Presentation #103.01 in the session “A Plethora of Icy Satellites”.
Given the limited information known about Callisto’s atmosphere as well as the interrelation between atmospheric and surface processes, it is difficult to ascertain composition, abundances, and sources and sinks. Thus, the integration of the few observations available into physical models is required to better understand Callisto’s atmosphere until forthcoming observations can provide more information. In this respect, the detection of the spatial extent of the H corona at Callisto , assuming, as suggested, that it is produced primarily by photodissociation of sublimated H2O, can in principle be used to help constrain the ice content on it surface. We explore this parameter space using Direct Simulation Monte Carlo  models of Callisto’s atmosphere composed of sublimated H2O and its photochemical products, H and H2. We also consider how these species are affected by interactions with a relatively dense O2 component suggested to be present (e.g., ). We focus on two significantly different models for H2O production in which: (1) the ice and dark, non-ice/ice-poor material are intimately mixed and H2O primarily sublimates at Callisto’s warm day-side temperatures (e.g., [4-7]); and (2) the ice and dark, non-ice/ice-poor material are segregated (e.g., [8-10]) and H2O sublimates only from the ice patches at their local temperatures .
References  Roth et al., 2017. Detection of a hydrogen corona at Callisto. Journal of Geophysical Research: Planets.  Bird, 1994. Molecular gas dynamics and the direct simulation of gas flows. Clarendon Press.  Cunningham et al., 2015. Detection of Callisto’s oxygen atmosphere with the Hubble Space Telescope. Icarus.  Liang et al., 2005. Atmosphere of Callisto. Journal of Geophysical Research: Planets.  Vorburger et al., 2015. Monte-Carlo simulation of Callisto’s exosphere. Icarus.  Hartkorn et al., 2017. Structure and density of Callisto’s atmosphere from a fluid-kinetic model of its ionosphere: Comparison with Hubble Space Telescope and Galileo observations. Icarus.  Carberry Mogan et al., 2021. A tenuous, collisional atmosphere on Callisto. Icarus.  Spencer and Maloney, 1984. Mobility of water ice on Callisto: Evidence and implications. Geophysical Research Letters.  Spencer, 1987. Thermal segregation of water ice on the Galilean satellites. Icarus.  Moore et al., 1999. Mass movement and landform degradation on the icy Galilean satellites: Results of the Galileo nominal mission. Icarus.  Grundy et al., 1999. Near-infrared spectra of icy outer solar system surfaces: Remote determination of H2O ice temperatures. Icarus.