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Publications

Publications

2023

  • Surface-plasma Interactions at Europa in Draped Magnetospheric Fields: the Contribution of Energetic Electrons to Energy Deposition and Sputtering (2023), Addison, P., Liuzzo, L., Simon, S., J. Geophys. Res. (Space Physics), doi: https://doi.org/10.1029/2023JA031734

In this study we map the spatial distribution of relativistic, magnetospheric electrons onto Europa’s surface, while including a realistic picture of the perturbed electromagnetic fields near the moon. We constrain the number flux, energy flux, and sputtering rates of neutral material from the surface at four points along a synodic rotation. We also compare these results with ion influxes and sputtering rates from our previous papers to constrain the relative contributions of ions and electrons to surface weathering and exosphere generation. We find that electron irradiation patterns at Europa are not strongly modified by the moon’s electromagnetic field perturbations, and rather than the patterns are determined by the global bounce motion of the electrons in Jupiter’s global magnetosphere. In contrast to previous studies, we find that electrons and ions deposit similar amounts of energy into Europa’s surface, and that the sputtering rates of the two species are similar within an order of magnitude. These findings will help inform both the scientific goals and spacecraft safety of future missions to Europa, including the Europa Clipper and JUICE spacecraft.

2022

  • Energetic Magnetospheric Particle Fluxes onto Callisto’s Atmosphere (2022), Liuzzo, L., Poppe, A., Addison, P., Simon, S., Nenon, Q., Paranicas, C., J. Geophys. Res. (Space Physics), doi: https://doi.org/10.1029/2022JA030915

In this study we constrain the role of Callisto’s time-varying plasma interaction in modifying the spatial distribution of ion and electron number and energy fluxes onto the moon’s surface. We find that the perturbations to the electromagnetic fields near Callisto strongly alter the influx patterns of charged magnetospheric particles. We also find that, while three times more electrons impact the surface each second than ions, ions deposit the majority of the energy onto the surface.

  • Effect of the Magnetospheric Plasma Interaction and Solar Illumination on Ion Sputtering of Europa’s Surface Ice (2022), Addison, P., Liuzzo, L., Simon, S., J. Geophys. Res. (Space Physics), doi: 10.1029/2021JA030136

In this study we combine the ion surface fluxes calculated by Addison et al., (2021) with the latest empirical models on sputtering yields from water ice in order to calculate the spatial distribution of the sputtering rate from Europa’s surface. Ours is the first study to calculate the sputtering rates while including a realistic picture of Europa’s perturbed electromagnetic environment. In addition, we investigate the role of solar illumination angle (local time) in deterring the regions of greatest sputtering. We find that the magnitude and spatial distribution of the sputtering rate is substantially modified by the presence of the local field perturbations, and that the sputtering rate of molecular oxygen (the main constituent of Europa’s exosphere) is highly dependent not only upon local time, but also upon the composition of Europa’s surface ice. Our results achieve excellent agreement with observed column densities measured by the Hubble Space Telescope, as well as with the detection of a highly localized, persistent water exosphere above Europa’s central trailing hemisphere.

2021

  • Formation of a Displaced Plasma Wake at Neptune’s Moon Triton (2021), Simon, S., Addison, P., Liuzzo, L., J. Geophys. Res. (Space Physics), doi: 10.1029/2021JA029958.

In this study we develop an analytical model to describe the displaced plasma wake hypothesized to form at Triton by the modeling study of Liuzzo et al., (2021) (see below). Based upon the original theoretical framework of sub-alfvenic moon-magnetosphere interactions laid out by Neubauer et al., (1980,1998), we prove using a simplified interaction model that such a displaced wake likely forms when certain conditions are met. We then derive simple expressions for these conditions, and discuss the implications of this framework on future Triton science.

  • Triton’s Variable Interaction with Neptune’s Magnetospheric Plasma (2021), Liuzzo, L., Paty, C., Cochrane, C., Nordheim, T., Luspay-Kuti, A., Castillo-Rogez, J., Mandt, K., Mitchell, K., Holmstom, M., Addison, P., Simon, S., Poppe, A., Vance, S., Prockter, S., J. Geophys. Res. (Space Physics), doi: 10.1029/2021JA029740

Neptune possesses one of the most unique and complex magnetospheres in the solar system, with a magnetic axis tilted by 47 degrees against the rotation axis and a magnetic moment that is displaced by nearly half a planetary radii from the planet’s center. In this study we constrain the structure of the satellite Triton’s local electromagnetic environment at two different orientations of the Neptunian background magnetic field. Our results show that the secondary magnetic field induced in Triton’s subsurface ocean dominates the plasma-interaction magnetic field perturbations near the surface. In addition, our model hypothesizes the existence of a plasma wake at Triton that is inclined against the moon’s geometric wake, a result of the unique magnetospheric parameters experienced by the satellite.

  • Role of the Ionospheric Conductance Profile In Sub-Alfvenic Moon-Magnetosphere Interactions: an Analytical Model (2021), Simon, S., Liuzzo, L., Addison, P., J. Geophys. Res. (Space Physics), doi: 10.1029/2021JA029191

This study develops an analytical model for describing the magnetic field and plasma flow perturbations inside of the Alfven wings associated with a sub-Alfvenic plasma interaction, assuming a exponential profile for the ionospheric conductance. A case study of Europa’s plasma interaction is then considered, showing that the number flux of impinging magnetospheric plasma is significantly reduced by the presence of the Alfven wing, supporting numerical modeling results outlined in Addison et al., (2021) (see below).

  • Influence of Europa’s Time-Varying Electromagnetic Environment on Magnetospheric Ion Precipitation and Surface Weathering (2021), Addison, P., Liuzzo, L., Arnold, H., Simon, S. J. Geophys. Res. (Space Physics), doi: 10.1029/2020JA029087

This study is the first to calculate the spatial distribution of magnetospheric ion flux onto Europa’s surface using a complete picture of the time-varying, perturbed electromagnetic fields near the moon. We calculate the ion surface flux of all major species and energies that were detected near Europa by the Galileo spacecraft, and at multiple locations of Europa during a synodic rotation of Jupiter. Our results show dramatic changes in the flux pattern compared to previous studies. The fluxes calculated in this study correlate strongly with the measured surface composition, suggesting Europa’s space environment exerts a strong influence on the evolution of its surface.