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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. 

Abstract We present a thermal observation of Callisto's leading hemisphere obtained using the Atacama Large Millimeter/submillimeter Array at 0.87 mm (343 GHz). The angular resolution achieved for this observation was ∼0.″16, which for Callisto at the time of this observation (D∼ 1.″05) was equivalent to ∼six elements across the surface. Our disk-integrated brightness temperature of 116 ± 5 K (8.03 ± 0.40 Jy) is consistent with prior disk-integrated observations. Global surface properties were derived from the observation using a thermophysical model constrained by spacecraft data. We find that models parameterized by two thermal inertia components more accurately fit the data than single thermal inertia models. Our best-fit global parameters adopt a lower thermal inertia of 15–50 J m⁻²K⁻¹s^−1/2and a higher thermal inertia component of 1200–2000 J m⁻²K⁻¹s^−1/2, with retrieved millimeter emissivities of 0.89–0.91. We identify several thermally anomalous regions, including spots ∼3 K colder than model predictions colocated with the Valhalla impact basin and a complex of craters in the southern hemisphere; this indicates the presence of materials possessing either a higher thermal inertia or a lower emissivity. A warm region confined to the midlatitudes in these leading hemisphere data may be indicative of regolith property changes due to exogenic sculpting.