Callisto's atmosphere and its space environment: prospects for the Particle Environment Package on board JUICE

Abstract

<p>The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on JUICE is designed to measure neutrals and ions and electrons at thermal, suprathermal, and radiation belt energies (eV to MeV). </p><p>In the vicinity of Callisto, PEP will characterize the plasma environment, the outer parts of Callisto's atmosphere and ionosphere and their interaction with Jupiter's dynamic magnetosphere. About 20 Callisto flybys with closest approaches between 200 km and 5000 km altitude are<br>planned over the course of the JUICE mission. In this presentation, we review the state of knowledge regarding Callisto's ambient environment and magnetospheric interaction with recent modeling efforts for Callisto's atmosphere and ionosphere to identify science opportunities for the PEP observations and to optimize scientific insight gained from the foreseen JUICE flybys. These considerations inform science operation planning of PEP and JUICE and they will guide future model development for the atmosphere and ionosphere of Callisto and their interactions with the plasma environment.</p>

Callisto's Atmosphere: First Evidence for H2 and Constraints on H2O

“…We assume they can penetrate the extended region of the atmosphere to get a rough upper limit on their effect. However, the local plasma at Callisto is highly variable (e.g., Galli et al., 2022 and references therein) and both temperature and density are not well constrained. Nevertheless, using, e.g., the range of smaller electron densities from Kivelson et al.…”

“…In addition to the above uncertainties for water ice on the surface and its relation to the production of water vapor, estimating the radiolytic source rate for H 2 at Callisto is extremely difficult due to the lack of observational constraints and the uncertainty of the surface composition as well as its exposure to the local plasma environment (e.g., Galli et al., 2022 and references therein). This uncertainty is exacerbated as H 2 can be radiolytically produced from hydrated sulfur (Cartwright et al., 2020) and hydrocarbons (McCord et al., 1997, 1998) in Callisto's nonice or ice‐poor material in addition to being produced from the ice, including from any carbonic acid therein (e.g., Johnson et al., 2004).…”

“…Similarly, although radiolysis is likely the primary source of O 2 in Callisto's atmosphere (Cunningham et al., 2015), the concomitant H 2 component has not yet been identified. Forthcoming exploration of Callisto by ESA's JUpiter ICy moons Explorer (JUICE; e.g., Galli et al., 2022), NASA's Europa Clipper, and CNSA's planned Gan De can help resolve such issues. With these missions as motivation we expand on our earlier simulations of Callisto's atmosphere (Carberry Mogan et al., 2021b) using the observation of its H corona (Roth et al., 2017a) to examine the limits of both its H 2 O and H 2 components.…”