Finite Element Modeling of the Electromagnetic Induction Response Produced by Europas Subsurface Structure

Icy moons are some of the most fascinating places in the solar system because of their potential for maintaining conditions suitable to harbor extant life. Analysis of data from NASAs Cassini and Galileo spacecraft revealed that two icy moons, Europa and Enceladus, are particularly interesting because of their suspected global subsurface oceans that can be probed through hydrothermal vents and surface fractures. Future lander missions have the potential to constrain these surface and subsurface features through the use of lightweight and low power onboard magnetometers. Electromagnetic induction theory asserts that conductive layers, like saline subsurface water, perturbed by an external time-varying magnetic field will produce an induced magnetic field observable at the surface. This paper leverages this principle to explore how the magnitude and direction of an induced field signal from subsurface structures can be used to reveal properties of the subsurface water layer for the jovian moon, Europa. We present a forward modeling technique using FEniCS, a finite element computational software, to examine the effect of electrically conductive fluid flow through hydrothermal vents in Europas subsurface on the surface-induced magnetic field. Additional methods such as the magnetotelluric and geomagnetic sounding techniques have been used to construct models of Europas subsurface environment. The finite element model is capable of resolving the induced field associated with arbitrary structures and allows for highly detailed testing of the near-surface environment, namely of the suspected hydrothermal vents where magnetic field fluctuations are greatest. With this approach, we can explore which structures will have a detectable magnetic signature at the surface and probe the range of ocean depths, salinity, ice shell thickness, and hydrothermal vent geometries that we could detect from the surface or from a spacecraft. Results obtained through use of the finite element model are presented and compared with measurements taken by the Galileo MAG instrument. This paper also comments on the detectability of the induced magnetic field on Europas surface and discusses factors to consider in ensuring that a magnetometer on a future lander mission to Europa is capable of measuring the induced field signal.