carl Schmidt2https://orcid.org/0000-0002-6917-3458Division of Geological and Planetary Sciences, California Institute of Technology , CA, USA ; zmilby@caltech.eduDivision of Geological and Planetary Sciences, California Institute of Technology , CA, USA ; zmilby@caltech.eduCenter for Space Physics, Boston University , MA, USAWe observed Io’s optical aurora in eclipse on six nights between 2022 and 2024 using Keck I/HIRES. Spectra revealed 13 new auroral emissions not identified previously, tripling the total number of optical emissions lines detected at Io. These included the O i lines at 777.4 and 844.6 nm, the Na i lines at 818.3 and 819.5 nm, the [S i ] lines at 458.9 and 772.5 nm, the S i triplet at 922.3 nm, the [O ii ] lines at 732.0 and 733.0 nm, and the [S ii ] lines at 406.9, 407.6, 671.6, and 673.1 nm. We leveraged these new detections by comparing with imaging data from the 2001 Cassini flyby to better understand the distribution of atmospheric species and their contribution to the observed auroral brightnesses. Our auroral emission model showed that the observed 557.7, 777.4, and 844.6 nm oxygen emission-line brightnesses could be explained by excitation by electron impact of canonical 5 eV torus electrons on an atmosphere composed of O, SO _2 , and an isoelectronic proxy for SO. The SO _2 emission did not decrease immediately after eclipse ingress, suggesting that the emitting column may be restricted to higher altitudes. The derived O/SO _2 mixing ratio was typically about 10%, but it also exhibited order-of-magnitude variance during some observations. Io’s 630.0 nm [O i ] brightness did not strongly vary with plasma sheet distance, suggesting that electron flux at Io varies substantially beyond model predictions.https://doi.org/10.3847/PSJ/ade0b1AuroraeIoNatural satellite atmospheresOptical astronomy |
| spellingShingle | Zachariah Milby Katherine de Kleer Carl Schmidt Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus The Planetary Science Journal Aurorae Io Natural satellite atmospheres Optical astronomy |
| title | Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus |
| title_full | Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus |
| title_fullStr | Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus |
| title_full_unstemmed | Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus |
| title_short | Detection of New Auroral Emissions at Io and Implications for Its Interaction with the Plasma Torus |
| title_sort | detection of new auroral emissions at io and implications for its interaction with the plasma torus |
| topic | Aurorae Io Natural satellite atmospheres Optical astronomy |
| url | https://doi.org/10.3847/PSJ/ade0b1 |
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