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Io’s Optical Aurorae in Jupiter’s Shadow

Schmidt, Carl and Sharov, Mikhail and de Kleer, Katherine and Schneider, Nick and de Pater, Imke and Phipps, Phillip H. and Conrad, Albert and Moore, Luke and Withers, Paul and Spencer, John and Morgenthaler, Jeff and Ilyin, Ilya and Strassmeier, Klaus and Veillet, Christian and Hill, John and Brown, Mike (2023) Io’s Optical Aurorae in Jupiter’s Shadow. Planetary Science Journal, 4 (2). Art. No. 36. ISSN 2632-3338. doi:10.3847/psj/ac85b0.

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Decline and recovery timescales surrounding eclipse are indicative of the controlling physical processes in Io’s atmosphere. Recent studies have established that the majority of Io’s molecular atmosphere, SO₂ and SO, condenses during its passage through Jupiter’s shadow. The eclipse response of Io’s atomic atmosphere is less certain, having been characterized solely by ultraviolet aurorae. Here we explore the response of optical aurorae for the first time. We find oxygen to be indifferent to the changing illumination, with [O i] brightness merely tracking the plasma density at Io’s position in the torus. In shadow, line ratios confirm sparse SO₂ coverage relative to O, since their collisions would otherwise quench the emission. Io’s sodium aurora mostly disappears in eclipse and e-folding timescales, for decline and recovery differ sharply: ∼10 minutes at ingress and nearly 2 hr at egress. Only ion chemistry can produce such a disparity; Io’s molecular ionosphere is weaker at egress due to rapid recombination. Interruption of a NaCl⁺ photochemical pathway best explains Na behavior surrounding eclipse, implying that the role of electron impact ionization is minor relative to photons. Auroral emission is also evident from potassium, confirming K as the major source of far red emissions seen with spacecraft imaging at Jupiter. In all cases, direct electron impact on atomic gas is sufficient to explain the brightness without invoking significant dissociative excitation of molecules. Surprisingly, the nonresponse of O and rapid depletion of Na is opposite the temporal behavior of their SO₂ and NaCl parent molecules during Io’s eclipse phase.

Item Type:Article
Related URLs:
URLURL TypeDescription
Schmidt, Carl0000-0002-6917-3458
Sharov, Mikhail0000-0003-3047-5368
de Kleer, Katherine0000-0002-9068-3428
Schneider, Nick0000-0001-6720-5519
de Pater, Imke0000-0002-4278-3168
Phipps, Phillip H.0000-0002-4323-4400
Conrad, Albert0000-0003-2872-0061
Withers, Paul0000-0003-3084-4581
Spencer, John0000-0003-4452-8109
Morgenthaler, Jeff0000-0003-3716-3455
Ilyin, Ilya0000-0002-0551-046X
Strassmeier, Klaus0000-0002-6192-6494
Veillet, Christian0000-0003-0272-0418
Hill, John0000-0003-2484-3670
Brown, Mike0000-0002-8255-0545
Additional Information:© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Support for the observations and analysis in this study was provided by the National Aeronautics and Space Administration (NASA) Solar System Observations program, 80NSSC22K0954 and 80NSSC21K1138. M.S. acknowledges support from the Massachusetts Space Grant Consortium. K.d.K. acknowledges support from NASA through grant No. HST-GO-15425.002-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. J.M. gratefully acknowledges support from the National Science Foundation program AST-2108416. Constraints on the plasma conditions at Io were posed via Juno data, and support for that analysis derives from NASA program 80NSSC19K0818. L.M. was supported by grant 80NSSC20K1045 issued through the NASA Solar System Workings program. We thank Jean McKeever of Yale University for her help with reduction of the Apache Point echelle data and Candace Gray and Russet McMillan for their assistance with those observations. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. The LBT Corporation partners are the University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Leibniz Institute for Astrophysics Potsdam, and Heidelberg University; and the Ohio State University, representing OSU, the University of Notre Dame, the University of Minnesota, and the University of Virginia. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
Massachusetts Space Grant ConsortiumUNSPECIFIED
NASA Hubble FellowshipHST-GO-15425.002-A
NASANAS 5-26555
LBT Corporation PartnersUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20230221-191105000.1
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:119326
Deposited By: George Porter
Deposited On:21 Feb 2023 23:48
Last Modified:21 Feb 2023 23:48

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