Effects of Europa's Moon-Plasma Interaction on Europa Clipper's Magnetic Induction Investigation

Jupiter's moon Europa harbors an ocean beneath its ice crust, making it a prime target for habitability studies. Europa's ocean was first discovered by the Galileo mission's magnetometer, which found that the moon generated an induced magnetic field that opposed the time-varying components of Jupiter's magnetic field [1]. This implied the presence of a salty ocean capable of conducting electric current. Though Galileo was able to detect its presence, there was insufficient data to establish a unique solution for the ocean's physical properties (i.e. ocean thickness and salinity).

The upcoming Europa Clipper Mission will carry a magnetometer. The planned orbits around Jupiter include 45 close flybys of Europa. Magnetometer data will provide enough coverage of the induction response to supply inputs into a magnetic inversion technique to retrieve oceanic properties. However, in addition to the perturbation caused by magnetic induction, there will also be a perturbation to the jovian field due to the plasma-moon interaction. This interaction generates an Alfvén-wing structure at Europa and creates a pile-up region upstream. In this study, we examine the moon-plasma perturbations along planned Europa Clipper flybys and determine to what extent the additional perturbations may interfere with the evaluation of Europa's magnetic induction response. We use outputs from a multi-fluid magnetohydrodynamic (MHD) model [2], which simulates the moon-plasma interaction for average plasma conditions [3] at different locations of Europa within Jupiter's plasma torus. We find that the moon-plasma interaction consistently produces significant perturbations to the magnetic field along each trajectory and must be subtracted to isolate the induction signal. The regions (i.e. upstream, closest approach, downstream) of lowest "plasma noise" along each flyby vary with flyby geometry. We determine which portions of each flyby are most affected by the plasma-interaction and investigate methods to reduce its impact on the retrieval of oceanic properties.

References

[1] Kivelson, M. G. et al. (1999), JGR, Vol. 104, No. A3, 4609-4625.

[2] Harris, C. D. K. et al. (2019), AGU Fall Meeting 2019, Abstract #SM33F-3279.

[3] Bagenal, F. et al. (2015), Icarus, Vol. 261, 1-13.