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Abstract We present spatially resolved measurements of SO2and NaCl winds on Io at several unique points in its orbit: before and after eclipse and at maximum eastern and western elongation. The derived wind fields represent a unique case of meteorology in a rarified, volcanic atmosphere. Through the use of Doppler shift measurements in emission spectra obtained with the Atacama Large Millimeter/submillimeter Array between ~346 and 430 GHz (~0.70–0.87 mm), line-of-sight winds up to ~−100 m s−1in the approaching direction and >250 m s−1in the receding direction were derived for SO2at altitudes of ~10–50 km, while NaCl winds consistently reached ~∣150–200∣ m s−1in localized regions up to ~30 km above the surface. The wind distributions measured at maximum east and west Jovian elongations and on the sub-Jovian hemisphere pre- and posteclipse were found to be significantly different and complex, corroborating the results of simulations that include surface temperature and frost distribution, volcanic activity, and interactions with the Jovian magnetosphere. Further, the wind speeds of SO2and NaCl are often inconsistent in direction and magnitude, indicating that the processes that drive the winds for the two molecular species are different and potentially uncoupled; while the SO2wind field can be explained through a combination of sublimation-driven winds, plasma torus interactions, and plume activity, the NaCl winds appear to be primarily driven by the plasma torus.
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Io’s Optical Aurorae in Jupiter’s Shadow
Abstract 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, SO 2 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 SO 2 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 SO 2 and NaCl parent molecules during Io’s eclipse phase.
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- Award ID(s):
- 2108416
- PAR ID:
- 10422046
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 4
- Issue:
- 2
- ISSN:
- 2632-3338
- Page Range / eLocation ID:
- 36
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/PSJ/ac85b0
