Although many properties like the vertical structure and global dynamics are still not well characterized, it appears that the average dayside atmosphere is quite stable. The atmospheric state before and during transient events in the torus and neutral clouds is also unknown and thus the role of the atmosphere for these events is not understood. We review the basic characteristics of the atmosphere here. Detailed reviews on Io’s atmosphere can be found in de Pater et al. (2023) and Lellouch et al. (2007).
Horizontal and temporal variability and the volcanic vs sublimation origin Io’s atmosphere is volcanic in origin, since the surface frosts that can sustain the atmosphere through sublimation are themselves produced from the accumulation of plume material condensed at the surface. Given that a gas plume can also interact with a “pre-existing” background atmosphere, the distinction between “volcanic” and “sublimation” atmospheres is ultimately somewhat specious. This question can probably be formulated in a slightly more accurate way: what fraction of Io’s atmosphere varies in a predictable way with environmental parameters (local time, distance to the Sun, location on the surface); what fraction shows “erratic” variability, associated with volcanic activity; and what are the orders of magnitude of these variations? This issue has been considerably clarified over the last ~20 years, leading to the perhaps unexpected result that Io’s atmosphere is generally “predictable,” though open questions persist.
Thermal/dynamical calculations also include DSMC models of volcanic plumes (Zhang et al. 2003, McDoniel et al. 2017, and references therein), either “pure” (i.e., night-side) or in the presence of a background sublimating atmosphere, and account for additional physics such as plume expansion and re-entry shocks, the former effect leading to cold temperatures (20 to 100 K) through most of the plume except in the re-entry region. These simulations include fully-3D simulations (McDoniel et al., 2015; Ackley et al. 2021), unsteady plumes interacting with a changing sublimation atmosphere (McDoniel et al., 2017) or undergoing 3D dynamic pulses (Hoey et al., 2021), and plumes at different locations on Io interacting with impinging streams of Jovian plasma and sunlight (Blöcker et al., 2018; McDoniel et al., 2019). All of these models predict an extraordinarily complex 3D thermal and wind structure for Io’s atmosphere, which thus appears critically under-constrained from the observational point of view.
Authors:
(1) L. Roth, KTH Royal Institute of Technology, Space and Plasma Physics, Stockholm, Sweden and a Corresponding author;
(2) A. Blöcker, KTH Royal Institute of Technology, Space and Plasma Physics, Stockholm, Sweden and Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Munich, Germany;
(3) K. de Kleer, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 USA;
(4) D. Goldstein, Dept. Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, TX USA;
(5) E. Lellouch, Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA), Observatoire de Paris, Meudon, France;
(6) J. Saur, Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany;
(7) C. Schmidt, Center for Space Physics, Boston University, Boston, MA, USA;
(8) D.F. Strobel, Departments of Earth & Planetary Science and Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA;
(9) C. Tao, National Institute of Information and Communications Technology, Koganei, Japan;
(10) F. Tsuchiya, Graduate School of Science, Tohoku University, Sendai, Japan;
(11) V. Dols, Institute for Space Astrophysics and Planetology, National Institute for Astrophysics, Italy;
(12) H. Huybrighs, School of Cosmic Physics, DIAS Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin 15, Ireland, Space and Planetary Science Center, Khalifa University, Abu Dhabi, UAE and Department of Mathematics, Khalifa University, Abu Dhabi, UAE;
(13) A. Mura, XX;
(14) J. R. Szalay, Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA;
(15) S. V. Badman, Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK;
(16) I. de Pater, Department of Astronomy and Department of Earth & Planetary Science, University of California, Berkeley, CA 94720, USA;
(17) A.-C. Dott, Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany;
(18) M. Kagitani, Graduate School of Science, Tohoku University, Sendai, Japan;
(19) L. Klaiber, Physics Institute, University of Bern, 3012 Bern, Switzerland;
(20) R. Koga, Department of Earth and Planetary Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan;
(21) A. McEwen, Department of Astronomy and Department of Earth & Planetary Science, University of California, Berkeley, CA 94720, USA;
(22) Z. Milby, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 USA;
(23) K.D. Retherford, Southwest Research Institute, San Antonio, TX, USA and University of Texas at San Antonio, San Antonio, Texas, USA;
(24) S. Schlegel, Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany;
(25) N. Thomas, Physics Institute, University of Bern, 3012 Bern, Switzerland;
(26) W.L. Tseng, Department of Earth Sciences, National Taiwan Normal University, Taiwan;
(27) A. Vorburger, Physics Institute, University of Bern, 3012 Bern, Switzerland.
