Dynamic Plasma Interaction at Io: Multispecies Hybrid Simulations

Abstract

The interaction between the Io plasma torus and Io exhibits significant dynamics resulting from temporal variations of both external conditions in the plasma torus and local conditions in Io's environment. We present analysis of an extensive simulation campaign of the Io plasma interaction under varying interaction conditions performed by using a hybrid multispecies simulation model. We test two models of electron impact ionization, one resulting in plasma production constrained to the upstream hemisphere of Io and the other producing a more symmetric distribution of the plasma with nonnegligible plasma production on the downstream side of Io. In the latter case, the simulation model provides high level of agreement with Galileo measurements of magnetic field obtained during the I0 flyby, where the model captures even smaller‐scale features of the magnetic field profile. Our simulated results provide strong support for the existence of Io's induced dipole field. In this model we assume that induced dipole field moment is antiparallel to the direction of the inducing magnetic field, equivalent to induction in a highly conductive Io. Our results further support the idea that Io's atmosphere collapsed during the Galileo I27 flyby, which manifests itself in the lack of ion heating due to pickup processes in the extended atmosphere. Our results show that the dominant torus species, O+ and S++, are depleted around Io and may exhibit temperature anisotropy, T⊥/T‖ < 1, resulting from merging of ion populations coming from opposite sides of Io along the magnetic field.

Io’s polar volcanic thermal emission indicative of magma ocean and shallow tidal heating models

“…A lack of enhanced polar volcanism suggests that solid-body dissipation in the deep mantle of Io is not taking place 27 . In addition to mapping the background thermal emission of Io, constraining the interior state of Io will probably depend on future spacecraft measurements of the strength of magnetic induction, having separated magnetic induction of Io from effects caused by the Io plasma torus 32,33 , coupled to measurements of the libration and diurnal tidal potential Love number of Io, k 2 (ref. 34).…”

The Space Environment of Io and Europa

“…Numerical simulations by Linker et al (1998) and Combi et al (1998) illustrate the generation and propagation of the three MHD wave modes. Numerical simulations (e.g., Blöcker et al, 2016, 2018; Dols et al, 2016, 2008, 2012; Lipatov et al, 2010, 2013; Rubin et al, 2015; Saur et al, 1998, 1999, 2002, 2003; Šebek et al, 2019), reveal the relative importance of each plasma process (ionization, charge exchange, and collision), constrain the neutral atmosphere distribution radially and longitudinally, estimate the local plasma production and neutral loss, and explore the presence of an induced magnetic field either in Io's asthenosphere (Khurana et al, 2011) and/or core (Roth et al, 2017), or in a subsurface ocean for Europa (Schilling et al, 2007, 2008; Zimmer et al, 2000), plus test evidence for plumes (Arnold et al, 2019; Blöcker et al, 2016; Jia et al, 2018).…”

Parallel Electron Beams at Io: Numerical Simulations of the Dense Plasma Wake

“…Sebek et al. (2019) propose multi‐species hybrid simulations of Io's plasma/atmosphere interaction and compare their results to the Galileo observations along the five close Io flybys. Io's size is downscaled by a factor 10 to limit the huge numerical resources that hybrid simulations require.…”