ALMA Observation of SO2 Gas Originating from Io’s Volcanic Plume and Lava Areas

Abstract

Abstract We detected the submillimeter spectrum of SO2 gas originating from volcanic plumes and lava areas in Jupiter’s moon Io by analyzing the ALMA archive data observed before and after ingress on 2018 March. As a result of synthesis imaging, high intensity regions of SO2 were found to be associated with the volcanically active areas around the Amaterasu Patera (305°W, 38°N) and around the Janus Patera (36°W, 4°S) and Kanehekili Fluctus (32°W, 17°S). By fitting the spectral lineshapes, the main and redshifted spectral components are identified around the Amaterasu Patera. The redshifted component can be attributed as the emission from the plume gas moving away in the line of sight. The rotational temperature and column density of SO2 were derived by employing the population diagram plots with spectral line intensities. The column densities of SO2 before ingress are (2.2 ± 1.1) × 1015 cm−2 around the Amaterasu Patera and (2.2 ± 1.1) × 1015 cm−2 around the Janus Patera. After ingress, the column densities are (1.8 ± 1.2) × 1015 cm−2 and (2.1 ± 0.1) × 1015 cm−2, respectively. This suggests that volcanic eruptions maintain the atmospheres in these regions during eclipse. The temperature around the Amaterasu Patera of 95 ± 28 K before ingress is similar to the temperature of 108 ± 48 K after ingress. On the other hand, the temperature around the Janus Patera increases from 151 ± 70 K before ingress to 311 ± 41 K after ingress. The result suggests that the atmospheric SO2 around the Janus Patera after ingress may be supplied by evaporation from the lava areas.