A First Look at Io’s Vertical Temperature Profile from ALMA

The vertical temperature profile of Io’s sulfur dioxide (SO₂) atmosphere, influenced by volcanic eruptions and surface ice sublimation, remains poorly constrained. This limits our understanding of the dynamic processes that shape Io’s atmosphere and its thermal structure. To bridge this gap, we utilize the Atacama Large Millimeter/submillimeter Array (ALMA) to probe Io’s lower atmosphere (within ~60 km of the surface) via rotational transitions of SO₂ observed on both the leading and trailing hemispheres. We analyze this data using an atmospheric model that divides Io’s atmosphere into multiple layers, each with adaptive lapse rate parameters. These parameters, along with SO₂ column density, are initially explored using Markov Chain Monte Carlo (MCMC) techniques combined with radiative transfer modeling. The MCMC analysis results provide initial estimates of the best-fitting model parameters, which are further refined using advanced minimization techniques. As a result of our analysis, we present the first retrieval of a vertical temperature profile for Io’s tenuous atmosphere. Our work enables improved interpretation of past and future remote sensing data. Additionally, our findings place new constraints on Io’s thermal structure and atmospheric dynamics—setting the stage for more precise atmospheric modeling and a deeper understanding of Io’s environment.