The Balance of Internal and External Drivers in Gas Giant Magnetospheres

Abstract

The magnetospheres of the gas giants are characterized by strong planetary magnetic fields, rapid rotation, and an intriguing, but not fully characterized, mix of external (solar wind) and internal driving of magnetospheric processes, including the aurorae. Determining the balance between these internal and external drivers is made difficult by the limitations of single-spacecraft measurements, which represent the vast majority of all in-situ magnetospheric measurements and upstream solar wind measurements at the giant planets. Simultaneous in-situ measurements, upstream solar wind monitoring, and remote sensing (e.g. multi-wavelength auroral imaging), gives the best chance to characterize internal and external drivers. Such data have only been taken once, during the brief coordination of the Galileo and Cassini spacecraft at Jupiter. In lieu of a large dataset of simultaneous measurements, advances in our statistical understanding of the balance between these internal and external drivers have been made by leveraging models of either the solar wind, giant planet magnetospheres, or both. In the coming years, additional in-situ data, upstream monitoring, and remote observations coordinated either between space- or earth-based observatories will provide more context for understanding the giant planet magnetospheres, including potential coordination between JUICE and Europa Clipper. In the meantime, improved statistical analysis of both models and data are our best tools to better understand these systems. To this end, we will present the Multi-Model Ensemble System for the outer Heliosphere (MMESH)-- a suite of analysis tools designed to improve the accuracy of solar wind propagation models at the outer planets by self-consistently quantifying modeling uncertainties and biases and forming ensemble models with estimated error. Robust ensembles models allow statistically meaningful analyses of the effects of various solar wind drivers on planetary magnetospheres and quantification of the extent of external control over giant planet magnetospheres. We will conclude by demonstrating the usefulness of these statistical techniques by showing early results of an investigation into external control over Jupiter's overall auroral power and discussing future applications and improvements of this technique.